California's health department has reported a third case of bird flu, known as H5N1, among farmworkers, raising concerns about the virus's impact on both animal and human health. If confirmed by the US Centers for Disease Control and Prevention (CDC), this would mark the 17th human case in the US since the virus was detected in cattle in March. The recent case, like the previous two in California, involves a farmworker who was in contact with sick dairy cattle, indicating potential animal-to-human transmission.

The situation is more severe than in other states, with California farmers and veterinarians warning of higher percentages of sick and dead cows in affected herds. Over 80 herds have been affected in California since late August, prompting the state's Department of Food and Agriculture to conduct bulk milk tank sampling to identify more affected herds.

Symptoms in humans have been mild, presenting as conjunctivitis with red, bloodshot eyes. However, experts like Dr. Jennifer Nuzzo from Brown University's Pandemic Center express worry that the outbreak is not under control and that those working with cattle may not be adequately protected. She warns that the potential for severe harm to human health increases with each new infection.

The higher infection and fatality rates in California have led scientists to question whether environmental factors, such as heat, may be contributing or if the virus is mutating to cause more severe infections. Transparency and timely sharing of genetic information about the virus are crucial for scientists to track its evolution and assess any potential increase in threat.

The CDC has shared the gene sequences of the viruses from the first two infected farmworkers in California on GISAID, a widely used data-sharing site. However, the sequences from dairy cattle shared by the USDA’s Animal and Plant Health Inspection Service lack vital information, such as the state of origin and collection dates, making it difficult for scientists to track the virus's progression.

Despite the mild symptoms observed in human cases so far, the ongoing spread of the virus among herds and the potential for more severe outcomes underscore the need for vigilance and improved protection measures for farmworkers. The situation also highlights the importance of rapid and comprehensive data sharing to enable a thorough understanding of the virus's behavior and to inform effective public health responses.