Saturday, March 8, 2025

#Sudan virus #disease - #Uganda {March 8 '25}

Situation at a glance

Since the outbreak of Sudan virus disease (SVD) was declared in Uganda on 30 January 2025, and as of 5 March 2025, a total of 14 cases (including 12 confirmed cases and two probable cases) including four deaths (two confirmed and two probable) have been reported. 

On 1 March 2025, the Ministry of Health released a press statement confirming the tenth case. The patient was a child under 5 years old who presented and died in the Mulago hospital on 23 February 2025. 

As of 5 March, two additional confirmed cases and two probable deaths have been reported that are linked to this case. Both of these cases are currently admitted to treatment facilities. 

Eight confirmed cases received care at treatment centres in the capital Kampala and in Mbale and were discharged on 18 February 2025. 

As of 5 March 2025, 192 new contacts have been identified and are under follow-up in Kampala, Ntoroko and Wakiso. In the absence of licensed vaccines and therapeutics for the prevention and treatment of SVD, the risk of potential serious public health impact is high.


Description of the situation

Since the second disease outbreak news on this event published on 21 February 2025, three additional laboratory-confirmed cases and two probable deaths of SVD have been reported in Uganda. 

As of 5 March 2025, 12 confirmed and two probable cases, among these four deaths (two confirmed, two probable) have been reported with a case fatality ratio (CFR) of 29%. 

The latest confirmed cases are reported to be epidemiologically linked to the two probable cases.  

The age range of confirmed cases is 1.5 years to 55 years, with a mean age of 27 years and males accounted for 55% of the total cases. 

The cases were reported from six districts in the country which include Jinja, Kampala, Kyegegwe, Mbale, Ntoroko and Wakiso (...).

On 1 March 2025, the Ministry of Health released a press statement about the confirmation of a new case. The case was an under 5-year-old child identified at the Mulago Hospital where the patient presented with signs and symptoms meeting the suspect case definition. 

A laboratory sample was collected, and the child was confirmed with SVD on 26 February by PCR. Following investigations, two probable deaths linked to this case have been reported. This includes the child’s mother who was pregnant at the time of symptom onset on 22 January and died on 6 February. Her newborn child died on 12 February. The three deaths did not have a supervised burial. On 3 March, an 11th case was confirmed, an adult female, contact of case 10, and on 4 March, a 12th case was confirmed, an adult female, contact of the probable case (the mother of case 10). Both of these cases are currently admitted to treatment facilities.

Since the start of the outbreak, eight cases have recovered and been discharged.

(...)

As of 5 March, there are 192 new contacts listed around the new cases and 299 previously listed contacts who had completed the 21-day follow-up period.  

SVD alert levels reported from the community and the health facilities have been low and efforts are ongoing to improve this. Mortality surveillance has also been set up since the declaration of the outbreak and will continue in Jinja, Kampala, Mbale, Ntoroko and Wakiso districts.

Retrospective epidemiological and laboratory investigations are ongoing to find the source of the outbreak while active case search in and around the community and health facilities linked to the case movements have been intensified. 


Epidemiology

Sudan virus disease is a severe disease, belonging to the same family as Ebola virus disease. It is caused by Sudan virus (SUDV) and can result in high case fatality. It is typically characterized by acute onset of fever with non-specific symptoms/signs (e.g., abdominal pain, anorexia, fatigue, malaise, myalgia, sore throat) usually followed several days later by nausea, vomiting, diarrhoea, and occasionally a variable rash. Hiccups may occur. 

Severe illness may include haemorrhagic manifestations (e.g., bleeding from puncture sites, ecchymoses, petechiae, visceral effusions), encephalopathy, shock/hypotension, multi-organ failure, and spontaneous abortion in infected pregnant women. 

Individuals who recover may experience prolonged sequelae (e.g., arthralgia, neurocognitive dysfunction, uveitis sometimes followed by cataract formation), and clinical and subclinical persistent infection may occur in immune-privileged compartments (e.g., central nervous system (CNS), eyes, testes). 

Person-to-person transmission occurs by direct contact with blood, other bodily fluids, organs, or contaminated surfaces and materials with risk beginning at the onset of clinical signs and increasing with disease severity. 

Family members, healthcare providers, and participants in burial ceremonies with direct contact with the deceased are at particular risk. The incubation period ranges from 2 to 21 days, but typically is 7–11 days. 


Public health response

Health authorities are implementing public health measures, including but not limited to the following:

-- Coordination:

The Ministry of Health (MoH) has activated the coordination structures at national and subnational levels, including the Incident Management Team and dispatched Rapid Response Teams to the affected districts. Regional Emergency Operation Centers have been activated in Fort Portal, Ntoroko, Kampala, and Mbale districts.

The country developed a National Response Plan (February-April 2025). The response plan has been updated to reflect current response priorities and builds on lessons learned from previous outbreaks. It deploys the basic minimum packages of activities across the districts according to risk.

