Colorado is investigating a second possible outbreak of bird flu in a dairy herd, the state veterinarian said this week.
The potential new outbreak — coming less than a week after Colorado identified its first outbreak — is an indicator of how rapidly health officials are trying to catch up to bird flu’s spread through dairy cattle.
Dr. Maggie Baldwin, who manages the Colorado Department of Agriculture’s Animal Health Division, did not provide additional details on the dairy or where it is located. She said the state is awaiting test results from the U.S. Department of Agriculture to confirm whether bird flu, also known as highly pathogenic avian influenza, is involved.
“USDA’s confirmatory testing is taking a little bit longer with the load that they’re getting currently for testing,” Baldwin said.
Nationwide, avian influenza has reached at least 36 dairy herds in nine states, and state and federal officials recently released new testing orders intended to more aggressively track its spread.
But does that make it something you have to worry about (assuming you’re not in the dairy business or a cow)? We asked Baldwin and others for their thoughts on some common questions.
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Wait, why is bird flu in cows?
H5N1 strains of avian influenza virus, such as the one currently circulating, primarily stick to birds, especially waterfowl. Those animals make ideal hosts for the virus because they generally don’t get sick from it and they are also often migratory — meaning they are basically in the virus transport business.
What has made this particular strain of bird flu somewhat unique is its staying power — the virus has been circulating in the United States for at least two years — and its continued ability to find new species to infect.
At The Sun, we have tracked infections as they moved from wild bird populations to commercial poultry farms. Baldwin said Tuesday the state has seen outbreaks at 34 poultry operations in the last two years, resulting in the loss or slaughter of 6.3 million birds.
Infections then started jumping over into mammals, affecting skunks, foxes, mountain lions, bears and others.
In many of these instances, including when nonwaterfowl birds are infected, the virus is extremely lethal. For instance, mass-mortality events of seals and sea lions in South America in recent months have been attributed to highly pathogenic avian influenza. That’s where the “highly pathogenic” part of the name comes from.
But it’s especially unusual to see bird flu in cattle, said Franklyn Garry, a professor at Colorado State University who specializes in livestock management.
“What’s really notable is there are very darn few flu viruses that substantially affect cows,” he said. “So in the cow world, we don’t really worry about flu because it just doesn’t happen much.”
Are dairy cows dying from bird flu?
No, which is good, obviously, but also makes it harder to track.
Flu viruses, as anyone who has ever caught one knows, are generally associated with respiratory illness: coughing, runny nose, etc. But cattle infected by HPAI generally show few respiratory symptoms. Instead, the main symptoms are fever, reduced appetite, reduced milk production and abnormal milk production — i.e., the milk is thick and discolored.
These symptoms resolve after what Baldwin called “supportive care.”
In sum, the virus in dairy cattle is “low pathogenic,” Garry said. Such mild symptoms mean that it is possible — likely even — that infections are being missed, making it harder to figure out how many cows are actually affected.
How did cows catch the virus to begin with?
This is where the mystery really heats up.
Bird flu was first detected in a dairy herd in the United States in March, in a herd in Texas. Baldwin said that genetic sequencing suggests the virus was introduced into dairy cattle from wild birds.
But subsequent spread appears to have been cow-to-cow, which Garry said is also unusual. Baldwin said neither of Colorado’s two herds — the one with a confirmed outbreak and the one under investigation — had known contact with an infected herd.
Garry said there is much still to learn about how the virus has moved around the country. But one possibility is that it spreads when cows move among herds.
This is why a new federal rule — adopted into state regulation Tuesday — requires dairy operators to conduct testing of lactating dairy cattle when moving them between states.
Only when they move between states? C’mon, how much is that going to do?
In the modern dairy industry, it turns out cows move around A LOT.
“There is a tremendous amount of movement of dairy cattle across the United States and between states,” Baldwin said.
Colorado has 106 dairies with about 200,000 cows. Baldwin said in the first quarter of this year, dairy farmers exported about 34,000 cattle from Colorado and imported about the same number. In other words, about 17% of Colorado’s population of dairy cattle turned over in three months.
This is partly due to consolidation and specialization within the dairy industry. Garry grew up on a dairy farm in upstate New York that had between 50 and 60 cows, about average for the time, he said. But the average dairy size today in Colorado — hardly a top-producing dairy state — is 2,000 cows.
Operators often have multiple dairy farms, sometimes in different states. They may also own, or contract with, specialty operations that raise young calves until they are ready to move back to milking herds. All of this leads to lots of movement of cattle.
