Moderate transmission but high prevalence of malaria in Madagascar

Vincent Robert (1, 2) , Gilbert Le Goff (1, 2) , Lala Andrianaivolambo (2) , Fara M. Randimby (2) , Olivier Domarle (2) , Milijaona Randrianarivelojosia (2) , Vaomalala Raharimanga (2) , Andrianirina Raveloson (3) , Charles Ravaonjanahary (3) , Frédéric Ariey (2)

1 IRD [ Madagascar] - Institut de Recherche pour le Développement
2 Unité de Recherche sur le Paludisme [Antananarivo, Madagascar]
3 Ministère de la Santé Publique - Ministry of Public Health [Antananarivo, Madagascar]

Malaria transmission remains poorly documented in areas of low transmission. A study has been carried out over two consecutive years in Analamiranga, a village located at an altitude of 885 m on the western edge of the Malagasy highlands, with the aim of generating and updating malariometric indexes for both mosquitoes and schoolchildren. In this village, no vector control measures were performed during the study period nor during previous decades. Mosquitoes were collected monthly when landing on human volunteers and in various resting-places. Blood samples were taken every 3 months from schoolchildren aged 6-12 years and microscopically examined. Of 7,480 mosquitoes collected on human subjects, 5,790 were anophelines. Ten anopheline species were represented and three of these, Anopheles funestus, Anopheles arabiensis and Anopheles mascarensis, accounted for 59.2% of the collection. Of these three species 4,640 were also collected in resting places. The proportion of mosquitoes fed on bovids was high; conversely, the anthropophilic rate (mosquitoes fed on human beings) was especially low: 31%, 7% and 1%, respectively, for A. funestus, A. arabiensis and A. mascarensis. The only confirmed malaria vector was A. funestus with a low sporozoite index (of 6,830 A. funestus, five were positive for Plasmodium falciparum and four for Plasmodium vivax). The annual entomological inoculation rate (number of bites of infected anophelines per adult person) was estimated at 2.49 with low variation over the 2 years. Overall, 909 thick blood smears were tested from blood samples taken from schoolchildren with 30.3% being malaria-positive. The four Plasmodium species infecting human subjects were detected in the following proportions: P. falciparum 78.9%, P. vivax 19.4%, Plasmodium malariae 1.0% and Plasmodium ovale 0.7%. The proportions of children who were infected with any Plasmodium ranged from 10.7% in February to 51.0% in September. Parasitemic children with fever (axillary temperature >37.5°C) accounted for 16.4% of the children sampled. This study demonstrates that there are substantial parasitological consequences of even a relatively low entomological transmission and also recommends including exterior resting-places of mosquitoes in future spraying campaigns in the highlands of Madagascar.

Mots clés: Malaria transmission; Plasmodium falciparum; Plasmodium vivax; Anopheles funestus; Anopheles arabiensis; Schoolchildren; Prevalence; Highlands

Domaines: Sciences du Vivant [q-bio]

Vincent Robert, Gilbert Le Goff, Lala Andrianaivolambo, Fara M. Randimby, Olivier Domarle, et al.. Moderate transmission but high prevalence of malaria in Madagascar. International Journal for Parasitology, 2006, 36 (12), pp.1273-1281. ⟨10.1016/j.ijpara.2006.06.005⟩. ⟨hal-03359149⟩