West Nile virus epidemics made worse by drought — Study
PARIS: Drought has sharply boosted the intensity of deadly West Nile virus epidemics, which are set to worsen with global warming, scientists reported yesterday.
Their research, published in the Royal Society journal Proceedings B, offers the best explanation of why the disease’s impact has varied so much from year to year since arriving in the US nearly two decades ago.
“We thought epidemics would coincide with the most ideal temperatures for transmission,” said co-author Marm Kilpatrick, a professor at the University of California at Santa Cruz ( UCSC).
“Instead, we found that the severity of drought was far more important.”
Birds are the main host for the West Nile virus, which is transmitted to humans by mosquitoes.
The study also issued a warning: over the next 30 years, the number of West Nile cases in some parts of the country could triple as climate change provokes more frequent and severe dry spells, it found.
West Nile virus — from the same family as yellow fever and Zika — was introduced into the US in 1999.
Since then, it has infected some 45,000 people and claimed about 2,000 lives, according to the US Centres for Disease Control and Prevention.
Like Zika, the virus causes no symptoms in up to 80 per cent of people infected. Others report fever, rash, body pain, headache, vomiting or diarrhoea.
In rare cases, brain swelling and neurologic infections can occur, sometimes resulting in death.
For years, epidemiologists have puzzled over fluctuations in the severity of the epidemics, which hit during the summer months.
In some years, there have been only a few hundred severe human cases across the nation. In others — notably 2002, 2003 and 2012 — some 3,000 people suffered brain- damaging meningitis or encephalitis each year, and almost three hundred died.
Variations from region to region were even more pronounced.
Human immunity built up with the spread of the disease was thought to be a factor, but still could not explain the differences. — AFP