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.
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.


CONCLUSIONS
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.
Department of Vector Ecology & Environment, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan. vergiss@nagasaki-u.ac.jp
Hitoshi
H
Kawada
Gabriel O
GO
Dida
George
G
Sonye
Sammy M
SM
Njenga
Charles
C
Mwandawiro
Noboru
N
Minakawa
D000818:Animals; D000852:Anopheles / Q000469:parasitology*; D001769:Blood; D002417:Cattle; D002675:Child, Preschool; D016172:DNA Fingerprinting; D004199:Disease Vectors; D005247:Feeding Behavior; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007305:Insecticide Resistance; D007630:Kenya; D016778:Malaria, Falciparum / Q000635:transmission*; D010963:Plasmodium falciparum / Q000302:isolation & purification*; D011722:Pyrethrins / Q000494:pharmacology*
D011722:Pyrethrins