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Avian influenza: No evidence of H5N1 infection in dairy cows outside the USA

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– German virus isolate can replicate in cow's udder after experimental infection

The Friedrich-Loeffler-Institut (FLI) is currently conducting an infection study on the susceptibility of dairy cows to the highly pathogenic avian influenza virus H5N1 (HPAIV H5N1, avian influenza virus). As a first interim result, not only the US isolate but also a recent H5N1 virus from a wild bird in Germany was able to multiply very well in the udder. Following direct infection of the udder through the teats, the dairy cows in both cases showed clear signs of disease such as a sharp drop in milk production, changes in milk consistency and fever. 

The FLI's risk assessment for avian influenza, including recommended measures, is not affected by this interim result, as the possibility of infection with other HPAIV H5 strains has already been taken into account in the current version of the assessment. Both the risk of the US HPAI H5N1 strain (B3.13) entering German cattle herds, including dairy farms, and the risk of cattle becoming infected with HPAI H5 viruses circulating in Europe are considered to be very low for Germany. Nevertheless, increased vigilance is recommended and HPAI H5 should also be considered in investigations, especially in the case of unclear and frequent cases of disease in dairy herds. In contrast to the USA, there is no evidence of similar cases of HPAIV H5N1 infection in Germany or other countries worldwide.

Direct infection of the udder by the virus seems to be of particular importance. Since the first detection of the pathogen 27 years ago in many countries, particularly in Asia, there has been possible contact of ruminants such as water buffalo and cattle with the faeces of infected wild birds, but no similar infection events have ever been observed. The exact circumstances that led to the outbreak in the USA are still unknown.

As a precautionary measure, the FLI has already tested around 1,400 bovine serum samples from cows from regions in Germany particularly affected by avian influenza for antibodies and around 350 tank milk samples from different regions for virus genomes using PCR, with negative results in each case. Further analyses of tank milk samples up to a total of around 1500 will follow.

Once the FLI infection study has been completed and analysed, the results will be published. The timing cannot be estimated at this stage, but the FLI will provide information in due course.

Milk, while milking (© Pixabay)

Milk, while milking (© Pixabay)