Exome-wide association of deltamethrin resistance in Aedes aegypti from Mexico.

Aedes aegypti is the major vector of a number of arboviruses that cause disease in humans. Without vaccines or pharmaceuticals, pyrethroid insecticides remain the major tool for public health protection. Pyrethroid resistance is now widespread. Replacement substitutions in the voltage-gated sodium channel (vgsc) that reduce the stability of pyrethroid binding account for most of the resistance, but metabolic mechanisms also inactivate pyrethroids. High-throughput sequencing and the A. aegypti L5 annotated physical map has allowed interrogation of the exome for genes and single-nucleotide polymorphisms associated with pyrethroid resistance. We exposed females of A. aegypti from Mexico to a deltamethrin discriminating dose to designate them as resistant (active after 1 h) or susceptible (knocked down with no recovery after 4 h). The vgsc on chromosome 3 had the highest association, followed by genes proximal to vgsc. We identified potential detoxification genes located singly (eg HPX8C) or within clusters in chromosome 2 [three esterase clusters, two of cytochrome P450 monooxygenases (CYP)] and chromosome 3 (one cluster of 16 CYP325 and seven CYP9 genes). Deltamethrin resistance in A. aegypti is associated with mutations in the vgsc gene and a large assortment of genes.

Multi-scale analysis of the associations among egg, larval and pupal surveys and the presence and abundance of adult female Aedes aegypti (Stegomyia aegypti) in the city of Merida, Mexico.

Despite decades of research, there is still no agreement on which indices of Aedes aegypti (Stegomyia aegypti) (Diptera: Culicidae) presence and abundance better quantify entomological risk for dengue. This study reports the results of a multi-scale, cross-sectional entomological survey carried out in 1160 households in the city of Merida, Mexico to establish: (a) the correlation between levels of Ae. aegypti presence and abundance detected with aspirators and ovitraps; (b) which immature and egg indices correlate with the presence and abundance of Ae. aegypti females, and (c) the correlations amongst traditional Aedes indices and their modifications for pupae at the household level and within medium-sized geographic areas used for vector surveillance. Our analyses show that ovitrap positivity was significantly associated with indoor adult Ae. aegypti presence [odds ratio (OR) = 1.50; P = 0.03], that the presence of pupae is associated with adult presence at the household level (OR = 2.27; P = 0.001), that classic Aedes indices are informative only when they account for pupae, and that window screens provide a significant level of protection against peridomestic Ae. aegypti (OR = 0.59; P = 0.02). Results reinforce the potential of using both positive collections in outdoor ovitraps and the presence of pupae as sensitive indicators of indoor adult female presence.

Incrimination of the mosquito, Aedes taeniorhynchus, as the primary vector of heartworm, Dirofilaria immitis, in coastal Yucatan, Mexico.

Mosquito collections were carried out on microfilaraemic dogs, positive for Dirofilaria sp., for 18 consecutive nights in the coastal town of Celestún, Yucatan, southeast Mexico, during the rainy season (August) of 2007. A total of 292 female mosquitoes representing 12 species of dipteran Culicidae were collected: Anopheles albimanus (Wiedemann); Anopheles crucians (Wiedemann); Anopheles pseudopunctipennis (Theobald); Culex coronator (Dyar & Knab); Culex interrogator (Dyar & Knab); Culex nigripalpus (Theobald); Culex quinquefasciatus (Say); Culex salinarius (Coquillett); Aedes aegypti (Linnaeus); Aedes scapularis (Rondani); Aedes sollicitans (Walker), and Aedes taeniorhynchus (Wiedemann). Aedes taeniorhynchus and Cx. quinquefasciatus were the species found most commonly feeding on the dogs. Filarial nematodes were observed by microscopy in nine of the mosquito species collected; however, third-instar larvae were only observed in Ae. taeniorhynchus and An. crucians. Of 76 Ae. taeniorhynchus specimens found positive for Dirofilaria sp. by dissection, 14 were confirmed to be positive for Dirofilaria immitis (Leidy) by polymerase chain reaction (PCR). The resulting infection rate for D. immitis confirmed by PCR (6.2%) is higher than any infection rate for Ae. taeniorhynchus previously reported from the Americas.

Use of the pupal/demographic-survey technique to identify the epidemiologically important types of containers producing Aedes aegypti (L.) in a dengue-endemic area of Venezuela.

As dengue continues to emerge as a major public-health problem world-wide, efforts to control the dengue vector Aedes aegypti must become more effective and efficient. Results from larval and pupal surveys applied in Venezuela illustrate the uniqueness of the information gained from pupal surveys; information that is lost when traditional Stegomyia indices are calculated. As most Ae. aegypti pupae will emerge to become adults, controlling the containers that produce the most pupae could have the greatest impact on the adult population. Pupal-survey results in Venezuela showed that large (150- to 200-litre) water drums produce the greatest number of pupae throughout the year. In the rainy season, approximately 70% of all pupae are found in these drums or in tyres, buckets and tanks. Over 80% of pupae in the dry season are found in drums and tanks alone. By targeting only those domestic breeding containers that produce the greatest number of pupae, control efforts may be streamlined to have the greatest impact on reducing the local adult Ae. aegypti population.

Toxoplasma gondii infections in chickens from Venezuela: isolation, tissue distribution, and molecular characterization.

The prevalence of Toxoplasma gondii, in free-ranging chickens is a good indicator of the prevalence of T. gondii oocysts in the soil because chickens feed from the ground. The prevalence of T. gondii in 46 free-range chickens (Gallus domesticus) from Venezuela was determined. Antibodies to T. gondii were assayed by the modified agglutination test (MAT). Antibodies were found in 16 (32%) chickens with titers of 1:5 in 1, 1:10 in 2, 1:40 in 2, 1:80 in 2, 1:160 in 2, 1:320 in 3, 1: 640 in 2, and 1:1,280 or higher in 2. Hearts, pectoral muscles, and brains of 13 chickens with MAT titers of 1:40 or more were bioassayed individually in mice. Tissues of each of 3 chickens with titers of 1:5 or 1:10 were pooled and bioassayed in mice. Tissues from the remaining 30 seronegative chickens were pooled and fed to 1 T. gondii-free cat. Feces of the cat were examined for oocysts; it did not shed oocysts. Toxoplasma gondii was isolated from 12 of 13 chickens with MAT titers of 1:40 or more. Toxoplasma gondii was isolated from pooled tissues of 1 of 2 chickens with titers of 1:10. Eight of these 13 isolates were virulent for mice. Genotyping of 13 of these isolates using the SAG2 locus indicated that 10 were type III, and 3 were type II. Phenotypically and genetically these isolates were different from T. gondii isolates from North America and Brazil. This is the first report of isolation of T. gondii from chickens from Venezuela.