Clade 2.3.4.4b highly pathogenic avian #influenza #H5N1 viruses: #knowns, #unknowns, and #challenges

ABSTRACT

Since 2020, the clade 2.3.4.4b highly pathogenic avian influenza (HPAI) H5N1 viruses have caused unprecedented outbreaks in wild birds and domestic poultry globally, resulting in significant ecological damage and economic losses due to the disease and enforced stamp-out control. In addition to the avian hosts, the H5N1 viruses have expanded their host range to infect many mammalian species, potentially increasing the zoonotic risk. Here, we review the current knowns and unknowns of clade 2.3.4.4b HPAI H5N1 viruses, and we highlight common challenges in prevention. By integrating our knowledge of viral evolution and ecology, we aim to identify discrepancies and knowledge gaps for a more comprehensive understanding of the virus. Ultimately, this review will serve as a theoretical foundation for researchers involved in related avian influenza virus studies, aiding in improved control and prevention of H5N1 viruses.

Source: Journal of Virology, https://journals.asm.org/doi/full/10.1128/jvi.00424-25?af=R

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#USA, Monitoring for Avian #Influenza A(#H5) Virus In #Wastewater (US #CDC, as of May 9 '25)

{Excerpt}

Time Period: April 27, 2025 - May 03, 2025

- H5 Detection: 8 sites (2.0%)

- No Detection: 402 sites (98.0%)

- No samples in last week: 67 sites

(...)

Source: US Centers for Disease Control and Prevention, https://www.cdc.gov/bird-flu/h5-monitoring/index.html

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#Clinical presentation and #epidemiological #assessment of confirmed #human #mpox cases in #DRC: a surveillance-based observational study

Summary

Background

Mpox, caused by the monkeypox virus, is a serious public health threat in Africa, especially in DR Congo. Previously limited to endemic areas with clade 1a, monkeypox virus has recently spread to non-endemic regions, where clade 1b has emerged. This study provides a clinical comparison of mpox cases in DR Congo regions where clade 1a and clade 1b are prevalent.

Methods

We conducted a retrospective observational study, analysing PCR-confirmed mpox cases reported from sentinel health zones in seven provinces between Oct 1, 2023, and Sept 31, 2024. Cases from the newly affected provinces (South-Kivu and Kinshasa) were described along with those from four endemic provinces (Mai-Ndombe, Tshuapa, Tshopo, South-Ubangi, and Équateur). Surveillance data, including type of exposure, demographic details, clinical presentation, complications, and outcomes were collected from national surveillance systems and local health facilities, with laboratory confirmation using quantitative PCR. All analyses were restricted to descriptive statistics.

Findings

Of 17 927 suspected cases identified, 10 986 were investigated, 5948 were PCR-positive, and 4895 met the inclusion criteria based on data completeness: 4436 in newly affected and 459 in endemic regions. In newly affected provinces, median age was 20 years (IQR 8–28), 2119 (47·8%) participants were female, and 2310 (52·1%) were male. In endemic provinces, median age was 15 years (7–26), 179 (39·0%) participants were female, and 277 (60·3%) were male. Direct or intimate human contact was reported by 1951 (44·0%) individuals in newly affected provinces versus 25 (5·4%) in endemic provinces, and zoonotic exposure in 11 (0·2%) and 99 (21·6%), respectively. The proportions of partcipants with systemic symptoms (3828 [86·3%] in newly affected provinces and 427 [93·0%] in endemic provinces) and respiratory symptoms (2450 [55·2%] and 219 [47·7%]), and median skin lesion counts (91 [IQR 37–200] and 163 [95–345]) were similar between newly affected and endemic regions. Complications included skin infections (2041 [46·0%] in newly affected provinces and 201 [43·8%] in endemic provinces), respiratory distress (82 [1·8%] and 29 [6·3%]), vision impairment (7 [0·2%] and 28 [6·1%]), and prostration (695 [15·7%] and 51 [11·1%]). The case-fatality rate was 0·7% (95% CI 0·4–1·3; 14 of 1924) in children and 0·6% (0·3–1·0; 14 of 2483) in adults in newly affected areas, compared with 5·9% (3·4–10·0; 14 of 236) in children and 2·7% (1·1–6·1; six of 222) in adults in endemic regions. 

Content note: this Article and its appendix contain graphic images of mpox lesions affecting various sites including the face and genitals.

Interpretation

Our study indicates concurrent mpox outbreaks in DR Congo, involving younger individuals, a higher proportion of women and girls, and distinct presentations with higher lesion counts and respiratory symptoms compared with clade 2b lineage B.1 outbreaks. The high proportion of infectious complications and case-fatality rates, especially in endemic regions, emphasise the need for timely antibiotic therapy and targeted vaccination to reduce morbidity and mortality.

Source: Lancet, https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(25)00152-7/abstract?rss=yes

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#Sweden - #Influenza A #H5N5 viruses of high pathogenicity (Inf. with) (non-poultry including wild birds) (2017-) - Immediate notification

{Source: Wikipedia, https://commons.wikimedia.org/wiki/File:White_tailed_eagle_raftsund_square_crop.jpg - Under CC: Christoph Müller (http://www.christophmueller.org), CC BY 4.0, via Wikimedia Commons}

A White tailed eagle was found dead. It was sent to the Swedish Veterinary Agency (formerly National Veterinary Institute) for laboratory analysis as part of the national surveillance program for avian influenza.

Source: WOAH, https://wahis.woah.org/#/in-review/6466?reportId=174166&fromPage=event-dashboard-url

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Adaptive #selection of #quasispecies during in vivo passaging in #chickens, #mice, and #ferrets results in host-specific strains for the #H9N2 avian #influenza virus

ABSTRACT

Sporadic human infections of avian influenza virus (AIV) raise significant public health concerns. A critical factor limiting the transmission of AIVs is the shift in receptor-binding preference from Siaα2,3 to Siaα2,6. To reveal the adaptive selection dynamics during the host adaptation process of AIVs, this study generated a viral library with random mutations in the HA gene of the H9N2 strain. Upon passaging the viral library in chickens and mice, the predominantly selected variants exhibited a preference for Siaα2,3 receptors. Notably, the wild-type strain remained dominant in both inoculated and direct-contact chickens, while variants with the ΔL226/R229I substitutions were preferentially selected in mice. Ferrets have a predominance of Siaα2,6 in their respiratory tract. As expected, the variant harboring the N289D mutation, which prefers Siaα2,6 binding, was enriched during in vivo passaging in ferrets. The mice-adapted variant with the ΔL226/R229I mutations causes reduced levels of TNF-α in the early days post-infection in mice, which correlated with an increase in its viral titers. Conversely, elevated levels of IL-6 and IL-1β at five dpi may contribute to the development of the cytokine release syndrome, potentially elucidating the higher fatality rate observed. In conclusion, based on the mutant spectra of the HA gene, this study elucidates the distinct quasispecies dynamics during the adaptation of H9N2 to different hosts, with receptor availability serving as one of the driving factors. Furthermore, a series of critical substitutions that influence the interspecific transmission potential of H9N2 AIVs were identified.

