#Genomic #wastewater #surveillance of seasonal and #zoonotic #influenza A viruses in #California during the 2024-2025 flu season

 

Abstract

Wastewater genomic surveillance provides an opportunity to detect human and animal influenza A virus (IAV). We aimed to implement an IAV genomic surveillance framework agnostic to subtype, which enables recovery of IAV from multiple hosts and estimation of proportions across subtypes. We conducted IAV genomic surveillance in wastewater during the 2024-2025 flu season at multiple sites in California and compared these data with available human clinical IAV sequences and test positivity. We applied a custom whole-genome, multi-host IAV probe enrichment panel and adapted our custom expectation-maximization (EM) algorithm to deconvolute IAV mixtures in wastewater and infer subtype relative abundances. Absolute IAV concentrations were quantified using RT-PCR-based assays. H5N1 wastewater and clinical sequences were further characterized by constructing a whole-genome maximum-likelihood phylogenetic tree. Finally, we performed variant analysis to examine amino acid substitutions detected in wastewater. Our IAV probe enrichment method and EM algorithm successfully enriched all eight segments of three circulating IAV subtypes and accurately estimated subclade relative abundances for mixed IAV samples. Seasonal human H1N1pdm09 and H3N2 were detected throughout the study period from both wastewater and clinical sequencing data, with H1N1 subclades 6B.1A.5a.2a.1 and 6B.1A.5a.2a co-circulating, and H3N2 dominated by subclade 3C.2a1b.2a.2a.3a.1. Wastewater surveillance consistently detected H5N1 clade 2.3.4.4b across three monitored wastewater sites, while clinical H5N1 detections, from anywhere in CA, were sporadic and rare. Whole-genome phylogenetic analysis revealed that wastewater H5N1 sequences clustered with reference sequences associated with dairy cow and avian infections, while all human clinical H5N1 sequences clustered exclusively with reference sequences associated with dairy cow infections. Amino acid substitutions were identified across viral segments, and no mutations associated with mammalian adaptation were observed from wastewater samples.

Competing Interest Statement

The authors have declared no competing interest.

Source: 

Link: https://www.medrxiv.org/content/10.64898/2026.06.10.26355323v1

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#USA, #Andes #Hantavirus Update: No Cases in #California (Dept. of Health, May 14 '26)

 

May 13, 2026​ | NR26-020

One additional Californian with possible exposure, no cases of Andes hantavirus disease in the state ​

    SACRAMENTO – The U.S. Centers for Disease Control and Prevention (CDC) has notified the California Department of Public Health (CDPH) of a fifth California resident with potential exposure to Andes hantavirus as a result of the outbreak aboard the MV Hondius cruise ship. 

    This individual disembarked the MV Hondius before the outbreak was identified, returned briefly to California and left for additional travel also before the outbreak was identified. 

    The individual is currently in the Pitcairn Islands, a British Overseas Territory in the South Pacific. Their health is being monitored by the CDC, in coordination with British health officials, and they remain asymptomatic. 

Andes Hantavirus Investigation in California 

    There are currently no reported cases of Andes hantavirus disease in California or in California residents, nor in United States residents.  ​

    In total, there are now five possibly exposed Californians undergoing monitoring for their health status. 

    In addition to the person in the Pitcairn Islands, two individuals are in California in Santa Clara and Sacramento counties, and two are in the National Quarantine Unit at the University of Nebraska Medical Center (UNMC) in Omaha, Nebraska. 

    At this time, CDPH does not have additional information to share regarding the two Californians in Nebraska, including when they will return to the state. 

    Currently, to our knowledge, all five individuals undergoing public health monitoring do not have any symptoms of illness from hantavirus, and the two individuals in California are in close contact with local public health officials to assure they remain healthy and following public health direction to limit interaction with others.    ​

    CDPH remains in close contact with the CDC and the World Health Organization (WHO). This is an evolving situation, and information is current as of May 13. New or changing information will be updated as it becomes available.   

Helpful Language for Media and Communicators 

    CDPH, in coordination with its partners, is monitoring five individuals with possible exposure. There are no cases in California or among California residents. 

