Infectious Diseases 2024

Infectious Diseases 2024

Dairy cows inoculated with HPAI virus H5N1

Nature . 2024 Oct 15 16 October, 2024

A peer-reviewed paper published in Nature investigates the impact of highly pathogenic avian influenza (HPAI) H5N1, specifically clade 2.3.4.4b genotype B3.13, on dairy cattle. Following the detection of H5N1 in a dairy cow in Texas in March 2024, a multi-state investigation revealed over 300 positive herds across 14 U.S. states. The study confirmed that HPAI H5N1 can cause severe disease in dairy cattle, leading to clinical signs such as mastitis, reduced milk production, and changes in milk quality. The initial transmission likely occurred from avian sources, with subsequent local transmission among cattle facilitated by the movement of infected animals. The virus can be transmitted to cattle through aerosol exposure or direct contact with contaminated environments or infected animals.
In the study, lactating cows were experimentally inoculated via an intramammary route, while heifers were inoculated through an aerosol respiratory route. Once the virus enters the host, it replicates in the respiratory and mammary tissues. High levels of viral RNA were detected in milk and mammary tissue, indicating significant viral replication. The presence of viral RNA suggests that the virus can effectively infect and multiply within the mammary gland. The infection leads to pathological changes in the mammary tissue, including alveolar epithelial degeneration and necrosis. This tissue damage is associated with the clinical signs observed in infected cows, such as changes in milk appearance (thick yellow milk) and reduced milk production. The host's immune response to the infection includes the production of antibodies and other immune mediators. The study confirmed seroconversion in infected animals, indicating that the immune system recognized the viral infection and mounted a response. The clinical disease observed in lactating cows included decreased rumen motility, changes in milk quality, and significant production losses. These symptoms are consistent with viral mastitis, a condition caused by viral infection of the mammary gland. The study also noted that the movement of live lactating cows contributed to the spread of the virus among dairy farms. Local transmission was observed within farms, suggesting that the virus can spread rapidly among cattle populations once introduced. The research contributes valuable insights into the implications of HPAI H5N1 in dairy cattle and emphasizes the need for ongoing research and monitoring efforts in the face of emerging infectious diseases.