The Study of H5N1 in Dairy Continues

The story behind the H5N1 virus in dairy cattle continues to unfold. Progress on identifying, studying and preventing the spread of the virus in dairy cattle, which was first confirmed on March 25 of this year, is moving ahead on multiple fronts.

Jamie Jonker, Chief Science Officer, National Milk Producers Federation: “...we have learned, we have learned a lot, but there's still a lot yet to learn. You know, certainly we now know that the movement of lactating dairy animals has played a role in some of that spread, and that's resulted in the USDA Federal Animal health order, which is requiring pre-movement testing of lactating dairy animals, crossing state lines.”

The movement of dairy cattle is believed to have been the mode of transfer for most of the 36 herds with the first confirmed cases that were found in nine states. As the industry has become more cautious with transporting dairy cattle, the spread has slowed. Twenty-two states currently have restrictions on the importation of dairy cattle. Canada has also tightened restrictions on the importation of dairy cattle.

Questions still remain as to why the symptoms of the virus in cattle are markedly different from those that appear in poultry.

Jamie Jonker, Chief Science Officer, National Milk Producers Federation:   You know, we see in the animal, the animal movement within a farm are still looking a lot like the spread of mastitis. You know, we're learning more about why the virus likes the mammary gland. There are some receptor cells in there that the virus has a high affinity for. It gets in there and it replicates at very high levels.  And so when you have common milking equipment that can be a mechanical conveyance between animals. So that's probably a very high likelihood that is a a predominant cause within a herd. 

Experts suggest that some of the slowing in new cases may be due to increasing temperature as the country moves into summer.

Jamie Jonker, Chief Science Officer, National Milk Producers Federation: “And we don't quite know the answer to that yet. Yeah, we we do know from the experience of the poultry sector that that the virus tends to die down as we get into summer because it doesn't like heat. And so, you know, it's possible we might see a bit of a lull here in summer and then, you know, maybe there's a resurgence in the fall. We don't know the answer to that because it's a new and dairy cattle.”

Others in the dairy industry suggest that part of the slowdown in new H5N1 cases in the nation’s dairy herd come from a reluctance of dairy owners to report or even test for active cases of H5N1 in their herds. Due to the potential for low test numbers and under reporting, the exact extent of how far the virus has spread is still unknown.

The passage of the virus from dairy cattle to humans has occurred three times. The first case was discovered in early April and the second was found last week when a Michigan dairy worker tested positive for bird flu. The worker had been in contact with cows presumed to be infected, AND experienced mild eye symptoms. 

The CDC announced a third infected worker this week, also from Michigan. The farmworker displayed symptoms of acute respiratory illness associated with influenza virus infection.

Officials with the Centers for Disease Control, say data indicates the virus detected in both cows and the first two human cases lack changes that indicate the virus has adapted to transmit between humans. The genetics of the third case have not been identified. To prevent further spread between animals and humans, the CDC recommends limiting close, long or unprotected exposure to sick or dead animals.

Also this week, the USDA’s Food Safety and Inspection Service announced the results of its most recent study on tissue samples from 96 culled dairy cows. It found H5N1 viral particles in one of the 96 samples. No meat from the 96 animals entered the food supply.

Samples of ground beef were purchased from retail channels in states with herds that had a positive test for the H5N1 influenza virus. Testing by FSIS found no virus particles present in the ground beef. Even if bird flu were to end up in consumer beef, USDA officials say, cooking the meat to an internal temperature of 165 degrees will kill the virus in the same manner as it destroys E. coli and other viruses.

Although milk from dairy cows that show symptoms of H5N1 infection are diverted from the food chain, tests of retail milk found deactivated virus remnants. The FDA believes that proper pasteurization of milk is an effective method of inactivating the virus. 

The FDA also recommends the dairy industry refrain from selling raw milk and raw or unpasteurized cheese products made from the milk of cows showing signs of the illness.

Testing of beef and milk products continues in the quest for a better understanding of the virus.

Jamie Jonker, Chief Science Officer, National Milk Producers Federation: “They've confirmed through virus viability studies from those products that the virus is not alive, it's dead, which means pasteurization does precisely what we kind of really thought it would do, particularly for a virus like this that is relatively intolerant…And so that's helping to confirm this isn't a food safety issue. It is an animal health issue. It is a potential safety issue for workers that are in close contact with infected animals, particularly with milk from the infected animals. But so far, you know, that's where it's at animal health and that potential worker safety issue and not a bigger issue.” 

For Market to Market, I’m Peter Tubbs.