Dairy Herds in Nevada Test Positive for Newer Bird Flu Strain Linked to Severe Human Infections

In a concerning development, dairy herds in Nevada have tested positive for a newer strain of avian influenza (H5N1), raising alarm among health officials and researchers. This strain, known as genotype D1.1, has previously been associated with severe human infections, including a fatal case in Louisiana. The detection of this strain in cattle marks another troubling instance of avian influenza spreading beyond wild birds and poultry, affecting livestock and posing potential risks to human health.

The U.S. Department of Agriculture (USDA) confirmed the presence of this H5N1 strain in six dairy herds across Nevada. These detections came as part of the USDA’s National Milk Testing Strategy, which has been monitoring raw milk samples nationwide since December 2024. The discovery of this newer strain suggests that multiple spillover events from wild birds to livestock may have occurred, increasing concerns about cross-species transmission.

Unlike earlier cases of bird flu in cattle, which involved the B3.13 genotype, this new strain is believed to have been introduced separately by wild birds. The D1.1 strain has been predominant among wild bird populations in North America during recent seasons, making its presence in dairy cattle particularly troubling for epidemiologists studying the virus’s transmission patterns.

While bird flu primarily affects birds, there have been increasing reports of human infections. According to the Centers for Disease Control and Prevention (CDC), at least 70 cases of H5N1 infections in humans have been reported in the United States since early 2024. Many of these cases have been linked to farm workers who had close contact with infected animals.

This new genotype of the virus has been associated with severe outcomes. In Canada, a teenage boy from British Columbia contracted the D1.1 strain and was hospitalized in critical condition. In the United States, a Louisiana senior citizen succumbed to complications from the virus, marking a rare but alarming fatality.

The severity of these human cases has prompted heightened surveillance efforts and stricter biosecurity measures on farms. Health officials are urging dairy farm workers to use protective equipment and maintain stringent hygiene practices when handling livestock to minimize the risk of transmission.

Following the confirmation of the virus in Nevada dairy herds, state agriculture officials have placed affected farms under quarantine to prevent further spread. Additionally, authorities are working to control populations of European starlings, a non-native bird species suspected of spreading the virus among cattle.

The USDA has also mandated testing for all lactating dairy cattle before interstate transport. This measure aims to limit the virus’s spread to other states and ensure the safety of dairy products. Although pasteurization effectively eliminates the virus in milk, unprocessed raw milk remains a potential risk.

The emergence of the D1.1 genotype in dairy cattle underscores the evolving threat of avian influenza and its potential to impact both animal and human health. While health agencies and agricultural authorities are actively monitoring and mitigating risks, the situation highlights the need for continued vigilance and preventive measures to curb further transmission of the virus.