Questions answered lead to more questions

As the number of dairy farms with confirmed cases of Highly Pathogenic Avian Influenze H5N1 continues to climb, so do the questions about how the disease is the spreading. Vigilant biosecurity continues to be the best answer for its prevention.

As of June 5, there were 82 herds in nine states — Colorado, Idaho, Kansas, Michigan, New Mexico, North Carolina, Ohio, South Dakota and Texas — with confirmed positive cases of H5N1. Three dairy farm workers — two in Michigan and one in Texas — have tested positive for the virus following exposure to infected cows. The third individual is the first human to report more typical symptoms of acute respiratory illness associated with influenza, according to the Centers for Disease Control and Prevention.

Dr. Kammy Johnson, a field epidemiologist with U.S. Department of Agriculture’s Animal and Plant Health Inspection Service, shared in a May 23 webinar hosted by the National Milk Producers Federation.

“We have seen the spread of H5N1 between states that was potentiated by cattle movement and now we have evidence of local spread between dairy farms in some states,” Johnson said. “Spread between dairy farms is likely multi-factorial. There is nothing really conclusive, so biosecurity becomes the key to mitigating the risk of spread between farms.”

As a response to risk mitigation, May 10, the USDA announced funding to help farmers dealing with confirmed cases of H5N1 to increase biosecurity measures, provide personal protective equipment for themselves and workers, properly dispose of discarded milk and help with covering veterinarian and testing costs associated with the virus.

On May 23, the USDA announced expansion of some programs to include all dairy farmers. Unaffected producers may receive up to $1,500 per premise to develop and implement biosecurity plans based on existing secure milk supply plans. This includes enhanced biosecurity protocols for industry workers frequenting multiple dairy farms. A $100 payment will be provided to dairy farmers who purchase and use an in-line sampler for their milking system.

Up to $2,000 per premise will be reimbursed for costs associated with collecting samples for testing performed beginning April 29, in accordance with the Federal Order. The cost to ship samples will be reimbursed as well up to $50 per shipment for two shipments per month.

Information will be forthcoming about compensation available to dairy farmers to offset lost milk production due to the virus.

Dr. Tavis Anderson, a member of the virus and prion research unit with the USDA’s National Animal Disease Center in Ames, Iowa, shared in the NMPF webinar about how the virus initially infected dairy cattle and how it is spreading among dairy cattle and into other species.

“Influenza A virus is relatively short, with just eight gene segments,” Anderson said. “It’s an RNA virus and doesn’t have any proofreading when it replicates, so it can accrue mutations in the genome rapidly. Within an individual animal you can get co-infection, and those two viruses can exchange genetic components. What emerges is a Frankenstein virus in a process known as reassortment and we call that antigenic shift.”

Anderson explained that a surveillance structure exists for monitoring H5 viruses in other species, and that infrastructure was easily deployed as researchers began trying to unravel how H5N1 found its way into dairy cattle. He said their first question was whether it was a single spillover.

“Did it come from a person, a pig?” Anderson said. “Was it out there in wild bird origins? Once into dairy cattle, was it multiple times? This is the unknown right now. There is a lot of active research trying to understand if dairy cattle are going to be plugged into the general influenza ecology or remain an unusual host event.”

Anderson said that all data of anything infected with H5 influenza over the past four years is being compared to over 220 influenza viruses isolated in dairy cattle from March through the end of April.

“One of the silver linings here is that it was a single spillover rather than multiple wild bird viruses getting into dairy cattle,” Anderson said. “We were able to date when that happened – approximately the end of December, give or take a couple weeks. That means there was essentially relatively limited local transmission, and (it) sort of bubbled away in dairy cattle for a couple of months, to that time and place where it spread relatively rapidly and was able to be noticed by producers and veterinarians in 2024.”

Anderson said he and his fellow researchers wondered whether there was anything unique about this virus that may have facilitated the interspecies transmission.

“All of the mammalian detections of H5 over the last four years have reflected what was circulating in wild birds, with viruses spilling over into mammals, then dead-ending,” Anderson said.

He said this process has happened over 100 times in the last four years, across 20 mammalian species. What was unique in this case he said was that there was a rarely detected virus out there in wild birds that had reassorted and accrued two different gene segments.

“That really rare virus is the one that got into dairy cattle,” Anderson said. “It truly was a very rare event, and it was that reassortment just prior to spillover at the end of 2023 that seems to have changed the phenotype of the virus, prior to it getting into dairy cattle.”

Anderson shared how it went from a single, confirmed case to hundreds.

“Animals are moved in modern agriculture, and unfortunately if they are infected with a virus, that virus is moved as well,” Anderson said. “Animals without any overt clinical symptoms were moved from Texas. That initial movement seeded three distinct epidemiological clusters; within those distinct clusters you can see movement across state boundaries and within locations as well.”

Anderson said concern remains that the virus found in dairy cattle may be evolving into something slightly different from that initial spillover from wild birds. More than 10 transmissions from cattle to other species such as poultry, cats, birds and other peridomestic animals such as raccoons have occurred.

“Additional experimentation is required to understand what is driving that transmission, whether it is people, shared water, food or contaminated surfaces,” Anderson said. “The more virus that is out there, the more probable you are to detect these interspecies transmission events.”

Anderson said that while the virus is moving from cattle to other species, there does not appear to be major changes going on in the virus at this time.

“The longer this persists in dairy cattle, the more potential there is for these types of mutations to emerge, and then sweep through that population,” Anderson said.