Inter-Annual Associations Between Precipitation and Human Incidence of West Nile Virus in the United States

Abstract

Higher-than-average precipitation levels may cause mosquito outbreaks if mosquitoes are limited by larval habitat availability. Alternatively, recent ecological research suggests that drought events can lead to mosquito outbreaks the following year due to changes in food web structure. By either mechanism, these mosquito outbreaks may contribute to human cases of West Nile Virus (WNV) in the recent United States outbreak. Using countylevel precipitation and human WNV incidence data (2002-2004), we tested the impacts of above and below-average rainfall on the prevalence of WNV in human populations both within and between years. We found evidence that human WNV incidence is most strongly associated with annual precipitation from the preceding year. Human outbreaks of WNV are preceded by above-average rainfall in the eastern United States and below-average rainfall in the western United States in the prior year. While no direct mechanism may be determined from this study, we hypothesize that differences in the ecology of mosquito vectors may be responsible for the opposite relationships between precipitation and WNV outbreaks between the eastern and western United States.

Climate change impacts on West Nile virus transmission in a global context

“…A common dogma in epidemiology is that above-average precipitation might lead to a higher abundance of mosquitoes and increase the potential for disease outbreaks in humans [51,52]. This pattern of a positive association with rainfall in the months preceding disease outbreaks has been demonstrated for WNV [42,53].…”

Effects of weather and landscape on the equine West Nile virus infection risk in Mississippi, USA

“…There is growing evidence that climate and dry weather may modulate the risk of human and horse WNv outbreaks spatially and temporally (This study; Landesman et al, 2007;Wang et al, 2010;AharonsonRaz et al, 2014). Wimberly et al (2008) found a quadratic relationship between the rate of human WNv diseases in 2003 and May-July precipitation of 2002 in the Great Plains in USA, with the 2003 rate of human WNv diseases decreasing when total May-July precipitation reached beyond 200 mm.…”

“…C. pipiens breeds better in drier weather than under wetter conditions because rain flushes C. pipiens larvae out of manmade containers, tires or tire ruts, thus reducing C. pipiens abundance (Koenraadt and Harrington, 2008). Dry weather of the previous year may increase C. pipiens and C. quinquefasciatus abundance the following year (Landesman et al, 2007;Van Dam and Walton, 2008). Studies found that equine WNv infections in C. pipiens were inversely related to the precipitation of the previous year (Landesman et al, 2007;Ruiz et al, 2010).…”

“…Dry weather of the previous year may increase C. pipiens and C. quinquefasciatus abundance the following year (Landesman et al, 2007;Van Dam and Walton, 2008). Studies found that equine WNv infections in C. pipiens were inversely related to the precipitation of the previous year (Landesman et al, 2007;Ruiz et al, 2010). Weather-induced increases in mosquito abundance and WNv infections in turn increased the transmission of WNv to horses.…”

Influence of Meteorological Variables on Mosquitoes Breeding in Theni District, Tamilnadu, India

“…Temperature increase causes an upsurge in the growth rates of mosquito populations, decrease the interval between blood meals, shorten incubation periods from infection to infectiousness in mosquitoes and accelerate the virus evolution rate (Baba et al, 2012). Above-average precipitation can also lead to a higher abundance of mosquitoes and increase the potential for disease outbreaks in humans (Landesman et al, 2007). A good knowledge of the changes and fluctuations that occur in natural populations of mosquito vectors is very important in the prevention and control of arboviral diseases in order to identify high and low risk transmission zones and periods (WHO, 1975).…”