-- Surveillance and contract tracing:

MoH with support from WHO and partners, is conducting alert management including the setup of an alert desk with toll-free numbers to detect and verify alerts from all over the country that meet the case definition. Since 30 January, over 1300 signals have been reported from all over the country and 112 alerts have been verified as suspected cases.

MoH with support from partners has allocated teams to conduct detailed case investigations around all confirmed and probable cases to identify and stop the chains of transmission.

MoH has allocated teams to conduct contact listing of cases and perform daily follow-up of contacts.

Following the declaration of the outbreak, MoH, with support from WHO, has established mortality surveillance. Over 770 non-trauma deaths were tested in communities and health facilities located in the affected districts, and one tested positive (case 10).

MoH set up a hotline for notification of suspected cases.

MoH is conducting exit screening of SVD signs and symptoms among travellers at Uganda’s 13 high volume points of entry (POE) including Entebbe International Airport

-- Case Management:

MoH with support from WHO and partners has set up four designated isolation and treatment units in Jinja, Kampala, Mbale and now Fort Portal, where confirmed cases receive optimized supportive care. Plans are underway to conduct therapeutic clinical trials. 

Patients who recovered from the disease are included in the survivor care programme for support and care.

MoH has scaled up its case management strategy to ensure sufficient capacities to provide care for all suspected and confirmed cases in all hot spots

-- Laboratory:

MoH and partners have strengthened laboratory capacities and deployed a mobile laboratory to Mbale to reduce turnaround time for laboratory results.

MoH has performed a full genome sequencing on the sample of the first confirmed case and findings indicate the outbreak is most likely the result of a spillover event. Sequencing was also performed on samples of subsequent confirmed cases,

-- Infection prevention and control:

MoH has activated their IPC response coordination mechanism.

MoH has activated the IPC ring around cases, which includes cleaning and disinfection of sites where confirmed cases passed through.

In their official press statement, the MoH provided recommendations to health workers, district leaders, and the public to strengthen detection of suspected cases and implement appropriate infection, prevention and control measures.

MOH is surging and strengthening IPC activities, with the support of partners, notably to improve screening, isolation and notification at health facilities in order to better detect suspected cases.

MoH is orienting health workers on IPC measures in the context of Ebola disease outbreak response.


Risk communication and community engagement (RCCE)

An integrated community engagement approach has been adopted whereby the RCCE team facilitate access to communities for other response pillars. This helps to build trust and enhance contact tracing, case investigation, surveillance, referral to isolation units and provision of psychosocial support.

Anthropological investigation is used to identify community concerns, risk behaviours, reduce hesitancy from communities and to enhance evidence-informed decisions across pillars.

Development and dissemination of public health messages to promote protective and health seeking behaviours, community engagement to build trust and provide psychosocial support.


Research and development

-- Research priorities: The Collaborative Open Research Consortium (CORC) for the Filoviridae Family held two global consultations to deliberate and identify the research priorities for Sudan ebolavirus in general and this outbreak in particular. Over 200 scientists from around the world participated in each of the two consultations.

-- Ring vaccination trial: After the outbreak was confirmed on 30 January, researchers from the Uganda Makerere University and the Virus Research Institute (UVRI), with support from WHO, swiftly mobilised to launch the vaccination trial. The trial was initiated only four days following the outbreak, reflecting the urgency of the response while maintaining rigorous ethical and regulatory standards. The trial follows the ring vaccination model, in which primary and secondary contacts of confirmed cases receive the vaccine, to create a protective barrier and help break chains of transmission.

The development of the protocols and research priorities has been done via the MARVAC Consortium and the Collaborative Open Research Consortium (CORC) for the Filoviridae Family, European Union (EU) Health Emergency Preparedness and Response (HERA) and Canada’s International Development Research Centre (IDRC) supported the development of these crucial trial protocols during the inter-epidemic, preparedness phase

EU HERA and IDRC also provided financial support for the trial, alongside WHO. The Coalition for Epidemic Preparedness Innovations (CEPI) is also providing support with additional support from the Africa Centres for Disease Control and Prevention (Africa CDC). The vaccine itself was donated by IAVI, with additional support from the Africa CDC.

-- Therapeutics trial: While several promising candidate therapeutics are currently advancing through clinical development, no licensed treatment is yet available to effectively address potential future outbreaks of Ebola virus disease caused by the Sudan virus species. If successful, this trial could play a critical role in enhancing outbreak control measures and supporting the future regulatory approval of the candidate vaccine. Numerous developers facilitated the availability of the candidate vaccine and treatments: MappBio provided their candidate Sudan monoclonal, Gilead provided remdesivir, an antiviral.

WHO is supporting the national authorities through:

- Risk assessment and investigation.

