Avian influenza in dairy cattle

Dear Prof McCrindle,

I read a news story about highly pathogenic avian influenza (HPAI) occurring among dairy cattle in Texas and Kansas in the US. What does that mean for farmers in South Africa? Kind regards, Anonymous

On 25 March this year, unpasteurised milk samples from sick dairy cattle in Texas and Kansas tested positive for HPAI (see avma.org/news/highly-pathogenic-avianinfluenza-found-texas-kansas-dairy-cattle).

It caused severe disease in older cows, including weakness and diarrhoea, with a drop in milk production. The milk was declared safe for human consumption as pasteurisation killed the virus. This report mentioned that dead birds found on the farms were identified as migratory geese. These are known to carry avian influenza and transmit it between continents during annual migration.

A statement by the Animal and Plant Health Inspection Service in the US gives details on the safety of pasteurised milk. However, it gives no details regarding decisions on the dairy cattle herds that are infected. In South Africa, avian influenza of any subtype is a controlled animal disease in terms of the Animal Diseases Act (No. 35 of 1984). Any suspected or confirmed case of avian influenza must be reported immediately to the responsible state veterinarian in terms of the act.

Over the past few years, many commercial poultry farms in South Africa have had to slaughter out all infected chickens. This is because HPAI is also infectious to human beings. Employees at poultry farms who are carriers are often the source of outbreaks. Avian influenza is also known to be an airbourne and water-bourne infection. In other words, when the humidity is high, influenza in people and animals can be transmitted by inhalation of infective droplets. Swine influenza is genetically related to avian influenza, but cross-transmission has not been described. It’s a relatively mild disease in pigs.

For some time there has been discussion about the value of vaccination as an aid to control of the avian influenza. This is particularly important in South Africa at present as HPAI is currently decimating our commercial layer and broiler flocks, as well as causing losses to small-scale poultry farmers. It is also impacting on food security as poultry eggs were previously a very affordable source of nutrients for children. Poultry meat is also a very affordable source of protein and essential nutrients for low-income consumers.

It’s known that HPAI infects mammals. The 2024 US outbreak occurred in dairy cows and goats. However, it’s not clear whether they were milch goats. Milk is an affordable nutrient for the very poor in South Africa and many small-scale farmers derive an income and a source of meat through ownership of goats.

Kind regards, Prof Cheryl McCrindle ȊȲSource: Shi J, Zeng X, Cui P et al. ‘Alarming situation of emerging H5 and H7 avian influenza and effective control strategies’. Emerg Microbes Infect. 2023 Dec;12(1):2155072. doi: 10.1080/22221751.2022.2155072. Visit pubmed.ncbi.nlm.nih.gov/36458831.

Cheryl McCrindle is an emeritus full professor in the Faculty of Veterinary Science at the University of Pretoria, and has extensive experience in animal health. Email her at farmersweekly@caxton.co.za. Subject line: Ask our vet.