Email updates

Keep up to date with the latest news and content from Parasites & Vectors and BioMed Central.

Open Access Highly Accessed Research

Reconsideration of Anopheles rivulorum as a vector of Plasmodium falciparum in western Kenya: some evidence from biting time, blood preference, sporozoite positive rate, and pyrethroid resistance

Hitoshi Kawada1*, Gabriel O Dida23, George Sonye3, Sammy M Njenga4, Charles Mwandawiro5 and Noboru Minakawa16

Author Affiliations

1 Department of Vector Ecology & Environment, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan

2 School of Public Health, Maseno University, Kisumu, Kenya

3 Springs of Hope, Mbita, Kenya

4 Eastern and Southern Africa Centre of International Parasite Control, Nairobi, Kenya

5 Kenya Medical Research Institute, Nairobi, Kenya

6 The Global Center of Excellence Program, Nagasaki University, Nagasaki, Japan

For all author emails, please log on.

Parasites & Vectors 2012, 5:230  doi:10.1186/1756-3305-5-230

Published: 10 October 2012

Abstract

Background

Anopheles 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.

Methods

Mosquitoes 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.

Results

Anopheles 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.

Conclusion

Given 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.

Keywords:
Permethrin; Deltamethrin; Resistance; Anopheles rivulorum; Anopheles funestus; Plasmodium falciparum; Kenya