IMPORTANCE

The mutation of viruses creates a quasispecies reservoir. In this study, we aimed to investigate the dynamics of quasispecies during the host adaptation of AIVs. We generated a viral library with random mutations in the HA gene of H9N2 and conducted serial passaging in chickens, mice, and ferrets for five generations, respectively. The wild-type strain was dominant in chickens, while mice selected viruses with the ΔL226/R229I substitutions. Both variants showed a preference for binding to Siaα2,3, which aligned with the abundance of Siaα2,3 found in the respiratory tract epithelial cells of chickens and mice. In ferrets, where Siaα2,6 is more prevalent, the variant with the N289D mutation, which prefers Siaα2,6, was found to be enriched. In summary, this study revealed the adaptive selection of H9N2 quasispecies in various hosts, contributing to our understanding of AIV host adaptation.

Source: Journal of Virology, https://journals.asm.org/doi/full/10.1128/jvi.00151-25?af=R

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#Genetic Characterization of #Kazakhstan Isolates: Avian #Influenza #H9N2 Viruses Demonstrate Their Potential to Infect #Mammals

Abstract

Low pathogenic H9N2 avian influenza viruses have become widespread in wild birds and poultry worldwide, raising concerns about their potential to spark pandemics or their role in enhancing the virulence and infectivity of H5Nx viruses through genetic reassortment. Therefore, influenza monitoring studies, including those of H9N2 viruses, are crucial for understanding, evaluating, and mitigating the risks associated with avian infections, and have broader implications for global public health. Although H9N2 viruses are not considered enzootic in Kazakhstan, they have been repeatedly detected in wild waterfowls and domestic poultry. In this study, all eight gene segments of influenza A/H9N2 viruses isolated in various regions of Kazakhstan between 2014 and 2020 were sequenced and analyzed. Molecular characterization revealed the presence of genetic markers associated with mammalian infectivity and disease potential. Furthermore, their predicted receptor binding site sequences indicate their potential capacity to attach to human-type receptors. These findings highlight the importance of continued surveillance and molecular investigation to better understand the evolution and zoonotic potential of H9N2 viruses in Kazakhstan.

Source: Viruses, https://www.mdpi.com/1999-4915/17/5/685

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#Influenza at the #human - #animal #interface - #Summary and #assessment, 22 April 2025 (#WHO)

Influenza at the human-animal interface Summary and risk assessment, from 20 March to 22 April 2025{1} 

• New human cases {2}: 

From 20 March to 22 April 2025, based on reporting date, the detection of influenza A(H5N1) in four humans and influenza A(H9N2) virus in three humans were reported officially. 

• Circulation of influenza viruses with zoonotic potential in animals: 

High pathogenicity avian influenza (HPAI) events in poultry and non-poultry continue to be reported to the World Organisation for Animal Health (WOAH).{3} The Food and Agriculture Organization of the United Nations (FAO) also provides a global update on avian influenza viruses with pandemic potential.{4} 

• Risk assessment {5}: 

Sustained human to human transmission has not been reported from these events. Based on information available at the time of the risk assessment, the overall public health risk from currently known influenza viruses circulating at the human-animal interface has not changed remains low. The occurrence of sustained human-to-human transmission of these viruses is currently considered unlikely. Although human infections with viruses of animal origin are infrequent, they are not unexpected at the human-animal interface.  

• IHR compliance: 

All human infections caused by a new influenza subtype are required to be reported under the International Health Regulations (IHR, 2005).{6} This includes any influenza A virus that has demonstrated the capacity to infect a human and its haemagglutinin (HA) gene (or protein) is not a mutated form of those, i.e. A(H1) or A(H3), circulating widely in the human population. Information from these notifications is critical to inform risk assessments for influenza at the human-animal interface.  

Avian influenza viruses in humans 

Current situation:  

Since the last risk assessment of 19 March 2025, single laboratory-confirmed human cases of A(H5N1) infection were reported to WHO from Cambodia, India, Mexico and Viet Nam.  

-- A(H5N1), Cambodia 

On 23 March 2025, Cambodia notified WHO of a human case of influenza A(H5N1) in a 3-year-old boy from Kratie Province. On 18 March, he developed symptoms and was seen at a local private clinic. On 21 March, he was admitted to hospital in critical condition. Upper respiratory specimens collected on 22 March tested positive for influenza A(H5N1) by reverse transcription-polymerase chain reaction (RT-PCR) at the National Institute of Public Health of Cambodia. The results were confirmed by the Institut Pasteur du Cambodge (IPC) on 23 March. The patient died on 23 March. Sequence analysis of the haemagglutinin (HA) gene revealed the virus belongs to A(H5) clade 2.3.2.1e (previously classified as clade 2.3.2.1c) and is similar to viruses circulating in poultry in Cambodia in 2025.  Early investigations revealed that several chickens died at the boy’s house between 16 and 17 March and were used in meal preparation. The boy played near the area where the chickens died at his house. The Cambodian Communicable Disease and Control Department (CDC), Ministry of Health (MoH), and local Rapid Response Team (RRT) established enhanced surveillance and conducted further investigations. As of 25 March 2025, upper respiratory specimens collected from all contacts tested negative for influenza A(H5N1). Samples from local poultry were collected, and test results are pending.    This case is the third human infection with influenza A(H5N1) reported in Cambodia in 2025. 

-- A(H5N1), India 

A human infection with an H5 clade 2.3.2.1a A(H5N1) virus was detected in Andhra Pradesh, India in a child in March 2025, who subsequently died, according to genetic sequence data available in GISAID (EPI_ISL_19836227; submission date 21 April 2025; ICMR-National Institute of Virology). WHO was notified of this case on 8 April 2025. Since early January 2025, several A(H5N1) outbreaks among animals have been reported in India. Multiple outbreaks of HPAI A(H5N1) have been reported in poultry farms across Andhra Pradesh state since January 2025.{7} This is the second human infection with an influenza A(H5N1) virus notified to the WHO from India; the first case was reported in 2021.    