- Providing operational, financial and technical support to the Ministry of Health to ensure swift response. A total of US$ 3.4 million was released from the Contingency Fund for Emergencies for the three levels of WHO to support the government-led response

- Supporting the national laboratory system to implement sample collection, transport and diagnostic testing.

- Providing strategic, technical and operational support to strengthen infection. prevention and control response measures and standards within health facilities and Ebola treatment units in Kampala, Mbale, Luwero districts. This includes supporting IPC ring activation activities, rapid assessments of health facilities, capacity building of health workers, mentorship and supportive supervision at designed health facilities and supporting development of key guidance, SOPs and tools.   

- Facilitating access to candidate vaccines and therapeutics and supporting the launch of the vaccine trial. Rings have been defined around all confirmed cases and their contacts have been invited to consent in the trial.  As part of this support, the "TOKEMEZA SVD" vaccine trial was launched on 3 February 2025 and the TOKOMEZA immuno (an add-on study) was launched on 1 March 2025.

- Providing technical and operation assistance for the setup of isolation centers for suspected cases and two Ebola treatment units in Kampala and Mbale.

- Mobilizing logistics to complement government supplies, including IPC supplies, drugs, resuscitation and monitoring equipment, admission packages, and mattresses.

- Deploying a team of 47 experts to Mbale, Kampala, Wakiso and Jinja districts to support across different response pillars including coordination, surveillance, laboratory, logistics, IPC, RCCE, and case management pillars.

- Supporting RCCE efforts to counter misinformation and enhance community engagement through the deployment of two anthropologists.

- Intensified and integrated risk communication and community engagement, including sensitization and training of Village Health Teams, traditional healers, religious leaders and teachers. 

- Collecting social and behavioural data and using evidence to respond to communities’ anxieties and concern, rumours, misinformation and disinformation


WHO risk assessment

Sudan virus disease (SVD) is a severe, often fatal illness affecting humans. Sudan virus (SUDV) was first identified in southern Sudan in June 1976. Since then, the virus has emerged periodically and up to now and prior to this current one, eight outbreaks caused by SUDV have been reported, five in Uganda and three in Sudan. The case fatality rates of SVD have varied from 41% to 70% in past outbreaks.

SUDV is enzootic and present in animal reservoirs in the region. Uganda reported five SVD outbreaks (one in 2000, one in 2011, two in 2012, and one in 2022).  The current outbreak is the sixth SVD outbreak in Uganda. Uganda also reported a Bundibugyo virus disease outbreak in 2007 and an Ebola virus disease outbreak exported from the Democratic Republic of the Congo in 2019. The latest SVD outbreak in Uganda was declared over on 11 January 2023. A total of 164 cases with 55 deaths were reported in nine districts.

Uganda has experience in responding to Ebola disease outbreaks including SVD. In the ongoing outbreak, cases have been reported from several districts including the capital city, Kampala, with high population movement. Cases have sought care in several health facilities, including traditional healers, and some cases have been detected at a late stage of the disease or death. The government, with support from partners is implementing several public health actions for effective control.

In the absence of licensed vaccines and therapeutics for the prevention and treatment of SVD, the risk of potential serious public health impact is high. Community deaths, care of patients in private facilities and hospitals and other community health services as well as at traditional healers with limited protection and infection prevention and control measures entail a high risk of many transmission chains. An investigation is ongoing to determine the source and the scope of the outbreak and the possibility of spread from the capital city, Kampala, to other districts. Exit screening has been set up at different points of entry to reduce the risk of potential exportation of cases to neighbouring countries.


WHO advice

Effective Ebola disease outbreak, including SVD, control relies on applying a package of interventions, including case management, surveillance and contact tracing, a strong laboratory system, implementation of infection prevention and control measures in health care and community settings, safe and dignified burials and community engagement and social mobilization.

Risk communication and community engagement is crucial to successfully controlling SVD outbreaks. This includes raising awareness of symptoms, risk factors for infection, protective measures and the importance of seeking immediate care at a health facility. Sensitive and supportive information about safe and dignified burials is also crucial. Awareness should be built through targeted campaigns and direct work with affected and proximate communities, with special attention to engage with traditional healers, clergy, ‘boda boda’ drivers and community leaders, who are important sources of information for the community. Findings from rapid qualitative assessments should continue to be implemented to collect socio-behavioural data, which can then be used to inform response pillars. Priority areas to strengthen, based on recent evidence are mortality surveillance, contact tracing and safe and dignified burials.  Misinformation and rumours should be addressed to foster trust and promote early symptom reporting.

Early initiation of intensive supportive treatment increases the chances of survival. All above-mentioned interventions need to be thoroughly implemented in affected areas to stop chains of transmission and decrease disease mortality. Cases, contacts and individuals in affected areas who present signs and symptoms compatible with case definitions should be advised not to travel and seek early care at designated facilities to improve their chances of survival and limit transmission.

