“From what we’ve seen in the field, based on all the information we have, we think it could be moving through aerosol,” Lombard said. “Moving in plumes from farm to farm and likely from cow to cow on individual farms.”
The USDA announcement in March 2024 was a concerning development because the virus had infected a new species and had the potential to spread through the country’s milk production system. (Dairy products have since been proved safe to consume if pasteurized.) Several states, including Colorado, Texas, Michigan, Ohio and California, experienced outbreaks in dairy herds throughout the summer and fall. In all, 17 states have detected the virus in dairy cattle, and nearly 1,000 herds have been impacted.
The USDA first reported this version of avian influenza in the U.S. in wild birds and poultry in January 2022. In poultry, the virus is particularly severe, with fatality rates approaching 100%. Dairy cattle, however, generally handle the disease better, with mortality rates ranging from 0%-20%, Lombard said. Infected cows do experience decreases in milk production, which has an economic impact for producers. Initial estimates suggest dairy producers can lose about $1,000 per cow infected with the disease.
Learning how the virus spreads is key to preventing or controlling future outbreaks. To better understand the virus’s behavior, Lombard — a veterinary epidemiologist, dairy specialist and associate professor with CSU’s College of Veterinary Medicine and Biomedical Sciences and the CSU AgNext program — has consulted with producers, health experts and public officials in multiple states. In Colorado, Lombard quickly launched a research study last spring, working with more than a dozen CSU students to regularly test for the virus in five dairy herds on the Eastern Plains.
“Farmers were reaching out to us, saying, ‘Hey, we think we might have this — what can we do?’” Lombard said. “For us, we really wanted to understand how transmission was occurring. If we can figure out how the virus moves around, then we’re better equipped to manage the spread.”
A picture of transmission
One of the early hints that the virus could be spreading through a route other than contact with infected milking machines, Lombard said, was that the virus was spreading through herds quickly, more quickly than would be the case with machine-based spread.
Another clue, he said, came from identifying that antibodies for the virus were first showing up in cattle’s bloodstream prior to detection in the milk. That finding, he said, suggested cattle were being exposed to the virus by a route other than from contact with infected machines.
Lombard is now in the process of collaborating with members of CSU’s Department of Atmospheric Sciences to try to better understand the potential for airborne spread. The researchers are attempting to match wind patterns to dates of infected farms from a recent outbreak in California, which could support the theory that the virus moves through the air. Another possibility, he said, is that the virus is being carried from farm to farm via another species, such as birds.
In addition to learning about how the virus spreads, there have been other initial takeaways from the sampling done by Lombard’s team. Notably, he said, they detected the virus intermittently, which can make the virus more difficult to track because an animal might not test positive one day but might still be shedding the virus. Generally, Lombard said, cattle also appeared to shed the virus for a particularly long period, in some cases more than 10 weeks.
Lombard said the team’s sampling also revealed that cattle could shed the virus up to seven days prior to showing clinical signs — a so-called “subclinical” period similar to how COVID-19 behaves in humans. “By the time you have clinical signs,” Lombard said, “it’s everywhere.” In addition to decreased milk production, the most common clinical signs, he said, have included nasal discharge, decreased feed intake and inflammation of the mammary glands.
Notably, Lombard said, the cattle they tested in Colorado showed a strong antibody response to the virus, suggesting that an avian influenza vaccine could be effective in dairy cattle.
In addition to sampling cattle, Lombard’s team also sampled for the virus on trucks that transport milk from the farm to production facilities. They found a single positive, he said, suggesting milk trucks are not a high risk for spreading the virus.
To accomplish the extensive sampling throughout the summer and fall, Lombard enlisted the help of 17 students, including multiple undergraduates, from the College of Agricultural Sciences and the College of Veterinary Medicine and Biomedical Sciences. The team collected nasal, urine and blood samples from 30 to 40 cattle weekly at five Colorado dairy farms. They also collected milk samples biweekly.
Sami Smith, a first-year student in CSU’s Doctor of Veterinary Medicine program, had been working with the CSU AgNext research intern program during the summer when she learned about the opportunity to contribute to Lombard’s avian influenza sampling project. “This was a very big project,” Smith said. “I was really excited to join and help out.”
Smith had not worked with dairy cattle before, but she was headed into her first year of vet school and had an interest in large animal medicine, so the project was a good fit. The sampling days were long and often started early. She would sometimes wake up at 3 a.m. so the team could be sure to catch the same cattle for sampling and avoid the afternoon heat.
Still, even on those early mornings, Smith found the work rewarding. “It was pretty exhausting,” she said. “But our team was great; I feel like we really understood each other. I learned a lot about how a team works.”
Erin Burke, a senior undergraduate studying animal science who was also an AgNext research intern, has always been interested in epidemiology and diseases and was eager to help when she learned about the opportunity to work with Lombard. “This wasn’t something I ever thought I’d be able to help with as an undergrad,” Burke said. “It’s a pretty hard-hitting topic, and to be able to take part in this work was really cool.”
In all, the group collected more than 5,300 samples from Colorado dairy cattle.
Lombard will continue with a new phase of the work this summer. He plans to sample the same herds, this time looking at how antibodies to the virus may have persisted in the cattle. “Determining the potential for long-term protective immunity will be important if we start vaccinating,” Lombard said.
He added, “It’s been exciting to be able to piece this puzzle together. We’re making progress, and it feels good that we’re finally starting to develop that picture of transmission.”
Source : colostate.edu