-- A(H5N1), Mexico 

On 2 April 2025, Mexico notified WHO of a laboratory-confirmed human infection with an avian influenza A(H5N1) virus in a child in the state of Durango. The patient did not have any underlying medical conditions and had no history of travel. On 7 March, the patient had onset of symptoms, was admitted to hospital on 13 March due to respiratory failure and died on 8 April due to respiratory complications. A nasopharyngeal swab collected on 18 March was positive for influenza A by real-time RT-PCR but was unsubtypeable. These results were confirmed at the Centro de Investigación Biomédica del Noroeste (CIBIN, by its Spanish acronym), IMSS Monterrey, along with simultaneous detection of parainfluenza 3 virus. On 31 March, the sample was forwarded to the Laboratorio Central de Epidemiología (LCE, by its Spanish acronym) where it was molecularly identified as influenza A(H5). On 1 April, the sample was received by the Instituto de Diagnóstico y Referencia Epidemiológicos (InDRE, by its Spanish acronym), where the positive result for influenza A(H5N1) was confirmed by RT-PCR. The sample was further characterized as avian influenza A(H5N1) clade 2.3.4.4b genotype D1.1 virus. The genotype D1.1 is currently the most frequently detected genotype in the Americas and has affected wild birds, poultry and been detected in mammals, including previous human cases of infection with A(H5N1) viruses. The source of infection in this case remains under investigation. Upper respiratory specimens collected from many of the case’s contacts tested negative for influenza A(H5N1). To date, no further cases of human infection with influenza A(H5N1) linked to this case have been identified. According to information from the National Service for Agrifood Health, Safety and Quality (SENASICA per its acronym in Spanish), between January 2022 and August 2024, 75 outbreaks of A(H5N1) in poultry were reported across various regions of Mexico. In 2025, high pathogenicity avian influenza (HPAI) A(H5N1) has been detected in captive birds in a zoo and wild birds in Durango.  This is the second reported human infection with avian influenza A(H5) in Mexico, and the first confirmed case of infection with an influenza A(H5N1) virus in the country. In 2024, Mexico detected influenza A(H5N2) in an individual.{8} 

-- A(H5N1), Viet Nam 

On 22 April 2025, Viet Nam notified WHO of a laboratory-confirmed human infection with an avian influenza A(H5N1) virus in child in Tay Ninh Province. The case developed fever, headache, and vomiting on 11 April 2025 and was seen at a hospital on the same day. On 13 April, the case was admitted to a tertiary children’s hospital in Ho Chi Minh City (HCMC) and was diagnosed with encephalitis. As of 21 April 2025, the patient was showing clinical improvement. On 13 and 16 April, cerebrospinal fluid (CSF) samples were collected. On 16 April, testing indicated possible A(H5N1) virus detection and treatment with antivirals was initiated.  On 17 April, nasopharyngeal (NP) swabs were collected and sent to the Oxford University Clinical Research Unit (OUCRU) of the Hospital of Tropical Diseases in HCMC, together with the CSF sample collected on 13 April, for RT-PCR testing. On the same day, the hospital also sent NP swabs and the CSF sample collected on 16 April to the Pasteur Institute (PI) in HCMC for RT-PCR testing. The CSF sample tested positive for influenza A(H5N1), while the NP sample tested negative for influenza A(H5N1) at both laboratories. Genomic sequencing conducted by the OUCRU indicated the virus belongs to the H5 HA clade 2.3.2.1e. The genomic sequencing results from PI HCM were pending at the time of reporting. Two weeks before developing symptoms, the case attended a burial for about 50 chickens in their village. At the time of notification, no other outbreaks of dead poultry were reported in the area where the patient lives. Samples collected from chickens from households near the patient’s residence tested negative for A(H5N1) virus. Epidemiological case investigations did not find any further cases among the close contacts of the patient. 

According to reports received by WOAH, various influenza A(H5) subtypes continue to be detected in wild and domestic birds in the Americas, Asia and Europe. Infections in non-human mammals are also reported, including in marine and land mammals. 

Risk Assessment for avian influenza A(H5) viruses:  

1. What is the current global public health risk of additional human cases of infection with avian influenza A(H5) viruses?  

Most human cases so far have been infections in people exposed to A(H5) viruses, for example, through contact with infected poultry or contaminated environments, including live poultry markets, and occasionally infected mammals and contaminated environments. While the viruses continue to be detected in animals and related environments humans are exposed to, further human cases associated with such exposures are expected but unusual. The impact for public health if additional cases are detected is minimal. The current overall global public health risk of additional human cases is low. 

2. What is the likelihood of sustained human-to-human transmission of currently circulating avian influenza A(H5) viruses?  

No sustained human-to-human transmission has been identified associated with the recent reported human infections with avian influenza A(H5). There has been no reported human-to-human transmission of A(H5N1) viruses since 2007, although there may be gaps in investigations. In 2007 and the years prior, small clusters of A(H5) virus infections in humans were reported, including some involving health care workers, where limited human-to-human transmission could not be excluded; however, sustained human-to-human transmission was not reported.  Available evidence suggests that influenza A(H5) viruses circulating have not acquired the ability to efficiently transmit between people, therefore the likelihood of sustained human-to-human transmission is thus currently considered unlikely at this time.  

3. What is the likelihood of international spread of avian influenza A(H5) viruses by travellers?  

Should infected individuals from affected areas travel internationally, their infection may be detected in another country during travel or after arrival. If this were to occur, further communitylevel spread is considered unlikely as current evidence suggests these viruses have not acquired the ability to transmit easily among humans.  

-- A(H9N2), China 

Since the last risk assessment of 19 March 2025, three human cases of infection with A(H9N2) influenza viruses were notified to WHO from China on 9 April 2025. The cases were detected in Guangxi, Guizhou and Henan provinces. One case, in an adult, had underlying conditions at the time of illness and was hospitalized with pneumonia. The other cases in children involved mild illnesses, were detected through the influenza-like illness (ILI) surveillance system, and the cases have recovered. Each case had a known history of exposure to poultry prior to the onset of symptoms. Environmental samples collected from areas associated with two cases tested positive for influenza A(H9) virus. No further cases were detected among contacts of these cases and there was no epidemiological link between the cases.  

Risk Assessment for avian influenza A(H9N2):  

1. What is the global public health risk of additional human cases of infection with avian influenza A(H9N2) viruses?  

Most human cases follow exposure to the A(H9N2) virus through contact with infected poultry or contaminated environments. Most human infections of A(H9N2) to date have resulted in mild clinical illness in most cases. Nearly 130 human infections with A(H9N2) cases have been reported to date since 2003, and six of these have been severe or fatal and three of these were known to have  underlying medical conditions. Since the virus is endemic in poultry in multiple continues in Africa and Asia{11}, further human cases associated with exposure to infected poultry are expected but remain unusual. The impact to public health if additional cases are detected is minimal. The overall global public health risk of additional human cases is low. 

2. What is the likelihood of sustained human-to-human transmission of avian influenza A(H9N2) viruses?  

At the present time, no sustained human-to-human transmission has been identified associated with the event described above. Current evidence suggests that influenza A(H9N2) viruses from these cases have not acquired the ability of sustained transmission among humans, therefore sustained human-to-human transmission is thus currently considered unlikely.  

3. What is the likelihood of international spread of avian influenza A(H9N2) virus by travellers?  

Should infected individuals from affected areas travel internationally, their infection may be detected in another country during travel or after arrival. If this were to occur, further community level spread is considered unlikely as current evidence suggests the A(H9N2) virus subtype has not acquired the ability to transmit easily among humans.  