WHO encourages countries to implement a comprehensive care programme to support people who recovered from Ebola disease with any subsequent sequelae and to enable them to access body fluid testing and to mitigate the risk of transmission through infected body fluids by adequate practices.

Collaboration with neighbouring countries should be enhanced to harmonize reporting mechanisms, conduct joint investigations, and share critical data in real-time. Surrounding countries should enhance readiness activities to enable early case detection, isolation and treatment.

A range of candidate vaccines and therapeutics are under different stage of development. Since 2020, WHO has convened scientific deliberations and set up an independent process to review candidate medical countermeasures (MCMs) prioritization and clinical trial designs. One candidate vaccine and two candidate therapeutics (a monoclonal antibody and an antiviral) have been recommended and are available in country and are being assessed (clinical efficacy and safety) through randomized clinical trial protocols.

Thanks to preparedness measures that the government took after the previous outbreak in 2022, and a global research collaboration led by WHO (first MARVAC now FILOVIRUS CORC), a trial of a candidate vaccine was launched just four days after the outbreak was declared. A therapeutics trial will start as soon as national authorities provide approval.

The two vaccines licensed against Ebola virus disease (from the Zaire species) will not provide cross-protection against SVD and cannot be used in this outbreak.

WHO advises against any restrictions on travel and/or trade to Uganda based on available information for the current outbreak. 

(...)

Source: World Health Organization, https://www.who.int/emergencies/disease-outbreak-news/item/2025-DON558

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Friday, March 7, 2025

Neutralizing #Antibody #Response to #Influenza A(#H5N1) Virus in Dairy #Farm #Workers, #Michigan, #USA

Abstract

Since March 2024, highly pathogenic avian influenza A(H5N1) viruses have caused outbreaks in dairy cattle and poultry in the United States, and they continue to spill over into humans. However, data on human immune response to those viruses is limited. We report neutralizing antibody responses in 2 dairy farm worker H5N1 cases.

Source: US Centers for Disease Control and Prevention, https://wwwnc.cdc.gov/eid/article/31/4/25-0007_article

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#USA, Monitoring for Avian #Influenza A(#H5) Virus In #Wastewater {March 7 '25}



{Excerpt}

Time Period: February 23 - March 01, 2025

- H5 Detection8 sites (1.8%)

- No Detection445 sites (98.2%)

- No samples in last week100 sites



(...)

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

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#UK, #England: #Lassa #fever contact #tracing underway

The UK Health Security Agency has been informed under the International Health Regulations that an individual travelled to England from Nigeria while they were unwell with Lassa fever at the end of February. The individual returned to Nigeria where they were diagnosed.

We are now working to identify people who were in contact with the affected individual while they were in the country.

Lassa fever does not spread easily between people and the overall risk to the public is very low. If you have not been contacted by UKHSA then you are very unlikely to have had any exposure to Lassa fever and do not need to take action.

Lassa fever causes acute infections which can range from very mild symptoms through to a severe viral haemorrhagic fever. People usually become infected with Lassa virus through exposure to food or household items contaminated with urine or faeces of infected rats – present in some West African countries where the disease is endemic. The virus can also be spread between people through contact with infectious bodily fluids.

Dr Meera Chand, Deputy Director at the UK Health Security Agency, said:

''Our Health Protection Teams are working at pace to get in touch with people who were in contact with this individual while they were in England, to ensure they seek appropriate medical care and testing should they develop any symptoms. The infection does not spread easily between people, and the overall risk to the UK population is very low.''

Source: UK Health Security Agency, https://www.gov.uk/government/news/lassa-fever-contact-tracing-underway

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#Russia - #Influenza A #H5N1 viruses of high pathogenicity (Inf. with) (non-poultry including wild birds) (2017-) - Immediate notification

 A wild Carrion Crow in Khabarovsk Region.

Source: https://wahis.woah.org/#/in-review/6304

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#UK - High pathogenicity avian #influenza #H5N1 viruses (#poultry) (Inf. with) - Immediate notification

{England} Commercial turkey fattening unit with 27,658 turkeys. Increased mortality and other clinical signs of HPAI reported. The samples were positive for HPAI H5N1.

Source: WOAH, https://wahis.woah.org/#/in-review/6314

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#Spain - #Influenza A #H5N1 viruses of high pathogenicity (Inf. with) (non-poultry including wild birds) (2017-) - Immediate notification

 This event will collect the detections made by sampling carried out in 2025. Peregrine falcon, adult male, transmitted to a Centre for the protection of endangered species on 05/02/2025 with nervous symptoms, that died on 06/02/2025. The necropsy was performed at the Wildlife Center for Analysis and Diagnosis.

