Expert says bovine influenza A virus (BIAV), also known as highly pathogenic avian influenza (HPAI) in cattle is found primarily in multiparous (second lactation or older) cattle.
For the first time in the US, highly pathogenic avian influenza (HPAI) has been identified in domestic livestock including goats and dairy cattle. To understand the threat HPAI poses to domestic livestock species, and to inform producers on actions that can be taken to reduce the risk of infection on-farm, the US-based Swine Health Information Center (SHIC) in collaboration with the American Association of Swine Veterinarians (AASV) recently hosted a webinar on influenza A viruses. The recent detection and confirmation of HPAI in domestic livestock by USDA has raised questions regarding the emerging threat and potential risks among production livestock.
Editor’s note: Webinar content has been edited for length and clarity. To watch the full webinar, please visit https://iastate.app.box.com/s/o6dhclv5irvspcbj5q8p21ujr4a9ei29.
Since highly pathogenic avian influenza (HPAI) has been detected in dairy cattle, industry specialists are looking at what this means for domestic livestock. The first case of HPAI in cattle was confirmed in Texas on March 25. As of the middle of April, there have been 29 confirmed herds of dairy cattle in eight states infected with HPAI. At a recent webinar hosted by the Swine Health Information Center and the American Association of Swine Veterinarians, National Milk Producers Federation Chief Science Officer Dr. Jamie Jonker talks about HPAI in dairy.
“Producers were initially seeing a mystery disease in the panhandle of Texas,” Jonker says. “Based on field observations, the initial spillover event probably occurred the beginning of February. To our knowledge, this is the first time HPAI has been detected in cattle anywhere in the world.”
The H5N1 HPAI in cattle is of the same clade found in migratory birds. Samples from migratory birds in Texas from as far back as November 2023 have the same genetic sequencing. This is identified as Eurasian Lineage Goose.
“We are seeing this in multiparous (second lactation or older) cattle,” Jonker says. “The cattle are often 150 days in milk or longer. When a herd is infected, we see approximately 10 percent of the lactating cattle with clinical symptoms. There is minimal mortality. We sometimes see mortality with secondary infections.”
Symptoms include decreased activity. There is a drop in rumination, feed and water intake, and milk yield. The milk shows a change in consistency, thicker and often yellowish to brown, resembling colostrum. Some animals are showing flakes in milk, which are generally an indication of mastitis. Cows with severe disease are affected in all quarters; some cows are affected in only 1 or 2 quarters. There is widespread increase in milk conductivity.
“When these animals become ill, they are separated from the general herd,” Jonker says. “This can be challenging on a farm where large numbers or 10 percent of the herd are having clinical symptoms. There is no specific treatment for HPAI in dairy cattle, so they are treated for symptoms. For example, animals are drenched to rehydrate them, or treated with NSAIDs when they have fever.”
When a farm has an outbreak, it takes a little less than a week to peak incidence. The illness moves through very quickly, with a tapering at about two weeks. However, it takes around 30 to 45 days for infected cows to fully recover. Some cows do not fully recover milk production in that time period. Other cows actually shut down milk production and become a dry animal.
“We do not know if this is a lasting condition until we start having some of these animals freshen back into the herd. That could be as far as six months from now or more,” Jonkers says. “There is still a lot to learn about the lasting impact of this on the clinically affected animals.”
Where did HPAI in dairy cattle come from?
Initially, HPAI is thought to come from migratory birds. However, there is much epidemiological investigation into transmission. While cows do not fly, HPAI has spread to other states. There has been linkage of some herd movement from affected areas of Texas to some other states.
“So far, the virus does not seem to have picked up any bovine or mammalian genetics. It seems to be self-limiting in cows,” Jonkers says. “We are seeing this in our lactating animals. But we are not seeing this in our calves, growing heifers, pregnant heifers, or in dry cows that were dry prior to infection in the herd. It is very unique that it seemingly is working in mammary glands more like a mastitis than a respiratory issue more typical of an influenza.”
Looking past the spillover event from migratory birds to dairy cattle, since March 25, there have been one egg layer in Texas panhandle and three egg layers in Michigan confirmed with the same HPAI H5N1. These locations have proximity to affected dairy farms. Therefore, lateral flow from the dairy farms to the egg-laying operations could be possible, and more research needs to be done to understand this transmission. For instance, this movement could be happening on clothing, or vehicles, etc. This is changing how the dairy industry is looking at biosecurity on our farms.
Further, more research needs to be conducted to answer some big questions:
- How and why is HPAI H5N1 being found in mammary glands?
- Is the virus starting as a respiratory issue and migrating to the mammary gland?
- How is this transmission occurring so rapidly in a dairy herd?
- Why is it acting like a mastitis organism in the dairy cow? Could mechanical milking processes potentially be involved?
- What are the biosecurity practices we need to address?
HPAI biosecurity on dairy farms
Producers are advised to look at management practices to protect cattle and people from exposure. Enhanced biosecurity measures should address potential pathways. Because dairy farms are generally very open, there are many potential pathways on and off the farm, including:
- feed, water, bedding
- people
- vehicles and equipment,
- rodents, birds, flies, wildlife
- airborne
- animals and animal products
These pathways and the lines of separation need to be understood to help control movement in and out. HPAI on dairy farms is requiring quickly tightening biosecurity processes. Biosecurity guidance for dairy farms and veterinarians may be found at several resources:
USDA
https://www.aphis.usda.gov/sites/default/files/recommendations-hpai-livestock.pdf
AABP
NMPF
FARM Biosecurity
https://nationaldairyfarm.com/dairy-farm-standards/farm-biosecurity/
Secure Milk Supply
In addition, specialists are emphasizing guidelines to protect farm workers. For example, workers in the milking parlor are of particular concern because of the potential for incidental contact between an asymptomatic animal that may be shedding virus in the milk and getting that milk in the eyes or other mucosa. Though workers already are advised to wear eye protection, this outbreak reinforces the recommendation. In one case, a farm worker became ill with conjunctivitis after exposure to sick animals.
“Farm workers should protect the mucosa of their eyes, noses and mouths,” Jonker says. “Employees should wear gloves and practice hand washing. It’s especially advised to wear protections in contact or close exposure with sick or dead birds or other animals. Also, wear protective gear when in contact with feces, milk and litter from sick birds or other animals.”
More information about HPAI in cattle may be found at https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-influenza/hpai-detections/livestock.
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