Table of California Possible Exposures 

    1) ​Exposure Location​: ​Onboard MV Hondius

        - ​Current Location: ​Santa Clara County

        - ​Current Status: ​Undergoing monitoring; asymptomatic

        - ​Number of California Residents: 1

    2-3) ​Exposure Location: ​Onboard MV Hondius  ​

        - ​Current Location: ​Nebraska

        - Current Status: ​Undergoing monitoring; asymptomatic

        - ​Number of California Residents: ​2

    4) ​Exposure Location: ​On Flight with Known non-CA Case

        - ​Current Location: ​Sacramento County

        - Current Status: ​Undergoing monitoring; asymptomatic

        - ​Number of California Residents: ​1

    5) ​Exposure Location: ​Onboard MV Hondius  ​

        - Current Location: ​Pitcairn Islands  

        - Current Status: ​Undergoing monitoring; asymptomatic  

        - Number of California Residents: 1

    -- ​Total: ​5​

Source: 

Link: https://www.cdph.ca.gov/Programs/OPA/Pages/NR26-020.aspx

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#USA, California DPH Confirms Four Californians Being Monitored for #Andes #Hantavirus Exposure Related to Cruise Ship ​​(May 12 '26)

 

May 11, 2026 | NR26-019

Three exposed on cruise ship, one     other exposed on international flight. Risk to the public is extremely low. 

-- What You Need to Know: 

CDPH continues to closely coordinate with federal and local public health officials following notification that three California residents were aboard the MV Hondius, a Dutch cruise ship that experienced an outbreak of Andes hantavirus. 

An additional California resident was identified who was on an international flight sitting near an ill returning cruise passenger who later was confirmed to have Andes hantavirus.  

SACRAMENTO – The California Department of Public Health (CDPH) continues to coordinate with the U.S. Centers for Disease Control and Prevention (CDC) and local health officials to monitor four Californians exposed to the outbreak of Andes hantavirus that occurred aboard the cruise ship MV Hondius.  

Two of these individuals have returned to their respective homes and are being monitored by their local public health officials. 

Two additional California residents have been transported to the United States by federal authorities. 

They will return to California once health assessments have been done and arrangements have been made to protect their and the public’s health. 

The risk to the public remains extremely low. 

On May 8, CDPH announced that one individual from California had returned to the state and is being monitored by local public health officials. 

This weekend, CDC notified CDPH of an additional contact now under active monitoring in California due to potential exposure with a confirmed case on a shared flight. 

Two other California residents who were on the MV Hondius have been evacuated to a secure medical facility in Nebraska. 

"We understand public concern about this unusual outbreak," said Dr. Erica Pan, State Public Health Officer and CDPH Director. 

"Decades of experience in South America have shown that this Andes hantavirus rarely spreads between people. We continue to work with federal and local officials to monitor the health of potentially exposed individuals and prepare for our Californians to come home.” 

The Californians currently in Nebraska will be transported home after further health assessment and appropriate arrangements have been made to protect their and public health. 

After their return, local health officials will monitor the returned passengers as necessary. 

Currently, public health monitoring protocol includes daily temperature checks, assessment for any symptoms consistent with hantavirus, and direction to modify activities. 

Prior to response efforts related to this outbreak, the CDPH Viral and Rickettsial Disease Laboratory (VRDL) was the only public health laboratory in the U.S. with a validated diagnostic hantavirus PCR assay to conduct testing for hantavirus. 

If any exposed individual develops symptoms consistent with infection, California has the capability to test in the state.  

CDPH VRDL is also providing technical assistance to other laboratories across the country to support testing capacity. 

CDPH is coordinating closely with hospitals who can care for potential hantavirus cases and has issued clinical health advisories to clinicians to provide guidance for appropriate care.  

The risk to the public remains extremely low. 

About Hantavirus & Transmission Ris​​k

Hantavirus is a group of viruses that spread through the urine, droppings (feces), and saliva of wild rodents. 

Hantaviruses include both the Sin Nombre and Andes virus strains. 

The Andes hantavirus identified in this cruise ship outbreak is found in the southern Andes region of Argentina and Chile. 

Andes hantavirus has also been associated with rare human‑to‑human transmission after close, prolonged contact with an ill infected person. 

Andes hantavirus is different than the Sin Nombre hantavirus, which is native to California and North America. Sin Nombre hantavirus has not been associated with person-to-person transmission. 

From 1980 to 2025, 99 California residents have been diagnosed with Sin Nombre hantavirus infection. 

Hantavirus Pulmonary Syndrome (HPS) is a rare but severe respiratory illness that can develop following exposure. 

Early symptoms resemble influenza, can include gastrointestinal symptoms, and can progress rapidly to life‑threatening respiratory distress. 

The fatality rate is approximately 30 - 40 percent. 

There is no antiviral treatment for hantavirus and HPS typically needs aggressive critical medical supportive care. 

