Population structure of Aedes albopictus from La Réunion Island (Indian Ocean) with respect to susceptibility to a dengue virus.

Ten F1 Aedes albopictus samples collected from Réunion Island in the Indian Ocean were tested for oral susceptibility to dengue 2 virus and 20 were analysed for genetic polymorphism by starch gel electrophoresis. Data from infection rates defined two distinct geographical areas: east coast vs. west coast. Genetic differentiation was found to be dependent on ecological factors and the biological characteristics of Ae. albopictus. These results have implications for the vector ecology and pattern of migration, and have importance in the understanding of dengue transmission.

[Chromosomal polymorphism of populations of Anopheles arabiensis (Diptera: Culicidae) from Reunion island and cross-fertility among continental African populations]. / Polymorphisme chromosomique des populations d'Anopheles arabiensis (Diptera: Culicidae) de l'île de La Réunion et inter-fertilité avec des populations d'Afrique continentale.

Cytological examination of a sample of Anopheles gambiae complex mosquitoes from Reunion island revealed the presence of An. arabiensis only. Chromosomal polymorphisms were observed only for inversion 3Ra, the standard homozygote form being predominant. Cross-mating experiments with laboratory specimens originating from continental Africa produced viable and fertile offspring with no chromosomal asynapsis observed in the F1 female progeny. There was no evidence for speciation of the Reunion island populations. The results are discussed with regard to the behaviour of the vector and its influence on the vectorial capacity of this species, and the history of malaria and malaria control in the South-West islands of the Indian Ocean and on Reunion island in particular.

[Evaluation of the vectorial capacity of Anopheles arabiensis (Diptera:Culicidae) on the island of Réunion: an approach to the health risk of malaria importation in an area of eradication]. / Evaluation de la capacité vectorielle d'Anopheles arabiensis (Diptera: Culicidae) à l'île de La Réunion: une approche du risque sanitaire lié au paludisme d'importation en zone d'éradication.

Following intensive control measures, malaria was eradicated from La Réunion Island (Indian Ocean) in 1979. However, potential vectors remain in coastal areas and, each year Public Health Services detect some imported cases from surrounding countries. Anopheles arabiensis is the only species which can be responsible for local transmission though its brief life cycle and its exophilic and zoophilic behaviour were found to be key elements in maintaining the eradication status of the disease on the island. Its vectorial capacity was measured at different seasons and in different areas with a view to assessing the health risks due to imported malaria and suggesting a more pertinent strategy of vector control.

[Control of malaria re-emergence in Reunion]. / Lutte contre la réintroduction du paludisme à la Réunion.

Réunion is currently posed with the operational problem of the last phase of the struggle against malaria, that is the consolidation and the maintenance of the state of cradication. The native parasite was eliminated, but the risk of resurgence of malaria remains on the island. This risk is even increasing from year to year because of the following: 1) the regular increase of the number of travellers originating from countries with malaria and consequently, the increase in the number of imported malaria cases; 2) the appearance of malaria strains resistant to amino-4-quinoleines, in the south-western regions of the Indian Ocean; 3) the persistence of the vector which cannot be eliminated because of its rapid evolutionary cycle and the multiplicity of its larval habitats. Furthermore, the reintroduction of malaria on the island would present serious consequences considering the disappearance of immunity in the population of Réunion. Thus it is necessary to maintain the struggle at a high level of intervention following a strategy based on: 1) the detection and the control of the malaria cases; 2) a targeted anti-vectorial activity based on a systematic anti-larval fight, eventually completed by the eradication of the adapted adult vectors. The reduction of personnel and the difficulties encountered in establishing a mechanization of the adapted tasks lead to a reduction of activities of insect eradication and endanger the existing strategy of the struggle. This strategy has been redefined during these last several years. The malaria situation in Réunion, satisfactory until today, rests on a careful epidemiological surveillance and on an optimized entomological surveillance. Currently, the treatments are abandoned in the least sensitive zones to the benefit of a better surveillance of priority zones (prospecting, entomological studies and treatments). Anopheles gambiae s.l. is present on the island and each year some parasites are imported to the Réunion territory. The requisite conditions for an eventual re-emergence of transmission of the native parasite would seem to be combined. However, this transmission is not observed. The role of the Applied Entomology Group is to evaluate the risk of malaria and to reorient, if necessary, the strategy of the antimalaria struggle in Réunion.

[Aedes albopictus and Aedes aegypti at Ile de la Réunion]. / Aedes albopictus et Aedes aegypti à l'Ile de la Réunion.

Aedes albopictus and Aedes aegypti are both found on the island. The former, being the probable vector of dengue on the island, is highly anthropophilic. It breeds in domestic environments as well as in natural breeding sites. The latter has a more restricted distribution and is never anthropophilic. Larvae of Ae. aegypti are only found in natural habitats, always associated with Ae. albopictus, but in small proportions. Such an ecology and behaviour for the typicus form of Ae. aegypti are abnormal. Several hypothetic explanations are proposed. Dengue prevention should be based solely on Ae. albopictus control.