Experimental Vertical Transmission of West Nile Virus byCulex pipiens(Diptera: Culicidae) : Table 1

Abstract

Despite the detection of West Nile (WN) virus in overwintering Culex pipiens L. in New York in February 2000, the mechanism by which this virus persists throughout the winter to initiate infections in vertebrate hosts and vectors the following spring remains unknown. After a blood meal, parous mosquitoes generally do not survive until spring and gonotrophic dissociation occurs in only a small percentage of the population. To investigate vertical transmission as a means of viral survival during interepizootics, we intrathoracically inoculated Cx. pipiens and Aedes albopictus (Skuse) with WN virus and subsequently tested their F1 progeny for the presence of virus. Among the Cx. pipiens, we recovered virus from two of 1,417 adult progeny that had been reared at 18 degrees C for a minimal filial infection rate (MFIR) of approximately 1.4/1,000 and four of 1,873 adult progeny reared at 26 degrees C (MFIR = 2.1/1,000). The mean titer of the positive pools was 10(5.6) plaque-forming units (PFU)/ml (=10(5.9) PFU/mosquito for positive mosquitoes) of virus. Overall, the MFIR was approximately 1.8/1,000 for Cx. pipiens. Although reports indicate that Ae. albopictus vertically transmit various viruses in the Japanese encephalitis virus complex, we did not detect WN virus in any of > 13,000 F1 progeny of WN virus-inoculated specimens. Female Cx. pipiens that are vertically infected during the late summer season and then survive the winter could serve as a source of WN virus to initiate an infection cycle the following spring.

Epidemiology of West Nile in Europe and in the Mediterranean Basin

“…Vertical transmission of WNV in mosquitoes (i.e. passage of virus from infected female to her offspring) was demonstrated in the laboratory [71, 72] and in the field [73]. In addition, the detection of WNV in pools of overwintering hibernating Culex pipiens mosquitoes in New York City in 2000 [74] clearly indicates the capacity of the virus to overwinter and to survive in hibernating infected adult mosquitoes.…”

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

“…Other modes of transmission have been demonstrated, including direct bird-to-bird transmission , vertical transmission in mosquitoes (that may facilitate overwintering of the virus) (Nasci et al 2001, Dohm et al 2002b, and nearly instantaneous transmission between infected and uninfected mosquitoes simultaneously feeding on the same host. This last mode was originally believed to be nonviremic transmission (Higgs et al 2005).…”

On a discrete West Nile epidemic model

“…When 0 < I v (0) < 10, then both infected populations increase to equilibrium levels with increasing time. It is known that vertical transmission of virus in the vector population is an important factor for contributing the spread of the disease [3,7,10]. We shall investigate this factor using our built model.…”

“…Since vertical transmission of the vector population has been found as an important mechanism in maintaining the virus in natural populations [3,7,10], we assume a constant fraction p, 0 ≤ p ≤ 1, of the offspring of the infectious vectors is infectious. Under these biological assumptions, the interaction between vector and avian populations are given below:…”

“…In [1,2], the models are expressed in terms of time unit t and nonnegativity of the solutions are derived using the quantity t and model parameters. Since data for the West Nile epidemics given in the literature [3,5,7,10,16] are in terms of days, our time unit is taken to be a day and model (2.1) does not involve time unit t as in [1,2]. We now impose the following conditions on the parameters so that solutions of (2.1) will remain nonnegative as shown in Proposition 2.1.…”