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U.S. Department of Agriculture detects second bird flu strain in dairy cattle

U.S. dairy cattle tested positive for a strain of bird flu that previously had not been seen in cows, the U.S. Department of Agriculture said on Wednesday, ramping up concerns about the persistent spread of the virus.

The H5N1 virus has reduced milk output in cattle, pushed up egg prices by wiping out millions of hens, and infected nearly 70 people since April as it has spread across the country.

Genome sequencing of milk from Nevada identified the different strain, known as the D1.1 genotype, in dairy cows for the first time, the USDA said. Previously, all 957 bird flu infections among dairy herds reported since last March had been caused by another strain, the B3.13 genotype, according to the agency.

Reuters reported news of the detection of the second strain on Wednesday ahead of USDA’s announcement.

The second strain was the predominant genotype among wild birds this past fall and winter and has also been found in poultry, the USDA said. It was identified in dairy cattle through an agency program that began testing milk for bird flu in December.

“We’re seeing the H5N1 virus itself be smarter than all of us,” said Beth Thompson, South Dakota’s state veterinarian.

“It’s modifying itself so it’s not just staying in the poultry and the wild waterfowl. It’s picking up a home in the mammals.”

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Inside the Swine Disease Reporting System - Dr. Guilherme Cezar

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In this episode of The Swine it Podcast Show Canada, Dr. Guilherme Cezar from Iowa State University explains how the Swine Disease Reporting System (SDRS) tracks emerging disease trends in the U.S. swine industry. He outlines patterns in pathogen activity, including positive developments with Mycoplasma hyopneumoniae and concerning surges in PRRS variants. Gain insights into disease surveillance, biosecurity, and cross-border collaboration potential. Listen now on all major platforms!

"The Swine Disease Reporting System aggregates diagnostic lab data to monitor and interpret trends in nine major swine pathogens."

Meet the guest: Dr. Guilherme Cezar / guilhermec-veterinario-037064168 is a veterinarian and Ph.D. candidate in Veterinary Preventive Medicine at Iowa State University, where he also serves as the Coordinator of the Swine Disease Reporting System (SDRS). With a strong background in swine health, biotechnology, and field epidemiology, he focuses on infectious disease trends and data-driven solutions.