Table 1. Properties of six viruses transmitted by an overlapping network of mosquito vectors.
| Virus (genus) | Primary vector spp. | Geographic range | Presentation and mortality | Epidemiology and Ecology |
|---|---|---|---|---|
| West Nile virus (WNV, Flavivirus) | Cx. modestus, Cx. pipiens, Cx. quinquefasciatus, Cx. tarsalis | Globally distributed | Febrile illness and encephalitis. 10% mortality in neuro-invasive cases. Long-term physical and cognitive disabilities. | The most common mosquito-borne disease in North America. Since invading in 1999, 7 million estimated infections, 22,999 neuroinvasive cases, and 2163 deaths in US; 5614 reported cases in Canada. Typically 100–300 cases annually in Europe, but over 1500 in 2018. Poor surveillance in Africa, but seroprevalence ~ 80% in some areas. Birds are main reservoir/amplification hosts. |
| St. Louis Encephalitis virus (SLEV, Flavivirus) | Cx. quinquefasciatus, Cx. tarsalis | Western hemisphere; western, midwestern, and southern US | Encephalitis. 5–15% mortality in diagnosed cases. | 92 cases and six deaths recorded in US from 2009 to 2018. Birds are main reservoir/amplification hosts. |
| Eastern Equine Encephalitis virus (EEEV, Alphavirus) |
Ae. triseriatus, Cs. melanura | Western hemisphere; eastern and midwestern US | Febrile illness and encephalitis. 33% mortality in diagnosed cases. Long-term cognitive disabilities. | 73 cases and 30 deaths recorded in US from 2009 to 2018. Birds are main reservoir/amplification hosts. |
| Western Equine Encephalitis virus (WEEV, Alphavirus) | Cx. tarsalis | Western hemisphere; western and midwestern US | Febrile illness and encephalitis. Low mortality, except in infants. | 640 cases recorded in US from 1964 to 2010. Birds are main reservoir/amplification hosts. WEEV is derived from a recombinant event between the ancestors of EEEV and SINV. |
| Sindbis virus (SINV, Alphavirus), also called Pogosta, Ockelbo, and Karelian Fever | Cx. torrentium, Cx. pipiens, Cx. univittatus | Europe, Africa, Asia and Australia, primarily northern Europe and southern Africa | Febrile illness, rash, and joint pain. No mortality, but long-term disability. | Poor surveillance except in Finland, where annual incidence is 2–26 per 100,000 people and seroprevalence can reach ~40%. Birds are main reservoir/amplification hosts. Long-distance migratory birds may spread the virus between temperate zones in Northern and Southern hemispheres. |
| Rift Valley Fever virus (RVFV, Phlebovirus) | Ae. mcintoshi, Ae. ochraceus, Ae. vexans, Cx. pipiens, Cx. poicilipes, Cx. theileri and many more | Africa and the Middle East | Febrile illness and encephalitis. < 1% mortality in total cases. 50% mortality in hemorrhagic cases, permanent blindness in 50% of ocular cases (<2% of cases). | Livestock are main reservoir/amplification hosts, and suffer mortality and abortion after being infected by mosquitoes. Most transmission to humans occurs via direct contact with infected livestock. Vertical transmission in vectors (via dormant eggs) can initiate epidemics. In eastern and southern Africa, there are large epidemics every 5–15 years driven by rainfall and blooms of Ae. spp. from low-lying flooded areas known as dambos. |
Sources: WNV (Centers for Disease Control and Prevention, 2018c; European Centre for Disease Prevention and Control, 2018; Golding et al., 2012; Government of Canada, 2018; Kilpatrick, 2011; Petersen et al., 2013; Ronca et al., 2019; Weaver and Barrett, 2004); SLEV (Centers for Disease Control and Prevention, 2018a; Weaver and Barrett, 2004); EEEV (Centers for Disease Control and Prevention, 2018b; Weaver and Barrett, 2004); WEEV (Ronca et al., 2016; Weaver and Barrett, 2004); SINV (Adouchief et al., 2016); RVFV (Braack et al., 2018; Linthicum et al., 2016; Sang et al., 2017; World Health Organization, 2018).