Further Reading and Upd​ates

More information on hantavirus is available on CDPH’s hantavirus website and from the CDC’s hantavirus web page. An update on the federal government evacuation and repatriation efforts was issued in a CDC health alert on Friday, May 8. 

This is a dynamic and evolving investigation and response. CDPH will continue to update the public as new information becomes available. ​

Source: 

Link: https://www.cdph.ca.gov/Programs/OPA/Pages/NR26-019.aspx

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Serologic #Evidence of #Influenza #H5N1 Virus #Infection in a #Veterinary Professional Exposed to an Infected #Cat — Los Angeles County, #California, Dec. '24–Jan. '25

 

Summary

-- What is already known about this topic?

- Transmission of influenza A(H5N1) viruses from domestic cats to humans has not been documented.

-- What is added by this report?

- During November 2024–January 2025, a total of 139 persons exposed to 19 A(H5N1)-infected domestic cats that consumed raw animal products were identified in Los Angeles County, California. Among 25 exposed persons who received serologic testing, one asymptomatic veterinary professional had serologic evidence of A(H5N1) infection after occupational exposure to an A(H5N1)-infected cat.

-- What are the implications for public health practice?

- These findings provide evidence of zoonotic transmission of influenza A(H5N1) virus from domestic cats to humans. Pet owners are advised not to feed raw animal products to cats. Veterinary professionals should be aware of infection risks, use appropriate personal protective equipment, and adhere to recommended infection control practices to reduce the risk for zoonotic transmission of influenza A(H5N1).

Abstract

Since 2021, avian influenza A(H5N1) clade 2.3.4.4b viruses have spread widely among wild birds and domesticated poultry in the United States, with sporadic spillover into mammals. During November 2024–January 2025, 19 domestic cats in Los Angeles County, California, became ill after consumption of commercially purchased raw milk, raw meat, or raw pet food; nine cats tested positive for influenza A(H5N1) virus (clade 2.3.4.4b genotype B3.13). Overall, 139 persons were exposed to the 19 infected cats, and all were monitored for symptoms. Although 30 persons reported influenza-like illness symptoms, none received a positive influenza A(H5) reverse transcription–polymerase chain reaction (RT-PCR) test result. In April 2025, the Los Angeles County Department of Public Health and CDC invited all exposed persons to participate in an influenza A(H5N1) serosurvey to determine whether transmission of influenza A(H5N1) virus occurred, including in those without symptoms. Sera from 25 (18%) of the 139 exposed persons were tested. Among these, antibodies specific to A(H5N1) clade 2.3.4.4.b (antigenically similar to the clade 2.3.4.4.b influenza A[H5N1] virus isolated from the infected cats) were detected in serum from one veterinary professional, who was asymptomatic. This person did not use respiratory or eye protection during the exposure, did not report influenza-like illness after the exposure, and reported no other known risk factors for A(H5N1) infection. These findings represent serologic evidence of possible transmission of influenza A(H5N1) clade 2.3.4.4.b virus from a domestic cat to a human, highlighting concerns about potential cat-to-human transmission of influenza A(H5N1) virus and the importance of infection control practices in veterinary settings.

Source: 

Link: https://www.cdc.gov/mmwr/volumes/75/wr/mm7517a1.htm?s_cid=OS_mm7517a1_e&ACSTrackingID=USCDC_921-DM155047&ACSTrackingLabel=Week%20in%20MMWR%3A%20Vol.%2075%2C%20May%207%2C%202026&deliveryName=USCDC_921-DM155047

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#Surveillance on #California dairy #farms reveals multiple possible sources of #H5N1 #influenza virus #transmission

 

Abstract

Transmission routes of highly pathogenic H5N1 between cows or to humans remain unclear due to limited data from affected dairy farms. We performed air, farm wastewater, and milk sampling on 14 H5N1-positive dairy farms across two different California regions. Infectious virus was detected in the air in milking parlors and in wastewater streams, while viral RNA was found in exhaled breath of cows. Sequence analysis of infectious H5N1 virus from air and wastewater samples on one farm revealed viral variants relevant for potential human susceptibility. Longitudinal analysis of milk from the individual quarters of cows revealed a high prevalence of subclinical H5N1-positive cows. Additionally, a heterogeneous distribution of infected quarters that maintained a consistent pattern over time was observed, inconsistent with shared milking equipment serving as the sole transmission mode. The presence of subclinically infected cows was further supported by detection of antibodies in the milk of animals that exhibited no clinical signs during the H5N1 outbreak on one farm. Our data highlight additional sources and potential modes of H5N1 transmission on dairy farms.