Source: WOAH, https://wahis.woah.org/#/in-review/6316

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Variable #DPP4 #expression in multiciliated cells of the #human #nasal #epithelium as a determinant for #MERS-CoV tropism

Significance

Middle East respiratory syndrome coronavirus (MERS-CoV) is a highly pathogenic coronavirus that continues to cause periodic outbreaks in humans with a case-fatality rate of approximately 35%. MERS-CoV generally transmits poorly, but superspreading events are well documented. Efficient human-to-human transmission of respiratory viruses generally correlates with a tropism for the upper respiratory tract, but this tropism for MERS-CoV remains poorly understood. Characterizing the MERS-CoV tropism in the human upper respiratory tract is of critical importance to understand its epidemiology and pandemic potential of future MERS-CoV variants and other dipeptidyl peptidase 4 (DPP4)-utilizing coronaviruses present in animal reservoirs.


Abstract

Transmissibility of respiratory viruses is a complex viral trait that is intricately linked to tropism. Several highly transmissible viruses, including severe acute respiratory syndrome coronavirus 2 and Influenza viruses, specifically target multiciliated cells in the upper respiratory tract to facilitate efficient human-to-human transmission. In contrast, the zoonotic Middle East respiratory syndrome coronavirus (MERS-CoV) generally transmits poorly between humans, which is largely attributed to the absence of its receptor dipeptidyl peptidase 4 (DPP4) in the upper respiratory tract. At the same time, MERS-CoV epidemiology is characterized by occasional superspreading events, suggesting that some individuals can disseminate this virus effectively. Here, we utilized well-differentiated human pulmonary and nasal airway organoid-derived cultures to further delineate the respiratory tropism of MERS-CoV. We find that MERS-CoV replicated to high titers in both pulmonary and nasal airway cultures. Using single-cell messenger-RNA sequencing, immunofluorescence, and immunohistochemistry, we show that MERS-CoV preferentially targeted multiciliated cells, leading to loss of ciliary coverage. MERS-CoV cellular tropism was dependent on the differentiation of the organoid-derived cultures, and replication efficiency varied considerably between donors. Similarly, variable and focal expression of DPP4 was revealed in human nose tissues. This study indicates that the upper respiratory tract tropism of MERS-CoV may vary between individuals due to differences in DPP4 expression, providing an explanation for the unpredictable transmission pattern of MERS-CoV.

Source: Proceedings of the National Academy of Sciences of the United States of America, https://www.pnas.org/doi/10.1073/pnas.2410630122

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A #human-infecting #H10N5 avian #influenza virus: #clinical features, virus #reassortment, #receptor-binding affinity, and possible #transmission routes

Abstract

Background

In late 2023, the first human case caused by an H10N5 avian influenza virus (AIV) was diagnosed in China. H10Ny AIVs have been identified in various poultry and wild birds in Eurasia, the Americas, and Oceania.

Methods

We analyzed the clinical data of the H10N5 AIV-infected patient, isolated the virus, and evaluated the virus receptor-binding properties together with the H10N8 and H10N3 AIVs identified in humans and poultry. The genomic data of the human-infecting H10N5 strain and avian H10Ny AIVs (n = 48, including 16 strains of H10N3 and 2 strains of H10N8) from live poultry markets in China, during 2019–2021, were sequenced. We inferred the genetic origin and spread pattern of the H10N5 AIV using the phylodynamic methods. In addition, given all available nucleotide sequences, the spatial-temporal dynamics, host distribution, and the maximum-likelihood phylogenies of global H10 AIVs were reconstructed.

Findings

The first H10N5 AIV-infected human case co-infected with seasonal influenza H3N2 virus was identified. Unfortunately, the patient died after systematic treatments. The H10N5 virus predominantly bound avian-type receptor, without any known mammalian-adapted mutations. Phylodynamic inference indicated that the H10N5 AIV was generated by multiple reassortments among viruses from Korea and Japan, central Asia, and China in late 2022, acquiring the seven gene segments from H10N7 or other low pathogenic AIVs in wild Anseriformes, except for the PA gene from H5N2 AIVs in Domestic Anseriformes. The HA gene of the H10N5 virus belongs to the North American lineage, which was probably introduced into Asia by migratory birds, subsequently forming local circulation.

Interpretation

Unlike the human-infecting H10N3 and H10N8 AIVs acquiring six internal protein-coding genes from H9N2 AIVs in domestic poultry, the human-infecting H10N5 AIV was generated through multiple reassortments among viruses mainly carried by wild Anseriformes. Furthermore, worldwide distribution, inter-continental transmission, and genetic exchanges between Eurasian and North American lineages call for more concerns about influenza surveillance on H10Ny AIVs, especially in the flyway overlapping areas.

Source: Journal of Infection, https://www.journalofinfection.com/article/S0163-4453(25)00050-7/fulltext

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#Belgium - #Influenza A #H5N1 viruses of high pathogenicity (Inf. with) (non-poultry including wild birds) (2017-) - Follow up report 8

Two wild cats, two European Polecats, Forty-four Domestic Mustelidae, Twenty-two foxes in various Regions.