Overall risk management recommendations: 

Surveillance and investigations 

• Due to the constantly evolving nature of influenza viruses, WHO continues to stress the importance of global strategic surveillance in animals and humans to detect virologic, epidemiologic and clinical changes associated with circulating influenza viruses that may affect human (or animal) health. Continued vigilance is needed within affected and neighbouring areas to detect infections in animals and humans. Close collaboration with the animal health and environment sectors is essential to understand the extent of the risk of human exposure and to prevent and control the spread of animal influenza. WHO has published guidance on surveillance for human infections with avian influenza A(H5) viruses. 

• As the extent of influenza virus circulation in animals is not clear, epidemiologic and virologic surveillance and the follow-up of suspected human cases should continue systematically. Guidance on investigation of non-seasonal influenza and other emerging acute respiratory diseases has been published on the WHO website. 

• Countries should:

- increase avian influenza surveillance in domestic and wild birds, 

- enhance surveillance for early detection in cattle populations in countries where HPAI is known to be circulating, include HPAI as a differential diagnosis in non-avian species, including cattle and other livestock populations, with high risk of exposure to HPAI viruses; 

- monitor and investigate cases in non-avian species, including livestock, 

- report cases of HPAI in all animal species, including unusual hosts, to WOAH and other international organizations, 

- share genetic sequences of avian influenza viruses in publicly available databases, 

- implement preventive and early response measures to break the HPAI transmission cycle among animals through movement restrictions of infected livestock holdings and strict biosecurity measures in all holdings, 

- employ good production and hygiene practices when handing animal products, and 

- protect persons in contact with suspected/infected animals.{12}  

• When there has been human exposure to a known outbreak of an influenza A virus in domestic poultry, wild birds or other animals – or when there has been an identified human case of infection with such a virus – enhanced surveillance in potentially exposed human populations becomes necessary. Enhanced surveillance should consider the health care seeking behaviour of the population, and could include a range of active and passive health care and/or communitybased approaches, including: 

- enhanced surveillance in local influenza-like illness (ILI)/SARI systems, 

- active screening in hospitals and of groups that may be at higher occupational risk of exposure, and 

- inclusion of other sources such as traditional healers, private practitioners and private diagnostic laboratories. 

• Vigilance for the emergence of novel influenza viruses of pandemic potential should be maintained at all times including during a non-influenza emergency. In the context of the cocirculation of SARS-CoV-2 and influenza viruses, WHO has updated and published practical guidance for integrated surveillance. 

Notifying WHO 

• All human infections caused by a new subtype of influenza virus are notifiable under the International Health Regulations (IHR, 2005).{13} State Parties to the IHR (2005) are required to immediately notify WHO of any laboratory-confirmed{14} case of a recent human infection caused by an influenza A virus with the potential to cause a pandemic{15}. Evidence of illness is not required for this report. 

• WHO published the case definition for human infections with avian influenza A(H5) virus requiring notification under IHR (2005): https://www.who.int/teams/global-influenzaprogramme/avian-influenza/case-definitions. 

Virus sharing and risk assessment 

• It is critical that these influenza viruses from animals or from people are fully characterized in appropriate animal or human health influenza reference laboratories. Under WHO’s Pandemic Influenza Preparedness (PIP) Framework, Member States are expected to share influenza viruses with pandemic potential on a timely basis{16} with a WHO Collaborating Centre for influenza of GISRS. The viruses are used by the public health laboratories to assess the risk of pandemic influenza and to develop candidate vaccine viruses.  

• The Tool for Influenza Pandemic Risk Assessment (TIPRA) provides an in-depth assessment of risk associated with some zoonotic influenza viruses – notably the likelihood of the virus gaining human-to-human transmissibility, and the impact should the virus gain such transmissibility. TIPRA maps relative risk amongst viruses assessed using multiple elements. The results of TIPRA complement those of the risk assessment provided here, and those of prior TIPRA analyses will be published at http://www.who.int/teams/global-influenza-programme/avian-influenza/toolfor-influenza-pandemic-risk-assessment-(tipra).  

Risk reduction 

• Given the observed extent and frequency of avian influenza in poultry, wild birds and some wild and domestic mammals, the public should avoid contact with animals that are sick or dead from unknown causes, including wild animals, and should report dead birds and mammals or request their removal by contacting local wildlife or veterinary authorities.  

• Eggs, poultry meat and other poultry food products should be properly cooked and properly handled during food preparation. Due to the potential health risks to consumers, raw milk should be avoided. WHO advises consuming pasteurized milk. If pasteurized milk isn’t available, heating raw milk until it boils makes it safer for consumption. 

• WHO has published practical interim guidance to reduce the risk of infection in people exposed to avian influenza viruses. 

Trade and travellers 

• WHO advises that travellers to countries with known outbreaks of animal influenza should avoid farms, contact with animals in live animal markets, entering areas where animals may be slaughtered, or contact with any surfaces that appear to be contaminated with animal excreta. Travelers should also wash their hands often with soap and water. All individuals should follow good food safety and hygiene practices.  

• WHO does not advise special traveller screening at points of entry or restrictions with regards to the current situation of influenza viruses at the human-animal interface. For recommendations on safe trade in animals and related products from countries affected by these influenza viruses, refer to WOAH guidance.  

Links:  

- WHO Human-Animal Interface web page https://www.who.int/teams/global-influenza-programme/avian-influenza 

- WHO Influenza (Avian and other zoonotic) fact sheet https://www.who.int/news-room/fact-sheets/detail/influenza-(avian-and-other-zoonotic) 

- WHO Protocol to investigate non-seasonal influenza and other emerging acute respiratory diseases https://www.who.int/publications/i/item/WHO-WHE-IHM-GIP-2018.2 

- WHO Public health resource pack for countries experiencing outbreaks of influenza in animals:  https://www.who.int/publications/i/item/9789240076884 

- Cumulative Number of Confirmed Human Cases of Avian Influenza A(H5N1) Reported to WHO  https://www.who.int/teams/global-influenza-programme/avian-influenza/avian-a-h5n1-virus 

- Avian Influenza A(H7N9) Information https://www.who.int/teams/global-influenza-programme/avian-influenza/avian-influenza-a-(h7n9)virus 

- World Organisation of Animal Health (WOAH) web page: Avian Influenza  https://www.woah.org/en/home/ 

- Food and Agriculture Organization of the United Nations (FAO) webpage: Avian Influenza https://www.fao.org/animal-health/avian-flu-qa/en/ 

- OFFLU http://www.offlu.org/ 

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{1} This summary and assessment covers information confirmed during this period and may include information received outside of this period. 

{2} For epidemiological and virological features of human infections with animal influenza viruses not reported in this assessment, see the reports on human cases of influenza at the human-animal interface published in the Weekly Epidemiological Record here.  

{3} World Organisation for Animal Health (WOAH). Avian influenza. Global situation. Available at: https://www.woah.org/en/disease/avian-influenza/#ui-id-2. 

