High Pathogenicity Avian Influenza (HPAI) in cattle

While high pathogenicity avian influenza (HPAI) primarily affects domestic and wild birds, multiple cases have confirmed its occurrence in cattle
(Bos taurus). This highly contagious viral disease has also been identified in other wild and domestic mammalian species. While the risk to humans remains low, HPAI presents a potential public health concern, especially for individuals with regular and close contact with cattle in the areas in which the virus is circulating, poultry and wild birds (e.g. the veterinary workforce and farmers).

Case definition for HPAI in cattle

Last updated 28 April 2025

What is HPAI in cattle? 

High pathogenicity avian influenza (HPAI) in cattle occurs when a bovine species is infected with an influenza A virus of high pathogenicity in poultry (or HPAI).

In March 2025, HPAI was detected for the first time in dairy cattle in the United States of America (USA). Since then, World Organisation for Animal Health (WOAH) has been notified of several cases. As of April 2025, the virus is predominantly circulating in the USA, and the dominant strand is H5N1. 

Clinical signs have primarily been observed in lactating dairy cattle, developing over 2–3 weeks. The virus is present mainly in mammary glands, digestive and respiratory systems, it has also been detected in milk and post-mortem in muscle tissue. In affected farms, the morbidity rate of HPAI in cattle typically ranges between 10% – 20%, reaching up to 40% in some cases. Although illness-related mortality remains low (below 5%), the total death rate in herds can surpass 5% due to selective culling of animals that do not return to their pre-disease production levels.

The current circulating strain has demonstrated the capacity to infect a wide range of species including cattle, wild and domestic birds, as well as aquatic and terrestrial wild and domestic mammals, including humans.  

HPAI in cattle is an emerging disease, according to Article 1.1.4 of the Terrestrial Code. Accordingly, upon detection, Veterinary Authorities have a responsibility to send an immediate notification, followed by regular updates, to WOAH through the World Animal Health Information System (WAHIS). 

How is HPAI in cattle transmitted?

The routes and modes of transmission between cattle, the duration of virus shedding as well as the infectious period remain under investigation. Evidence suggests that cattle-to-cattle transmission may occur, likely via direct contact with infected milk, inhalation of the aerosolised virus, or indirect transmission through contaminated clothing and equipment. Additionally, there are also indications of horizontal virus transmission from infected lactating cows to other animals including calves, cats and poultry.

The clinical severity of the disease varies. Infected cattle can present as either asymptomatic or mild illness, or non-specific clinical signs such as reduced milk production with abnormal milk (thicker-colostrum‐like milk), reduced appetite, lethargy, fever, dehydration, altered faecal consistency, respiratory distress and abortions.  

Zoonotic potential: are humans at risk?

While the risk to humans remains low, the ongoing circulation of HPAI in cattle increases the risk of HPAI viruses’ potential adaptation to mammals and potentially spilling over to other livestock species or humans. To date, there is no evidence of specific viral adaptation of HPAI to humans and no evidence of human-to-human transmission.  

Studies have shown that commercial milk pasteurisation inactivates the virus making it safe for human consumption. 

Sporadic human infection with HPAI has been reported, especially in humans who have come into close contact with infected dairy cattle or wild or domestic birds. Those most at risk include professionals working closely with susceptible or infected animals, notably veterinary personnel and farmers. 

Recommended precautions for those at high risk include:  

  • Wearing appropriate personal protective equipment (PPE), including eye protection, gloves and nose and mouth coverings 
  • Regularly cleaning and disinfecting outerwear 
  • Thoroughly washing hands after animal contact and before eating 
  • Exercising caution when handling raw milk, faeces or bedding material from suspected or infected animals   

The general public is advised to:  

  • Avoid direct contact with sick or fallen wild birds, and with sick wild or domestic mammals unless under veterinary supervision or as part of animal care responsibilities 
  • Maintain regular good hygiene practices, including handwashing with warm water and soap, particularly after returning home and before handling food 
  • Avoid consuming raw milk or dairy products from milk that has not been pasteurised or heat treated 

What is WOAH doing? 

WOAH is committed to supporting its Members in mitigating the risks associated with avian influenza and is closely monitoring the evolution of HPAI in cattle. Close Collaboration with WOAH’s expert network, OFFLU, continues to be a priority. We are also working with other International Organisations to assess the broader implications for animals and for public health within the framework of the One Health Quadripartite and the Global Framework for Transboundary Animal Diseases
(GF-TADs). 
 
We strongly encourage our Members to monitor the occurrence of avian influenza in animals other than birds and to promptly notify relevant events to WOAH through its information system WAHIS.   

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