Avian influenza, commonly known as bird flu, continues its spread across the United States, causing apprehension among health experts as they work to contain the virus. The recent identification of a second bird flu strain, D1.1, in dairy cows marks a concerning development. Previously found only in wild birds and poultry, this strain's emergence in cows suggests a recent cross-species transmission.

Following this discovery, Nevada confirmed its first human case of bird flu in a dairy farm worker, identified as the D1.1 strain by the Centers for Disease Control and Prevention (CDC). This strain has been linked to severe illness in humans, including a severe case in British Columbia and a fatality in Louisiana. Both individuals had underlying health conditions.

While the CDC maintains that the risk to the public remains low and there's no current evidence of human-to-human transmission, infectious disease specialists express concern. The detection of D1.1 calls for increased surveillance and raises questions about potential mutations. Dr. Dean Blumberg, chief of pediatric infectious diseases at UC Davis Health, points out the risk of further mutations facilitating human-to-human transmission, which could lead to a pandemic. He emphasizes the importance of vigilance without causing undue alarm.

Dairy cows at the USDA's National Animal Disease Center research facility in Ames, Iowa. (Charlie Neibergall/AP, FILE)

Virus Adaptation and Mutation Potential

Until recently, bird flu in U.S. dairy herds was primarily the B3.13 strain. The emergence of D1.1 in cattle indicates viral adaptation, according to Dr. Benjamin Anderson, an assistant professor at the University of Florida. This adaptation could mean easier transmission of H5N1 by migratory birds. Each new case presents an opportunity for mutation, potentially leading to increased infectivity or human-to-human transmission.

Dr. Michael Payne, a researcher at UC Davis, finds it encouraging that the D1.1 strain in Nevada cattle showed no mutations facilitating transmission between cows or to humans. The absence of changes in the H5 portion of the virus, which aids attachment to mammalian cells, is reassuring. This suggests that cows recovered from the older strain may have antibodies effective against D1.1.

Strengthening Surveillance Efforts

Experts advocate for enhanced surveillance and detection systems given the rising D1.1 cases in animals and humans. While the CDC recommends testing asymptomatic workers, the extent of asymptomatic infection remains unclear, according to Dr. Blumberg. A recent CDC report revealed three veterinary professionals working with dairy cattle and/or poultry had bird flu antibodies despite being asymptomatic and unaware of exposure.

Influenza A (H5N1/bird flu) virus particles. (CDC and NIAID)

Blumberg emphasizes the need for further research and data sharing. Anderson highlights the variation in surveillance intensity among states and points to Nevada's detection of D1.1 through the USDA's National Milk Testing Strategy as a successful example. He recommends broader coordination of surveillance activities across states.