Advances in the study of Anopheles funestus, a major vector of malaria in Africa

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Abstract

The recent literature on cytogenetic and molecular studies of Anopheles funestus, a major vector of malaria in Africa, is reviewed. Molecular data from West and Central Africa suggest a new species in the group closely allied to Anopheles rivulorum. Cytogenetic and molecular studies of populations from West, Central, East and southern Africa indicate considerable genetic structuring within An. funestus itself, which may well restrict the spread of pyrethroid resistance that has been demonstrated in southern Africa.

Introduction

Anopheles funestus is one of the two major vectors of malaria parasites in Africa, in some cases far outstripping An. gambiae in its ability to transmit Plasmodium falciparum (Gillies and De Meillon, 1968). In many places, An. funestus is the major vector responsible for malaria transmission and sometimes for malaria epidemics (Fontenille et al., 1990, Hargreaves et al., 2003). Parasite rates of 22% (De Meillon, 1933) and 27% (Swellengrebel et al., 1931) have been recorded in South Africa and more recently 11% in Tanzania (Shiff et al., 1995). In West Africa, rates of 2.6% and 3.3% have been observed in Senegal (Dia et al., 2003, Fontenille et al., 1997), between 2.8% and 14.6% in Burkina Faso (Costantini et al., 1999) and around 5% in Cameroon (Antonio-Nkondjio et al., 2002). In Burkina Faso, Costantini et al. (1999) recorded up to 50% of An. funestus in one village in November 1991 (n=56) positive for P. falciparum circumsporozoite protein.

Despite its obvious importance as a vector, An. funestus has been sadly neglected for almost half a century, with most of the research focusing on members of the An. gambiae complex. Undoubtedly, this has been due to the adaptability of the An. gambiae complex to laboratory conditions and the ease with which species in the group can be colonized. In the last five years, however, molecular and cytogenetic studies on An. funestus and its allied species have become more prevalent in the literature. This paper reviews the progress to date and discusses the implications of the research findings.

Section snippets

The Anopheles funestus group

An. funestus belongs to a group of nine species that are morphologically very similar in the adult stage. Four species, An. funestus, An. vaneedeni, An. parensis and An. aruni, have identical morphology at all life stages and are known as the Funestus sub-group (Gillies and De Meillon, 1968, Gillies and Coetzee, 1987). Of the other species in the group, An. leesoni is the most distinct at both egg and larval stage, while An. confusus is easily identified on larval characteristics. Anopheles

Cytogenetic studies

Following Green and Hunt (1980), there were no further publications on the cytogenetics of An. funestus for 12 years, until Boccolini et al. (1994) and then Costantini et al. (1999) documented chromosomal and bionomic heterogeneities within An. funestus populations in Burkina Faso. Cytogenetic studies conducted in several African countries and in Madagascar have shown the presence of at least 11 paracentric chromosomal inversions on chromosomes II and III (Green and Hunt, 1980, Boccolini et

Conclusions

The information being generated by the renewed interest in the An. funestus group indicates that this group may be as complex and problematic as the An. gambiae group. The existence of a species complex within An. funestus s.s. will not be surprising considering that almost every anopheline taxon studied so far has exhibited this phenomenon (e.g. An. maculipennis, Swellengrebel and De Buck, 1938; An. punctulatus, Bryan, 1970; An. pharoensis, Miles et al.,1983; An. pseudopunctipennis, Coetzee et

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