Exposure to sunlight may help impede the spread of chickenpox, claim researchers.
The University of London team found chickenpox less common in regions with high UV levels, reports the journal Virology.
Sunlight may inactivate viruses on the skin, making it harder to pass on.
However, other experts say that other factors, including temperature, humidity, and even living conditions are equally likely to play a role.
The varicella-zoster virus is highly contagious, while it can be spread through the coughs and sneezes in the early stages of the infection, the main source is contact with the trademark rash of blisters and spots.
UV light has long been known to inactivate viruses, and Dr Phil Rice, from St George’s, University of London, who led the research, believes that this holds the key why chickenpox is less common and less easily passed from person to person in tropical countries.
It could also help explain why chickenpox is more common in the colder seasons in temperate countries such as the UK – as people have less exposure to sunlight, he said.
He examined data from 25 earlier studies on varicella-zoster virus in a variety of countries around the world, and plotted these data against a range of climatic factors.
This showed an obvious link between UV levels and chickenpox virus prevalence.
Even initially confusing results could be explained – the peak incidence of chickenpox in India and Sri Lanka is during the hottest, driest and sunniest season.
However, Dr Rice found that, due to atmospheric pollution, UV rays were actually much lower during this season compared with the rainier seasons.
He said: “No-one had considered UV as a factor before, but when I looked at the epidemiological studies they showed a good correlation between global latitude and the presence of the virus.”
Professor Judy Breuer from University College London said that while UV could well be contributing to the differences in the prevalence of chickenpox between tropical and temperate regions, there were other factors which needed to be considered.
She said: “Lots of things aside from UV could affect it – heat, humidity and social factors such as overcrowding.
“It’s quite possible that UV is having an effect, but we don’t have any firm evidence showing the extent this is happening.” (BBC News)