U.S. Department of Agriculture orders dairy farmers to test milk-producing cows for highly pathogenic avian influenza (HPAI H5N1) infections before animals are transported to another state following virus discovery in samples of pasteurized milk collected by the United States Department of Agriculture. and Medication Administration.
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U.S. Department of Agriculture orders dairy farmers to test milk-producing cows for highly pathogenic avian influenza (HPAI H5N1) infections before animals are transported to another state following virus discovery in samples of pasteurized milk collected by the United States Department of Agriculture. and Medication Administration.
Justin Sullivan/Getty Images
Officially, there is only one documented case of bird flu being transmitted from cows to humans during the current outbreak in the United States.
But epidemiologist Gregory Gray suspects the real number is higher, based on what he heard from veterinarians, farm owners and workers themselves as the virus hit their herds in his state.
“We know that some workers sought medical care for flu-like illness and conjunctivitis just as H5N1 was ravaging dairy farms,” says Gray, an infectious disease epidemiologist at the University of Texas Medical Branch at Galveston.
“I have no way of measuring this, but it seems biologically quite plausible that they too are suffering from the virus,” he says.
Gray has spent decades studying respiratory infections in people who work with animals, including dairy cattle. He points out that “a clustering of flu-like illnesses and conjunctivitis” has been documented in previous outbreaks involving avian flu strains that are deadly to poultry like this one.
Fortunately, genetic sequencing of the virus does not indicate that it evolved to spread easily between humans.
Still, epidemiologists say it’s critical to track every possible case. They worry that some human infections may go unnoticed, especially if they are mild and transient, as was seen in the Texas dairy worker who caught the virus.
“I think, based on the number of documented cases in cows, there’s probably a decent amount of human exposure,” says Dr. Andrew Bowman, associate professor of veterinary preventive medicine at Ohio State University. “We just don’t really know.”
Limited testing raises concerns
36 herds were affected in nine states. Local and state health departments have tested about 25 people for the virus and monitored more than 100 symptoms, federal health officials said during a press briefing Wednesday.
These people are “on the footprints of where the cattle detections are,” says Dr. Demeter Daskalakis, who works for the Centers for Disease Control and Prevention, although he did not provide details on the locations real.
“There is a very low threshold for individuals to get tested,” he adds.
The lack of testing early in the outbreak is not necessarily surprising. In places like Texas and Kansas, veterinarians weren’t thinking about bird flu when illnesses emerged in early March, and it took time to identify the virus as the culprit.
But the total number of tests done on humans at this point seems low to Jessica Leibler, an environmental epidemiologist at the Boston University School of Public Health.
“If the idea was to try to identify the fallout from these facilities on human populations, you would have to try to test as many workers as possible,” says Leibler, who has studied the risk of new zoonotic and livestock flu . .
Furthermore, Gray notes, the virus is likely much more widespread geographically in livestock than reported cases show, “perhaps spreading much more to humans than we knew, or are aware of.”
The federal government was quick to assess the security of the dairy supply. On Wednesday, the Food and Drug Administration released results showing that the infectious virus was not present in about 200 samples taken from dairy products across the country. The first results on ground meat are also reassuring.
However, there still remain “serious gaps” in public health officials’ ability to detect avian flu in those who work with cows, a task made all the more difficult because some cases may not be symptomatic, says Leibler. “There is a very widespread possibility of worker exposure to this virus.”
Which only complicates matters: The true extent of the outbreak in cattle remains unclear, although new federal testing requirements for interstate movement of cattle may help fill in the picture.
“Some dairy herds appear to have clinically normal but potentially infected animals, making it very difficult to know where to conduct surveillance,” says Bowman.
Call for proactive measures to track possible human cases
The health system would be susceptible to detecting any alarming increase in human cases of bird flu, according to modeling by the CDC.
Federal health officials are monitoring flu activity in emergency departments and hospitals. Hundreds of clinical laboratories that perform tests are responsible for reporting results. And in early April, a CDC health alert was sent to clinicians advising them to be on the lookout for anyone with flu-like symptoms or conjunctivitis who has worked with livestock.
But even these guarantees may not be enough to anticipate an epidemic.
“I worry that if we wait until we see a spike in these systems, we may already be seeing much more widespread community transmission,” says Dr. Mary-Margaret Fill, deputy epidemiologist for the Tennessee Department of Health. Instead, she says there should be proactive testing.
In the filler notes, there are anecdotes about farmworkers suffering mild illness while working with livestock in some of the areas where the virus has spread and “not enough visibility on testing being done or not in these populations to understand what could be happening.”
To get ahead of the virus, Leibler says not only workers need to be screened, but also their family members and other community members, in case the virus evolves to spread easily between humans.
Dr. Rodney Young says doctors in the Texas panhandle have been vigilant for any flu cases, especially among those near livestock, but so far there is no indication what anything out of the ordinary.
“We just didn’t see people fitting that description and so we had to go through a lot more testing,” says Young, regional chair of the department of family and community medicine at Texas Tech Health Sciences Center School of Medicine in Amarillo..
Getting buy-in from dairy farms
Gray says it can be difficult to detect and measure illness in these rural workers for many reasons: their remoteness, reluctance to seek health care, lack of health insurance, concerns about employment status immigration and the reluctance of farmers “to wave the flag” that there are infections.
The farms he works with consider protecting workers and combating the spread of this virus “a major priority,” but right now they are bearing all the risks of public disclosure, he says.
Dr. Fred Gingrich says this is a major obstacle to closer cooperation between federal health officials and industry during the current crisis.
Dairy cattle farmers are currently not compensated for reporting infections in their herds, unlike poultry farmers who receive compensation for losses from killing birds when they discover cases, says Gingrich, executive director of the American Association of Bovine Practitioners.
“So what is their incentive to report? » he said: “It’s the same virus. It just doesn’t kill our cows.”
Gray managed to begin collecting samples from humans and cattle at several dairy farms that have recently encountered the virus. It’s part of a study he launched before the H5N1 outbreak in response to concerns about the spread of SARS-CoV-2 on farms.
They will look for evidence of exposure to new flu, including avian flu – something he is able to do because of his experience in this area and his assurance that farms will remain anonymous in published work.
What worries him most is the possibility of the outbreak spreading to another type of farm.
“We know when it hits poultry farms because the birds die, but the pigs may or may not show serious disease,” he says. “The virus can just move around, make many copies of itself and it’s likely to spread to those workers. It’s much bigger.”
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