{4} Food and Agriculture Organization of the United Nations (FAO). Global Avian Influenza Viruses with Zoonotic Potential situation update. Available at: https://www.fao.org/animal-health/situation-updates/global-aiv-withzoonotic-potential. 

{5} World Health Organization (2012). Rapid risk assessment of acute public health events. World Health Organization. Available at: https://iris.who.int/handle/10665/70810. 

{6} World Health Organization. Case definitions for the 4 diseases requiring notification to WHO in all circumstances under the International Health Regulations (2005). Case definitions for the four diseases requiring notification in all circumstances under the International Health Regulations (2005).   

{7} WOAH. WAHIS. India - High pathogenicity avian influenza viruses (poultry) (Inf. with). Event 6344. Available at: https://wahis.woah.org/#/in-event/6344/dashboard. 

{8} World Health Organization (14 June 2024). Disease Outbreak News; Avian Influenza A(H5N2) in Mexico. Available at: http://www.who.int/emergencies/disease-outbreak-news/iten/2024-DON524 

{9} A list of bird and mammalian species affected by HPAI A(H5) viruses is maintained by FAO.

{9} World Organisation for Animal Health (WOAH). Avian influenza. Global situation. Available at: https://www.woah.org/en/disease/avian-influenza/#ui-id-2. 

{10} Food and Agriculture Organization of the United Nations. Global Avian Influenza Viruses with Zoonotic Potential situation update. Available at: https://www.fao.org/animal-health/situation-updates/global-aiv-withzoonotic-potential/bird-species-affected-by-h5nx-hpai/en. 

{11} Food and Agriculture Organization of the United Nations (FAO). Global Avian Influenza Viruses with Zoonotic Potential situation update. Available at: https://www.fao.org/animal-health/situation-updates/global-aiv-withzoonotic-potential. 

{12} World Organisation for Animal Health. Statement on High Pathogenicity Avian Influenza in Cattle, 6 December 2024. Available at: https://www.woah.org/en/high-pathogenicity-avian-influenza-hpai-in-cattle/. 

{13} World Health Organization. Case definitions for the four diseases requiring notification in all circumstances under the International Health Regulations (2005).    

{14} World Health Organization. Manual for the laboratory diagnosis and virological surveillance of influenza (2011). Available at: https://apps.who.int/iris/handle/10665/44518 

{15} World Health Organization. Pandemic influenza preparedness framework for the sharing of influenza viruses and access to vaccines and other benefits, 2nd edition. Available at: https://iris.who.int/handle/10665/341850 

{16} World Health Organization. Operational guidance on sharing influenza viruses with human pandemic potential (IVPP) under the Pandemic Influenza Preparedness (PIP) Framework (2017). Available at: https://apps.who.int/iris/handle/10665/25940 

Source: World Health Organization, https://www.who.int/publications/m/item/influenza-at-the-human-animal-interface-summary-and-assessment--22-april-2025

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The #Impact of Public #Health and Medical #Theory on the Societal #Response to the 1889 Russian #Flu

Abstract

The 1889 Russian (also called ‘Asiatic’) Flu epidemic can be described as one of the first modern pandemics. The development of extensive railroad and shipping networks during and prior to this period facilitated the previously unprecedented movement of goods and people around the world. It additionally propagated the process of shrinking the barriers between the countryside and major metropolises. While the COVID-19 pandemic resulted in lockdown measures nearly worldwide and prompted widespread social, economic, and cultural disruptions, the Russian Flu was not accompanied by such drastic changes. In this article, it is argued that the blunted historical consciousness of this epidemic were a result of a combination of factors, including the nascent state of scientific research and understanding of infectious diseases, the circumscribed reach of media, implicit comparisons to other contemporary epidemics, temporal closeness to the Spanish Flu and suppression of memory, and most substantially the lack of an organized public health apparatus to act upon the epidemic. As a result, the 1889 Russian pandemic, though significant in terms of its mortality and economic impact, was quickly forgotten from the collective consciousness and has long been a hidden lesson from history.

Source: Journal of Medical Humanities, https://link.springer.com/article/10.1007/s10912-025-09952-7

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A genetically engineered therapeutic #lectin inhibits #human #influenza A virus #infection and sustains robust virus-specific #CD8 T cell expansion

Abstract

Seasonal influenza continues to be a global health problem. Current existing vaccines and antivirals against influenza have limited effectiveness, and typically do not stay ahead of the viral evolutionary curve. Broad-spectrum antiviral agents that are effective therapeutically and prophylactically are much needed. We have created a promising new broad-spectrum anti-influenza agent using molecular engineering of a lectin from bananas, H84T, which is well-tolerated and protective in small animal models. However, the potency and effect of H84T on human immune cells and influenza-specific immune responses are undetermined. We found that H84T efficiently inhibited influenza A virus (IAV) replication in primary human dendritic cells (DCs) isolated from blood and tonsil, preserved DC viability and allowed acquisition and presentation of viral antigen. Excitingly, H84T-treated DCs subsequently initiated effective expansion of IAV-specific CD8 T cells. Furthermore, H84T preserved the capacity of IAV-exposed DCs to present a second non-IAV antigen and induce robust antigen-specific CD8 T cell expansion. Our data support H84T as a potent antiviral in humans as it not only effectively inhibits IAV infection, but also preserves induction of robust pathogen-specific adaptive immune responses against diverse antigens, which likely is clinically beneficial.

Abstract

Influenza causes large-scale, global morbidity and mortality. Current antiviral treatments and vaccines have significant limitations, especially when dealing with evolving strains of the virus. Banana lectin (BanLec) has broad antiviral effects on enveloped viruses, including influenza, but also causes harmful T cell proliferation and inflammation (mitogenicity). We previously used targeted molecular engineering to produce H84T BanLec (H84T), which is effective against all isolates of influenza tested and is not mitogenic. However, the effect of H84T on the human immune response to influenza had not been ascertained. Here we assessed the effect of H84T on human dendritic (antigen-presenting) cells and virus-specific T cell immune responses against influenza infection and unrelated antigen. We found that H84T treatment allowed dendritic cells to maintain their function during viral infection. H84T prevented the damage caused by viral replication and preserved the ability of dendritic cells to present not only influenza but also secondary, non-influenza antigens to T cells. Thus, H84T could be a valuable tool for controlling influenza infection and potentially preserving responses to secondary infections, which are common and often deadly in influenza patients. H84T holds promise as a novel antiviral that combines control of viral replication with enhancement of the immune response.

Source: PLoS Pathogens, https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1013112

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Wastewater surveillance for avian influenza: national patterns of detection and relationship with reported outbreaks and infections

Abstract

Background. 

Influenza A virus (IAV) is a major cause of morbidity and mortality globally, causing seasonal influenza in humans and infecting birds and some mammals. In 2024, IAV H5N1 highly pathogenic avian influenza (HPAI) in the United States moved into cattle. While the outbreak is currently of low risk to the general public, there is an urgent need to monitor the disease and prevent spread. 

