In humans, circadian rhythm affects sleep cycle, immune system, body temperature, drug toxicity and, possibly, our susceptibility to infection. A new study suggests that people are more inclined to get an infection at certain times of the day, because our body clock affects the ability of viruses to replicate and spread between cells.

"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," said Professor Akhilesh Reddy, the study's senior author. "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."

Does the time of day affect your chances of getting an infection? Photo courtesy of Pexels

Researchers studied circadian rhythm’s relationship with susceptibility to, or progression of, infection by comparing mice infected with the herpes virus at different times of the day.

“Our results suggest that the clock in every cell determines how successfully a virus replicates. 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,” Dr Rachel Edgar, the first author, said.

Using cell cultures, the researchers also found that herpes viruses manipulate the molecular “clockwork” that controls our circadian rhythms, helping the viruses to progress.

"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," Professor Reddy added.

Source: Edgar, RS et al. Cell autonomous regulation of herpes and influenza virus infection by the circadian clock. Proceedings of the National Academy of Sciences, 2016.

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