It is time to disabuse our minds of the old notion that West Nile virus (WNV) epidemics spread in "most ideal temperatures of transmission".

A new study suggests otherwise — West Nile virus transmission is higher during drought.

The study, published in Proceedings of the Royal Society B on Feb. 8, found out that drought is the key driver in the increased intensity of the WNV epidemics in the United States.

The UC Santa Cruz-led researchers have discovered that WNV incidence is higher during the period of drought — based on a 15-year data they had analyzed.

Post-doctoral researcher Sara Paull, together with UC Santa Cruz associate professor Marm Kilpatrick, explored several weather variables like summer temperature, precipitation, winter severity, and drought.

"We found that drought was the dominant weather variable correlated with the size of the West Nile virus epidemics," Paull said.

One data indicated that there was no increase of population of mosquitoes during drought but only an increase in the number of mosquitoes infected with WNV. It was not established, however, why the transmission is higher during drought.

WNV, first reported in 1999 in North America, is the leading mosquito-borne disease in the country. Other noticeable arboviral diseases include dengue. The mosquito, Culex pipiens, is the known carrier of the infectious virus.

One in every five persons infected with WNV generally will develop fever and suffers headache, body aches, joint pains, vomiting, diarrhea, or rashes. The WNV infection, in very few cases, led to neurologic illness like encephalitis or meningitis.

Symptoms of the infection generally disappear but severe cases need immediate medical attention.

Human Immunity Is Vital In The Decrease Of Incidence Subsequently

The UC Santa Cruz-led research also probed into the hypothesis of a wave-like pattern at the initial outbreak and diminished in number in subsequent cases.

There is a "strong evidence that in some regions the spread...was indeed wave-like, with large outbreaks followed by fewer cases," Paull, who is now with the National Center for Atmospheric Research, said.

This finding goes to show that fewer people are prone to acquire the infection as they developed immunity from the disease.

Links Between Drought, Immunity, And WNV Can Help Map Out Future Epidemics

The findings will prove to be a valuable tool to guide public health initiatives in addressing the epidemics.

The researchers, with the help of Stanford University climate experts Dan Horton and Noah Diffenbaugh, are trying to project the effects of climate change on future outbreak of the disease. The projection cover the next 30 years where most part of the United States will experience drought.

It is projected that as drought increases so with the size of WNV epidemics. This is most expected in regions that have not yet suffered severe outbreaks in the past.

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