Source: WOAH, https://wahis.woah.org/#/in-review/4971?reportId=172740&fromPage=event-dashboard-url

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#Risk to People in #USA from Highly Pathogenic Avian #Influenza A(#H5N1) Viruses {as of Feb. 28 '25}



As of February 28, 2025

CDC assessed the risk from H5N1 viruses to the U.S. general population and to populations in the United States with contact with potentially infected animals, including through contaminated surfaces or fluids. Risk describes the potential public health implications and significance of an outbreak for populations assessed. See definitions below for more detail.


{Risk posed by H5N1 viruses to the United States. Please see methods section for further information on definitions of terms.}

___

The purpose of this assessment is to evaluate the current public health risk of H5N1 viruses to the general U.S. population and to those in contact with potentially infected animals or contaminated surfaces or fluids, and to inform public health preparedness efforts.

CDC assessed risk by considering both likelihood and impact of infection in each population (...). Both the likelihood and impact of infection are assessed at a population level. Likelihood of infection refers to the probability of infection occurring in the population of interest and considers factors such as the likelihood of transmission to or within the population, the number of people exposed and/or infected, population immunity against infection, and effectiveness or capacity of public health measures to limit spread. Impact of infection considers factors such as the severity of disease, level of population immunity against severe disease, availability of resources to limit impact, and necessary public health response resources.

This assessment outlines the current risk posed by H5N1 viruses to populations in the United States based on currently available data; however, this risk could change. H5N1 viruses are of public health concern because of their pandemic potential. If an H5N1 virus acquires the ability through genetic mutation or reassortment to cause sustained human-to-human transmission, it could cause a pandemic. Because influenza viruses constantly change, CDC monitors these viruses routinely, works to prevent further spread of H5N1 viruses between animals and people, and coordinates H5N1 preparedness activities. CDC will update this risk assessment as needed.


Risk assessment for general U.S. population


{Risk posed by H5N1 viruses to the general U.S. population. Please see methods section for further information on definitions of terms.}

___

Risk

CDC assesses the overall risk to the general U.S. population as low, with moderate confidence. Of note, for any individual in this population, risk will vary depending on nature of, frequency, and time spent in contact with infected or potentially infected animals or contaminated surfaces or fluids. We also include a section below on factors that could change our assessment.

Likelihood

CDC assesses the likelihood of infection for the general U.S. population as very low. Factors that informed our assessment of likelihood include the following:

- To date, there has been no evidence of human-to-human spread of H5N1 viruses in the United States, and there have been very few reported cases among people in the general population to date. The majority of confirmed human H5N1 cases in the United States since 2024 (67 of 70) were associated with exposure to infected animals, including poultry and dairy cows. Three U.S. cases in humans with no known exposure to infected animals have been identified.

- The likelihood of exposure is higher among people in settings where infected birds or dairy cows have been identified, including occupational settings. See our risk assessment for populations in contact with potentially infected animals below.

- To date, there has been little evidence of genetic changes that suggest adaptation to humans.

- Genetic analysis of samples from the fatal Louisiana case detected low frequency changes that may result in the increased ability of these viruses to infect the human upper respiratory tract. These or similar changes or mutations may be needed for H5N1 viruses to be able to spread more easily to and among humans.

- The observed genetic changes in the patient's H5N1 virus, when compared with the virus identified from the patient's backyard poultry (the presumed source of human infection), suggest that the changes were likely generated by virus replication in this patient after hospital admission for advanced disease and were not present at the time of infection.

- Genetic analysis of samples from the Wyoming and Nevada cases found mutations that have previously been associated with more efficient H5N1 virus replication in mammalian cells and in people.

- The likelihood of exposure is higher among people consuming raw (unpasteurized) milk from infected animals, although the chance of people acquiring H5N1 virus infection from consuming raw milk is not clear at this time.

- Consumption of raw milk can lead to other serious health outcomes, especially for certain populations. CDC and FDA recommend against consuming raw milk.

- Raw milk sold commercially in California has tested positive for H5N1 virus. While USDA's National Milk Testing Strategy tests milk samples from across the country before pasteurization, raw milk in many states can be purchased directly from the farms where it is produced, and may not be captured in these testing protocols.

- There are no confirmed cases of human H5N1 virus infection associated with consuming contaminated raw milk. However, animals such as mice and cats have been infected following consumption of milk contaminated with H5N1 virus, and the possibility of human infection with H5N1 virus through ingestion of raw milk cannot be ruled out.

- The United States has resources to detect symptomatic human cases of H5N1 and can implement measures to reduce opportunities for onward spread, at the current rate of infection (on average, approximately six to seven cases per month since April 2024).

