Despite infected cows and milk, the risk of H5N1 bird flu for humans is ‘low’

Although cows have been infected for the first time with the H5N1 bird flu and virus remains have been found in milk, the World Health Organization (WHO) and the US Centers for Disease Control and Prevention (CDC) characterize the current risk to humans as “low”.

The risk to people exposed to infected birds and other animals is low to moderate, they add.

So far in the current outbreak, there have been no cases of bird flu being transmitted from person to person – only from infected birds and animals to humans.

The last human-to-human transmission of avian flu was identified in 2017 and involved infections between a small group of healthcare workers.

Only a person was infected in the current outbreak in US dairy herds when a man who worked on a Texas dairy farm developed conjunctivitis. Swabs from the man’s throat and eye tested positive for H5N1, but he had mild symptoms and did not infect anyone in his household.

Meanwhile, about 220 employees working at the 36 U.S. dairies affected by the H5N1 outbreak have been screened, but none have been infected with the virus, Dr. Todd Davis of the US CDC, speaking before a WHO Information Network for Epidemics (EPI-WIN) briefing on Monday.

“After sequencing several hundred viruses in cattle, we do not see any molecular changes that would indicate an increased risk of infection or person-to-person transmission,” Davis said.

“So we still consider these risks to public health to be quite low. I think some of the exceptions may be long-term unprotected exposure to infected dairy cattle, so there are likely risks associated with occupational exposure.”

Risks for milk and meat

About 20% of milk samples collected by the US Food and Drug Administration (FDA) tested positive for H5N1 viral RNA, said Dr. Richard Webby, director of the WHO Collaborating Center for Research on the Ecology of Influenza in Animals and Birds .

Meanwhile, a smaller sample, focused on states where outbreaks had occurred, found that 40% of milk products contained viral remains, added Webby, who is based at St Jude Children’s Research Hospital in Memphis in the US.

“A relatively large number of samples have been tested, but so far from a safety perspective it appears that the pasteurization process is removing viable viruses from those samples,” Webby said.

Dr. Moez Sanaa, head of the WHO’s Standard and Scientific Advice on Food Nutrition, confirmed that while viral RNA has been found in pasteurized milk, none of it was live virus “suggesting that the pasteurization process effectively inactivates H5N1,” said Dr.

“Preliminary results (from ongoing studies) indicate that the virus is inactivated by a heat treatment similar to pasteurization,” Sanaa said, but added that more research on milk with a higher viral load was still needed. He warned people to avoid raw milk.

Meanwhile, the USDA’s Food Safety and Inspection Service (FSIS) last week announced that all 30 samples of ground beef from stores in states with infected dairy herds tested negative for H5N1. These results once again confirm that the meat supply is safe.

Webby’s group also tested eggs and found them to be free of H5N1.

Cow transmission: mechanical?

The genomic analysis shows that the outbreak on dairy farms stemmed from “a single introduction” but that “the movement of dairy cattle spread it to multiple farms and different locations,” said Dr. David Swayne, an American flu vet. .

Swayne added that since the transmission appeared to occur “in the unique environment of a parlor,” there were two leading hypotheses as to how the rapid transmission occurred.

One of these was that there was ‘mechanical transmission’, where infections were spread, for example, through milking machines.

The other was that transmission occurred during “continuous cleaning” in dairies, which enabled virus spread through “large droplets produced during that washing process.”

Meanwhile, Dr. Aspen Hammond comes out The WHO Global Immunization Program (GIP) said H5N1 was found in other animals near the affected dairy herd, including cats, raccoons and wild and domestic birds in the area.

‘One Health in action’

Dr. Maria van Kerkhove, WHO’s acting chief of Epidemic and Pandemic Prevention and Preparedness (EPP), described the outbreak as “one health in action”.

“You can’t look at the risks to human health without looking at the risks in animals,” Van Kerkhove said, emphasizing that partnerships with animal health agencies were essential.

“Right now there’s a lot of focus on the US, but we’re seeing a global epidemic of bird flu, and we’ve seen H5N1 infections in wild birds, poultry, marine mammals and land mammals,” she said.

“But what is worrying is that we are seeing new strains becoming infected… We need much stronger surveillance of animals worldwide, not just in the US, looking at the species we know could be infected with H5N1, but also at the animal-human interface. “

She urged those conducting surveillance to continue sequencing and sharing those sequences to allow for regular assessments of the viruses, as well as “what any changes in these viruses mean in terms of transmissibility in terms of severity. ”

Van Kerkhove also emphasized that occupationally exposed people must be protected against infections, including by using personal protective equipment and washing hands regularly, “because prevention is key”.

She also said that although it was not yet necessary, the current H5N1 flu was covered by the vaccine candidates in the flu prevention pipeline.

Image credits: pxfuel, Charyse Reinfelder.