Long-term evolution of Plasmodium falciparum gametocytes index during a village scale malaria vector control program comparing durable lining, long-lasting treated net and indoor residual spraying in Angola

Abstract

Rationale: Due to the serious side effect of some anti-gametocyte drugs on G6PG efficiency carriers, a special attention was given to the possible influence of vector control on the evolution of P. falciparum gametocyte index (GI) in the framework of the long-term village scale malaria vector control project implemented in 8 villages around the Balombo town (Angola). The aim of the project was to compare, in paired villages, the epidemiological efficacy of Long lasting deltamethrin Insecticide Treated Nets (δLLIN), lambdacyhalothrin Inside Residual Spraying (ʎIRS), and deltamethrin Insecticide Treated Plastic Sheeting (δITPS) applied on the indoor walls of houses, used alone, or associated with δLLIN or after the 2 rounds of λIRS. Methods: The program started in 2007 and full vector control (VC) implementation was done in December 2008 owing two years of baseline data collection in the 8 selected villages around Balombo city. Parasitological evaluation was based upon regular cross-sectional surveys (CSS) on randomized samples of population for each survey, focusing ≤ 15 years children, to compare GI before/after and here/there according to each VC method. Field made thick blood smears (TBS) were microscopically examined by the same team of the Medical Department of the Angolese Sonamet Company, which supported the trial, with 10% of randomized slides double-checked in OCEAC, Yaoundé (Cameroon). Results: 234 cross-sectional surveys were carried between 2007 and 2018. P. falciparum gametocytes were observed in 574 of the 23,822 thick blood smears examined for a GI of 2.41%. During the 3 years following the VC full implementation, the GI decreased by 71%, from 4.05% (n= 6,697) before VC to 1.17% (n= 7,667 after VC) with similar influence of each VC method. During the 5 following years GI remained at a very low level (0.23%; n=2,992). Due to the national malaria outbreak, an increase was noticed after 2015. The general CSS survey done in February 2018, 11 years after the first one (February 2007), showed in the same 5 villages a significant 80% decrease of GI, from 6.98% (n=773) to 1.42% (n=421). Conclusion: The trial showed that a long-term malaria village scale vector control program had a long lasting and significant impact on P. falciparum gametocytes and the influence of VC on GI could therefore be recommended as another relevant objective of the National Malaria Control Program.