Nonviremic transmission of West Nile virus

Abstract

West Nile virus (WNV) is now the predominant circulating arthropod-borne virus in the United States with >15,000 human cases and >600 fatalities since 1999. Conventionally, mosquitoes become infected when feeding on viremic birds and subsequently transmit the virus to susceptible hosts. Here, we demonstrate nonviremic transmission of WNV between cofeeding mosquitoes. Donor, Culex pipiens quinquefasciatus mosquitoes infected with WNV were fed simultaneously with uninfected ''recipient'' mosquitoes on naïve mice. At all times, donor and recipient mosquitoes were housed in separate sealed containers, precluding the possibility of mixing. Recipients became infected in all five trials, with infection rates as high as 5.8% and no detectable viremia in the hosts. Remarkably, a 2.3% infection rate was observed when 87 uninfected mosquitoes fed adjacent to a single infected mosquito. This phenomenon could potentially enhance virus survival, transmission, and dispersion and obviate the requirement for viremia. All vertebrates, including immune and insusceptible animals, might therefore facilitate mosquito infection. Our findings question the status of dead-end hosts in the WNV transmission cycle and may partly explain the success with which WNV established and rapidly dispersed throughout North America.Culex ͉ mosquito vector

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

“…This last mode was originally believed to be nonviremic transmission (Higgs et al 2005). Recent evidence suggests that infection of these cofeeding mosquitoes appears to be caused by a transient viremia from virus injected into the host by the infected mosquito, rather than by nonviremic transmission (Reisen et al 2007b).…”

Importance of Bird-to-Bird Transmission for the Establishment of West Nile Virus

“…Recently, transmission of WNV between cofeeding mosquitoes was experimentally demonstrated (Higgs et al 2005). As little is known about the frequency at which co-feeding occurs, we modeled the number of cases as a small quantity .…”

“…Two other routes of transmission have been demonstrated, both of them between mosquitoes: from an infected female mosquitoes to their offspring (vertical transmission) (Baqar et al 1993, Dohm et al 2002, Goddard et al 2002, and horizontal transmission between co-feeding mosquitoes (Higgs et al 2005), albeit with very low infection rates.…”

West Nile Virus in American White Pelican Chicks: Transmission, Immunity, and Survival

“…Several laboratory studies have documented uninfected mosquitoes becoming infected simply by feeding on a non-viremic host that had been fed on by an infected mosquito. [38][39][40] Although most pelican chicks that die of WNV are larger with a greater blood volume than vertebrate hosts tested in laboratory studies (e.g., mice and house finches [Carpodacus mexicanus]), at both Chase Lake and Bitter Lake, pelicans share the nesting islands with thousands of breeding egrets and herons that have relatively small chicks in nests at the time that WNV causes pelican chick mortality. Non-viremic transmission could accelerate the spread of WNV, because additional mosquitoes can become carriers without waiting for the virus to replicate in a vertebrate host.…”