REDFIELD, Iowa (DTN) -- One of the biggest challenges for dairy farmers dealing with the H5N1 flu virus is how it has affected all farms despite whether they are infected, to prevent the spread of the disease. A recent USDA mandate requires all lactating dairy cows to be tested free of the virus prior to movement and all positive results to be reported.

"The federal order means lactating dairy cows must be tested within seven days of movement and be free of the virus before they are moved to another farm," said Iowa's state veterinarian, Jeff Kaisand, during a recent webinar. "Samples must be collected by an animal health official, and once results are found, the cow must have a certificate of veterinary inspection listing her permanent identification."

It's the hope of USDA that this, along with mandatory reporting of positive cows, will help prevent further spread of the virus. Keith Poulsen, director of the Wisconsin Veterinary Diagnostic Laboratory, agrees that USDA's recent testing requirement is an important measure to mitigate the virus's spread between states. The current guidance requires each cow to be tested in herds containing 30 animals or fewer, and farmers moving more than 30 animals across state lines only need to test 30 animals. An accredited veterinarian must collect or oversee the sampling.

"Normally, at least 50,000 dairy cows cross state lines to move throughout the country each week," Poulsen explained. "With the movement of so many cows, the testing requirement could strain farmers, veterinarians and diagnostic labs."

Poulsen said all the factors involved can be challenging for dairy producers, as they need to act with caution and implement a conservative approach to minimize further spread of the virus. But they also rely on the productivity of their herds to make a living.

"When you're managing a multibillion-dollar industry that deals with food and public safety, we want to make sure we're not giving out bad advice," he explained.

RESEARCH CONTINUES TO EVOLVE

Recent tests conducted on dairy products by USDA show pasteurization is effective in inactivating highly pathogenic avian influenza or influenza A in dairy products. Testing by USDA on ground beef reported negative tests, showing the meat supply is safe. Pasteurization of milk renders the virus inactive, and thus, the milk supply is safe also.

"The main finding is the virus can be present in the milk," said Drew Magstadt, clinical associate professor at Iowa State University's College of Veterinary Medicine. "We have limited data of how long these affected cattle stay positive with a PCR test of their milk."

One group of 20 cows that tested positive for the virus and were tested every week did show almost no sign of the virus in their milk at three weeks past breaking with clinical disease. This is a very small group but is believed to be common for cows.

Since this disease has no mortality connected to it, there are literally no tissue samples that have been tested. Other samples, including nasal swabs, serum, blood, feces and urine, will show an occasional positive, but are very low in virus. Milk tests show the highest amount of virus. Ongoing research is being conducted on mammary glands to find out if there are cell types present in this area of the cow that allow the virus to enter and replicate.

Researchers are trying to determine what are the best types of samples to test in non-lactating cows. Magstadt said it is clear that milk samples are the best way to test, but when determining virus presence or previous infection in other non-lactating cattle, it's important to know what type of samples to use. Antibodies appear to be present in these animals 10 to 14 days after infection, which should help determine what animals may have been previously infected. Determining if the non-lactating cattle are a risk to the lactating cattle is important to assess as well.

Transmission is an important factor in slowing down the disease.

"This is new and uncharted territory," Magstadt said. "There really isn't a model for a disease like this. How exactly did this get into cows in the first place from wild birds? There appears to be transmission between lactating cows also -- so how is that occurring? Is it aerosolized, or is part of the milking parlor involved? We need to figure that out to help control the spread and keep it out of uninfected sites."

LEARNING FROM POULTRY INFECTIONS

Highly pathogenic avian influenza is what affected the poultry industry and traces back to 1996. But this influenza, also an H5N1 flu, has seen several mutations throughout the years, including being found in several mammalian hosts. A high mortality rate is seen, especially in chickens, but it is not as highly pathogenic in other birds such as ducks.

Yuko Sato, Iowa State University Extension poultry veterinarian, said HPAI is what it is called in birds, but not in cattle or humans. Similarly, the H5N1 virus is what is being spread in mammals. She said the good thing about when it hits the mammalian species, many appear to be dead-end hosts. As of April 2022, red foxes appeared to be up to 40% of the mammals affected by H5N1. They became infected by scavenging on birds carrying the virus. In general, if the virus is not fatal to the animal, they will stop shedding virus after recovering from the sickness.

The PCR testing that is used with milk samples shows if the virus is there or virus particles are present. The other test is the Eliza test, which uses a blood sample and looks at the exposure of the animals and if antibodies are present. Both tests are used in the poultry industry to determine when the birds can be moved.

"We have learned a lot since the 2015 outbreak," Sato said. "In 2015, we had a low presence of virus in the wild bird population, and 85% of the cases were spread from farm to farm, as compared to the current outbreak, which has had more in the wild birds. As many as 9,000 detections were found in wild birds. Less than 20% of our cases this time are farm to farm spread. That's how we learned from the outbreak."

Sato encouraged the dairy industry to take a proactive stance and look at creative solutions to dealing with the virus instead of waiting for guidance from the government. Novel strategies need to be used to combat the virus and prevent further spread.

Kaisand stressed the importance of reaching out to local and state veterinarians for help with dealing with the H5N1 virus. As of May 6, no further positives had been reported to USDA since April 25. A total of 36 cases have been found in dairy cattle in nine states, including Texas, Colorado, Michigan, Kansas, New Mexico, Idaho, South Dakota, North Carolina and Ohio.

Jennifer Carrico can be reached at jennifer.carrico@dtn.com

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