Methods. 

We conducted a nationwide study evaluating the relationship between H5 hemagglutinin gene RNA concentrations in wastewater and reported outbreaks of IAV H5N1 in animals and humans. We utilized an H5-specific droplet digital RT-PCR test to quantify H5 RNA in wastewater in 40 states across the United States, and 1) examined the temporal association between outbreaks and wastewater detections and 2) utilized linear mixed models (LMM) to determine the relationship between measurements in wastewater and outbreak-related factors in the local area. 

Results. 

We find that there is a significant temporal association between wastewater H5 detections and the incidence of outbreaks in poultry and wild birds, but not in cattle or with human infections. However outbreaks tended to occur at the same time across populations - wild bird detections were also associated with H5N1 in herds, poultry, and humans. Utilizing a LMM, we find that for individual sites, there is a relationship between H5 measurements in wastewater and both poultry outbreaks and the presence of dairy industry locally, but that there was either no relationship or a negative relationship with H5 measurements and either combined systems that accept storm water or those with detection of H5 in wild birds. 

Conclusions. 

The study highlights how wastewater monitoring can supplement traditional surveillance, providing vital data that reflects public health threats. The findings underscore the potential of scaled wastewater surveillance as a proactive tool in monitoring and managing future outbreaks.

Source: MedRxIV, https://www.medrxiv.org/content/10.1101/2025.05.06.25327100v1

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A Highly Protective Clade 1 and 2 Cross-Reactive #Pandemic #Influenza Virus #Vaccine Based on a 4th Generation Fully Deleted Adenoviral Vector of a Rare Serotype

Abstract

The GreVac vaccine technology was created as a fast and flexible plug-and-play vaccine platform based on a 4th generation architecture of fully deleted (fd) helper virus independent (hi) adenoviral (Ad) vectors. For the initial proof-of-principle studies, we at Greffex had engineered an avian influenza vaccine, which delivered a transgene expression cassette for an avian influenza virus H5 hemagglutinin and N1 neuraminidase genes in a capsid of the common human Ad serotype 5 (Ad5). This vaccine proved highly immunogenic and protective in mice. These studies revealed that intramuscular (i.m.) delivery proved more efficient than subcutaneous (s.c.) or intranasal (i.n.) routes. In the human population, pre-exposure to the Ad5 virus is common. To minimize interference by pre-existing anti-Ad5 immunities, we created a new GreVac-based avian influenza vaccine, in which the fd Ad genome was packaged into a capsid of the rare human Ad serotype 6 (Ad6). We now report that at very low doses, the resulting GreFluVie6 vaccine given i.m. fully protected mice and ferrets against lethal challenges with the clade 1 A/Vietnam/1203/2004 avian influenza virus associated with induction of potent immune cellular and humoral immune responses. The recipient serum antibodies strongly crossreacted with clade 2.1.3.2 (A/Indonesia/05/2005) and clade 2.3.4.4b H5 hemagglutinins.

Source: BioRxIV, https://www.biorxiv.org/content/10.1101/2025.04.30.651579v1

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Unique Phenomenon of #H5 Highly Pathogenic Avian #Influenza Virus in #China: Co-circulation of Clade 2.3.4.4b #H5N1 and #H5N6 results in diversity of H5 Virus

Abstract

Recently, Clade 2.3.4.4b H5N1 virus has been widely prevalent globally. Although no outbreaks of Avian Influenza have occurred in poultry in China recently, Clade 2.3.4.4b H5 virus can still be isolated from wild birds, live poultry markets and environment, indicating the ongoing co-circulation of H5N1 and H5N6 viruses. In this study, phylogenetic analysis of global Clade 2.3.4.4b viruses and 20 laboratory-isolated H5 strains revealed that Chinese H5N1 and H5N6 viruses since 2021 cluster into two distinct groups, G-I and G-II. Bayesian phylodynamic analysis reveals that G-I H5N6 virus has become an endemic virus in China. In contrast, G-II H5N1 virus, with South China as its main epicentre, has been disseminated in China and its surrounding countries, with its transmission more reliant on the connections of wild birds and waterfowl. Reassortment analysis indicates that since 2023, Clade 2.3.4.4b H5 viruses isolated in China have formed seven genotypes. The genome of H5 viruses has undergone changes compared to those previously prevalent in China. Animal experiments have shown that prevalent H5 viruses exhibit significant lethality in chickens. Additionally, certain H5 viruses have shown the capability of systemic replication in mice. It is noted that H5N6 viruses with HA genes derived from H5N1 viruses demonstrate stronger virulence and pathogenicity in chickens and mice compared to G-I H5N6 viruses. Our study indicates that the co-circulation of H5N1 and H5N6 viruses in China has increased the diversity of H5 viruses, making continuous surveillance of H5 viruses essential.

Source: Emerging Microbes and Infections, https://www.tandfonline.com/doi/full/10.1080/22221751.2025.2502005

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Single-dose replicon #RNA #Sudan virus #vaccine uniformly protects female guinea pigs from disease

Abstract

The Sudan virus (SUDV) outbreaks in Uganda in 2022 and 2025 created public health concerns in-country and the entire East African region. There are currently no licensed countermeasures against SUDV. We developed a SUDV vaccine candidate based on a nanocarrier (LIONTM) complexed with an alphavirus-based replicon RNA. Here, we compare the protective efficacy of the LION-SUDV vaccine either encoding the SUDV glycoprotein (GP) alone or in combination with the Ebola virus (EBOV) GP (LION-Combination). A LION-EBOV vaccine which is protective against EBOV was also included to determine the potential for cross-protection against SUDV infection. Single-dose vaccinations were conducted three weeks before challenge with a lethal dose of guinea pig-adapted SUDV using a female guinea pig disease model. We demonstrate 100% survival and protection with the LION-SUDV and the LION-Combination vaccines, while the LION-EBOV vaccine achieved 50% protection. Antigen-specific humoral responses correlate with decreased virus replication and survival. This result warrants further studies in larger animal species to ensure that protective efficacy is maintained with the single-dose LION-SUDV vaccine.

Source: Nature Communications, https://www.nature.com/articles/s41467-025-59560-1

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Antiviral #CD4+ T and myeloid cell responses to #influenza #vaccines are attenuated in older #adults

Abstract

Recent influenza vaccine formulations have improved the magnitude of B-cell antibody responses in older adults; however, older adults remain significantly at risk for severe influenza-related illness. Although antibodies are an important metric of vaccine effectiveness, they only represent one aspect of the immune response. In this study, we combined in vitro and ex vivo assays with human samples to investigate B, CD4+ T, and myeloid cell responses to influenza vaccine antigens. We found that older adults mounted equivalent antibody titers to younger adults but had fewer influenza-specific CD4+ T cells and reduced antiviral-associated T helper cell populations. Single-cell transcriptomics revealed that older adults had attenuated interferon transcriptional signatures in T helper and myeloid cell subsets. These data suggest that with aging, transcriptional programming alterations in myeloid cells contribute to reduced antiviral T cell responses, and formulating vaccines tailored to myeloid responses is necessary to improve outcomes in older adults.

