Effects of indoor residual spraying and outdoor larval control on Anopheles coluzzii from São Tomé and Príncipe, two islands with pre-eliminated malaria

Abstract

BackgroundVector control is a key component of malaria prevention. Two major vector control strategies have been implemented in São Tomé and Príncipe (STP), indoor residual spraying (IRS) and outdoor larval control using Bacillus thuringiensis israelensis (Bti). This study evaluated post-intervention effects of control strategies on vector population density, composition, and knockdown resistance mutation, and their implications for malaria epidemiology in STP.MethodsMosquitoes were collected by indoor and outdoor human landing catches and mosquito light traps in seven districts. Mosquito density was calculated by numbers of captured adult mosquitoes/house/working hour. Mitochondrial cytochrome c oxidase subunit I (COI) was PCR amplified and sequenced to understand the spatial–temporal population composition of malaria vector in STP. Knockdown resistance L1014F mutation was detected using allele-specific PCR. To estimate the malaria transmission risks in STP, a negative binomial regression model was constructed. The response variable was monthly incidence, and the explanatory variables were area, rainfall, entomological inoculation rate (EIR), and kdr mutation frequency.ResultsMalaria vector in STP is exophilic Anopheles coluzzii with significant population differentiation between Príncipe and São Tomé (mean FST = 0.16, p < 0.001). Both vector genetic diversity and knockdown resistance mutation were relatively low in Príncipe (mean of kdr frequency = 15.82%) compared to São Tomé (mean of kdr frequency = 44.77%). Annual malaria incidence rate in STP had been rapidly controlled from 37 to 2.1% by three rounds of country-wide IRS from 2004 to 2007. Long-term application of Bti since 2007 kept the mosquito density under 10 mosquitoes/house/hr/month, and malaria incidence rate under 5% after 2008, except for a rising that occurred in 2012 (incidence rate = 6.9%). Risk factors of area (São Tomé compared to Príncipe), rainfall, outdoor EIR, and kdr mutation frequency could significantly increase malaria incidence by 9.33–11.50, 1.25, 1.07, and 1.06 fold, respectively.ConclusionsIndoor residual spraying could rapidly decrease Anopheles density and malaria incidence in STP. Outdoor larval control using Bti is a sustainable approach for controlling local vector with exophilic feature and insecticide resistance problem. Vector control interventions should be intensified especially at the north-eastern part of São Tomé to minimize impacts of outbreaks.

Dynamic changes in genetic diversity, drug resistance mutations, and treatment outcomes of falciparum malaria from the low-transmission to the pre-elimination phase on the isolated islands of São Tomé and Príncipe

“…In contrast, isolated islands have less complicated human mobility and vectorial-parasitological systems, which are positive for malaria elimination. Some of the most remarkable successes have been reported from African island nations, such as the Comoros in East Africa [5], Cape Verde in West Africa [6], and our study site, São Tomé and Príncipe (STP) in Central Africa [7][8][9]. The success of malaria pre-elimination on these islands were majorly due to effective vector control, improved case treatment, and surveillance [5][6][7][8].…”

Long-lasting microbial larvicides for controlling insecticide resistant and outdoor transmitting vectors: a cost-effective supplement for malaria interventions

“…So far, LLML has only been evaluated in Kenya, although the conventional formulation of the same microbial larvicides has been tested/used and cost has been evaluated in other African [ 22 – 29 , 35 – 40 , 46 ] as well as Asian countries [ 49 – 52 ]. The results have been shown to be promising across different ecological settings, which is especially relevant in low transmission areas that are targeting the goal of malaria elimination [ 53 ].…”

Investigation of Ctenocephalides felis on domestic dogs and Rickettsia felis infection in the Democratic Republic of Sao Tome and Principe

“…A campaign against malaria implementing integrated vector management was initiated by the joint efforts of the local authorities and the Taiwan Anti-malaria Advisory Mission since 2003. As a result, incidence of malaria has greatly decreased after a series of interventions, leading to a slide positivity rate less than 5%, which has satisfied the criteria of pre-elimination stage, on Principe Island (Chen et al, 2019;Lee et al, 2010;Tseng et al, 2008). To further improve the wellness of the people and reduce fever cases, attempts have been made on identifying vector-borne and zoonotic pathogens other than Plasmodium circulating in the region in recent years.…”