DANE COUNTY, WI, – MAY 8:Cows being milked at Mystic Valley Dairy, in Dane County, Wisconsin on May … [+]
A new strain of bird flu, H5N2, was just identified in Mexico City, following the death of a 59-year-old man. The strain, different from the H5N1 bird flu that has infected three dairy farm workers in the U.S., has not been previously seen in people. Part of the worry is that the man had been bedridden at home and had no known exposure to birds or animals.
The man did have underlying diabetes and chronic kidney failure, both of which make people more susceptible to infections. He became ill on April 17 with fever, shortness of breath and diarrhea. He died on April 24. None of his contacts have had positive tests for flu A to date. However, El Universal reported that “12 contacts (seven symptomatic and five asymptomatic) were identified near the patient’s residence” and that serology is pending. H5N2 has been known to be circulating in birds in the area.
It’s confusing to keep all the names of the different flu types straight—H5N1, H5N2, bird flu, swine flu, flu A, flu B and more.
The three main types of flu, A, B and C, are named after core proteins. We have annual outbreaks of influenza A, which is the most serious. Influenza A H1N1 caused the deadly 1918 outbreak. Flu B is usually less severe and causes infections every few years. Flu C hasn’t caused epidemics.
The “H” and “N” in the names refer to surface proteins, hemagglutinin and neuraminidase, which help the virus stick to and invade the cells. Sometimes, the strains mutate and swap genetic material, making it more infective. This happened when H1N1 and H2N2 combined and mutated in birds, resulting in a “bird flu” that could now infect people. This resulted in the 1957 influenza pandemic in Asia from H2N2, a novel (new to humans) strain.
Strains are also divided into highly pathogenic avian influenza or low pathogenic. The biggest concern in recent months has been HPAI H5N1.
The best illustration of the relationship between different flu strains in people and animals is that by David McCandless.
Who can catch which flu?
H5N1 is the strain decimating some poultry flocks and dairy herds. We know it has spread to cause illness in a few people, but we don’t know the extent because only limited and inadequate testing is being done.
“We’re making the same mistakes today that we made with COVID. And what do I mean by that? We’re not testing to really see how many people have been exposed and got asymptomatically infected,” Deborah Birx, former Covid-19 response coordinator, told CNN. “We could be pool testing every dairy worker. I do believe that there’s undetected cases in humans, because we’re once again only tracking people with symptoms. When we did that with COVID, the virus spread throughout the Northeast undetected.”
Influenza specialist Andy Pekosz, Ph.D. echoed this, saying, “Right now, there should be extensive, perhaps weekly testing of all dairy farm workers coupled with increased availability and training of workers to use protective gear.”
He added, “My understanding is that those programs have capacity, but because they are voluntary, they need agreement from farmers and farmer workers to participate. CDC cannot mandate testing, but they can provide it. I think increased testing and protective gear can be done in a way that is minimally disruptive to a dairy farm operation, but clearly there is reticence to take part in these voluntary programs.”
With this Mexican patient, the consensus among experts is that this is likely an isolated “spillover” case, and the risk to the general population is very low. However, there is growing concern that this or the H5N1 virus in the U.S. will mutate and become more infectious. H5 viruses are reportedly more likely to infect people than other strains.
There has been an ongoing outbreak of H5N1 in Asia with a much higher mortality. Pekosz said there has been “better documentation of the case-fatality rate there,” given their higher numbers. “The large number of cases in Asia are primarily due to increased human-poultry contact in that part of the world. If you limit things like live bird markets and provide poultry farm workers with some basic protective gear, you can drastically limit human H5N1 cases anywhere, but particularly in Southeast Asia.”
The H5N1 virus is increasingly found in various wild animals, most recently cats and mice. Dr. Rick Bright, virologist, pandemic expert and former head of the U.S. Biomedical Advanced Research and Development Authority, told The Telegraph, “This brings the virus closer to human homes. It increases the risk of direct exposure and infection.” It will make any control efforts far more difficult as the mice can quickly spread infection. Rodents are notorious for causing epidemics, from the Black Death (bubonic plague), to Lassa fever in Africa, to Hantavirus in the Southwest U.S.
Another criticism of current control efforts is that there is a delay of weeks in making data public, and genetic sequencing to see similarities between strains is also not being made public. Bright noted, “Need to urgently see sequences to know if it was fully avian virus, or possible reassortant with human H3N2 virus.”
People are also calling for vaccinations to be offered for dairy workers, which is being started in Finland.
For now, your best safety precautions are to wear masks and goggles if in the vicinity of cows being milked and to avoid raw dairy products. I would also recommend avoiding 4H club shows or county fairs. If you can’t resist going, it would be safest to wear a mask and goggles, given what we currently know about transmission.