Source: 

Link: https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3003761

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Highly Pathogenic Avian #Influenza #H5N1 Virus #RNA in #Bovine #Semen, #California, #USA, 2024

 

Abstract

Since March 2024, highly pathogenic avian influenza (HPAI) A(H5N1) virus has infected dairy cattle in the United States, prompting concern about novel transmission routes. During an outbreak in California, HPAI H5N1 RNA was detected in an asymptomatic bull’s semen. Although infectious virus was not isolated, semen-associated transmission risks and biosecurity practices remain a concern.

Source: 

Link: https://wwwnc.cdc.gov/eid/article/32/5/25-1639_article

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Rapid #Decline of #Nesting Peregrine #Falcons in the San Francisco Bay Region of #California Synchronous with an #H5N1 #Outbreak

 

Abstract

After rebounding from near extirpation during the organochlorine era, breeding Peregrine Falcons (Falco peregrinus) in California are again facing adversity, this time consistent with an outbreak of a highly pathogenic avian influenza. Following the first detection of the H5N1 variant clade 2.3.4.4b virus in California wild birds in July 2022, we assembled data from long-term monitoring (2000-2025) of peregrine breeding territory occupancy in the broad vicinity of San Francisco Bay to examine possible impacts on falcon populations. Prior to the outbreak, 47 focal breeding territories had shown nearly complete occupancy by pairs (98.5% of 390 site-years), with very few vacancies, single birds in attendance, or subadult pair members. Within 8 mo of the outbreak, occupancy had dropped to 65.1%, and 2 yrs later (2025), only 36.2% of sites remained occupied. An uptick in site-occupancy by single birds also occurred after the outbreak, but it is unclear whether these were survivors or floaters attempting to fill vacant territories where both pair members had perished. The high vacancy rates signaled an impact upon floaters (nonbreeding adults) that normally buffer breeding site-occupancy in healthy peregrine populations. From October 2022 through November 2025, 17 peregrine fatalities were diagnosed with H5N1 within the counties comprising our study area. Evidence that H5N1 caused these territory vacancies includes, (1) the striking temporal coincidence of occupancy loss with the outbreak, and (2) the lethality of the virus to peregrines and its confirmed presence in peregrine prey in our study area. Our study reaffirms the value of long-term territory occupancy monitoring in this sentinel species.

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

Helen and Will Webster Foundation

Ahmanson Foundation, https://ror.org/01eywvb34

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.02.11.705416v1

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One confirmed and one potential #human case of #influenza #H5N1 detected through an expanded subtyping protocol

 

ABSTRACT

Current U.S. surveillance for highly pathogenic avian influenza A(H5N1) in humans prioritizes individuals with known animal exposures, potentially missing community-acquired infections. To address this gap, we implemented universal H5 subtyping of all influenza A-positive respiratory samples collected within our hospital system, regardless of patient exposure history. Between August 2024 and April 2025, we subtyped 4,488 influenza A-positive samples and identified two cases positive for H5 RNA in Alameda County, California, USA. The first case was a 14-month-old girl with mild respiratory symptoms and no H5N1 exposure risks; sequencing of the sample revealed an H5 gene closely related to clade 2.3.4.4b, genotype B3.13 viruses circulating in U.S. dairies. The second case was a 79-year-old male, also with no known exposures, whose sample reproducibly tested positive with a high cycle threshold value but could not be confirmed by public health laboratories. Both patients had evidence of co-infection with other common respiratory viruses. These findings, while requiring cautious interpretation due to low virus levels and the presence of potential confounding factors, highlight limitations in exposure-based testing and demonstrate the potential for cryptic H5N1 circulation. This report underscores that broader, geographically targeted surveillance may be a critical tool for early detection of potential community transmission of pandemic-capable pathogens.

