Humans are more susceptible to infection in the mornings as our body clock mechanism is prone to be weaker to the ability of viruses to replicate and spread between cells, said a new research study by the University of Cambridge.
The major impact is on night-shift workers whose body clocks are routinely disrupted, making them prone to more infections or chronic diseases than others, said the study published in the Proceedings of the National Academy of Sciences.
Prof. Akhilesh Reddy of the Wellcome Trust-Medical Research Council Institute of Metabolic Science, University of Cambridge, compared normal ‘wild type’ mice infected with herpes virus at different times of the day, measuring levels of virus infection and its spread. The mice lived in a controlled environment where 12 hours were in daylight and 12 hours were dark.
The team of researchers found that virus replication in those mice infected in the mornings – equivalent to sunrise, when these nocturnal animals start their resting phase – was ten times greater than in mice infected ten hours into the day, when they are transitioning to their active phase.
“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,” explains Professor Akhilesh Reddy. 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, he said.
In addition, the researchers found similar time-of-day variation in virus replication in individual cell cultures, without influence from our immune system. Abolishing cellular circadian rhythms increased both herpes and influenza A virus infection, a dissimilar type of virus – known as an RNA virus – that infects and replicates in a very different way to herpes.
Dr Rachel Edgar, the first author, adds: “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.”