Bird flu detected in Colorado dairy herd for the first time

Colorado on Friday became the ninth state to confirm bird flu in dairy cattle, increasing evidence of a nationwide epidemic among dairy herds of the highly contagious — but still not yet threatening to humans — H5N1 avian influenza virus.

The state Department of Agriculture said in a news release that the outbreak involves a dairy herd in northeastern Colorado, but provided no more specific information on the herd’s location or how many animals were believed to be infected.

The state veterinarian’s office was notified Monday of a dairy herd “demonstrating clinical signs consistent with (avian influenza) in cattle.” These signs can include reduced appetite, lower milk production and production of milk that the department described as “colostrum-like.”

“We continue to see this ongoing HPAI outbreak evolve and over the last month have seen transmission of the virus now move into dairy cattle,” Dr. Maggie Baldwin, the state veterinarian, said in a statement, using the acronym for highly pathogenic avian influenza, another name by which the virus is known. “While we don’t yet completely understand the mechanism of transmission of this virus, we do know that it appears to be spreading from cow to cow and between herds.”

After first being detected in a dairy herd in Texas last month, reported bird flu infections in dairy cattle have grown rapidly. Prior to detection in Colorado, outbreaks were reported in two neighboring states, Kansas and New Mexico.

Samples taken from milk suggest a much bigger epidemic. Federal regulators found inactive fragments of bird flu virus in 20% of retail milk samples tested in one analysis, while other researchers have found viral fragments in more than one-third of samples.

These fragments are not live viruses, and they are not capable of sickening humans. Pasteurization — the process of heating milk to kill harmful pathogens — prevents live flu viruses from making it into milk sold at stores.

The same may not be true for raw milk. Concerns over bird flu making its way into raw milk helped kill a bill at the state Capitol this year that would have legalized sale of the unpasteurized product.

This week, the U.S. Department of Agriculture issued an order requiring lactating dairy cows to be tested for bird flu before being moved across state lines, though subsequently issued guidance on how to carry out the order narrowed the requirement. A spokeswoman for the state Department of Agriculture told The Sun via email Thursday that the state is working to draft its own guidelines.

The current bird flu epidemic had been ongoing for at least two years, striking wild birds and domesticated poultry in Colorado before crossing over into mammals such as bears, mountain lions and skunks. 

Bird flu is not currently seen as a risk to humans. There have been only two reported infections in humans in the United States. Neither resulted in serious illness, and one of those — in a Colorado man working on a commercial poultry farm in Montrose County — may have not even been a full infection. No person-to-person transmission has been observed.

But there is concern among public health leaders that, the longer the outbreak in mammals goes on, the more chances there are for the virus to evolve in ways that make it easily transmissible to and harmful to humans.

Type of Story: News

Based on facts, either observed and verified directly by the reporter, or reported and verified from knowledgeable sources.

John Ingold is a co-founder of The Colorado Sun and a reporter currently specializing in health care coverage. Born and raised in Colorado Springs, John spent 18 years working at The Denver Post. Prior to that, he held internships at... More by John Ingold