Aedes aegypti L. is the primary dengue vector in southern Taiwan. This article is the first report on a large-scale surveillance program to study the spatial-temporal distribution of the local Ae. aegytpi population using ovitraps stratified according to the human population in high dengue-risk areas. The sampling program was conducted for 1 yr and was based on weekly collections of eggs and adults in Kaohsiung City. In total, 10,380 ovitraps were placed in 5,190 households. Paired ovitraps, one indoors and one outdoors were used per 400 people. Three treatments in these ovitraps (paddle-shaped wooden sticks, sticky plastic, or both) were assigned by stratified random sampling to two areas (i.e., metropolitan or rural, respectively). We found that the sticky plastic alone had a higher sensitivity for detecting the occurrence of indigenous dengue cases than other treatments with time lags of up to 14 wk. The wooden paddle alone detected the oviposition of Ae. aegypti throughout the year in this study area. Furthermore, significantly more Ae. aegypti females were collected indoors than outdoors. Therefore, our survey identified the whole year oviposition activity, spatial-temporal distribution of the local Ae. aegypti population and a 14 wk lag correlation with dengue incidence to plan an effectively proactive control.
BackgroundTaiwan is geographically located in a region that spans both tropical and subtropical climates (22–25°N and 120–122°E). The Taiwan Centers for Disease Control have found that the ecological habitat of Aedes aegypti appears only south of 23.5°N. Low temperatures may contribute to this particular habitat distribution of Ae. aegypti under the influence of the East Asian winter monsoon. However, the threshold condition related to critically low temperatures remains unclear because of the lack of large-scale spatial studies. This topic warrants further study, particularly through national entomological surveillance and satellite-derived land surface temperature (LST) data.MethodsWe hypothesized that the distribution of Ae. aegypti is highly correlated with the threshold nighttime LST and that a critical low LST limits the survival of Ae. aegypti. A mosquito dataset collected from the Taiwan Centers for Disease Control was utilized in conjunction with image data obtained from the moderate resolution imaging spectroradiometer (MODIS) during 2009–2011. Spatial interpolation and phi coefficient methods were used to analyze the correlation between the distributions of immature forms of Ae. aegypti and threshold LST, which was predicted from MODIS calculations for 348 townships in Taiwan.ResultsAccording to the evaluation of the correlation between estimated nighttime temperatures and the occurrence of Ae. aegypti, winter had the highest peak phi coefficient, and the corresponding estimated threshold temperatures ranged from 13.7 to 14 °C in the ordinary kriging model, which was the optimal interpolation model in terms of the root mean square error. The mean threshold temperature was determined to be 13.8 °C, which is a critical temperature to limit the occurrence of Ae. aegypti.ConclusionsAn LST of 13.8 °C was found to be the critical temperature for Ae. aegypti larvae, which results in the near disappearance of Ae. aegypti during winter in the subtropical regions of Taiwan under the influence of the prevailing East Asian winter monsoon.
Since the 1970s, no information on simian malaria has been documented in Taiwan, an area that is free from human malaria. To update the prevalence of simian malaria, a molecular-based survey was performed. Blood samples from 286 Formosan macaques ( Macaca cyclopis ) were tested for Plasmodium species by microscopy and nested polymerase chain reaction. Furthermore, the field isolates were characterized by sequencing the 42-kDa fragment of the merozoite surface protein 1 (MSP-1(42)). Of the 286 blood samples analyzed, 7 (2.4%) were positive by microscopy and nested PCR. All malaria-infected Formosan macaques were those collected from southern Taiwan, whereas no evidence of malarial parasites was observed among monkeys from eastern and northern Taiwan. Molecular and phylogenetic analyses based on the asexual stage small subunit ribosomal RNA (SSU rRNA) gene clearly identified these samples as a single infection with Plasmodium inui . Furthermore, phylogenetic analysis of the MSP-1(42) gene showed that the 7 field isolates were closely related to P. inui strains Taiwan I and II, which were obtained from Formosan macaques in 1963. These findings indicate that P. inui is the only cause of simian malaria in Taiwan, has been circulating in Formosan macaques at least for 46 yr, and has a geographic preference for southern Taiwan.
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