Source: 

Link: https://journals.asm.org/doi/10.1128/asmcr.00165-25

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#Influenza A Virus detection in Bulk Tank and Pen Level #Milk from #Dairies Affected by Highly Pathogenic Avian Influenza #H5N1

 

Abstract

Highly pathogenic avian influenza virus H5N1 has been infecting dairy herds in the U.S. since its initial incursion into cows in early 2024. Although national strategies have aimed to detect affected herds, the best way to surveil herds for the H5N1 virus has not been formally studied and we also do not understand herd-level patterns of infection. To understand infection patterns of H5N1 in dairy herds over time, we conducted early surveillance of non-affected farms in California in the Fall of 2024 in an observational study. Daily bulk tank milk (BTM) samples were submitted from each herd and tested for influenza A (IAV) via rRt-PCR. In a subset of herds, IAV testing of multiple excretion types from cattle of different classes and pen-level daily milk was also completed soon after BTM detection. Daily detections of IAV occurred in BTM for a minimum of 33 days, with some herds continuing to have detection beyond a 75-day window. BTM Ct nadirs were seen between 1-3 weeks of detection. In herds that were tested, virus was detected in the milk from all pens of cattle within a very short time frame after BTM detection, or prior to the initiation of pen level sampling. A very low percentage (2.8%) of individual cow samples tested positive for IAV when collected soon after BTM detection, and although the virus was found in all excretion types, a majority of positive samples were from milk. This suggests that BTM may be the best early indicator of herd infection, and that movement of the virus to all lactating pens of cattle after herd incursion is relatively quick. These results also suggest that surveillance strategies with a long interval between BTM testing days may miss herds with short infection windows. Because most herds experienced test days where some submitted BTM samples had virus detected while others did not, and virus was detected in pen level milk samples when the BTM from the herd had become test negative, this work also highlights the necessity of studying the test sensitivity of IAV rRt-PCR detection in aggregate milk samples.

Competing Interest Statement

The authors have declared no competing interest.

Funding Statement

This project was completed using Federal funds provided through the United States Department of Agriculture, Cooperative Agreement 25-9419-0731 and the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Department of Health and Human Services, under Contract No. 75N93021C00016.

Source: MedRxIV, https://www.medrxiv.org/content/10.1101/2025.10.26.25338833v1

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Unexpected #Detection of Highly Pathogenic Avian #Influenza (HPAI) #H5N1 virus in #bovine #Semen

 

Abstract

Since March 2024, HPAI H5N1 virus has infected dairy cattle in the U.S., prompting concern about novel transmission routes. During an outbreak in California, HPAI H5N1 RNA was detected in an asymptomatic bull's semen. Although infectious virus was not isolated, questions remain about semen-associated transmission risks and biosecurity practices.

Competing Interest Statement

The authors have declared no competing interest.

Source: BioRxIV, https://www.biorxiv.org/content/10.1101/2025.10.16.682947v1

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Highly Pathogenic Avian #Influenza #H5N1 Virus #Infection in a #Child with No Known Exposure — San Francisco, #California, December 2024–January 2025

 

Summary

-- What is already known about this topic?

- As of January 1, 2025, 37 human cases of highly pathogenic avian influenza (HPAI) A(H5N1) had been detected in California, none of which occurred in San Francisco.

-- What is added by this report?

- On January 9, 2025, a case of HPAI A(H5N1) infection was identified in a school-aged child in San Francisco through enhanced surveillance (influenza A virus subtyping of a sample of specimens weekly). No source of exposure was identified, and investigations found no laboratory evidence of human-to-human transmission among close contacts.

-- What are the implications for public health practice?

- Enhanced surveillance and timely subtyping of a subset of influenza A–positive specimens, including specimens from persons without known A(H5N1) exposure, are important to detect avian influenza A virus infections. Public health investigations are critical to monitoring for human-to-human transmission.

Abstract

In response to a highly pathogenic avian influenza (HPAI) A(H5N1) outbreak in U.S. dairy cows detected in March 2024, with subsequent identification of human cases, the San Francisco Department of Public Health instituted enhanced influenza surveillance (influenza A virus subtyping of a sample of specimens weekly) in June 2024. As of January 1, 2025, 37 human cases of influenza A(H5N1) had been detected in California, none of which occurred in San Francisco. On January 9, 2025, enhanced surveillance detected a human influenza A(H5N1) virus genotype B3.13 infection in a school-aged child in San Francisco with mild illness. Case investigation and contact tracing were conducted to ascertain exposures and detect possible human-to-human transmission. Activities comprised a household visit that included an environmental assessment, close contact interviews and surveys, and molecular and serologic testing. Sixty-seven close contacts (household, school, and health care) were identified. Upper respiratory tract specimens collected from seven asymptomatic household contacts and four symptomatic school contacts all tested negative for influenza virus by real-time reverse transcription–polymerase chain reaction (rRT-PCR). Although antibodies against influenza A(H5N1) were detected in the index patient, serologic testing of a convenience sample of nine close contacts identified no detectable A(H5)-specific antibodies. Despite an extensive investigation, the infection source remains unknown; no human-to-human transmission was identified among close contacts by rRT-PCR and serologic testing. Continued enhanced surveillance and timely subtyping of a subset of influenza A–positive specimens are essential components of a comprehensive strategy to detect human novel influenza A virus infections, including among persons without known exposures to A(H5N1) viruses.

