As Highly Pathogenic Bird Flu Spreads in U.S., Should Americans Be Worried?

The United States Department of Agriculture has detected the presence of highly infectious avian flu in a backyard flock of birds in Kalamazoo County, Michigan.

It is the latest in a spate of infections across the U.S. As of Friday, the USDA has recorded seven cases involving poultry meant for consumption in three states—Delaware, Kentucky and Indiana. Five cases have been confirmed in backyard non-poultry flocks—two in Maine, plus one each in Virginia, New York and Michigan.

The USDA is also tracking influenza infections in wild birds, with 10 states reporting cases since the start of the year—including zoo animals in Florida.

According to the Centers for Disease Control and Prevention, the outbreak began in January and is the first in the United States since 2016.

The CDC advises that there is little risk to the public, but bird flu can spread to humans.

A.J.W. te Velthuis, a researcher at Princeton's Department of Molecular Biology, told Newsweek: "The natural reservoir for influenza viruses is birds. This means that influenza viruses can infect wild birds without much harm to these birds. The strains that wild birds carry are slightly different from human influenza viruses.

"This means that we don't have any immunity against them and thus that these viruses can potentially cause severe disease."

When avian flu mutates, te Velthuis added, it can gain the ability to spread from human to human, potentially causing severe respiratory disease with a high mortality rate. He explained: "Since we don't have any good antivirals against flu and no pre-existing immunity against avian flu, it would have the ability to cause a pandemic.

"There have been vaccines in development against some avian flu strains, and these may be deployed to protect us."

According to Professor Peter Barlow, chair of immunology and infection in the School of Applied Sciences at Edinburgh Napier University: "Transmission [to humans] can occur where individuals who have prolonged close contact with infected birds can become infected themselves."

The CDC says this usually occurs when infected birds shed the virus in their saliva, mucus and feces and this gets into a person's eyes, nose or mouth, or is inhaled.

It can happen when the virus is in the air in droplets or even possibly dust and a person breathes it in, or when a person touches something that has the virus on it and then touches their mouth, eyes, or nose.

Although human infection usually occurs when a person has unprotected contact with infected birds or surfaces contaminated with viruses, the CDC does say rare infections have been identified where direct contact is not known to have occurred.

Barlow says: "The advice from the CDC is that the most effective way of preventing avian influenza in humans is to avoid sources of exposure. Animal workers should also follow the guidance provided by CDC on the use of personal protective equipment."

Can Bird Flu Pass From Human to Human?

Once a human is infected with avian flu, how easily can this spread to other humans? Is the virus highly pathogenic in people, as it is in birds? Barlow says no.

He told Newsweek: "The virus does not transmit effectively between humans, and so transmission will only occur in rare instances. While the virus will likely spread further through bird populations in the United States, the risk to the human population is very low."

Professor Munir Iqbal, head of the avian influenza virus group at the U.K.'s Pirbright Institute, explained why avian flu does not spread as easily among humans. He told Newsweek: "Since the birds and humans are very different, influenza viruses must adapt and change in order for avian viruses to establish transmission in humans."

Iqbal added that the proteins that the virus interacts with inside the infected cells are different in humans and birds, so avian viruses find it hard to replicate themselves in humans.

He continued: "In addition, the behavior of humans and birds means the transmission routes are different.

"Water carrying fecal matter plays a large role in the transmission of avian influenza between birds, whilst between humans, transmission via droplets in the air is the common transmission mechanism."

Iqbal said this meant the virus must alter itself to facilitate the different transmission modes.

Can Bird Flu Spread Through Infected Food?

Birds meant for human consumption, such as turkeys and broiler chickens, have been affected by avian flu in three states, so can consumption of food be a route to infection for people?

Barlow told Newsweek that the risk of catching bird flu through infected food was extremely low. He said: "There's no evidence that the virus can be contracted by eating contaminated food as the primary method of transmission would be by inhalation.

"Irrespective, as there are inherent microbiological risks associated with handling raw meat, it is always advisable to ensure that good hygiene practices are always followed."

The CDC recommends that chicken, other poultry and eggs are cooked to internal temperatures of at least 165 degrees Fahrenheit—in order to destroy germs, bacteria and virus cells. The health agency also warns that raw poultry must be handled hygienically.