Ecological studies of enzootic Venezuelan equine encephalitis in north-central Venezuela, 1997-1998.

From 1997-1998, we investigated the possible continuous circulation of epizootic Venezuelan equine encephalitis (VEE) virus suggested by a 1983 subtype IC interepizootic mosquito isolate made in Panaquire, Miranda State, Venezuela. The study area was originally covered by lowland tropical rainforest but has been converted into cacao plantations. Sentinel hamsters, small mammal trapping, mosquito collections, and human serosurveys were used to detect active or recent virus circulation. Six strains of subtype ID VEE virus were isolated from hamsters that displayed no apparent disease. Four other arboviruses belonging to group A (Togaviridae: Alphavirus), two Bunyamwera group (Bunyaviridae), and three Gamboa group (Bunyaviridae) arboviruses were also isolated from hamsters, as well as 8 unidentified viruses. Venezuelan equine encephalitis-specific antibodies were detected in 5 small mammal species: Proechimys guairae, Marmosa spp., and Didelphis marsupialis. Mosquito collections comprised of 38 different species, including 8 members of the subgenus Culex (Melanoconion), did not yield any virus isolates. Sera from 195 humans, either workers in the cacao plantation or nearby residents, were all negative for VEE virus antibodies. Sequences of 1,677 nucleotides from the P62 gene of 2 virus isolates indicated that they represent a subtype ID lineage that is distinct from all others characterized previously, and are unrelated to epizootic VEE emergence.

Spatial dispersion of adult mosquitoes (Diptera: Culicidae) in a sylvatic focus of Venezuelan equine encephalitis virus.

We studied the spatial localization of mosquitoes in sylvatic focus of Venezuelan equine encephalitis virus in western Venezuela to identify mosquito species potentially involved in the hypothesized transport of viruses out of enzootic foci. The following criteria were used to identify species with potential for virus export: (1) common in the forest and surrounding area, (2) feeding on a wide range of vertebrates; (3) long dispersal capabilities, and (4) established vectorial competence for enzootic or epizootic VEE viruses. CDC traps baited with light/CO2 were operated for four and 12-h intervals to collect mosquitoes at four stations along two forest/open area transects from September to November 1997. We collected 60,444 mosquitoes belonging to 11 genera and 34 species. The most common species were Aedes serratus (Theobald), Ae. scapularis (Rondani), Ae. fulvus (Wiedmann), Culex nigripalus Theobald, Cx, (Culex) "sp", Cx. mollis Dyar & Knab, Cx. spissipes (Theobald), Cx. pedroi Sirivanakarn and Belkin, Psorophora ferox (Humboldt), Ps. albipes (Theobald), and Ps. cingulata (F.). Very few mosquitoes were captured during the (day in the open area outside the forest, suggesting that any virus export from the forest may occur at night. The following mosquitoes seemed to be mostly restricted to the forest habitat: Ae. serratus, Ps. ferox, Ps. albipes, sabethines, Cx. spissipes, Cx. pedroi, Cx. dunni Dyar, and Ae. fulvus. The main species implicated its potential virus export were Cx. nigripalpus, Ae. scapularis, and Mansonia titillans (Walker).

Phylogenetic relationships among eighteen neotropical Culicini species.

The subgeneric relationships among 8 generic and infrageneric taxa of the Culicini tribe were examined by cladistic analysis based on 30 larval mouthpart characters (maxillae and mandibles) of 7 subgenera of Culex L. and 1 of Deinocerites Theobald. We analyzed 18 ingroup species as well as Deinocerites melanophylum Dyar and Knab as a sister group, and Aedes taeniorhynchus Wiedemann as an outgroup. A parsimony analysis using the Nona program resulted in 2 trees each of 109 steps (consistency and retention indices = 0.88). The topologies obtained were similar to the current classification of the tribe, based on nonexplicit methods mainly including adult characters, with 2 exceptions. In the present work, the monophyly of the tribe Culicini (Culex + Deinocerites) was supported by 4 synapomorphies. The subgenus Lutzia Theobald formed the most basal clade in the tribe Culicini and the placement of Phenacomyia Harbach and Peyton as a subgenus was validated by its location as a sister group of the subgenus Culex and other subgenera. The subgenus Carrollia Lutz was the most robust taxon, supported by 5 synapomorphies, and was congruent with the infragroups of the current classification. The relationships among Deinocerites, Anoedioporpa Dyar, Microculex Theobald, and Melanoconion Theobald were unresolved, but were placed in the most internal clade of the tribe. The 1st exception to the accepted classification was the poorly resolved boundary between Anoedioporpa and Microculex The 2nd was the strong support (with 11 synapomorphies) for the inclusion of Deinocerites as a subgenus of Culex in the Culicini, which is proposed here.