Source: US Centers for Disease Control and Prevention, MMWR, https://www.cdc.gov/mmwr/volumes/74/wr/mm7433a2.htm?s_cid=OS_mm7433a2_e&ACSTrackingID=USCDC_921-DM149891&ACSTrackingLabel=Week%20in%20MMWR%3A%20Vol.%2074%2C%20September%204%2C%202025&deliveryName=USCDC_921-DM149891

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#Surveillance on #California dairy #farms reveals multiple #sources of #H5N1 #transmission

Abstract

Transmission routes of highly pathogenic H5N1 between cows or to humans remain unclear due to limited data from affected dairy farms. We performed extensive air, farm wastewater, and milk sampling on 14 H5N1 positive dairy farms across two different California regions. Virus was detected in the air in milking parlors and from exhaled breath of cows. Infectious H5N1 virus was detected in the air and water streams; sequence analysis revealed viral variants on a farm in these locations. Longitudinal analysis of milk from the individual quarters of cows revealed a high prevalence of subclinical H5N1 positive cows and a heterogeneous distribution of infected quarters that maintained a consistent pattern over time. Our data highlight potential modes of H5N1 transmission on dairy farms.

Competing Interest Statement

SSL and LCM receive funds from Flu Lab and NIH. ASL receives funds from Flu Lab, NIH, and CDC. ASL receives consulting fees and research support from Roche, outside of the submitted work.

Source: BioRxIV, https://www.biorxiv.org/content/10.1101/2025.07.31.666798v1

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Potential #impacts of 2.3.4.4b highly pathogenic #H5N1 avian #influenza virus #infection on Snow #Goose (Anser caerulescens) movement #ecology

Abstract

While wild waterfowl are known reservoirs of avian influenza viruses and facilitate the movement of these viruses, there are notable differences in the response to infection across species. This study explored differential responses to infection with highly pathogenic avian influenza in Snow Geese (Anser caerulescens) located in the California Central Valley. Though H5 antibody prevalence was high across years among birds sampled in the winter (75% in both years via hemagglutination inhibition), these values were even higher among birds sampled in summer that failed to migrate (i.e., August 2023 = 100% and August 2024 = 93% via hemagglutination inhibition). Birds that failed to migrate were also generally lighter than birds sampled in the winter and presented notable damage to cerebrum and cerebellum. In December 2022, a single individual positive for infection with H5N1 at the time of sampling indicated reduced movement during the 14 days following sampling but completed spring migration comparably with uninfected conspecifics. However, while no birds were actively infected during sampling and marking in 2023, two marked geese departed for migration late and one did not migrate at all. Additional banded birds marked in August have been reencountered in scenarios ranging from hunter harvest at a different site over a year later to found dead shortly after banding. Our data indicate that Snow Geese infected with HPAI have the potential to express variable outcomes following infection with highly pathogenic H5N1, ranging from rapid recovery within a migratory season to death. These data also suggest that the abnormal failure of some Snow Geese to migrate from the Central Valley is likely driven by HPAI infection.

Source: PLoS One, https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0328149

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Isolation of Highly Pathogenic Avian #Influenza #H5N1 Virus from #Cat #Urine after Raw #Milk Ingestion, #USA

Abstract

In 2024, 3 domestic cats in California, USA consumed raw milk contaminated with highly pathogenic avian influenza A(H5N1) virus. Fever and neurologic signs developed; 2 cats died. The surviving cat’s urine tested positive for H5N1 virus by reverse transcription PCR. Raw dairy products pose a risk to both animal and human health.

Source: US Centers for Disease Control and Prevention, https://wwwnc.cdc.gov/eid/article/31/8/25-0309_article

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#Evidence of #Viremia in Dairy #Cows Naturally Infected with #Influenza A {#H5N1} Virus, #California, #USA

Abstract

We confirmed influenza A virus (IAV) by PCR in serum from 18 cows on 3 affected dairy farms in California, USA. Our findings indicate the presence of viremia and might help explain IAV transmission dynamics and shedding patterns in cows. An understanding of those dynamics could enable development of IAV mitigation strategies.

