Co-Evolution of the Presence of Long Lasting Insecticide Treated Nets and Plasmodium falciparum Welch, 1897 Prevalence in Cahata Village (Benguela Province, Angola) during a Village Scale Long-Term of Malaria Vector Control Program

A long term village scale vector control programme was implemented since 2007 in 8 villages around Balombo town (Benguela Province) to compare the efficacy of 4 methods of vector control (1,2). One of them are deltamethrin treated Long Lasting Nets (“LLIN”) “Perma©Net 2.0” with a complete coverage of every sleeping units in 2008 in 2 villages, Caala and Cahata. Cahata was surveyed for 10 years with regular parasitological cross sectional parasitological surveys. During the 3 years following LLIN implementation, a check of their actual usage in every house, or on sleeping units of each patient examined during every parasitological surveys showed that 3 years after the full LLIN distribution less than 50% were still in use, and this percentage regularly decreased to reach 10% and less in 2015 (with 0% during the survey done in October 2005). But Plasmodium falciparum prevalence still decreased with low level until 2014 then it started (slightly) increasing in 2015, and the following years, which correspond to both the National malaria outbreak and the least percentage of LLIN used! But even at that time the plasmodial load was significantly lower in “LLIN users” than in non users showing some maintained personal protection.

Even 10 years after the full coverage in LLIN no rebound effect was actually noticed in such natural conditions of life and plasmodial prevalence was even 2 times lower than before the implementation of vector control.

Information gained were of great importance for the National Malaria Control program in term of nets replacement with 50% missing in 3 years underlining the need of “stronger” nets and community sensitization for the sustainability of positive results gained with LLIN.