Pierre Carnevale

Author    Correspondence author
Journal of Mosquito Research, 2026, Vol. 16, No.   
Received: 01 Jan., 1970    Accepted: 01 Jan., 1970    Published: 06 May, 2026

Objectives At the request, and with the National Malaria Control Program of Angola (NMCPA), a comprehensive program was planned, and implemented, in villages around Balombo town (Benguela Province) with two objectives: to compare, in natural conditions, the efficacy of four methods of vector control; and to check for any parasitological rebound effect several years after vector control. Patients and Methods Four vector control methods were implemented: long-lasting deltamethrin treated nets (LLIN), PermaNet®2.0 (P2) alone; P2 combined with deltamethrin insecticide-treated plastic sheeting (ITPS) model ZeroFly®; ITPS model ZeroVector® alone, and two rounds of lambdacyhalothrin indoor residual spraying (IRS) followed by ITPS installation. Each method was implemented in one village. Several analyses of short-term entomological, parasitological, and immunological impact had already been published. The long-term, eleven years, parasitological evaluation was performed in these four villages, and was based upon regular cross-sectional surveys on random samples of volunteer’s asymptomatic children ≤15-year-old. Thick blood films were made in the field, and examined by optical microscope in the medical department of the Angolese Sonamet® Company in Lobito which implemented, and supported, its Malaria Control Program (MCP) in Benguela Province. The Balombo program was a part of this MCP. Three parasitological indicators were analyzed: Plasmodium parasite prevalence, parasite load and gametocyte index. Results From the year 2007 to the year 2018, 136 parasitological cross-sectional surveys were performed. 12,525 thick blood films (TBF) were prepared. Plasmodium were observed in 2,392 TBF, i.e., a parasite prevalence of 19.1%, and gametocytes in 247 blood films, i.e., a gametocyte rate of 1.97%. Parasite prevalence (PP) for the two years before vector control (years 2007-2008) (PP=39.4%; n=4,302) and the nine years after (years 2009-2018) (PP=8.5%; n=8,223) showed a significant 78.4% decrease. This decrease was similar with all four methods: -77.8% with treated nets alone; -76.9% with the combination nets + ITPS ZeroFly®; -80.8% with ITPS ZeroVector® alone; and -76.8% with indoor spraying followed by ITPS installation. After vector control there was observed an evolution of the parasite prevalence in three successive steps: first an important drop of 61% the first year following vector control and another 64% the following year. Then, over several years, occurred a plateau, which remained at a low parasite prevalence level (< 5%) until the 2015 national malaria outbreak, which induced an increase of the parasite prevalence. But, even during this time, the parasite prevalence (PP=17.8%; n=991) was still significantly lower than before vector control. The impact of the national malaria outbreak was also clearly observed on the parasite load which increased significantly. The gametocyte index, and the parasite load, had the same “three steps” evolution as parasite prevalence after vector control. The several years of low plasmodial infections were a crucial epidemiological indication. No rebound effect of parasite prevalence was noticed ten years after vector control. Conclusion The four methods of vector control similarly reduced Plasmodium prevalence, gametocyte index, and parasite load. Ten years after vector control, the parasite prevalence was still lower than before vector control despite the national malaria outbreak and no rebound was noticed. During the malaria outbreak it was observed a significant increase of the parasite load which could be matter of concern. Actual community participation, observed during ITPS installation inside their homes, was a crucial point for the sustainability, and therefore efficacy, of this vector control method. Therefore, ITPS alone, or in combination with treated-nets, could be recommended, as an additional complementary, tool in the arsenal of the National Malaria Control Program of Angola, and other countries.