West Nile Virus Mosquito Vectors in North America

Abstract

In North America, the geographic distribution, ecology, and vectorial capacity of a diverse assemblage of mosquito species belonging to the genus Culex determine patterns of West Nile virus transmission and disease risk. East of the Mississippi River, mostly ornithophagic Culex pipiens L. complex mosquitoes drive intense enzootic transmission with relatively small numbers of human cases. Westward, the presence of highly competent Culex tarsalis (Coquillett) under arid climate and hot summers defines the regions with the highest human risk. West Nile virus human risk distribution is not uniform geographically or temporally within all regions. Notable geographic ‘hotspots’ persist with occasional severe outbreaks. Despite two decades of comprehensive research, several questions remain unresolved, such as the role of non-Culex bridge vectors, which are not involved in the enzootic cycle, but may be involved in virus transmission to humans. The absence of bridge vectors also may help to explain the frequent lack of West Nile virus ‘spillover’ into human populations despite very intense enzootic amplification in the eastern United States. This article examines vectorial capacity and the eco-epidemiology of West Nile virus mosquito vectors in four geographic regions of North America and presents some of the unresolved questions.

Increased mosquito abundance and species richness in Connecticut, United States 2001–2019

“…The second limitation to understanding longitudinal trends in mosquito population is the central focus on either single species or community dynamics in the context of disease transmission 9 . A single species (or pathogen) surveillance approach has increased the prevalence of long-term data on West Nile virus (WNV) transmission in the U.S., especially in regards to the Culex pipiens (Linnaeus) species complex 10 and the invasion dynamics of Aedes albopictus (Skuse) 11 , yet these data sets do little to improve the understanding of mosquito species community dynamics in general. This lack of general mosquito community ecology knowledge is a critical gap in our ability to control mosquito populations and forecast disease (re)emergence 12 .…”

“…(WNV) transmission in the U.S., especially in regards to the Culex pipiens (Linnaeus) species complex 10 and the invasion dynamics of Aedes albopictus (Skuse) 11 , yet these data sets do little to improve the understanding of mosquito species community dynamics in general. This lack of general mosquito community ecology knowledge is a critical gap in our ability to control mosquito populations and forecast disease (re)emergence 12 .…”

Does Plasmodium Infection Affect Mosquito Attraction?

“…For instance, uninfected vectors highly attracted toward infected hosts would initially increase transmission in local populations (Gandon, 2018). Generalist mosquito species feeding on birds and mammals (depending on host availability; Abella-Medrano et al, 2018) play important roles in the transmission of zoonotic pathogens (e.g., Culex pipiens transmitting West Nile virus (WNV) and Usutu (USUV) virus among birds, equids, and humans; Brugman et al, 2018;Rochlin et al, 2019). Thus, investigating drivers of mosquito host selection is essential to understand the dynamics of vertebrate-vector-pathogen systems.…”

“…Although Culex mosquitoes have a broad range of hosts, some are predominantly mammophilic and others are ornithophilic (e.g., Culex theileri vs. Cx. pipiens), yet their feeding behaviors depend on the species and population of origin, which also affects the parasites they transmit (Santa-Ana et al, 2006;Farajollahi et al, 2011;Rochlin et al, 2019).…”

Comparison of vector competence of Aedes vexans Green River and Culex pipiens biotype pipiens for West Nile virus lineages 1 and 2

“…and birds (Chancey et al, 2015). Some mosquito species feeding on both birds and mammals (“bridge vectors”) are capable of transmitting the virus to dead‐end hosts like humans and horses via virus‐containing saliva (Rochlin, Faraji, Healy, & Andreadis, 2019). Mosquito species, experimentally proven to be vector competent for WNV, include members of the Culex pipiens complex (Farajollahi, Fonesca, Kramer, & Kilpatrick, 2011; Vogels, Fros, Göertz, Pijlman, & Koenraadt, 2016; Vogels, Göertz, Pijlman, & Koenraadt, 2017), Aedes japonicus (Veronesi et al, 2018; Wagner et al, 2018), Aedes albopictus (Fortuna et al, 2015) and Aedes vexans (Goddard, Roth, Reisen, & Scott, 2002; Tiawsirisup et al, 2008).…”