- Human cases of H5N1 are nationally notifiable, meaning every identified case is investigated by local and state public health and reported to CDC.

- CDC and a wide range of public health and healthcare partners conduct regular monitoring for influenza viruses and illness activity, reviewing data from case reporting, public health laboratory monitoring, clinical laboratory trends, ED visits, and wastewater surveillance.

- As of February 2025, more than 136,000 specimens have been tested using a protocol that would have detected A(H5) virus, and more than 15,000 people have been monitored after exposure to animals infected with H5N1 virus.

- CDC now recommends subtyping of all influenza A virus-positive specimens from hospitalized patients on an accelerated basis.

- CDC has also provided interim recommendations for prevention, monitoring, and public health investigations that indicate, where feasible, an expansion of testing to include an offer of testing to asymptomatic individuals with high likelihood of unprotected exposure to H5N1 virus.

- Three commercial testing laboratories (Quest Diagnostics, Labcorp, and ARUP) in the United States now offer A(H5) testing, significantly increasing testing access and diagnostic capacity.


Impact

CDC assesses the impact of infection for the general U.S. population as moderate. Factors that informed the assessment of impact include the following:

- The majority of reported U.S. cases have had mild illness characterized by conjunctivitis and/or upper respiratory symptoms, irrespective of the genotype. Of the three confirmed cases of H5N1 in humans in 2025, one was in a dairy worker, and two people had exposure to poultry and experienced severe illness requiring hospitalization.

- On December 13, 2024, CDC confirmed a severe case of H5N1 in an individual in Louisiana. The patient was infected with a genotype of H5N1 virus closely related to viruses recently detected in wild birds and poultry in the United States and in recent human cases in British Columbia, Canada, Iowa, and Washington State. The patient in Louisiana died, and the patient in British Columbia was critically ill.

- Historically, there has been a wide clinical spectrum of H5N1 illness (mild to severe), and deaths have occurred. Prior to the current U.S. outbreak, most reported human H5N1 cases since 1997 were identified late in the course of illness after hospital admission and with severe disease (e.g., pneumonia).

- The general population is not known to have specific immunity against H5N1 virus.

- Medical countermeasures are available to help limit the severity of disease should a member of the general U.S. population become infected.

- Genetic analysis suggests that that H5N1 viruses currently circulating among wild birds, poultry, and dairy cattle in the United States are susceptible to available FDA-approved influenza antiviral medications. Antiviral treatment is currently recommended for patients with confirmed or suspected H5N1 virus infection.

- Antiviral post-exposure prophylaxis can be used to help prevent infection or illness and could be used specifically in those who had unprotected exposure to infected animals.

- Additionally, prompt treatment has been shown to attenuate severe seasonal influenza disease.

- No FDA-authorized or approved vaccines for prevention of H5N1 virus infection are currently commercially available for the general population in the United States.

- However, under the National Pre-Pandemic Influenza Vaccine Stockpile (NPIVS) program, the Department of Health and Human Services routinely develops vaccines against a wide range of novel influenza A viruses, including H5N1 viruses, and efforts are under way to accelerate the availability of a well-matched vaccine and increase inventory.

- The animal and public health response to outbreaks in poultry and dairy cows has societal and economic impacts for the U.S. general population, including the rise of egg prices, a decrease in milk production, and food recalls.


Confidence

CDC has moderate confidence in this assessment. This degree of uncertainty is due to several factors, including variability in levels of testing among different animal populations and by geography, as well as the role of wild bird exposure in causing human infections, as the prevalence of H5N1 virus infections in wild birds is difficult to assess. There is additional uncertainty on likelihood of human exposures from other infected animals, including exposure to infected cats (house cats or big cats in zoo and animal sanctuary settings). CDC also recognizes uncertainty in impact, as the effects of transmission route and virus genotype in human infection are unclear.


Risk to populations in contact with potentially infected animals or contaminated surfaces or fluids


{Risk posed by H5N1 viruses to populations in contact with potentially infected animals or contaminated surfaces or fluids. Please see methods section for further information on definitions of terms.}


Risk

The risk posed by H5N1 viruses to humans in contact with potentially infected animals or contaminated surfaces or fluids is moderate to high. Of note, for any individual in this population, risk will vary depending on use of workplace controls including personal protective equipment (PPE), nature and frequency of exposure, and time spent in contact with infected or potentially infected animals or contaminated surfaces or fluids. We also include a section below on factors that could change our assessment.


Likelihood

CDC assesses the likelihood of infection for populations in contact with potentially infected animals or contaminated surfaces or fluids as low to high. Individual risk will vary depending on the frequency, duration, and nature of contact with potentially infected animals. The likelihood of exposure from important classes of animals are outlined below:

- The likelihood of exposure to H5N1 viruses from infected commercial poultry and dairy cows is moderate to high.

