H5N1 bird fluThe virus, more commonly known as bird flu, has infected more than 100 million birds in the United States and nearly 500 dairy herds in 15 states. The virus has appeared in mammals such as seals, goats, foxes and house cats.

Despite widespread spread among animals, federal health authorities maintain the risk to the U.S. public is low. There have been only 46 confirmed human cases in the United States during the current outbreak. All but one of these individuals had known exposure to affected poultry or cattle. According to the US Centers for Disease Control and Prevention (CDC) and all of their illnesses were mild. CDC says There is currently no evidence that the virus spreads from person to person.

However, the latest news has some people worried. Canadian health officials on November 12 announced The critical condition and difficulty breathing of an otherwise healthy teenager who contracted bird flu from an unknown source underscores the potential seriousness and sometimes mysterious spread of the disease.

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In October, the US Department of Agriculture also rang alarm bells. announced A pig in Oregon tested positive. This is a concerning development because pigs can be infected with swine, human and bird flu viruses, making them primary “mixing vessels”, says Meghan Davis, an associate professor of environmental health and engineering at the Johns Hopkins Bloomberg School of Public Health. Davis explains that if a pig is infected with more than one strain of flu at the same time, the viruses can potentially combine to form a new strain capable of spreading widely among humans. That’s how it happened During the 2009 “swine flu” epidemic.

“There are a lot of things I worry about,” Davis says. “This is one of them.”

Another cause for concern: Flu season is starting in the U.S., and with the seasonal flu virus circulating, “people, we can be a mixing bowl,” Davis says. If a person were infected with bird flu and seasonal flu at the same time, the two viruses could theoretically combine to create a more contagious strain.

The good news is that, as of now, there is no evidence that the avian virus has undergone significant enough changes. easily infected and spread between peoplesays Troy Sutton, assistant professor of veterinary medicine and biomedical sciences at Penn State University.

If the virus is not good at infecting humans, why do some people get sick? At a high enough dose – if farm worker For example, the patient is in close contact with animals; Sutton says the virus can sometimes enter human cells, although it wasn’t designed to do exactly that. However, the virus, which is of critical importance for public health, does not appear to have evolved in a way that makes it easier for those who become ill to transmit the disease to others.

This is partly because the virus is not good at growing in the human nose, Sutton says. Seasonal flu is highly contagious because it takes root in the upper respiratory tract. An infected person can expel infectious respiratory droplets when they cough, sneeze, or even talk. The bird flu virus is not as prevalent in the upper respiratory tract, making it less contagious among humans, Sutton says.

However, this does not mean that respiratory spread is impossible. Two recent studies in ferrets:One by researchers at the CDC and One A study led by a researcher at the University of Wisconsin-Madison raised this possibility. Researchers isolated the strain of bird flu that makes people sick. first person infected in the current outbreak and tested how contagious it was among ferrets. Researchers found that bird flu virus, although not as contagious as seasonal flu, can spread among ferrets through droplets.

But Sutton says there are important caveats. Although ferrets are widely used in flu research, they are not a perfect parallel to humans. And the strain studied is similar but not identical to the strain now widely spread among cows. CDC in general concluded“The virus still does not have the ability to spread effectively between humans via respiratory droplets compared to seasonal flu viruses.”

Still, health officials are preparing in case the situation changes. U.S. Strategic Preparedness and Response Administration (ASPR) in October Donated $72 million to pharmaceutical companies It directs companies producing H5 flu vaccines to use the funds to prepare vaccines “if needed now or in the future,” according to the agency’s statement. ASPR representatives said they took this step “out of an abundance of caution.” Federal health officials do not recommend anyone take it vaccinated against H5N1and the footage is not available to the public.

Regular seasonal flu vaccination does not protect against bird flu, but Still, it’s a good idea to buy one—especially for people who work or have regular contact with animals. The CDC also recommends that agricultural workers wear personal protective equipment such as masks and goggles and take flu antivirals as soon as possible if exposed.

But health officials say there isn’t much that can be done for the general public at this point. Avoid drinking raw milk (because virus can survive without pasteurization), avoid handling dead or sick animals, and get your seasonal flu vaccine.