Bionomics of Anopheles Mosquitoes in Ehlanzeni District Municipality, Mpumalanga

Abstract

Malaria, vectored by Anopheles mosquitos, remains a persistent public health threat in South Africa, where it is endemic in the provinces of Limpopo, Mpumalanga, and KwaZulu-Natal. Efforts to eliminate malaria are hindered by the presence of residual transmission. This study aimed to characterise selected aspects of An. gambiae complex vector bionomics in the Ehlanzeni district. Surveillance data collected from 2009 to 2021 in the Ehlanzeni district was analysed to understand vector bionomics in the province better. The dominant vector species recorded in the province was Anopheles merus, followed An. arabiensis. There was no significant correlation between vector abundance and climate at a broad scale (across 13 years). However, significant correlations may exist on a smaller scale (on a year-by-year basis). Further exploration of the data revealed important information regarding annual and seasonal population dynamics, and the efficacy of various collection methods. This study further aimed to characterise the chemical and bacterial composition of Anopheles gambiae complex larval habitats in Mpumalanga, as well as examining their effects on the gut microbiota of wild An. gambiae complex from the region. In addition, standardised bioassays were performed on adults originating from larvae from two sentinel sites at Vlakbult and Block A in the Ehlanzeni district to determine their insecticide resistance profiles. The adults emerging from larvae collected from Vlakbult and Block A were fully susceptible to both DDT and deltamethrin. Diversity of the bacterial samples from larval breeding sites were affected by the source. Larvae were found to harbour microbes potentially involved in insecticide degradation. The water samples were remarkably high in heavy metal pollution, but a range of pollutants were present. This study also aimed to investigate the potential of four common agricultural pollutants to cause hormetic effects in an insecticide-unselected (SENN) and insecticide-selected (SENN DDT) laboratory strain of An. arabiensis under controlled conditions. The results show that there is a possibility that common agri-pollutants, particularly chloride, may induce hormetic responses in An. arabiensis when reared under laboratory conditions. This may have implications for An. gambiae s.l. vector populations in the field. Finally, this study aimed to investigate the effects of sub-lethal exposure of a common larviciding agent, temephos, on the gut microbiota composition and adult longevity of an insecticide-unselected (SENN) and insecticide-selected (SENN DDT) laboratory strain of An. arabiensis. Treatment affected the abundance of bacteria associated with both pesticide degradation and Plasmodium protection. Furthermore, sub-lethal exposure viii to temephos significantly shortened adult longevity in a strain specific manner. This study has shown that the fine-tuning of surveillance activities may be necessary to shift Mpumalanga from a control framework to an elimination framework. Chronic exposure to pollutants in breeding habitats may have implications for the development of insecticide resistance and alteration of key life-history traits of An. gambiae s.l. in Ehlanzeni. Insecticide resistance is a major barrier to malaria elimination programs. Surveillance activities should be tailored to a per-region basis and include monitoring of the effects of pollution on insecticide resistance, life-history traits, gut microbiota and vector competence. Understanding and accounting for these factors in control programs will assist in achieving South Africa’s goal of eliminating malaria by 202