Aedes aegypti(L.) andAedes polynesiensisMarks (Diptera: Culicidae) in Moorea, French Polynesia: A Study of Adult Population Structures and Pathogen (Wuchereria bancroftiandDirofilaria immitis) Infection Rates to Indicate Regional and Seasonal Epidemiological Risk for Dengue and Filariasis

Abstract

Populations of Aedes aegypti (L.) and Aedes polynesiensis (Marks) on Moorea Island, French Polynesia, the local vectors of dengue and filariasis, respectively, were sampled by landing/biting collection at nine localities on the east, north, and west coasts, during the late dry season, early and late wet season (September-May) 2003 and 2004, to investigate epidemiologically important features of the populations and compare them between regions and months. Biting rates of both species tended to increase (but not always significantly) for each species in each region each month from the late dry season to the late wet season, and the north coast region had significantly higher biting rates of Ae. aegypti. Insemination rates of Ae. polynesiensis females (94.5-98.8%) were consistently greater than those of Ae. aegypti (87.5-93.5%) throughout the study, but there was no significant difference in the insemination rates of either species between months and regions. Parity rates were generally highest in north coast samples and lowest in west coast samples for both species and generally increased (albeit not always significantly) by month for each species, with a range of 52.9-88.8% for Ae. polynesiensis and 28.6-53.6% for Ae. aegypti, although the high gravid rate (15.8-45.9%) of Ae. aegypti samples (reflecting its feeding more than once in a gonotrophic cycle) confounded both intraspecific and interspecific comparisons. Filarial infection was rare in Ae. aegypti, although both W. bancrofti and D. immitis were recorded, and infection rates in Ae. polynesiensis increased through the study period in each region for both filarias, with up to 4.6% infected and 1.4% infective for W. bancrofti and up to 6.3% infected and 2.5% infective for D. immitis. For W. bancrofti, infection rates were significantly lower on the west coast and also in the dry season, whereas rates for infective stages were significantly greater in the late wet season. For D. immitis there was no significant difference in infection rates between regions, but rates were significantly greater in the late wet season. Rainfall in all months sustains populations of both vectors and explains the relatively few significant differences between seasons; however, the wet season may provide for increased vector abundance and longevity, and present a potentially increased risk for transmission. Although the differences shown between regions also were limited in a statistical sense, there were increased risks for the northern and eastern regions, where both locals and tourists are concentrated and where the seaports and airport are located, and these areas should be priority targets for disease surveillance and vector control.

Molecular Xenomonitoring Using Mosquitoes to Map Lymphatic Filariasis after Mass Drug Administration in American Samoa

“…In addition, earlier xenomonitoring efforts have revealed that W. bancrofti prevalence in Ae. polynesiensis collected at a single location can vary substantially over the course of a year or even between collection periods separated by as few as ten days [58], [25]. Together, these factors, along with the difficulty of collecting large numbers of vectors and the resulting wide confidence interval estimates, suggest that xenomonitoring currently has limited usefulness for quantifying the progress of LF elimination in American Samoa.…”

Estimation of Population Size and Dispersal ofAedes polynesiensison Toamaromotu, French Polynesia

“…In nature, bloodmeal sources may be unpredictable but ≈80% of wet season Toamaro females caught in BG traps were parous (i.e., ≥1 clutch of eggs already produced); on Moorea (≈125 km southeast of Raiatea but within the Society Archipelago), parity rates for Ae. polynesiensis ranged between 52.9– 88.8% for wet and dry seasons (Russell et al 2005a). We can estimate that between 10% (securing bloodmeal on first day of seeking) and 50% (low success rate at securing bloodmeal, the more likely scenario in view of attack rates in the field) of females will actively seek bloodmeals at any given time.…”

“…Aedes polynesiensis Marks (Diptera: Culicidae) is the primary vector of Wuchereria bancrofti (Cobbold) and Dirofilaria immitis (Spirurida: Onchocercidae), the causative agents of human lymphatic filariasis and dog heartworm, respectively (Rosen 1955, Laigret et al 1965, Russell et al 2005a), and a secondary vector of dengue virus in French Polynesia (Rosen et al 1954, Maguire et al 1971). This highly anthropophilic, exophilic species is diurnal with peak periods of host-seeking during early morning and late afternoon hours (Russell et al 2005a).…”

“…This highly anthropophilic, exophilic species is diurnal with peak periods of host-seeking during early morning and late afternoon hours (Russell et al 2005a). Control of the vector is complicated by its use of dispersed and varied habitats for larval development; these habitats include phytotelmata and deciduous plant matter (especially rat-chewed coconuts), rock pools, artificial containers, and burrows of the land crab Cardisoma carnifex Herbst (Decapoda: Gecarcinidae) (Lardeux et al 2002).…”

Changes in the Genetic Structure ofAedes aegypti(Diptera: Culicidae) Populations in Queensland, Australia, Across Two Seasons: Implications for Potential Mosquito Releases

“…In contrast, in tropical French Polynesia, populations of Ae. aegypti can be sustained by rainfall events each month so that no differences in activity between the wet and dry seasons are observed, although the wet season is thought to promote vector abundance and longevity and result in an increased risk of disease transmission (Russell et al 2005a). Between these extremes, in subtropical Argentina, a population peak occurs in March at the time of maximum rainfall, but is reduced in winter due to low relative humidity, which affects oviposition (Micieli and Campos 2003).…”