Source: US Centers for Disease Control and Prevention, https://wwwnc.cdc.gov/eid/article/31/7/25-0134_article

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#Human Cases of Highly Pathogenic Avian #Influenza A(#H5N1) — #California, September–December 2024

Summary

-- What is already known about this topic?

- Persons with occupational exposure to highly pathogenic avian influenza (HPAI) A(H5N1) virus–infected dairy cattle are at increased risk for infection.

-- What is added by this report?

- During September 30–December 24, 2024, a total of 38 persons received a positive test result for HPAI A(H5N1) viruses in California; 37 were dairy farm workers with occupational exposure to sick cows. One, a person aged <18 years with an undetermined exposure, was the first pediatric patient detected with influenza A(H5) infection in the United States.

-- What are the implications for public health practice?

- Public health agencies should investigate influenza-like illness or conjunctivitis in workers with occupational exposure to animals infected with HPAI A(H5N1) virus. Thorough investigations of all human HPAI A(H5N1) virus infections are necessary to identify potential exposure sources, including monitoring the virus for concerning genetic changes that indicate the potential for person-to-person transmission.

Abstract

Persons who work closely with dairy cows, poultry, or other animals with suspected or confirmed infection with highly pathogenic avian influenza (HPAI) A(H5N1) viruses are at increased risk for infection. In September 2024, the California Department of Public Health was notified of the first human case of HPAI A(H5N1) in California through monitoring of workers on farms with infected cows. During September 30–December 24, 2024, a total of 38 persons received positive test results for HPAI A(H5N1) viruses in California; 37 were dairy farm workers with occupational exposure to sick cows, and one was a child aged <18 years with an undetermined exposure, the first pediatric HPAI A(H5N1) case reported in the United States. All patients had mild illness. The identification of cases associated with occupational exposure to HPAI A(H5N1) viruses on dairy farms highlights the continued risk for persons who work with infected animals. The pediatric case was identified through routine surveillance. Given recent increases in the prevalence of HPAI A(H5N1) viruses among some animal populations, public health agencies should continue to investigate cases of HPAI A(H5N1) in humans as part of control measures, pandemic preparedness, to identify concerning genetic changes, and to prevent and detect potential human-to-human transmission of the virus. To date, no human-to-human transmission of HPAI A(H5N1) virus has been identified in the United States.

Source: US Centers for Disease Control and Prevention (MMWR), http://dx.doi.org/10.15585/mmwr.mm7408a1

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#USA, After #Birdflu Detected in Local #Cat, County #Health Officials Say #Pet Owners Should Contact Veterinarian When Their Pets are Sick

Redwood City — State veterinary and health officials have confirmed a case of H5N1 (bird flu) in a domestic stray cat in San Mateo County. 

The infection, which is not related to the recent instance of bird flu in a backyard flock, was found in a stray cat in Half Moon Bay that had been taken in by a family. 

When it showed symptoms, they took it to Peninsula Humane Society, whose veterinarians examined it and requested testing. Lab results confirmed H5N1. 

It is not known how the cat was infected and it was euthanized due to its condition.

Cats may be exposed to bird flu by consuming infected bird, being in environments contaminated with the virus and consuming unpasteurized milk from infected cows or raw food. Inside domestic animals, such as cats and dogs, that go outside are also at risk of infection.​​​​​​​

According to the Centers for Disease Control and Prevention, the risk of cats spreading H5N1 to people is extremely low, though it is possible for cats to spread some strains of bird flu to people.

While there are no human cases of H5N1 related to this case, this detection in a cat highlights the importance of being proactive about preventing the spread of the virus.

Residents whose pets show signs of illness should contact their veterinarian.

Pets infected with H5N1 may experience a loss of appetite, lethargy and fever, along with neurologic signs, including circling, tremors, seizures or blindness. The illness may quickly progress to:

-- Severe depression

-- Discharge from eyes or nose

-- Other respiratory signs, such as rapid shallow breathing, difficulty breathing and sneezing or coughing

-- Pets with severe illness may die.

If a pet is showing signs of illness consistent with bird flu and has been exposed to infected (sick or dead) wild birds or poultry, residents should contact a veterinarian and monitor their own health for signs of fever or infection.

“We all want to make sure our companion animals are healthy and safe from disease,” said Lori Morton-Feazell, San Mateo County’s chief of Animal Control and Licensing. “If your pet is sick, your veterinarian can determine whether it should be tested for bird flu or any other virus or disease.”

