H5N1 in cattle in the USA
Dr Albert Picado de Puig Principal Scientist Animal Health Global innovation
In January 2024, a mystery illness began affecting dairy cows in Texas. The affected cattle exhibited flu-like symptoms like fever and thick and discolored milk. The illness impacted nearly 10% of the animals in the affected herds, causing reduced feed consumption and up to 20% decline in milk production. Despite the significant impact of this illness, the causative agent remained unidentified for several weeks. It was not until March 25, 2024, that the pathogen responsible for this illness was identified as the H5N1 virus, also known as avian influenza virus or bird flu 1 . By then, cases were reported in several states in the USA. This marked a significant change in the epidemiology of this disease, as the detection of H5N1 in cattle was never before reported. H5N1 is a type of influenza virus that primarily affects birds but can also infect various mammals, including humans. H5N1 was first reported in domestic waterfowl in Southern China in 1996. Since then, it has spread across the globe and has caused the deaths of millions of birds and it has been reported in multiple mammals including cats, pigs, coyotes, and marine mammals such as sea lions causing thousands of deaths in some of these species. The identification of H5N1 in cattle has raised concerns among public health officials and the agricultural industry due to the potential implications for both human and animal health as well as the economy. It represents an expansion of the host range of the virus, which increases the risk of human exposure, especially among those who have close contact with infected cattle, such as farmers and veterinarians. The presence of H5N1 in a new host species could potentially facilitate the emergence of a new, more dangerous strain of the virus. Finally, the detection of H5N1 in cattle could have significant implications for food safety, particularly in relation to dairy products. The risk has been mainly associated with high viral loads in raw milk. However, pasteurization, a process that involves heating milk to a specific temperature for a set period of time, has been found to be effective in destroying the H5N1 virus. This process is a standard safety measure in the dairy industry and is crucial in preventing the spread of pathogens. To date (12 th July 2024) 146 herds in 12 states have been infected by H5N1 avian influenza according to the US Department of Agriculture (USDA) (Figure 1) 2 . Four human cases of H5N1 virus infection have been reported in people exposed to sick cows 3 . All cases showed mild symptoms and the CDC continues to believe that the overall risk to human health associated with the ongoing outbreaks of H5N1 viruses remains low. Surveillance and control measures have been put in place to limit the spread of H5N1 in cattle herds and to protect people at
higher risk of exposure (e.g. farm workers, veterinarians) and the general public. A program to test dairy cattle and milk has been put in place. In conclusion, the recent identification of H5N1 in cattle in the USA underscores the need for ongoing surveillance of influenza viruses in both humans and animals, as well as the importance of implementing effective measures to prevent the spread of the virus and protect public health.
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Figure 1: H5N1 confirmed cases in livestock herds in the USA (12th July 2024). Source: USDA.
References: 1. Federal and State Veterinary, Public Health Agencies Share Update on HPAI Detection in Kansas, Texas Dairy Herds | Animal and Plant Health Inspection Service (usda.gov) https://www.aphis.usda.gov/news/agency- announcements/federal-state-veterinary-public- health-agencies-share-update-hpai 2. HPAI Confirmed Cases in Livestock | Animal and Plant Health Inspection Service (usda.gov) https://www.aphis.usda.gov/livestock-poultry- disease/avian/avian-influenza/hpai-detections/ hpai-confirmed-cases-livestock 3. CDC Reports Fourth Human Case of H5 Bird Flu Tied to Dairy Cow Outbreak | CDC Online Newsroom | CDC https://www.cdc.gov/media/releases/2024/p- 0703-4th-human-case-h5.html
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