Source: BioRxIV, https://www.biorxiv.org/content/10.1101/2025.04.30.651528v1?rss=1

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#Influenza #H1N1pdm09 Virus #Resistance to #Baloxavir, #Oseltamivir and Sialic Acid Mimetics in Single and Dual #therapies: Insights from Human Airway Epithelia and Murine Models

Highlights

• Reconstituted human airway epithelia (HAE) are more effective than cell lines or mouse models for generating and predicting resistance-conferring mutations.

• The resistance barrier of oseltamivir is superior to baloxavir or HA targeting compounds in HAE or mouse model.

• HA-targeting therapeutics quickly led to resistant HA mutations without compromising viral fitness.

• A baloxavir-resistant virus with PA mutations E23G and C241Y was isolated in HAE.

• Combined therapy using clinical antiviral compounsd and HA-targeting compounds did not prevent the emergence of HA mutations.

Abstract

Influenza viruses pose a significant threat due to annual epidemics and pandemic potential. Resistance to current antivirals underscores the need for new drugs and strategies to prevent its emergence. We previously developed two novel HA-targeting compounds (CD-6’SLN and CD-SA) with demonstrated efficacy against influenza A and B strains. Here, we compared their resistance barrier to that of FDA-approved oseltamivir (OS) and baloxavir marboxil (BXM). We established a resistance testing assay in human airway epithelia (HAE) and in mice. We also evaluated the impact of combination therapies on resistance emergence. In HAE, highly reduced inhibition (HRI) by CD-6’SLN and CD-SA occurred within 2 and 4 weeks respectively without fitness loss, while reduced inhibition (RI) by baloxavir acid (BXA) emerged within 4 weeks. No reduction of susceptibility to OS was observed in the same time frame. Of note, emergence of RI by CD-SA was not delayed in BXA/CD-SA co-treatment, and slightly reduced upon OS/CD-SA co-treatment. In mice, RI by CD-SA was observed after 8 passages in one of three mice treated with OS/CD-SA, but not in mice with single therapies. This study demonstrates that (1) HAE represents a relevant model to detect emergence of resistance and (2) HA-targeting compounds are prone to induce resistance followed by BXA and OS. Importantly, combination of clinically available antivirals and HA-targeting compounds did not prevent the emergence of variants with HA substitutions. Additional research is needed to develop anti-influenza antivirals with high resistance barrier and compounds should be tested in HAE before moving to animal experimentation.

Source: Antiviral Research, https://www.sciencedirect.com/science/article/abs/pii/S0166354225001007?via%3Dihub

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Return of the Biennial #Circulation of #Enterovirus D68 in #Colorado #Children in 2024 Following the Large 2022 #Outbreak

Abstract

Enterovirus D68 (EV-D68) caused large biennial cyclical outbreaks of respiratory disease and cases of acute flaccid myelitis from 2014 to 2018 in the USA. An anticipated outbreak did not occur in 2020, likely due to non-pharmaceutical interventions targeting the COVID-19 pandemic. A large respiratory disease outbreak occurred again in 2022, but uncertainty remained regarding if circulation of EV-D68 would return to the pre-pandemic patterns. We conducted prospective active surveillance of clinical respiratory specimens from Colorado children for EV-D68 in 2023 and 2024. A subset of residual specimens positive for rhinovirus/enterovirus (RV/EV) were tested for EV-D68 via a validated in-house EV-D68 reverse transcription–PCR assay. During epi weeks 18–44 in 2023, 525 residual specimens positive for RV/EV all tested negative for EV-D68. In 2024, during epi weeks 18–44, 10 (1.8%) of the 546 RV/EV-positive specimens were EV-D68-positive. The EV-D68-positive cases were predominantly young children (median age 4.8 years) receiving treatment with asthma medications. Following the 2022 EV-D68 outbreak, an anticipated outbreak did not occur in 2023. While EV-D68 was detected in 2024, the number of cases was not as significant as in prior outbreak years. Continued surveillance for EV-D68 will be important to understand the future dynamics of EV-D68 circulation and prepare for future outbreaks.

Source: Viruses, https://www.mdpi.com/1999-4915/17/5/673

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Genesis and Spread of Novel Highly Pathogenic Avian #Influenza A(#H5N1) Clade 2.3.4.4b Virus #Genotype EA-2023-DG #Reassortant, Western #Europe

Abstract

In Europe, highly pathogenic avian influenza (HPAI) virus circulates in avian wildlife, undergoing frequent reassortment, sporadic introductions in domestic birds, and spillover to mammals. An H5N1 clade 2.3.4.4b reassortant, EA-2023-DG, affecting wild and domestic birds was detected in western Europe in November 2023. Six of its RNA segments came from the EA-2021-AB genotype, but the polymerase basic 2 and polymerase acidic segments originated from low pathogenicity avian influenza viruses. Discrete phylogeographic analyses of concatenated genomes and single polymerase basic 2 and polymerase acidic segments suggested reassortment in summer 2023 near the southwestern Baltic Sea. Subsequent continuous phylogeographic analysis of all concatenated EA-2023-DG genomes highlighted circulation in northwestern Europe until June 2024 and long-distance dispersal toward France, Norway, England, Slovakia, Switzerland, and Austria. Those results illustrate the value of phylodynamic approaches to investigate emergence of novel avian influenza virus variants, trace their subsequent dispersal history, and provide vital clues for informing outbreak prevention and intervention policies.

Source: US Centers for Disease Control and Prevention, https://wwwnc.cdc.gov/eid/article/31/6/24-1870_article

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Intranasally administered whole virion inactivated #vaccine against clade 2.3.4.4b #H5N1 #influenza virus with optimized #antigen and increased cross-protection

Abstract

The global spread, frequent antigenic changes, and pandemic potential of clade 2.3.4.4b highly pathogenic avian influenza H5N1 underscore the urgent need for robust cross-protective vaccines. Here, we developed a clade 2.3.4.4b H5N1 whole inactivated virus (WIV) vaccine strain with improved structural stability, productivity, and safety. By analyzing the evolutionary trends of clade 2.3.4.4b H5N1 viruses, we identified a key mutation (R90K) that increases heat stability while preserving antigenicity. Additionally, the PB2 gene of PR8 was replaced with a prototypical avian PB2 gene to increase replication efficiency in embryonated chicken eggs and reduce replication efficiency in mammalian cells, thereby improving productivity and biosafety. We found that our optimized clade 2.3.4.4b H5N1 vaccine strain (22W_KY), inactivated with binary ethylenimine (BEI), had superior antigen internalization into respiratory epithelial cells compared to those inactivated with formaldehyde or beta-propiolactone. Following intranasal administration to mice, the BEI-inactivated 22W_KY also elicited significantly stronger systemic IgG, mucosal IgA, and T-cell responses, especially in the lungs. Protective efficacy studies revealed that the BEI-inactivated 22W_KY vaccine provided complete protection against heterologous viral challenges and significant protection against heterosubtypic viral challenges, with no weight loss and complete suppression of the viral load in the respiratory tract in 2 of 3 mice. These results indicate that the BEI-inactivated 22W_KY vaccine could serve as a promising candidate for a safe, stable, cost-efficient, and broadly protective intranasal influenza vaccine against zoonotic and pandemic threats.

