Malaria in urban and rural Kinshasa: the entomological input

Mosquitoes were collected on human bait over a 16-month period (September 1988 to December 1989) in an urban and a rural area of Kinshasa, Zaïre. P. falciparum malaria sporozoite rates were determined by ELISA. In the urban area Culex quinquefasciatus accounts for 96% of the 121 bites/person/night (b/p/n). The only anopheline is Anopheles gambiae, sensu stricto, with an average of 5.1 b/p/n and a sporozoite rate of 1.86%. The entomological inoculation rate (EIR) averages 0.08 infective b/p/n. Malaria transmission is almost interrupted at the end of the dry season. In the rural area mosquito nuisance is small (20 b/p/n), almost entirely due to six species of Anopheles including four vectors of malaria: An.gambiae (13.3 b/p/n), An.funestus (2.4 b/p/n), An.nili (0.4 b/p/n) and An.brunnipes (0.7 b/p/n) with mean sporozoite rates of 7.85%, 6.60%, 6.63% and 0.53% respectively. An.paludis (0.4 b/p/n) and An.hancocki (0.2 b/p/n) were not found infective. Malaria transmission is intense and perennial: the overall EIR varies monthly between 0.60 and 3.29 infective b/p/n. The specific contributions of An.gambiae, An.funestus and An.nili average 1.07, 0.14 and 0.03 infective b/p/n respectively. Malaria transmission peaks during the rainy season in both study areas. The daily mean survival rates for An.gambiae were 0.91 and 0.78 in the rural and urban area, respectively. All An.gambiae examined belonged to the forest cytotype (Coluzzi et al., 1979). Through its effect on the sporozoite rate, the higher vector survival rate in the rural environment appears to be the major determinant of the greater malaria transmission rate in the rural area as compared to urban Kinshasa.