Drought-induced amplification of West Nile virus transmission in the northeastern United States

Background/Question/Methods

West Nile virus (WNV), first introduced into the North America in 1999, has become the most economically and medically important arbovirus active in the United States. Current research suggests that inter-annual climate variability can have a direct influence on the epidemiology of WNV by affecting the biology and ecology of the pathogen and its vector and avian host species. The purpose of this study was to examine the influence of inter-annual variations in temperature and precipitation on seasonal mosquito abundances, the ability of local mosquito communities to maintain and transmit WNV (vector community competence), and the prevalence of WNV in the northeastern United States. Local vector and virus surveillance took place within Middlesex County in New Jersey (USA) over two transmission seasons (2010/2011). In addition to the local analysis, the long-term regional impacts of inter-annual climate variability on WNV transmission were analyzed over a nine-year period (2003-2011) using statewide climate and surveillance data.  

Results/Conclusions

Drought conditions occurring during the 2010 season resulted in significant increases in the number of blood-fed Culex spp. mosquitoes collected per week (85.5±56.6) and in the ability of local vector communities to transmit WNV (0.45±0.08%), measured as vector community competence, when compared to the milder 2011 season (40.9±36.5; 0.35±0.08%). These increases correlated to increases in weekly WNV infection rates during the 2010 season (18.44±8.5/1000) compared to the 2011 season (8.3±3.5/1000). Additionally, the positive influence of drought on the amplification of WNV was also confirmed at the state level where early seasonal (June-July) increases in temperature and decreases in precipitation were strongly correlated (r = 0.78; 0.63 respectively) with increases in yearly WNV infection rates over a nine-year period (2003-2011). These data provide concrete evidence that early seasonal drought conditions positively impact the transmission dynamics of WNV at both the local and regional levels.