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Source: County of San Mateo, https://www.smcgov.org/ceo/news/after-bird-flu-detected-local-cat-county-health-officials-say-pet-owners-should-contact

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#USA - High pathogenicity avian #influenza #H5N9 viruses (#poultry) (Inf. with) - Immediate notification

Highly pathogenic avian influenza (HPAI) H5N9, Eurasian lineage goose/Guangdong clade 2.3.4.4b and HPAI H5N1 clade 2.3.4.4b were confirmed in a commercial duck premises in Merced County, CA. This is the first confirmed case of HPAI H5N9 in poultry in the United States. The USDA Animal and Plant Health Inspection Service (APHIS), in conjunction with State Animal Health and Wildlife Officials, are conducting comprehensive epidemiological investigations and enhanced surveillance in response to the HPAI related events.

Source: WOAH, https://wahis.woah.org/#/in-review/6201

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#USA, Novel #Influenza A #H5N1 Virus: One Pediatric Case in #California {FluView}

 {Excerpt}

One confirmed human infection with influenza A(H5) virus was reported to CDC this week. To date, human-to-human transmission of influenza A(H5) virus has not been identified in the United States.

This case was reported by the California Department of Public Health and occurred in a child less than 18 years old with no known contact with influenza A(H5N1) virus-infected animals or humans. The investigation into the source of infection for this case is ongoing, and no human-to-human transmission has been identified.

A specimen from the individual was tested at a public health laboratory using the CDC influenza A(H5) assay before being sent to CDC for further testing. The specimen was positive for influenza A(H5) virus using diagnostic RT-PCR at CDC. Additional analysis including genetic sequencing is underway. In response to this detection, additional case investigation and contact monitoring are being conducted by public health officials in California.

There have now been 38 total confirmed human A(H5) cases and one probable human case of A(H5) case in California. This is the second reported pediatric case in California and in the United States.

Notification to WHO of this case was initiated per International Health Regulations (IHR). More information regarding IHR can be found at http://www.who.int/topics/international_health_regulations/en/.

The CSTE position statement, which includes updated case definitions for confirmed, probable, and suspected cases is available at http://www.cste.org/resource/resmgr/position_statements_files_2023/24-ID-09_Novel_Influenza_A.pdf

An up-to-date human case summary during the outbreak by state and exposure source is available at www.cdc.gov/bird-flu/situation-summary/index.html

Information about avian influenza is available at https://www.cdc.gov/flu/avianflu/index.htm.

Interim recommendations for Prevention, Monitoring, and Public Health Investigations are available at https://www.cdc.gov/bird-flu/prevention/hpai-interim-recommendations.html.

The latest case reports on avian influenza outbreaks in wild birds, commercial poultry, backyard or hobbyist flocks, and mammals in the United States are available from the USDA at https://www.aphis.usda.gov/aphis/ourfocus/animalhealth/animal-disease-information/avian/avian-influenza/2022-hpai.

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Source: US Centers for Disease Control and Prevention, https://www.cdc.gov/fluview/surveillance/2025-week-02.html

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#USA, #California: Current #H5N1 #Influenza in #Human #Situation as of January 15 '25: One new case, total = 38

Current Bird Flu Situation

Updated January 15, 2025​

-- ​​​​The current risk to the public remains low.  ​​

-- No person-to-person spread of bird flu has been detected in California. 

-- People rarely get bird flu, but those who interact​ with infected dairy cows, poultry, or wildlife ​have a greater risk of infection.​​

-- Pasteurized milk and dairy products are safe to consume. Pasteurization inactivates the bird flu virus.​​

-- CDPH is working to protect public health related to bird flu. We monitor infection data, evolving science, and the people affected. Our knowledge will change as we learn more. We are committed to reducing the impact to those at highest risk.

Human Cases in Califo​rnia​

-- ​​​​​​​Confirmed Human Cases​:  38 {+1}

​These numbers were last updated on January 15, 2025.

California has 1 additional probable case with dairy cow exposure that meets the  Council of State and Territorial Epidemiologists (CSTE) ​probable case definition (PDF)​. That case tested positive by a local lab and confirmatory testing at CDC was negative.​​

Confirmed human case summary during the 2024 outbreak, by exposure source.

​-- Cattle​​​​: ​36

-- ​Poultry: ​0

-- ​Unkn​own: ​2

--- ​Total: ​38

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Source: Department of Health, https://www.cdph.ca.gov/Programs/CID/DCDC/Pages/Bird-Flu.aspx

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