How do mosquito species and resistance trends impact malaria transmission?
Malaria is a life-threatening disease caused by parasites transmitted to humans through the bites of infected Anopheles mosquitoes. In South Africa, malaria transmission is seasonal and occurs mainly in the Limpopo, Mpumalanga, and KwaZulu-Natal provinces.
Symptoms can range from fever, chills, and headaches to severe illness with seizures, respiratory distress, and in some cases, death. Young children, pregnant women, travelers, and people with weakened immune systems are most at risk of serious outcomes.
Vector control is the cornerstone of malaria prevention in South Africa, relying primarily on indoor residual spraying and limited larval source management. However, residual transmission persists due to outdoor-feeding mosquitoes and insecticide resistance, especially in certain Anopheles species. These challenges highlight the importance of continuous vector surveillance to track mosquito populations and inform control strategies.
The following report presents malaria vector surveillance findings from January to December 2023 in South Africa’s three endemic provinces, based on specimens referred to the Vector Control Reference Laboratory (VCRL) of the Centre for Emerging Zoonotic and Parasitic Diseases (CEZPD), NICD, as well as specimens collected and analysed by the UP Institute for Sustainable Malaria Control (UP ISMC).
Materials and Methods
Anopheles mosquitoes and larvae were collected at selected sentinel sites in KwaZulu-Natal, Mpumalanga, and Limpopo from January to December 2023, either on a weekly or monthly basis. These specimens were either collected by VCRL and UP ISMC personnel or were referred to the VCRL by partner institutions and provincial malaria control programme entomology teams.
Adult Anopheles mosquitoes were collected via CO2-baited tent traps, cattle-baited tent traps, human landing catches, CDC and Encephalitis Vector Survey (EVS) traps, cattle-kraal collections, pit traps, pyrethrum spray collections, outdoor-placed clay pots, modified plastic buckets and discarded tyres.
Results
In total, 9 206 Anopheles mosquitoes (larvae and adults) were collected from the uMkhanyakude, King Cetshwayo, and Zululand districts of KwaZulu-Natal, the Ehlanzeni District of Mpumalanga, and the Vhembe and Mopani districts of Limpopo.
Most of the specimens were collected from Limpopo (67%, n=6 172), followed by KwaZulu-Natal (27%, n=2 525) and Mpumalanga (6%, n=509). These were subsequently clustered as either An. gambiae complex (37%, n=3 408), An. funestus group (12%, n=1 137), or other (miscellaneous) Anopheles species (51%, n=4 661). Anopheles pretoriensis predominated the collections (25%, n=2 263), especially in Limpopo, while An. arabiensis (16%, n=1 504) and An. merus (8%, n=732) predominated the collections from KwaZulu-Natal and Mpumalanga, respectively.
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