Time of day influences body's susceptibility to infection

The time of day and disruption to one's circadian rhythms may have significant influence on susceptibility to infection, according to a new study published in Proceedings of the National Academy of Sciences.

Circadian rhythms are known to control many aspects of our physiology and bodily functions like sleep patterns, body temperatures and the release of certain hormones. To determine whether these rhythms influence the progression of or susceptibility to infectious disease, researchers infected mice with the herpes virus at different times of day and monitored infection levels.

Researchers found that the amount of virus replication was 10 times greater in mice infected with the virus at the beginning of their active period than those infected 10 hours later. Time-of-day variation also increased the replication of both herpes and influenza A — which is very dissimilar to herpes in terms of replication — in individual cell cultures.

"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, PhD, a researcher at the Wellcome Trust-Medical Research Council Institute of Metabolic Science at University of Cambridge in the UK, and 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."

Additionally, researchers simulated biological clock disruption by observing cell cultures uninfluenced by immune system circadian rhythms. In said cultures, infection replication for both herpes and influenza A increased.

Dr. Rachel Edgar, also with the University of Cambridge and the study's first author, said, "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."

More articles on infection control: 
Update: Bat found in Palos Community Hospital had rabies 
Lab-made proteins could help fight antibiotic resistance 
2 children infected with polio in Nigeria: CDC eradication efforts undergo setback

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