In recent weeks, concerns have been growing among researchers worldwide about the spread of highly pathogenic avian influenza (H5N1) in US dairy cows. However, experts are increasingly criticizing the lack of information and transparency from the US Department of Agriculture (USDA) regarding the outbreak.

As of now, the USDA has reported that 32 herds in eight states - Idaho, Kansas, Michigan, New Mexico, North Carolina, Ohio, South Dakota, and Texas - have been affected by the virus. It remains unclear whether these herds are connected in a single outbreak chain or if the virus has spread multiple times from different sources. While some cases can be explained by the movement of cattle between herds, the USDA has not clarified the extent of the virus's transmission.

Initially, infections in Texas were linked to dead wild birds found on dairy farms. However, the USDA has stated that the infections do not appear to be solely linked to the Texas cases. The virus is believed to be spreading through cow-to-cow transmission, but the exact mode of transmission remains unknown. Speculations suggest that contaminated milking equipment may be responsible for the virus's spread.

Adding to the uncertainty, The New York Times reported that one infected herd in North Carolina did not show any symptoms of the virus, raising concerns about the possibility of silent transmission in asymptomatic herds and states. In response, the USDA has encouraged testing for H5N1 when herds exhibit clinical symptoms. Interestingly, the agency has also started reimbursing farms for testing asymptomatic cows.

The USDA has also noted evidence of H5N1 spreading from dairy farms back into birds in nearby poultry farms. The specific mechanism behind this transmission remains unknown, adding to the concerns about the virus's evolution and potential to infect mammals, including humans.

International experts have criticized the USDA for not sharing enough genetic data and other crucial information related to the outbreak. Last week, amid mounting criticism, the USDA announced the release of 239 genetic sequences to the Global Initiative on Sharing All Influenza Data (GISAID) and stated its commitment to providing data on a rolling basis. However, some experts emphasize the need for data confirming the effectiveness of pasteurization in killing the virus if it were to enter the milk supply.

Despite the concerns, both the USDA and the US Centers for Disease Control and Prevention (CDC) have maintained that the risk to the public remains low. Nonetheless, they advise farmworkers and other individuals with direct contact with infected animals to take necessary precautions.

The USDA's chief veterinarian, Dr. Rosemary Sifford, acknowledged the criticism and emphasized the agency's efforts to generate more information. Though the virus appears relatively mild in cows, with no reported deaths, contaminated milk is being destroyed to prevent any potential harm. The Food and Drug Administration assures the public that pasteurization effectively eliminates viruses like H5N1 in milk.

As the outbreak continues to unfold, researchers and experts await further updates and data to better understand the extent and implications of the avian influenza outbreak among US dairy cows.