Mosquito vectors of West Nile virus during an epizootic outbreak in Puerto Rico.

The purpose of this investigation was to identify the mosquito (Diptera: Culicidae) vectors of West Nile virus (WNV; family Flaviviridae, genus Flavivirus) during an epizootic WNV outbreak in eastern Puerto Rico in 2007. In June 2006, 12 sentinel chicken pens with five chickens per pen were deployed in six types of habitats: herbaceous wetlands, mangrove forests, deciduous forests, evergreen forests, rural areas, and urban areas. Once WNV seroconversion in chickens was detected in June 2007, we began trapping mosquitoes using Centers for Disease Control and Prevention (CDC) miniature (light/CO2-baited) traps, CMT-20 collapsible mosquito (CO2- and ISCA SkinLure-baited) traps, and CDC gravid (hay infusion-baited) traps. We placed the CDC miniature traps both 2-4 m and >30 m from the chicken pens, the collapsible traps 2-4 m from the pens, and the gravid traps in backyards of houses with sentinel chicken pens and in a wetland adjacent to an urban area. We found numerous blood-engorged mosquitoes in the traps nearest to the sentinel chickens and reasoned that any such mosquitoes with a disseminated WNV infection likely served as vectors for the transmission of WNV to the sentinels. We used reverse transcriptase-polymerase chain reaction and isolation (C636) on pools of heads, thoraxes/ abdomens, and legs of collected blood-engorged mosquitoes to determine whether the mosquitoes carried WNV. We detected WNV-disseminated infections in and obtained WNV isolates from Culex nigripalpus Theo (minimum infection rate [MIR] 1.1-9.7/1,000), Culex bahamensis Dyar and Knab (MIR 1.8-6.0/1,000), and Aedes taeniorhynchus (Wied.) (MIR 0.34-0.36/1,000). WNV was also identified in and isolated from the pool of thoraxes and abdomens of Culex quinquefasciatus Say (4.17/1,000) and identified in one pool of thoraxes and abdomens of Culex habilitator Dyar and Knab (13.39/1,000). Accumulated evidence since 2002 suggests that WNV has not become endemic in Puerto Rico.

Nocodazole delays viral entry into the brain following footpad inoculation with West Nile virus in mice.

West Nile virus (WNV) infection in humans can cause neurological deficits, including flaccid paralysis, encephalitis, meningitis, and mental status change. To better understand the neuropathogenesis of WNV in the peripheral and the central nervous systems (PNS and CNS), we used a mouse footpad inoculation model to simulate a natural peripheral infection. Localization of WNV in the nervous system using this model has suggested two routes of viral invasion of the CNS: axonal retrograde transport (ART) from the PNS and hematogenous diffusion via a breakdown in the blood-choroid-plexus barrier. C57BL/6J mice were treated with nocodazole, a microtubule inhibitor that blocks ART, prior to infection with WNV. Nocodazole-treated WNV-infected mice developed a viremia 1.5 log(10) greater than untreated WNV-infected control mice at days 3 to 4 post infection (PI). Although viremia was greater in nocodazole-treated mice, detection of virus in brain tissue (spinal cord, cortex, brainstem, and cerebellum), as measured by real-time reverse transcriptase-polymerase chain reaction (RT-PCR), did not occur until day 7. At these later time points (7 and 9 days PI), nocodazole-treated WNV-infected animals attained viral titers in these tissues similar to titers in the untreated WNV-infected control animals. These results demonstrate that a single dose of nocodazole delays, but does not block, WNV infection of the brain.