New research from the University of Cambridge shows that we are more susceptible to infection at certain times of day as our body clock affects the ability of viruses to replicate and spread between cells. According to a Science Daily news report, the findings may help explain why shift workers are more prone to health problems, including chronic disease and infections. To test whether circadian rhythms affect susceptibility, or the progression of, infection, researchers compared normal ‘wild type’ mice infected with the herpes virus at different times of day and measured levels of virus infection and spread.

The mice lived in a controlled environment where 12 hours were in daylight and 12 hours were in dark. The research team found that virus replication in those mice infected at the very start of the day, which was equivalent to sunrise and when the animals were starting their resting phase, was ten times greater than in mice infected 10 hours into the day when they were transitioning to their active phase. When the research experiment was repeated in mice lacking Bmal1, the researchers found high levels of virus replication regardless of the time of infection.

“The time of day of infection can have a major influence on how susceptible we are to the disease, or at least on the viral replication, meaning that infection at the wrong time of day could cause a much more severe acute infection,” says senior author of the study Professor Akhilesh Reddy. “This is consistent with recent studies which have shown that the time of day that the influenza vaccine is administered can influence how effectively it works.”

The researchers also found similar time-of-day variation in virus replication in individual cell cultures, without influence from our immune system, reports Science Daily. “Each cell in the body has a biological clock that allows them to keep track of time and anticipate daily changes in our environment. Our results suggest that the clock in every cell determines how successfully a virus replicates,” says Dr Rachel Edgar, first author of the study.

Bmal1 undergoes seasonal variation, and the researchers speculate that this might explain why diseases such as influenza are more likely to spread through populations during winter. Edgar adds, “When we disrupted the body clock in either cells or mice, we found that the timing of infection no longer mattered — viral replication was always high. This indicates that shift workers, who work some nights and rest some nights and so have a disrupted body clock, will be more susceptible to viral diseases. If so, then they could be prime candidates for receiving the annual flu vaccines.”

“Given that our body clocks appear to play a role in defending us from invading pathogens, their molecular machinery may offer a new, universal drug target to help fight infection,” Reddy says.

Source: Science Daily