| Summary: | <p>Abstract</p> <p>Background</p> <p>Characterizing the breeding site of <it>Anopheles sinensis </it>is of major importance for the transition from malaria control to elimination in China. However, little information is available especially regarding the characteristics and influencing factors of breeding sites of <it>An. sinensis </it>in Yongcheng City, a representative region of unstable malaria transmission in the Huang-Huai River region of central China. The aims of this study were to determine the breeding site characteristics of <it>An. sinensis </it>and related environmental and physicochemical parameters, to find out which breeding site characteristics could best explain the presence of <it>An. sinensis </it>larvae, and to determine whether the breeding habit of <it>An. sinensis </it>has changed or not.</p> <p>Methods</p> <p>Random repeated cross sectional study was undertaken in six villages of the Yongcheng city characterized by different levels of the historical incidence of <it>P. vivax </it>malaria. The potential breeding sites of <it>An. sinensis </it>larvae in each village were examined twice per month both in the household courtyards and the village surroundings. The larval sampling was done by the standard dipping method. Some important breeding site characterizations were recorded and characterized. The anopheline mosquito larvae and emerged adults were identified to the species level morphologically and to sub-species by the ribosomal DNA PCR technique. Chi-square analysis and logistic regression analysis were applied to determine the importance of factors for explaining the presence or absence of <it>An. sinensis </it>larvae.</p> <p>Results</p> <p>According to the ribosomal DNA PCR assay, all sampled anopheline mosquito larvae and emerged adults belonged to <it>An. sinensis</it>. Only 3 containers that were sampled from the household courtyards were found to contain <it>An. sinensis </it>larvae. There were no differences in the species composition of mosquito larvae among containers that contained water in the household courtyards (P > 0.05). <it>An. sinensis </it>larvae were shown to be present in a total of 60 breeding sites in the village surroundings, this included 8 (13.3%) river fringes, 26 (43.3%) ponds, 23 (38.3%) puddles, and 3 (5.0%) irrigation/drainage ditches. Logistic regression analysis revealed that the breeding site type, water depth, chemical oxygen demand (COD), ammonia nitrogen, and sulphate were found to be the key factors determining the presence of <it>An. sinensis </it>larvae. Approximately 94.9% of <it>An. sinensis </it>larvae inhabited relatively large and medium-sized water bodies, with depths between 0.5 m and 1.0 m (73.3%), COD lower than 2 mg/L (75%), ammonia nitrogen lower than 0.4 mg/L (86.7%), and sulphate lower than 150 mg/L (58.3%), respectively.</p> <p>Conclusion</p> <p>These results indicate that the majority of <it>An. sinensis </it>larval breeding sites were relatively large and medium-sized water bodies with depths between 0.5 m and 1.0 m, and containing low levels of COD, ammonia nitrogen, and sulphate, respectively. For effective <it>An. sinensis </it>larval control, the type of breeding site, water depth, COD, ammonia nitrogen, and sulphate should be given higher priority over other factors in areas where it is the primary vector.</p>
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