Temperature, Viral Genetics, and the Transmission of West Nile Virus by Culex pipiens Mosquitoes

Abstract

The distribution and intensity of transmission of vector-borne pathogens can be strongly influenced by the competence of vectors. Vector competence, in turn, can be influenced by temperature and viral genetics. West Nile virus (WNV) was introduced into the United States of America in 1999 and subsequently spread throughout much of the Americas. Previously, we have shown that a novel genotype of WNV, WN02, first detected in 2001, spread across the US and was more efficient than the introduced genotype, NY99, at infecting, disseminating, and being transmitted by Culex mosquitoes. In the current study, we determined the relationship between temperature and time since feeding on the probability of transmitting each genotype of WNV. We found that the advantage of the WN02 genotype increases with the product of time and temperature. Thus, warmer temperatures would have facilitated the invasion of the WN02 genotype. In addition, we found that transmission of WNV accelerated sharply with increasing temperature, T, (best fit by a function of T4) showing that traditional degree-day models underestimate the impact of temperature on WNV transmission. This laboratory study suggests that both viral evolution and temperature help shape the distribution and intensity of transmission of WNV, and provides a model for predicting the impact of temperature and global warming on WNV transmission.

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

“…A more quickly replicating virus spurred by warmer conditions precedes an increase in mosquito infection [59,84]. It was detected that warmer temperatures facilitated the displacement of the WNV NY99 genotype by the WN02 genotype [30]. In a study in suburban Chicago, Bertolotti et al [85] discovered high genetic variation of WNV at fine temporal and spatial scales, while variation in local temperature was offered as one explanation for this.…”

“…Increased temperatures cause an upsurge in the growth rates of vector populations, decrease the interval between blood meals, shorten the incubation time from infection to infectiousness in mosquitoes, accelerate the virus evolution rate and increase viral transmission efficiency to birds [22,23,30,32,35,36].…”

West Nile Virus Vector Competency of Culex quinquefasciatus Mosquitoes in the Galápagos Islands

“…Because viral development changes over time and is liable to interact non-linearly with temperature, 36,38,44 we chose to examine the status of mosquito infection and transmission ability and consider the effect of (i)incubation time post-exposure and (ii)temperature variation. The Galápagos ecosystem experiences seasonal variation with a hot, humid, rainy season with temperatures exceeding 30°C in JanuaryApril.…”

“…46 Briefly, mosquito legs were first removed from bodies and separately triturated in a microfuge tube containing 1 mL of mosquito diluent (phosphate-buffered saline, 20% fetal bovine serum [FBS], and antibiotics) and a ball-bearing. To check for transmission ability, salivary secretions were obtained by using a modified in vitro capillary transmission assay 36,47 in which the mosquito proboscis is inserted into a capillary tube containing a 1:1 mixture of FBS and 50% sucrose. This procedure invokes a reflex action by the live mosquito to secrete its saliva into the solution and after 30 minutes the contents of the capillary are dispensed into 300 μL of mosquito diluent.…”

“…30,[32][33][34][35] There are noticeable influences on mosquito susceptibility to WNV infection including extrinsic (e.g., initial viral dose, temperature, and length of incubation) and intrinsic (e.g., genetic strain, midgut physiology) factors. 32,[36][37][38] Generally, longer incubation periods, higher viral doses, and higher temperatures are expected to yield higher rates of infection. 30,32,39 However, Cx.…”