Source: Virology Journal, https://virologyj.biomedcentral.com/articles/10.1186/s12985-025-02760-4

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History of Mass Transportation: The FS ALn 668 Autorail

 

Distributed via CC (Creative Common), Source: Wikipedia: https://it.wikipedia.org/wiki/Automotrice_FS_ALn_668

Credit: Di Phil Richards - Flickr: 14.11.95 Palermo Centrale ALn668.1609, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=21836099

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Avian #Influenza A(#H5N1) Isolated from Dairy #Farm #Worker, #Michigan

Abstract

Influenza A(H5N1) viruses have been detected in US dairy cow herds since 2024. We assessed the pathogenesis, transmission, and airborne release of A/Michigan/90/2024, an H5N1 isolate from a dairy farm worker in Michigan, in the ferret model. Results show this virus caused airborne transmission with moderate pathogenicity, including limited extrapulmonary spread, without lethality.

Highly pathogenic avian influenza A(H5N1) clade 2.3.4.4b viruses have displayed unprecedented global spread among wild birds leading to numerous spillover infections in mammalian species. Of note, outbreaks in dairy cattle and gallinaceous birds have resulted in human infections in the United States during 2024–2025 (1). Increased frequency of H5N1 viruses crossing species barriers has caused concern that the avian influenza viruses are adapting to mammals. A critical component of influenza pandemic preparedness is early identification of emerging novel influenza viruses that cause disease and transmit efficiently in humans. A clade 2.3.4.4b H5N1 virus, A/Michigan/90/2024 (MI90), genotype B3.13, was isolated from a conjunctival swab specimen collected from a human patient in Michigan with conjunctivitis after exposure to infected cattle (2,3). In this article, we report the pathogenesis, transmission, and airborne exhalation of MI90 virus in ferrets, the standard animal model for influenza virus risk assessments (4).

We inoculated 18 ferrets with MI90 virus as previously described (5,6). We euthanized 3 ferrets on 3 and 5 days postinoculation (dpi) to assess virus spread in tissues. We used 6 ferrets to assess transmission in a cohoused, direct contact setting as a direct contact transmission model and through the air in the absence of direct or indirect contact as a respiratory droplet transmission model. We paired each ferret with a naive contact, as previously described (4). We observed clinical manifestations daily and collected nasal wash (NW), conjunctival, and rectal swab samples every 2 days postinoculation or postcontact. We confirmed transmission by testing for seroconversion to homologous virus in the contact animals.

Although all MI90-infected ferrets survived the 21-day study, we noted moderate disease. In inoculated ferrets, the mean maximum weight loss was 9.8%, fever (1.8°C above baseline) and lethargy were transient, and nasal and ocular discharge and sneezing were evident on days 4–9 dpi (Table). We detected virus 3 dpi primarily in respiratory tract tissues; titers were highest in ethmoid turbinate samples (7.4 log10 PFU/mL) and at low levels in brain and gastrointestinal tissues. We observed similar results in tissues collected 5 dpi.

(...)

During the direct contact transmission experiment, inoculated ferrets shed virus in NW that peaked at 4.7–5.4 log10 PFU/mL at 1–5 dpi (Figure, panel A). Four of 6 cohoused contact animals had virus in NW (peak 2.5–4.9 log10 PFU/mL) at 5–7 days postcontact, whereas all 6 contact animals had viral RNA detected (3.6–7.7 log10 copies/mL) in NW (7) and seroconverted to MI90 virus, indicating that transmission was 100% (6/6 animals). In the respiratory droplet transmission experiment, NW collected from inoculated animals peaked 2.6–4.8 log10 PFU/mL at 1–3 dpi, whereas 3/6 contact ferrets had detectable virus in NW by day 7 postcontact (peak 2.6–4.8 log10 PFU/mL; days 9–11 postcontact) (Figure, panel B) as well as viral RNA (6.7–8.2 log10 copies/mL), and seroconverted, confirming transmission through the air in 50% of ferrets (3/6). We also detected infectious virus in conjunctival and rectal samples from inoculated animals, but only from 2 contact animals (Table).

To further evaluate the level of virus exhaled by MI90-inoculated ferrets and the potential for airborne transmission, we collected aerosol samples 1 time each day at 1–5 dpi for 1 hour from the 3 ferrets that were euthanized at 5 dpi. Air samples were analyzed for infectious virus and viral RNA by using the BC251 cyclone-based sampler (kindly provided by Dr. William Lindsley, National Institute for Occupational Safety and Health) and the SPOT water condensation sampler (Aerosol Devices, https://aerosoldevices.comExternal Link), as described previously (8) (Figure, panel D). The highest mean titer of virus was detected at 2 dpi in NW collected from all 3 inoculated ferrets (6.5 log10 PFU/mL) (Figure, panel C). Airborne virus was highest at 3 dpi as measured in both samplers, up to 133 and 41 PFU/hour, supporting transmission observed in both contact models within 3–5 days after exposure.

Overall, MI90 virus displayed reduced virulence in ferrets compared to another H5N1 virus isolated from a dairy farm worker in Texas (8,9); the Texas virus possesses a genetic marker in the polymerase basic 2 protein (E627K), known for enhanced replication and pathogenesis in mammals. At this position, MI90 encodes 627E, like most other viruses isolated from cattle, and contains polymerase basic 2 M631L, which is associated with mammal adaptation (3,9). In addition, polymerase acidic 142N/E has been linked to increased virulence in mice (10); the Texas virus has an E and MI90 virus has a K at this position. Both viruses have identical hemagglutinin sequences associated with receptor binding and the multi-basic cleavage site. Despite differences in virulence, both viruses transmitted in the ferret model with similar proficiency and levels of airborne virus.

Because avian H5N1 viruses cross the species barrier and adapt to dairy cattle, each associated human infection presents further opportunity for mammal adaption. This potential poses an ongoing threat to public health and requires continual surveillance and risk assessment of emerging viruses to improve our ability to predict and prepare for the next influenza pandemic.

Dr. Brock is a microbiologist in the Influenza Division, National Center for Immunization and Respiratory Diseases, at the Centers for Disease Control and Prevention. Her research interests include the pathogenicity, transmissibility, and host response associated with emerging strains of influenza virus.

Source: US Centers for Disease Control and Prevention, https://wwwnc.cdc.gov/eid/article/31/6/25-0386_article

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