West Nile virus is spread by infected mosquitoes. The disease, once in a person, targets the central nervous system. Most people who become infected with West Nile virus do not develop any symptoms. However, around 1 in 5 people who become infected will develop a fever together with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash.
The disease has shown an increased rate of incidence in the U.S. and scientists are keen to know why and also find a means to alert health authorities should there be signs that the disease is likely to spread. This is the basis of the new model.
Essentially the new research model has found a connection between the occurrence of West Nile virus disease and above average temperatures in the preceding year. This is because the weather influences West Nile virus activity through affecting the breeding habitats and abundance of Culex species mosquitoes. Warmer temperatures appear to accelerate the development of mosquito larvae. Furthermore, the weather also affects populations of infected birds. These birds pass on the virus to mosquitoes, and then the mosquitoes pass on the virus to people.
Data collated between 2004 to 2012, shows that the temperature effect is most pronounced in counties in the Northeast and Southeast. Here an annual temperature increase of 1 degree Celsius (1.8° Fahrenheit) above the typical temperatures meant a fivefold increased likelihood of an above-average outbreak of West Nile virus.
The finding matches earlier research, reported by Digital Journal, which showed that mosquitoes which transmit diseases like West Nile fever and Chikungunya fever are less likely to infect people and are also more susceptible to insecticides if they are reared in cooler climates.
The research is a collaborate effort between the U.S. National Center for Atmospheric Research (NCAR) and the U.S. Centers for Disease Control and Prevention (CDC). The findings have been published in the American Journal of Tropical Medicine and Hygiene. The paper is called “Meteorological Conditions Associated with Increased Incidence of West Nile Virus Disease in the United States, 2004-2012.”
