Isolated cases of HPAIV H5N1 infections in dairy cows have been reported from three U.S. states (Texas, New Mexico and Kansas). Individual, mainly older cows in one herd apparently showed an acute drop in milk production of up to 20 per cent. So far, there is no precise information on further clinical symptoms. The virus was detected in the milk of the animals, in some cases with high virus loads, and in at least one case also from a nasal swab. HPAIV-infected wild birds were found dead in the area of the affected farms, so that entry points via indirect contact with wild birds (e.g. drinking water, feed) are suspected. Whether there could also have been transmission between cows or indirectly, e.g. via contaminated milking utensils, is currently being intensively investigated. The virus detected is a genotype of HPAIV H5N1 of clade 2.3.4.4b, which is known in the USA but has not been dominant to date. The U.S. authorities consider the pasteurisation of milk to be a sufficient inactivation process and do not believe it poses a risk to human health. The precautionary killing of animals in affected herds is currently not planned.
Furthermore, a case of a dead newborn goat with an HPAIV H5N1 infection has been reported in the USA. The animal came from a farm in Minnesota where the goats had contact with free-range poultry in a small flock. Several newborn kids died there, but HPAIV H5N1 was only detected in one animal. The infections occurred several days or weeks ago, as an HPAIV infection was not part of the expected pathogen spectrum of the cases described and corresponding investigations were only initiated late.
The reports are cause for extended and intensified investigations of ruminants in the U.S.A. However, they should also be seen as an exclamation mark in this country: Transmissions of HPAIV H5N1 to mammals in Germany have so far been limited to individual wild carnivores (especially foxes) and a few harbour seals or grey seals. However, it cannot be ruled out that farm animals (ruminants, pigs) could also be susceptible under certain conditions. Livestock owners are therefore advised to remain vigilant and be aware of the risks if their animals come into contact with areas to which waterfowl also have access. In addition, further investigations should be initiated in the event of unclear and frequent cases of illness, which should then also include HPAIV H5.
The risk of human infection with HPAIV H5N1 viruses of clade 2.3.4.4b is still classified as low (ECDC).
Sources:
USDA (2024) Federal and State Veterinary, Public Health Agencies Share Update on HPAI Detection in Kansas, Texas Dairy Herds, from March 25, 2024
Cohen, J. (2024). Bird flu discovered in U.S. dairy cows is ‘disturbing’. Science. DOI: 10.1126/science.z9sk33v
EFSA (2024). Avian influenza overview December 2023–March 2024. DOI: 10.2903/j.efsa.2024.8754
