People are more susceptible to infection at certain times of the day, new research has shown.

Academics from the University of Cambridge found that the body clock affected the ability of viruses to replicate and spread between cells, with those in a resting phase or with a disrupted body clock more likely to succumb to illness.

The findings, published in the Proceedings Of The National Academy Of Sciences (PNAS), may help explain why shift workers, whose body clocks are routinely disrupted, are more prone to health problems, including infections and chronic disease.

When a virus enters the body, it hijacks cells to help it replicate and spread. The resources of cells fluctuate throughout the day, partly in response to our circadian rhythms — in effect, our body clock — which controls functions including sleep patterns, body temperature, our immune systems and the release of hormones.

A study of mice saw creatures infected with herpes at different times of the day, with scientists measuring levels of infection and spread.

Researchers found that virus replication in those mice infected at the very start of the day — equivalent to sunrise, when these nocturnal animals start their resting phase — was 10 times greater than in mice infected 10 hours into the day, when they are transitioning to their active phase.

The experiment was repeated in mice lacking the gene Bmal1, which helps control the body clock, and they found high levels of virus replication regardless of the time of infection.

Research was conducted at the Wellcome Trust-Medical Research Council Institute of Metabolic Science at the University of Cambridge.

“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 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.”

When the body clock was disrupted in either individual cells or mice, researchers found the timing of infection no longer mattered — viral replication was always high.

Rachel Edgar, the first author, said: “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.”

The genes that control the body clock also undergo seasonal variation, and are less active in the winter months, when diseases such as influenza are more likely to spread through populations.

Researchers hope the molecular machinery of the body clock may offer the potential for new drugs to help fight infection.


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