Academic journal article Bulletin of the World Health Organization

Insecticide Resistance in Anopheles Sacharovi Favre in Southern Turkey

Academic journal article Bulletin of the World Health Organization

Insecticide Resistance in Anopheles Sacharovi Favre in Southern Turkey

Article excerpt

Voit page 691 le resume en francais. En la pagina 692 figura un resumen en espanol.

Introduction

Malaria is endemic in southern Anatolia. The number of cases has increased in recent years, particularly in south-east Anatolia where the GAP (Southeast Anatolia Project) irrigation and development project is about to be completed. Under the project, irrigation began three years ago, and the area covered by it is increasing annually.

The principal vector of the malaria parasite in Turkey is Anopheles sacharovi Favre; A. superpictus Grassi is also a vector (1, 2). The population densities of both species are highest in malarious areas but even here the distribution of A. superpictus is rather localized. This species occurs in small populations with lower densities in midsummer and is still susceptible to many insecticides.

In Turkey, A. sacharovi has been subjected to continuous field selection pressure by many insecticides that have been used for both agricultural and public health purposes since the introduction of DDT (clofenotane) in 1952. Residuals were introduced throughout the country for malaria control in the following sequence: DDT, [Gamma]-hexanechlorocyclo-hexane ([Gamma]-HCH), dieldrin, malathion, pirimiphos-methyl, bendiocarb. DDT and [Gamma]-HCH were used during the 1950s and 1960s but resistance developed to them in A. sacharovi in 1959 (3). Dieldrin resistance was detected in A. sacharovi in 1970, and malathion (an organophosphorus insecticide) then replaced the organochlorines (4-6). Resistance to malathion was first recorded in 1974 (5), and cross-resistance developed to a wide range of organophosphorus and carbamate insecticides, even though they had never been used for house spraying (7, 8). The use of malathion was discontinued in 1984 because A. sacharovi developed resistance to malathion and because householders objected to its unpleasant odour and the stains it left on walls (9). Pirimiphos-methyl replaced malathion in 1984 and was used successfully until 1990 when it was replaced by bendiocarb. A. sacharovi was still susceptible to p'nimiphos-methyl in 1992 (10) and was still so even in 1996 (11). In recent years, pirimiphos-methyl, bendiocarb and various residual pyrethroids have been used by the malaria control authorities.

Hemingway et al. (12) reported that DDT resistance in A. sacharovi was being scattered in the population in 1984 despite the replacement of DDT by malathion for malaria control 13 years previously. They also reported that populations of this species in Cukurova had an altered acetylcholinesterase resistance mechanism, conferring broad-spectrum resistance against organophosphates and carbamates. Specimens of A. sacharovi collected in the field in 1989-90 were still resistant to DDT, organophosphates and carbamates, although at lower frequencies than in 1984 (11, 13).

The present study compares baseline data on susceptibility under WHO test conditions with results obtained on field samples, in order to evaluate current trends in insecticide resistance in southern Turkey.

Materials and methods

Study sites

The study was carried out in five malarial areas in southern Turkey, which varied in insecticide usage, geographical features, social infrastructure, agricultural development and tourism characteristics -- factors that might have had a bearing on the emergence of insecticide resistance.

* Adana is situated in the centre of the Cukurova Plain on the Mediterranean coast, where malaria has long been endemic. Samples of A. sacharovi were collected in Karatas-Tuzla, which had a high population density of mosquitos.

* Antalya is located 560 km west of Adana. Orchards and irrigated cotton crops are common in this, area. Few cases of malaria occur and there is intensive vector control, conducted by private bodies and the National Malaria Service. Most of the specimens of A. sacharovi were obtained in the village of Kucuk Belkis, which was not sprayed before collecting was carried out. …

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