Bird flu viruses are able to replicate at higher temperatures, meaning humans are more susceptible to infections, as the viruses beat the fever response. A new study led by the universities of Cambridge and Glasgow and published in Science identified a gene that plays an important role in setting the temperature sensitivity of a virus.

According to a report by Medical Xpress, which wrote a report on the study, other deadly pandemics can show how the viruses thrive.  In the pandemics of 1957 and 1968, this gene transferred into human flu viruses, and the resulting virus thrived.

The international team led by scientists at both Cambridge and Glasgow simulated in mice what happens during a fever in response to influenza infections. To carry out the research, they used a laboratory-adapted influenza virus of human origin, known as PR8, which does not pose a risk to humans. Although mice do not typically develop fever in response to influenza A viruses, the researchers were able to mimic its effect on the virus by raising the ambient temperature where the mice were housed (elevating the body temperature of the mice).

The researchers concluded that raising body temperature to fever levels is effective at stopping human-origin flu viruses from replicating, but it is unlikely to stop avian flu viruses.

But because this fever was induced by environmental factors and not one naturally occurring, is this even an effective study?

Human flu viruses cause millions of infections every year. The most common types of these viruses, which cause seasonal flu, are known as influenza A viruses. They tend to thrive in the upper respiratory tract, where the temperature is around 33°C, rather than deep in the lungs in the lower respiratory tract, where the temperature is around 37°C.

Unchecked, a virus will replicate and spread throughout the body, where it can cause illness, occasionally severe. One of the body’s self-defense mechanisms is fever, which can cause our body temperature to reach as high as 41°C, though until now it has not been clear how fever stops viruses—and why some viruses can survive. –Medical Xpress

This study’s timing coincides with the first H5N5 human death from the bird flu. The patient in Washington state who was infected with the H5N5 strain of the avian influenza has died.  It is important to note, however, that the patient was an older adult with underlying conditions. They were treated in the hospital, but still died on November 21st.

First Human Bird Flu Case In 9 Months: Person Was Infected With A New Strain

Avian influenza viruses differ from human flu viruses in that they tend to thrive in the lower respiratory tract. In fact, in their natural hosts, which include ducks and seagulls, the virus often infects the gut, where temperatures can be as high as 40°C–42°C.