Risk Assessment of Spread of the Influenza A Virus in Cows in South Bulgaria.

In this article, we present an assessment of the risk of the potential introduction and spread of highly pathogenic avian influenza (HPAI) in cows in Bulgaria. In the spring of 2024, we witnessed an unprecedented spread of the virus in dairy herds in the USA. This crossing of interspecies barriers by the virus creates a real danger of pandemic manifestations in humans. The continued spread of H5N1 clade 2.3.4.4b in dairy populations and other mammalian species and efficient animal-to-animal transmission increases the risk of infection and subsequent spread of the virus in human populations. According to registers, as of 1 November 2022, a total of 559,544 cattle were bred in Bulgaria. The total number of dairy cows decreased by 5.2% year-on-year to 197,996. Farms breeding dairy cows as of 1 November 2022 were 12,439, which is 22.1% less than the previous year. The production of cow's milk in 2022 amounted to 748,278 thousand liters. Traditionally, the largest share in the total yield of cow's milk is occupied by the south-central region with 25.9%, followed by the southeastern region with 18.5%. Due to potential risk factors such as the high concentration of dairy cows in high-risk areas for avian influenza A, the possibility of HPAI jumping the interspecies barrier and spreading in dairy herds in Bulgaria is very high. We therefore set out to assess the risk of virus penetration in these herds.