- H5N1 viruses are widespread in U.S. poultry and dairy cows, with detections in more than 160,000,000 birds in all 50 states since January 2022 and more than 970 dairy herds in 17 states since January 2024.

- The majority of individuals with confirmed H5N1 virus infection (67 of 70) had exposures associated with commercial agriculture or backyard poultry.

- Of these, 41 were exposed to dairy herds (cows) and 24 were exposed to poultry farms and culling operations.

- Some workers were identified as cases before any animals on the farm had tested positive for H5N1.

- Among dairy workers (including veterinarians), the likelihood of exposure may be particularly high among those working in milking parlors and other environments with contaminated surfaces and fluids.

- Use of PPE is low among this population, and increased availability and use can decrease the likelihood of exposure, especially for workers in direct contact with animals or their secretions.

- Several serosurveys have been conducted to identify recent infections that may not have been detected. For example, in a serosurvey of bovine practitioners, evidence of infection was found in three individuals who were asymptomatic, including two without exposures to animals with known or suspected H5N1 virus infection and one who did not practice in a state with known infected cattle. In a serosurvey of dairy workers in Michigan and Colorado, 7% of those tested had serologic evidence of infection.

- The likelihood of exposure to H5N1 viruses from infected non-commercial poultry and wild birds is moderate.

- H5N1 viruses also circulate among non-commercial poultry and wild birds, and among some other wild animals. H5N1 viruses have been detected in more than 12,000 wild birds across 52 jurisdictions in the United States since January 2022.

- Exposure to sick or dying birds infected with H5N1 viruses, including potentially through contaminated fluids or surfaces, raises the likelihood of human infection. Exposure risk may be elevated in populations with animal contact, such as backyard poultry farmers and wild bird or waterfowl hunters.

- The likelihood of exposure to H5N1 viruses from recreational animal activities, such as visiting agricultural fairs, livestock shows, or petting zoos, is low to moderate.

- None of the reported cases had a known exposure to an animal involved in a recreational animal activity.

- Animal monitoring and infection control measures have the potential to reduce the likelihood of exposure to H5N1 viruses for people.

- USDA Federal Orders require mandatory testing of lactating dairy cows prior to interstate movement, and require herd owners with positive cows to provide epidemiological information to facilitate contact tracing and disease monitoring. Additionally, national testing programs are in place for monitoring wild birds and poultry.

- Extensive monitoring of exposed persons and public health control efforts are in place. CDC has interim recommendations for prevention, monitoring, and public health investigations of human cases of H5N1. CDC also has recommendations for worker protection and use of personal protective equipment (PPE) to reduce the risk of exposure.

- People with job-related or recreational exposures to birds or infected mammals can reduce their chance of infection using appropriate precautions to protect against H5N1.


Impact

CDC assesses the impact of human infection via exposure to potentially infected animals as moderate. In addition to the factors outlined in the Impact section for the general population, CDC notes economic and policy impacts, including the financial loss associated with population culling, product disposal, and loss of production. As of November 2024, more than $1.4 billion has been spent on response to ongoing H5N1 outbreaks in animals, and egg demand continues to exceed supply.


Confidence

CDC has moderate confidence in this assessment. This degree of uncertainty is due to factors including variability in levels of A(H5) testing among different animal populations and by geography, as well as the role of wild bird exposure in human infection, as the true prevalence of infection in animal populations is difficult to assess. There is additional uncertainty on likelihood of exposure to other infected animals, including exposure to infected cats (house cats or big cats in zoo and animal sanctuary settings). CDC also notes uncertainty in impact due to limited evidence on whether illness severity differs by transmission route and virus genotype.


Future Risk

This assessment outlines the risk posed to the United States by H5N1 viruses as of February 28, 2025, but CDC stresses this risk could change, as influenza A viruses can mutate quickly, and therefore have the potential to cause pandemics.

The viral changes needed to cause a pandemic are unpredictable. However, the high prevalence of H5N1 virus infections among animals in close contact with humans increases opportunities for mutation or reassortment that could lead to sustained person-to-person spread, causing a pandemic. It is possible that co-infections with seasonal influenza A and H5N1 viruses in the same person or animal provide opportunities for reassortment of genes between two influenza A viruses, potentially resulting in an influenza A virus with characteristics of both seasonal influenza A and H5N1 viruses that is more efficiently transmitted among people than current H5N1 viruses circulating among birds, cows, and other animals.

H5N1 virus infection can cause severe illness in people; H5N1 viruses historically have caused severe cases in humans. CDC has developed H5 candidate vaccine viruses (CVVs) that are expected to be effective against H5N1 viruses now circulating among wild birds, poultry, and cows in the United States. These H5 CVVs could be used to produce a vaccine for people, if needed, thereby reducing the risk for severe disease among humans. Access to antivirals for treatment or post-exposure prophylaxis could also decrease future risk of severe illness or transmission.

(...)


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