Time of infection affects severity in viral infections

Time of infection affects severity of a viral infection
According to a new study, the time of day plays an important role in the severity of viral infections. The study of British scientists shows that herpesviruses reproduce much faster in mice when the animals are infected at the beginning of their resting phase.

Time of infection affects severity of an infectious disease
Although each person can become infected with countless pathogens, some become more ill, others almost never. This is partly because some people are more susceptible to infections. For example because her immune system is weakened due to a lot of stress or an unhealthy diet. The severity of an infectious disease is not the same in all patients. Why this is so could possibly be related to the timing of the infection, as British researchers have discovered.

Researchers have found that the time of infection plays an important role in the severity of a viral infection. (Picture: Picture-Factory / fotolia.com)

Heart attack risk depending on the time of day
The fact that the time of day has an influence on human health has already been shown in various studies. Thus, US researchers reported that the risk of heart attack depends on the time of day. And according to Spanish scientists, a heart attack in the morning is worse than in the evening. A British research team has now found that the time of day plays an important role in the severity of a viral infection. Their study shows that herpesviruses multiply dramatically faster in mice when the animals become infected at the beginning of their resting phase.

Shift workers more susceptible to diseases
As the team around Professor Akhilesh Reddy of the University of Cambridge wrote in a statement from the university, the discovery may explain in part why vaccination also affects the time of day, why shift workers are susceptible to disease or why infectious diseases are more likely to occur in winter. "Contagion at the wrong time of day could cause a much more serious acute infection," the study authors said.

Pathogens proliferate much more at the beginning of the resting phase
The results of the study were published in the Proceedings of the US National Academy of Sciences ("PNAS"). As the news agency dpa reports, the scientists first infected mice at different times of the day through the nose with the herpesvirus MuHV-4. It turned out that the pathogens at the beginning of the resting phase - that is, in the morning in the nocturnal rodents - multiplied by about ten times more than in an infection to the active phase.

In the case of genetically modified mice lacking Bmal1 - a key gene for the internal clock - the time of day did not influence the infection process. "When we disrupted the body clock in mice, the timing of the infection did not matter anymore," first author Rachel Edgar said. "The viruses were constantly multiplying."

Viruses may affect the cell clock
The severity of an infection in cell cultures also depended on the particular phase of the day. But in cells without the Clock Bmal1, the herpes viruses increased at any time similarly strong. It is said that further tests even indicated that the viruses actively influenced the cell clock in order to develop optimally.

When the researchers subsequently tested the proliferation of influenza viruses on cells, they came to a similar conclusion. "The similar effect of cellular arrhythmia on two distinct, clinically significant virus families shows that the internal clock and its special components, such as Bmal1, have a major impact on viral infections," the authors said.

More illnesses in winter
Perhaps this effect could even contribute to epidemics. For example, the Clock Bmal1 is less active in humans during the winter months. "We speculate that this may contribute to the spread of viruses at the population level because many viruses, such as influenza, are more likely to cause infections in winter," the researchers said. But there could be other explanations for that.

For example, Cambridge University scientists reported last year in the journal Nature Communications that our immune system is changing with the seasons. According to the experts, their discovery offers a possible explanation for the fact that certain diseases occur more often or worse in winter and that people tend to stay healthy during the summer months.

Influenza vaccine in the morning more effective
According to the authors of the study, the results of the current study could also explain why shift workers whose body clock is disturbed are susceptible to chronic diseases, possibly also to viral diseases. In addition, the effectiveness of vaccinations may depend on the time of day. This was pointed out recently by a study of people over the age of 65.

The team led by Anna Phillips of the University of Birmingham, UK, had reported in the journal "Vaccine" that flu shots in the morning, compared to those in the afternoon, boosted the production of antibodies within one month. (Ad)