Continued learning leads to federal order

Testing of lactating dairy cows mandated prior to interstate movement


Over six weeks have passed since the illness affecting dairy cattle in the southwestern United States was identified as highly pathogenic avian influenza H5N1, or bovine influenza A virus. In the days since, questions about H5N1 have been answered and many more have arisen.

To slow the spread of the virus, especially because cow-to-cow transmission is yet to be understood, effective April 29, the U.S. Department of Agriculture mandated that lactating dairy cattle receive a negative test for the influenza A virus from an approved National Animal Health Laboratory Network laboratory for interstate commerce.

As of May 6, lactating dairy cattle have tested positive for H5N1 in 36 herds in Colorado, Idaho, Kansas, Michigan, New Mexico, North Carolina, Ohio, South Dakota and Texas.

According to a USDA press release April 24, the federal order was spurred because cow-to-cow spread was identified within a herd. As well, the spread of the virus from cows to poultry and from dairy farm to dairy farm coincided with the movement of cattle. The press release also said that cows not showing clinical signs of the virus were testing positive.

Dr. Diego Diel, director of the virology laboratory at Cornell University’s Animal Health Diagnostic Center, spoke April 30 during a webinar hosted by the National Milk Producers Federation.

Initially, producers dealing with infected cows were asked to submit a broad variety of samples for testing, including nasal swabs and samples of whole blood, serum, urine, feces and raw milk. Samples collected from euthanized cows included tissue from lungs, lymph nodes, small and large intestines, and the mammary gland.

According to Diel, a few positive results were detected in samples of whole blood, serum and nasal swabs, but the vast majority of positive polymerase chain reaction results were found in samples of raw milk and mammary gland tissue.

“It seems like the virus is actively replicating in the mammary gland tissue based on the results we have,” Diel said. “Is there an infectious virus being shed in milk from those affected animals? The answer to that is, yes. The milk samples contain high viral loads in clinically affected animals and can serve as a source of spread to other animals.”

In an April 26 webinar hosted by the University of Minnesota Extension and the Minnesota Board of Animal Health, Dr. Joe Armstrong, UMN Extension, said that while the majority of affected dairy cows tend to be multiparous cows in mid-to-late lactation, the virus has been seen in other populations in affected herds.

“It is important to look at all animals in the herd and monitor them for symptoms,” Armstrong said. “Symptoms in individual cows are lasting about 3-5 days. Herds appear to be impacted for 14-21 days before returning to near normal feed intake and milk production.”

In addition to the first-reported symptoms that included decreased feed intake, rumination and milk production, and abnormal milk appearance, Armstrong said that some cows present with diarrhea while others present with dry, tacky feces as a result of dehydration. Fever, clear nasal discharge and lethargy have also been reported among affected cows.

Armstrong said on average, about 5% of the cows in affected herds present with clinical symptoms. The only treatment for infected cows is supportive care.

According to a USDA press release, on April 16, Animal and Plant Health Inspection Service microbiologists identified a shift in an H5N1 sample from a cow in Kansas that could indicate that the virus has an adaptation to mammals. Based on their analysis of that specimen sequence, the Centers for Disease Control and Prevention has not changed its overall risk assessment for the general public, because the substitution has been seen previously in other mammalian infections.

In the UMN Extension webinar, Dr. Stacy Holzbauer, the CDC’s epidemiology field officer for the Minnesota Department of Health, detailed concern surrounding the control of H5N1, which prompted the issue of the federal order.

“This particular virus is an influenza A virus, which is circulating in wild birds,” Holzbauer said. “They are constantly changing. Influenza A virus widely circulates in humans, wild birds, domestic birds, swine and equine. But all of these viruses, including the seasonal influenza viruses we get vaccinated for every year, have an origin in wild birds at some point in time.”

Holzbauer said these viruses have epidemic potential because they are constantly changing and exchanging genes with other viruses. The virus can mutate and infect other species.

“The concern is that we have more mammal-to-mammal spread, that this virus may mutate to where it can then spread to people more easily and then spread person to person,” Holzbauer said. “That is why we are very interested in what is happening in both our poultry and dairy industries. We have people and animals in the same environment working together. The fear is we will have a person who is infected with a human seasonal influenza virus and then also happens to get infected with the avian H5N1 virus and those two viruses essentially swap their genes. Then, we have this new human virus that could circulate person to person.”

According to Holzbauer, avian influenza viruses are typically spread to people through direct contact with infected birds or their environment.

“Person-to-person spread of these viruses is rare and limited,” Holzbauer said. “We expect there to be occasional spillover for the people who have direct contact, especially with poultry, but we don’t see person-to-person spread. So, it’s not a risk to the public, and it’s not a food safety risk either.”

Based on what they have learned through avian influenza infections in domestic poultry flocks, Holzbauer said the response to monitor people having direct contact with infected dairy cattle would be to initiate active surveillance for 10 days after the cows on the affected dairy farm have recovered from clinical signs.

Holzbauer said the use of personal protective equipment by people working with infected animals is their best defense to avoid infection from the H5N1 virus.

“Our PPE recommendations for people working on dairy farms in direct contact with ill cattle are gloves, goggles, N95 masks, coveralls and boots,” Holzbauer said. “We know these PPE recommendations are difficult in operations where these are not normal types of PPE.”

The key message is to protect mucus membranes — eyes, nose and mouth — to prevent fluids that may be carrying the virus from entering the body through these access points as much as possible.


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