UV Found To Control Chickenpox And Shingles
As reported by ScienceDaily (12/11) Ultraviolet Rays Believed to Prevent Chickenpox Spreading -Ultraviolet
rays help prevent the spread of chickenpox, meaning people in milder climates
are more at risk of catching the disease, according to new research. The
discovery could lead to new ways of preventing chickenpox and its more severe
A researcher at St George's, University of London has found that chickenpox is
much less common in places with high UV ray levels, compared with those with
low levels. It has long been known that UV rays can inactivate viruses.
However, virologist Dr Phil Rice believes his findings indicate that UV rays
could inactivate the varicella-zoster virus -- the herpes virus responsible for
chickenpox and shingles -- on the skin before it transmits to another person.
This explains why there is less transmission in the tropics, where chickenpox
is much less frequent than in temperate countries. It would also explain why
chickenpox peaks in temperate zones -- where it is seasonal -- in winter and
spring, when UV rays are lowest.
Previously, it was thought that geographical differences in chickenpox incidence
were related to heat, humidity, population density, or infection with other
viruses that protect against it. Dr Rice examined data from 25 studies on
varicella-zoster virus prevalence patterns in both temperate and tropical areas
across the globe. He plotted the data against a range of climatic factors, to
examine what might be the most likely causes of increased prevalence. The data
showed that -- once other factors were ruled out -- UV rays were the only
factor to match the infection patterns in each country studied. Dr Rice, whose
study has been published in Virology Journal, 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. "One convincing factor of the hypothesis is that there was an
explanation for every anomaly. For example, the peak incidence of chickenpox in
India and Sri Lanka is during the hot, dry, sunny season. You would expect
chickenpox to be at its lowest at this time, so at first this didn't fit the
theory. However, this was explained because UV rays are actually much lower in
the dry season compared with the monsoon period. In the dry season, the
pollution in the atmosphere reflects the UV rays back into space before they
reach us. But in monsoon season, the rains wash away the pollution, meaning the
UV rays can get through."
Dr Rice also believes his findings show why two distinct genetic types of the
virus have formed -- a temperate type and a tropical one. He found that the
temperate genotype only transmitted in the tropics when UV radiation was either
reduced or negated. It was found to transmit in the home, for example, but not
outside. The tropical genotype, however, was found to transmit in the tropics
in the presence of UV rays, suggesting it has some resistance. Dr Rice believes
this is because the temperate virus line -- which broke off from the original
tropical genotype -- has lost the UV resistance still present in the tropical
line. "For the temperate virus line to have lost the selective advantage of
resistance to UV rays as it broke off from the original tropical virus, it must
have gained an advantage in the virus life cycle as an evolutionary trade off.
An obvious advantage would be an ability to reactivate more easily, as
shingles. The virus can only have one of these survival advantages, not both.
This might explain why shingles appears to be so much less common in people
from the tropics, and why the temperate virus reactivates much more readily
than the tropical type."
When the existing chickenpox vaccine was created in the 1970s, it was not known
that there were two types of the virus. Dr Rice believes his findings could aid
the development of new treatments for chickenpox and shingles, which causes
considerable pain and discomfort in later life. He says further studies are
needed to fully examine the effect of UV rays on the virus.