Study Identifies Transmission Mechanism of Bat Influenza

Solving a years-old mystery, investigators have discovered that MHC-II molecules can provide a gateway for bat influenza to infect human cells.

In addition to harboring diseases that can be fatal to humans, such as the Ebola virus and rabies, it appears that bats can also potentially transmit the influenza virus to people, joining the ranks of other animals, such as birds and pigs. However, the transmission mechanism of influenza viruses from bats to humans differs from the mechanism by which other creatures pass influenza to people. A team of investigators at the University of Zurich was recently able to solve the puzzle of just how bat influenza can infiltrate human bodies, publishing its results in the journal Nature.

At issue is the fact that all influenza viruses up until this point have been understood to infect different species, including humans, via a cellular substance known as sialic acid. A glycoprotein in the virus, haemagglutinin, binds to cells that have sialic acid on their surfaces; this sialic acid acts as the entry point for the virus to infect the body. Bat influenza, however, does not use sialic acid as the gateway. Instead, this type of influenza relies on molecules known as MHC-II to penetrate host cells, as the investigators discovered in their research.

“We tested many different cell lines to find out which ones can be infected,” Silke Stertz, MD, assistant professor in the Institute of Medical Virology at the University of Zurich, and an author of the study, told Contagion®. “We then compared cells that can be infected with cells that cannot be infected, and found out which factors are only present in cells that can be infected. These candidates were then further tested, and it turned out that MHC-II is necessary for infection.”

After establishing, via cell-line testing, that MHC-II is the facilitator for the bat virus to enter human cells, the investigators then continued to test using mice. They found that mice infected with bat influenza experienced high levels of viral replication in the upper respiratory tract. “Often the entry factor used by a virus determines where in the body the virus can replicate,” said Dr. Stertz. “[For example], hepatitis viruses usually have a receptor that is only present in the liver and so they can only infect liver cells. It will therefore be interesting [to see] where in the body of different animal models bat influenza viruses can replicate. We would expect that this pattern correlates with MHC-II expression patterns.”

To date, there have been no cases of influenza in humans that have been definitively linked to bats. The investigators have shown that such a circumstance is possible, though, and would like to expand their research to determine whether these transmissions do, in fact, occur. Right now, according to Dr. Stertz, no evidence exists to support the theory that bat influenza would be any more dangerous to humans than influenza contracted from other animals.

Influenza viruses originating in bats have been identified in Central and South America, according to the investigators. Given migration and travel patterns worldwide, the possibility exists that bat influenza could turn up in Europe or other locales. Should people be concerned about being infected with influenza from a bat? “I don’t think that anyone needs to worry about or prepare in any way for bat influenza,” said Dr. Stertz. “We are simply saying that we should look closer and find out if these viruses can infect other mammals.”