Abstract
BackgroundAnopheles gambiae, An. arabiensis, and An. funestus are widespread malaria vectors in Africa. Anopheles rivulorum is the next most widespread species in the An. funestus group. The role of An. rivulorum as a malaria vector has not been fully studied, although it has been found to be a minor or opportunistic transmitter of Plasmodium falciparum.MethodsMosquitoes were collected indoors over a 12-hour period using a light source attached to a rotating bottle collector in order to determine peak activity times and to provide DNA for meal source identification. Gravid female mosquitoes were collected indoors via an aspirator to generate F1 progeny for testing insecticidal susceptibility. Blood meal sources were identified using a multiplexed PCR assay for human and bovine cytochrome-B, and by matching sequences generated with primers targeting vertebrate and mammalian cytochrome-B segments to the Genbank database.ResultsAnopheles rivulorum fed on human blood in the early evening between 18:00 and 20:00, when insecticide-treated bed nets are not in use, and the presence of Plasmodium falciparum sporozoites in 0.70% of the An. rivulorum individuals tested was demonstrated. Susceptibility to permethrin, deltamethrin, and DDT is higher in An. rivulorum (84.8%, 91.4%, and 100%, respectively) than in An. funestus s.s. (36.8%, 36.4%, and 70%, respectively), whereas mortality rates for propoxur and fenitrothion were 100% for both species. Resistance to pyrethroids was very high in An. funestus s.s. and the potential of the development of high resistance was suspected in An. rivulorum.ConclusionGiven the tendency for An. rivulorum to be active early in the evening, the presence of P. falciparum in the species, and the potential for the development of pyrethroid resistance, we strongly advocate reconsideration of the latent ability of this species as an epidemiologically important malaria vector.
Highlights
Anopheles gambiae, An. arabiensis, and An. funestus are widespread malaria vectors in Africa
This study reports the vectorial and behavioral characteristics and the insecticide susceptibility of An. rivulorum in western Kenya, and strongly recommends a reevaluation of this species as a minor vector of P. falciparum
The Mbita and Suba districts are 2 focal points identified as high vector transmission areas in Kenya, and more than 50% of the population is exposed to malaria at a rate of ≥40% PfPR2-10 (Pf parasite rate corrected to a standard agerange of 2 to less than 10 years old) [19]
Summary
An. arabiensis, and An. funestus are widespread malaria vectors in Africa. Anopheles gambiae Giles, An. arabiensis Patton, and An. funestus Giles are widespread malaria vectors in Africa. Both An. gambiae s.s. and An. funestus s.s. are highly anthropophilic [1,2], while An. arabiensis prefers to feed on humans but will feed on other hosts as well [3]. Previous studies have demonstrated that An. rivulorum has the potential to replace other major malarial vectors such as An. funestus s.s. after spraying of indoor insecticides eliminates the more abundant species [11]. The increase in the use of ITNs in Kenya has led to an increase in insecticide resistance [14,15,16] and in the replacement of vector species [17]
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