Second strain of bird flu detected in U.S. dairy cows for first time

USA – A second strain of bird flu has been detected in U.S. dairy cows for the first time, according to a report by the U.S. Department of Agriculture. 

The USDA announced on Wednesday that the D1.1 strain of avian influenza, previously found only in wild birds and poultry, has now been identified in dairy cattle in Nevada.

The detection was made through the USDA’s national milk testing program, which was launched in early December to monitor the presence of bird flu in dairy herds. 

USDA’s Animal and Plant Health Inspection Service reported that the agency is working closely with the Nevada Department of Agriculture to conduct further investigations, testing, and epidemiological analysis. 

“USDA APHIS continues to work with the Nevada Department of Agriculture by conducting additional on-farm investigation, testing, and gathering additional epidemiological information to better understand this detection and limit further disease spread,” the agency stated.

So far, 957 cattle infections have been confirmed in 16 states, with recent data indicating 36 new cases in California and Nevada over the past 30 days. 

Until this discovery, all bird flu detections in dairy herds involved the B3.13 strain, making this the first known instance of D1.1 infecting cows.

Health officials have also noted that D1.1 has been linked to human infections. 

Since April 2024, 67 cases of bird flu have been detected in humans in the U.S., with one fatality reported in Louisiana. 

The patient, who was over 65 and had underlying health conditions, was exposed to a backyard poultry flock. 

A 13-year-old girl in British Columbia, Canada, was also hospitalized with the same strain in November, though the source of her infection remains unknown.

The Centers for Disease Control and Prevention said in a statement on Thursday that it is closely monitoring the situation but maintains that the risk to the general public remains low. 

“Risk remains low despite what appears to be the introduction of a different genotype of avian influenza A (H5N1) virus into dairy cows based on the USDA’s Animal and Plant Health Inspection Service Stakeholder Registry email,” the agency stated. 

The CDC also emphasized that there is no evidence of human-to-human transmission at this time.

In response to the ongoing spread of bird flu in dairy herds, the USDA issued a federal order late last year requiring raw milk samples to be collected and tested nationwide. 

This directive was part of the National Milk Testing Strategy, an initiative aimed at enhancing disease surveillance in the dairy sector. 

The USDA stated that the detection of D1.1 does not alter its eradication strategy and reaffirmed confidence in the strength of its monitoring efforts. 

APHIS has indicated that it will release a technical brief and make the genetic sequence data publicly available in the coming week.