New strain of H5N1

Nearly a year after the first cases of HPAI H5N1 were confirmed in Texas dairy cows, the disease continues to create new questions.

Until recently, dairy cow infections were limited to the B3.13 strain, tracing back to a single spillover event that occurred in Texas in late 2023.

The Wisconsin Department of Agriculture, Trade and Consumer Protection confirmed that a new strain of H5N1 has been detected in both Nevada and Arizona, through compliance with the National Milk Testing Strategy. The new strain, D1.1, originated in wild migratory birds.

A Feb. 11 press release from the Arizona Department of Agriculture said the confirmation of D1.1 at a Maricopa County dairy farm was unrelated to the recent detection of the strain in Nevada. The press release said every dairy farm in Arizona has been tested at least once in the month of January, with only one facility testing positive.

According to the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service website, as of Feb. 18, a total of 972 cases have been confirmed in 17 states. In the past 30 days, 36 new confirmed cases have been documented in Arizona, California, Michigan and Nevada.

Most states have enrolled in the NMTS and are currently performing active surveillance. Three states — Colorado, Mississippi and Pennsylvania — have all achieved unaffected status, reaching stage four of the NMTS with ongoing testing and surveillance activities demonstrating the absence of disease.

On Feb. 17, Wisconsin DATCP announced plans have been finalized to join into the federal order that established the NMTS, utilizing samples already being collected for routine milk testing.

In a Feb. 4 webinar hosted by the National Milk Producers Federation, Dr. Jennifer Siembieda from USDA APHIS Veterinary Services said the path towards stage four unaffected status depends on the size and scope of each state’s dairy industry.

“Mississippi doesn’t have a huge dairy industry,” Siembieda said. “They were able to do on-farm bulk tank testing and achieved three negative tests on 100% of their herds. That is the simplest route to stage four.”

Reaching stage five, absence or elimination of the disease across the country, will be achieved when all states have reached and maintained stage four status throughout a prolonged period of testing.

Dr. Jason Lombard of Colorado State University has been studying disease transmission on farms but said the data varies from farm to farm, noting that one farm had 33% of clinical cows and 19% of non-clinical cows shedding the virus, while another saw 95% of cows exhibiting clinical symptoms shedding along with 30% of non-clinical cows.

Lombard said the likelihood of aerosol transmission is gaining traction in his mind.

“Most of the positive environmental samples are from the parlor surfaces and liner samples, that goes with the high viral load we see in milk,” Lombard said. “As quick as disease spreads throughout the herds, if we were looking at transmission purely through milking machines, I don’t think it would move as fast as it is moving. I do think it could move through aerosol transmission in the parlor — there is a lot of milk splashed, water sprayed.”

In addition, Lombard has been looking at what the post-infection future looks like for affected cows.

“There are some changes in 21-day pregnancy risk after the cattle introduced clinical symptoms,” Lombard said. “We don’t know how much of that is impact of the actual disease or an impact of resource allocation — the people normally responsible for that work were relegated to treatment of sick cows.”

Changes in the incidence of abortion are inconclusive as well and could be impacted by many factors, Lombard said.

Future milk production for affected cows as they finish that lactation shows decreases of 10% on average. Things are looking more promising for cows that have returned to the milking string, commencing their next lactation, with mature equivalent projections being in line with pre-infection numbers.

Lombard’s research has also looked at how comorbidities might affect cows that contract H5N1, finding no association in H5N1 viral shedding with bovine viral diarrhea, bovine leukemia virus or Johne’s disease.

Researchers have been working on developing vaccines to guard against H5N1 infection, but achieving an approved product may be in the distant future, according to Dr. David White, with the USDA APHIS Veterinary Services Center for Veterinary Biologics.

According to White, eight ongoing field studies are working towards a vaccine, but none have provided data back. White said most of the studies are considered confidential information at this time.

Dr. Jamie Jonker, the NMPF’s chief science officer and vice president of sustainability and scientific affairs, said trade issues can complicate the use of vaccines in dairy cattle.

“The use of vaccines in dairy cattle is complex,” Jonker said. “There are a number of promising candidates in field trials that will result in several that could be useful in the toolbox, but it is unlocking that toolbox for usage that is complex. … We confirmed that pasteurization completely destroys the live virus. The use of vaccines can be a trade-limiting issue in poultry, there are concerns in some sectors of the poultry industry about the potential trade disruptions from vaccine use in dairy cattle.”