Viruses infect more effectively during the morning, scientists say

The study confirms why the flu virus may be more effective when given in the morning, as well as suggests an ideal time of day to attack infections.

By Stephen Feller

CAMBRIDGE, England, Aug. 17 (UPI) -- Viruses are better at invading cells at certain times than at others, according to researchers in England.

The circadian rhythms of the body and its individual cells help or hinder the ability of a virus to infect its host, with morning hours appearing to be the most likely time for effective infection by a virus, University of Cambridge researchers report in a study published in the Proceedings of the National Academy of Sciences.


Circadian rhythms, the body's internal clock, control parts of physiology and basic bodily function by regulating the action and resources of cells.

Individual cells have their own internal clocks allowing them to anticipate changes to the environment and when to take certain actions. This, the researchers say, means exposure to a virus at the most opportune time would allow for faster, more effective infection and proliferation.

Experiments in lab dishes and with mice in the new study are in line with theories on the flu vaccine's efficacy being linked to the time of day it's administered, and suggests another method of fighting disease.

"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," Dr. Akhilesh Reddy, a professor and researcher at the University of Cambridge, said in a press release.


For the study, researchers tested levels of virus infection and proliferation in mice infected with herpes virus at different times of day. The mice, who lived in an environment with 12 hours of "daylight" and 12 hours of "night," were most susceptible to infection when entering their resting phase.

In experiments with mice lacking a gene connected to circadian rhythms, Bmal1, the virus replicated at higher levels regardless of the time of day they infected the rodents. The effect was seen in cell cultures whose cellular circadian rhythms had been blocked, with both herpes and the influenza A virus.

The results suggest people with irregular circadian rhythms, such as night shift workers, could be more susceptible to flu. The study also helps explain why influenza spreads more readily during winter, when Bmal1 undergoes seasonal changes.

"It's a big difference," Reddy told The BBC. "The virus needs all the apparatus available at the right time, otherwise it might not ever get off the ground, but a tiny infection in the morning might perpetuate faster and take over the body."

The researchers say the study showed viruses are more likely to infect during the day -- the mice used in the study are nocturnal, so their resting phase occurs around the time of sunrise -- suggesting at least some guidance on the best time to be careful of infection, as well as when to treat it.


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