Viruses are far more dangerous when they infect victims in the morning, a University of Cambridge study suggests. The studies on mice also found a disrupted body clock – such as a person feeling the effects of shift-work or jet lag – is always vulnerable to infection.
The findings, published in PNAS (Proceedings of the US National Academy of Sciences), show viruses are 10 times more effective if the infection starts before lunchtime.
The researchers say the findings could lead to new ways of stopping pandemics.
Unlike bacteria or parasites, viruses depend on “hijacking” the machinery inside cells to replicate. But those cells change dramatically in the 24-hour pattern we call the body clock.
In the study, mice were infected with either influenza, which causes flu, or herpes virus, which can cause diseases including cold sores.
Mice infected in the morning had 10 times the viral levels of those infected in the evening.
As the BBC News website describes it, “The late viruses were failing after essentially trying to hijack a factory after all the workers had gone home.”
One of the researchers, Professor Akhilesh Reddy, says: “It’s a big difference.
“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.”
He believes the findings could help control outbreaks of disease.
“In a pandemic, staying in during the daytime could be quite important and save people’s lives. It could have a big impact if trials bear it out.”
Further tests show disrupting the animal’s body clock means they are “locked in” to a state that allowed the viruses to thrive.
The lead author of the study, Dr Rachel Edgar, says: “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 researchers used only two viruses in the study. One was a DNA virus and the other an RNA virus, which leads the research team to suspect the morning risk may be a broad principle that applies across a wide number of viruses.
About 10% of genes – the code for running the body – change activity throughout the day, and this is controlled by the internal clock.
The research focused on one clock gene called Bmal1, which has its peak activity in the afternoon in both mice and people.
Professor Reddy says: “It’s the link with Bmal1 that’s important, since when that’s low (in the early morning), you’re more susceptible to infection.”
Bmal1 becomes less active in people during the winter months – suggesting it may have a role in the greater risk of infections at that time of the year.
Scientists have previously pinpointed a relationship between the body clock and susceptibility to infections. Flu jabs appear more effective in the morning and jet lag affects the malaria parasite.