Effect of physicochemical parameters on Anopheles and Culex mosquito larvae abundance in different breeding sites in a rural setting of Muheza, Tanzania

Translated abstract

Background

Malaria and lymphatic filariasis (LF) are diseases of great public health important in East Africa. Malaria is transmitted by Anopheles while LF is transmitted by both Anopheles and Culex mosquitoes. There is limited evidence on the effects of physicochemical parameters on these mosquitoes in rural settings of Tanzania. This study aimed at assessing the effects of physicochemical parameters on Anopheles and Culex larvae abundance in different breeding sites in a rural setting of Muheza district .

Methods

A cross-sectional study was conducted in 13 villages in Muheza district, between December 2015 and May 2016. Mosquito larvae were sampled using standard dipping techniques. Physicochemical parameters were measured by a Multi-parameter pH meter in different mosquito breeding sites. Mosquito larvae and pupa densities were compared between the ≤33th (lower) and ≥67th (upper) percentiles of physicochemical parameters. An. gambiae ( s.l.) and An. funestus were identified by polymerase chain reaction (PCR) to reveal their sibling species.

Results

Abundance of Anopheles larvae was significantly higher (76.6%) than Culex (66.9%) χ ² = 5.73, df = 1, P = 0.017). The presence of late instars of Anopheles was significantly higher (78.2%) than that of Culex (64.5%) ( χ ² = 0.984, df = 1, P = 0.017). A model adjusted for larval stage showed that the likelihood of finding Culex larvae was lower by 38.2% (95% CI: 16.9–54.1, df = 1, P = 0.001) compared to Anopheles. Upper percentiles of salinity (OR = 7.05; 95% CI: 1.19–41.88, P = 0.032) and conductivity (OR = 5.47; 95% CI: 1.01–29.67, P = 0.056) were significantly associated with the presence and with increased density of Anopheles larvae. PCR results showed that, within the gambiae complex, 53.3% ( n = 136) were An. gambiae ( s.s.) and 46.7% ( n = 119) were An. arabiensis. In An. funestus group, 91.1% ( n = 41) were An. funestus ( s.s.) , 4.4% ( n = 2) were An. rivulorum, 2.2% ( n = 1) were An. leesoni and 2.2% ( n = 1) were An. parensis.

Conclusion

High salinity and conductivity were significantly associated with increased density of Anopheles larvae. To our knowledge, this is the first study to demonstrate the occurrence of Anopheles larvae in polluted breeding sites in rural settings of Tanzania. The study has found both Anopheles and Culex mosquito larvae co-existed in breeding sites. The possible reasons for tolerance to a higher level of physicochemical parameters among Anopheles mosquitoes need to be ascertained.