H5N1 influenza: From avian to bovine to feline and beyond

In March 2024, dairy and poultry veterinarian Kay Russo, DVM, MAHM, DACPV, consulted with Barbara Petersen, DVM, MBA, who was working up sick cattle on a dairy farm in Texas.

The cattle were displaying respiratory and gastrointestinal signs including high fevers, respiratory distress, decreased rumination, and significantly decreased milk production. They had high morbidity rates and low mortality rates—and they were testing negative for all the usual suspects.

Since the farm’s veterinarian had already ruled out bovine syncytial virus, coronavirus, salmonella, and bovine viral diarrhea, Russo knew to be on the lookout for something atypical. She reports that it was the combination of signs, including the mammary involvement, that really made her consider influenza.

That’s when she posed a question that would have an ominous answer. “What are the birds doing on the farms?” she asked, referring to wild birds such as pigeons and grackles.

Then answer came back, “the birds are all dead.”

And those who hadn’t died yet were showing severe neurologic signs.

Russo quickly advised those who were in the field to obtain as many samples as possible from the birds to send out for testing at the National Veterinary Services Laboratories.

When those samples came back positive for H5N1 (one of the two strains associated with highly pathogenic avian influenza or HPAI), Russo felt a pit in her stomach. She knew the cattle needed to be tested as well.

On March 21, 2024, Drew Magstadt, DVM, MS, from the Iowa State Veterinary Diagnostic Lab confirmed the individual milk samples from the sick dairy cattle to be positive on PCR for influenza A. On March 25, 2024, the NVSL (National Veterinary Services Laboratory) confirmed the type of influenza A to be H5N1.