(Bloomberg) -- For influenza viruses, imperfection is a strength. They constantly mutate, producing new strains that challenge immune systems primed to fight earlier varieties. That’s what makes flu a life-long threat to humans and the animal species — mainly birds — that are vulnerable to it.
Since 2020, a strain of highly pathogenic avian influenza called H5N1 has been decimating both wild and domestic birds. Now it’s spreading among US dairy cows, and has infected dozens of people, mainly US farmworkers exposed to sick cattle and poultry. In December, a patient was hospitalized in Louisiana with bird flu — the first severe human case in the country. California, the biggest US milk producer, declared a state of emergency to help expedite a response as the outbreak sweeps through its dairy herds.
The US Centers for Disease Control and Prevention and the World Heath Organization say the overall risk to the general public remains low, but public-health officials are on alert for any indication of the most feared outcome: human-to-human transmission that could trigger a pandemic.
When did H5N1 begin spreading?
The H5N1 strain was first discovered in 1996 in geese bred in southern China. It’s proved to be alarmingly adept at jumping continents and species and has rampaged through captive, commercial birds across the globe; governments ordered millions of birds slaughtered to limit the contagion.
A variant that emerged in 2020, clade 2.3.4.4b, led to infections in mammals like farmed mink in Spain and Peruvian sea lions. The same strain is ripping through wild birds and poultry in the US and has gained a foothold among dairy cows, with cases popping up among people who work with sick animals.
While those infections spurred heightened attention, the period from 2017-2024 has been the quietest period of H5N1 activity in humans since the virus first appeared, said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota.
What do we know about H5N2?
Not much yet. The strain is related to H5N1; both are in the influenza A virus family. But there’s been little research on H5N2. It gained attention in June, when a man in Mexico died with it. While that was the first laboratory-confirmed case in a person, researchers have identified people with antibodies that could signal prior infections. The death was surprising because the 59-year-old patient, who had underlying health conditions, had no history of exposure to the animals most likely to transmit the virus.
How bad is bird flu for humans?
Bird flu can be fatal. Since the start of 2020 through Nov. 1, 78 confirmed human cases of H5N1 had been reported globally to the World Health Organization, resulting in nine deaths. The hospitalization of the Louisiana resident was the first severe infection in humans in the US, the CDC said on Dec. 18. The health implications among most US cases have been limited. The patients diagnosed with avian influenza through early September had symptoms that were treatable with antiviral drugs. None died.
What are the symptoms?
There have been 61 reported cases in the US this year, mostly farmworkers in close contact with dairy cows or poultry, many of whom reported irritated eyes. A September case in Missouri was the first with no known occupational exposure to sick or infected animals.
Health authorities are looking for conjunctivitis, also known as pink eye, as an indication that someone may be infected with bird flu. Eyes are the only part of the human body with “avian” receptors that the virus is adept at attaching to.
Patients in Colorado and Michigan also experienced upper respiratory infections, raising concerns about transmission. The CDC is monitoring the virus for genetic mutations that could make it more dangerous, with no sign yet of worrisome changes. As of December, there continues to be no evidence of human-to-human spread, the CDC said.
How are people infected with bird flu treated?
Anyone with a suspected or confirmed infection should be treated immediately with one of the antiviral drugs known as neuraminidase inhibitors, such as Roche Holding AG’s Tamiflu, according to the CDC. Patients should get the medicine regardless of the severity of the disease or the length of time since symptoms began, the agency said. It also issued, on an emergency basis, instructions to medical professionals on how to give drugs like Tamiflu preventively to people who have been exposed to the viruses with pandemic potential, in an effort to block infection.
Is there a bird flu vaccine for humans?
Bird flu vaccines are being stockpiled, but aren’t currently available to the public. The US asked vaccine-maker CSL Seqirus to produce 4.8 million doses this summer, to add to hundreds of thousands already on hand. However, experts warn a future strain of the virus that transmits between humans would likely require a different shot. The CDC isn’t recommending immunization for farmworkers because infections have been relatively mild, Nirav Shah, principal deputy director of the CDC, said in July.
The US Department of Health and Human Services awarded Moderna Inc. $176 million for testing an mRNA vaccine that targets several influenza strains, including the current bird flu viruses. The hope is that the newer technology could be quickly updated if needed.
The US Department of Agriculture, meanwhile, is looking into a potential H5N1 vaccine for cows, said Eric Deeble, acting senior adviser for H5N1 response. The agency has approved several field safety trials for vaccines designed to protect cows from the bird flu.
How many US cows and birds have been impacted?
As of December 18, 865 cow herds across 16 states have tested positive for bird flu. The CDC has previously said it believes the cows are transmitting it to each other via contact with infected milk. Commercial milking machines are often used on dozens of cows per day, and milk droplets can remain infectious on contaminated equipment for hours.
The number of reported cases is likely an underestimate due to testing challenges, Osterholm said. Wastewater surveillance tools used to detect Covid-19 are now being used to track bird flu in humans and cattle. The testing of dairy cows moving between states has been required since late April, and the USDA further bolstered surveillance by issuing a federal order on Dec. 6 for the national collection and testing of raw milk samples. Dairy farmers will also need to share epidemiological information to aid with contact tracing.
US officials haven’t recommended the destruction of infected cows, which often recover, while millions of birds have been culled. The virus has affected more than 120 million birds across the country.
While milk from infected cows, which may be discolored or thickened, is being diverted or destroyed, the losses shouldn’t have a major impact on supply, according to the USDA.
So long as dairy products have been pasteurized, a process that kills viruses and most bacteria, products such as milk, cheese and ice cream are safe for consumption. US health agencies suggest Americans avoid raw milk and unpasteurized products.
What are scientists looking for?
Scientists recently discovered that cow udders contain receptors that avian and human influenza viruses can latch onto. Having both kinds of receptors makes it possible for other animals such as pigs to transmit diseases between species, which is what happened with the deadly 2009 swine flu pandemic. The finding raises concern about what might happen if a cow gets simultaneously infected with bird flu and human influenza. In late October, government officials said a pig kept on a backyard farm in Oregon tested positive for the H5N1 bird flu for the first time in the US, a development that scientists have feared because it could help the virus further evolve and put humans at risk.
- The USDA maps bird flu infections in mammals in the US.
- Alerts about infections in dairy cows from the USDA.
- Read Bloomberg’s reporting on US testing gaps.
--With assistance from Madison Muller, Jessica Nix, Gerson Freitas Jr. and John Lauerman.
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