On 24 March, the Department for Environment, Food and Rural Affairs (Defra) confirmed an outbreak of highly pathogenic avian influenza A virus (HPAIV) H5N1 in a single sheep on a farm in Yorkshire. Avian influenza had been detected in birds kept on the farm and routine testing was carried out on the other animals kept on the farm. The affected ewe showed signs of mastitis but no other signs of disease. She tested positive for avian influenza in her milk and was euthanised. All other sheep tested negative. The local authorities are applying the usual control measures for avian influenza.
This is the first known case of a ruminant infected with the avian influenza virus in Europe. So far, only ruminants in the United States have been affected, mainly dairy cows and, in one case, young goats.
It is known from the outbreak in dairy cows in the USA and from an infection study carried out by the FLI that HPAIV of subtype H5N1 replicates very well in the udder. In the case of the US outbreak, milking appears to play a critical role in the spread of infection within a farm.
The case in the UK shows that single infections in ruminants are possible under high H5N1 virus pressure. Therefore, cattle, sheep and goats in direct contact with infected poultry, wild birds or infected captive birds in the context of an avian influenza outbreak should be included in the outbreak investigation. In particular, if there are signs of mastitis, avian influenza should be investigated as a possible cause. Environmental investigations in poultry farms with outbreaks of HPAI should include not only ruminants but also pigs, dogs and cats kept on these farms.
