Malaria vector surveillance in the endemic areas in South Africa over a five-year period: a retrospective study

Malaria in South Africa is seasonal and primarily occurs in the endemic provinces of Limpopo, Mpumalanga and KwaZulu-Natal. Malaria transmission depends on the occurrence of mosquito vector populations and thus malaria control relies heavily on the implementation of vector control interventions. Vector surveillance is essential for optimal vector control, and, as the country moves towards malaria elimination, enhanced vector surveillance is necessary to obtain comprehensive information on those primary and potential vectors that are responsible in varying degrees for ongoing residual transmission.

This retrospective study collated Anopheles mosquito collections from sentinel sites in the three endemic provinces from 01 March 2017 to 28 February 2022. Field-collected specimens were identified to species by morphology and polymerase chain reaction assays.

A total of 32,955 Anopheles mosquitoes were collected and identified from sentinel sites in the KwaZulu-Natal (n=25,359; 77.0%), Limpopo (14.5%) and Mpumalanga (8.6%) provinces. Of the collected Anopheles specimens, 73.7% (n= 24,304) were identified as members of vector species/populations in South Africa, i.e., Anopheles arabiensis (58.8%), An. parensis (6.7%), An. vaneedeni (2.2%), and An. merus (6.1%). Furthermore, the collections included species implicated as vectors in other countries (11.9%). Anopheles arabiensis (major vector) was the predominant species collected through all seasons in KwaZulu-Natal and in autumn in Mpumalanga. Anopheles pretoriensis and An. rufipes (potential vectors) were the most abundant species in spring and summer in Limpopo. In Mpumalanga, An. merus (potential vector) predominated the collection in winter, spring and summer.

The occurrence of major and potential vector species in all malaria-endemic districts under vector surveillance shows that these regions remain receptive to malaria transmission, but to varying degrees and at different times/seasons. This supports ongoing implementation of vector control strategies in each endemic province. We recommend ongoing vector surveillance and the collection of insecticide susceptibility data for vector populations in endemic districts.