Eastern Cottontail Rabbits (Sylvilagus floridanus) Develop West Nile Virus Viremias Sufficient for Infecting Select Mosquito Species

Abstract

The potential of the eastern cottontail rabbit (CTR; Sylvilagus floridanus) to contribute to an enzootic West Nile virus (WNV) cycle was demonstrated by characterizing the WNV viremia profile of 15 CTRs and demonstrating that mosquitoes could become infected by feeding on these CTRs. Eight CTRs were infected with a titer of 10(5.0) cell-infectious dose 50% endpoints (CID50s) of WNV (NY99-Crow) by needle and seven CTRs by bite of one or more WNV-infected mosquitoes. There were no marked differences between the WNV viremia profiles of CTRs infected by either method. West Nile virus was detected in serums of all CTRs by 24 h p.i. The daily mean titers of all 15 CTRs on days 1-4 p.i. were 10(4.1+/-0.4), 10(4.7+/-0.3), 10(4.1+/-0.6), and 10(3.7+/-0.6) respectively, declining to 10(1.2+/-0.1) CID50s/ml of serum by day 6 p.i. No virus was detected in the blood of any CTR on day 7 p.i. The average duration of WNV titers of >or=10(4.3) and <10(5.0) CID50s/mL for all CTRs was 2.2 +/- 0.6 and 1.0 +/- 0.1 days, respectively. The minimum estimated infection rates (MEIRs) of Culex pipiens (L.) and Culex salinarius (Coq.) that fed on CTRs with titers of >or=10(4.3) and >10(5.0) were 11.5 +/- 5.5 and 21 +/- 6.0%, respectively. These rates increased to 20.5 +/- 6.4% and 25.0 +/- 3.0% when CTR serum titers were >10(5.0) CID50s/mL. Neither Aedes aegypti (L.) nor Aedes albopictus (Skuse) were infected by feeding on CTRs with titers of <10(5.0) CID50s/mL. The MEIRs of these two species were 11.5 +/- 3.5% and 1.5 +/- 0.5% after feeding on CTRs with titers of >10(5.0) CID50s/ml. None of the CTRs infected by mosquito bite or by needle showed any symptoms of WNV disease.

Arboviruses in North Dakota, 2003–2006

“…It increased to 35.5% and 60.0% in early September. Aedes vexans may become infected by feeding on small or medium-sized mammals, which have been reported to have specific antibodies to WNV, 47 shown to produce viremias sufficient to infect mosquitoes, [48][49][50][51] and found naturally infected in the field. 52 The risk that humans will acquire an infectious bite was greatest from the middle of July through the end of August with transmission still occurring in early September (Supplemental Table 4).…”

Ecology of West Nile Virus Transmission and Its Impact on Birds in the Western Hemisphere

“…Laboratory infection studies to estimate host competence have been published for 44 species of nondomesticated birds in 23 families and 11 orders Reisen et al 2005aReisen et al , b, 2006Reisen et al , 2007aClark et al 2006;Nemeth et al 2006;Owen et al 2006;Reisen and Hahn 2007;Platt et al 2008), 3 species of wild mammals (Tiawsirisup et al 2005b, Root et al 2006, Platt et al 2007, and 5 species of reptiles and one amphibian Komar 2003, Klenk et al 2004). In these experiments, animals are infected by either allowing infectious mosquitoes to feed on them or by an intramuscular or subcutaneous injection of virus.…”

Detection of Antibodies against Japanese Encephalitis Virus in Raccoons, Raccoon Dogs and Wild Boars in Japan

“…In most mammals, levels of viremia sufficient to infect mosquitoes do not develop. However, in the infection cycle of West Nile virus in the U.S.A., mammals such as the golden hamster (Mesocrietus auratus) [17], fox squirrel (Sciurus niger) [12], eastern cottontail rabbit (Sylvilagus floridanus) [16] and eastern chipmunk (Tamias striatus) [11] become sufficiently viremic for mosquito infection. In Wakayama, many wild animals were highly seropositive for JEV.…”