There is so much movement, in fact, that it has led to what some public health experts criticize as a gaping loophole: When an operation is moving large numbers of cattle, the new federal rule requires them to test only a sample of 30 cows for bird flu.
Still, Baldwin said the new rule will provide a good level of surveillance testing.
“I think we will be catching a really broad sample,” she said.
Why are only lactating cows being tested?
The answer here is simple, though somewhat speculative: The flu virus appears to concentrate in the mammary glands of cows.
“On a given dairy with the virus, the nonlactating and young animals are asymptomatic and don’t appear to have any problems,” Garry said.
So that makes milk-producing cows the most likely culprit for harboring and spreading the virus. But Garry said that is far from confirmed — just one of the unknowns about how the virus infects cows, how it moves within their bodies and gets shed back out, and how it makes its way into a new animal.
Whoa, whoa, WHOA. Does this mean there could be bird flu in milk?
Yep, but this doesn’t seem like much to worry about for most people.
Testing raw milk is one of the methods currently being used to track the virus’s spread, so virus definitely gets shed by infected cows into their milk. The commercial milk supply appears safe, though.
The reason is because milk sold in stores is pasteurized — meaning it’s heated up to kill harmful pathogens in the milk. This process kills the flu virus.
Federal authorities and others have tested samples of milk from stores and found bird flu particles in about one-fifth of them. But follow-up tests confirmed that all of those virus particles were dead, dead, dead. They couldn’t infect anyone, and they couldn’t replicate.
What about raw milk?
This could be more of a concern. Raw milk is not pasteurized, so live virus could remain in the milk.
It’s unknown whether that poses an infection risk to humans. But there is one study that documented deaths in cats who were fed raw milk on a dairy farm where cows were infected with bird flu.
Subsequent testing on two of those cats revealed that they had been infected by bird flu. It’s not certain that the cats got sick from drinking the milk, though the study’s authors call it “a likely route of exposure.”
These concerns were enough to scuttle a bill at the state Capitol this year that would have legalized sales of raw milk. (Raw milk remains available in Colorado, though, to people who buy a share in a cow from a dairy farm.)
What about beef? Could my filet give me flu?
The answer appears to be no — again with the caveat that knowledge is evolving.
Similar to what it did with milk, the federal government took samples of ground beef sold in stores to look for bird flu virus. It didn’t find any. (And if there were, safe cooking practices would kill it.)
Garry said there also haven’t been any reports of outbreaks in feedlots or other commercial beef operations.
OK, let’s get to the big one: Could this jump to humans?
The signs are encouraging right now, but viruses have a way of surprising.
There have been two people in the United States who are known to have been infected by bird flu. One was a worker on a commercial poultry farm in Colorado. The other worked on a dairy farm in Texas.
Both had minor symptoms — for the dairy worker, it was an eye infection — and they recovered quickly. (There has also been at least one infection internationally, in a man named Gosling who kept ducks as pets in his home. He also recovered but was heartbroken when his flock was culled, according to the BBC.)
H5N1 bird flus, historically, have been nasty when they get into humans. Hundreds of people have been infected with bird flu strains worldwide since 2003, with a fatality rate above 50%.
The current virus doesn’t appear to be evolving much in ways that make it more likely to infect humans, according to a genetic analysis of the virus taken from the Texas patient.
The concern, though, is that the longer the virus circulates, the more opportunity it will have to mutate into a more dangerous form — especially if it jumps into a more frequent incubator for future human infections, like pigs. This is why public health leaders are calling for greater testing in the U.S., including better testing of dairy workers to see how many (if any) may actually be getting infected and not know it.
This may be especially difficult in the dairy industry, a 24/7 business where workers, many of them immigrants, may be reluctant to seek medical attention if not feeling well. Dairy farmers nationwide have been reluctant to allow health officials onto their land for testing, one veterinarian said.
“This particular disease is looked at as a scarlet letter,” said Dr. Kay Russo, a Colorado veterinarian who consulted with doctors in Texas about the outbreak there.
“We do not know what we do not measure,” she told the Associated Press. “Unfortunately, the horse left the barn and took off a lot faster than we were able to mobilize.”
Baldwin defended the response so far, saying officials have worked as quickly as possible to get a handle on the problem.
“We’re building the plane as we’re flying it,” Baldwin said.
And they have a lot more to learn.
“There are more unknown things than there are known things,” Garry said. “Because this is so new and because we haven’t seen it before, we have to find out a whole bunch of stuff about this virus.”