Survival and infection probabilities of anthropophagic anophelines from an area of high prevalence of Plasmodium falciparum in humans

Abstract

Delayed and immediate oocyst rates; parous rates and sporozoite rates were obtained in Anopheles gambiae Giles, A. arabiensis Patten and A. funestus Giles from two villages in the Kilombero Valley, southern Tanzania during the wet season of 1991. Collection methods included light trap, indoor resting collection and nets with holes cut in their side. Mosquito survival estimates from parous rates obtained from light trap collections, were compared with estimates from capture-recapture experiments and from that obtained during a population decline. Methods of estimating the proportion of feeds infectious to mosquitoes, K, were also compared. This proportion varied between villages and species and was highest in the village with the greatest proportion of A. gambiae. We propose that absolute estimates of K should be obtained by determining the immediate oocyst rate and measuring the parous rate using the same host seeking mosquitoes. This estimate was only available from one village and ranged from 1.9% for A. gambiae s.l. to 3.4% for A.funestus.

Dry season refugia of malaria-transmitting mosquitoes in a dry savannah zone of east Africa.

“…gambiae to An. arabiensis increases with distance from the river 9,10 (and Lyimo EO, unpublished data). As the rains continue An.…”

“…7,8 As the rains continue An. gambiae may become the predominant member of the complex inside houses 9 or in breeding sites. 10 The relative proportion of An.…”

“…funestus becomes the dominant mosquito, particularly in outlying areas where rice is grown. 9,11,12 After the rains a cool dry season (July and August) is followed by a hot dry season that can last for several months, especially if the short rains do not arrive. At the end of the rains vector densities decline, the An.funestus population doing so more slowly than either An.…”

Understanding the link between malaria risk and climate

“…During the EIP, malaria parasites go through various developmental stages and very many replication cycles before migrating to the salivary glands where they can be transmitted to humans. The speed of this development depends on host, parasite and environmental factors, but estimates are on the order of 10-14 days in areas of high malaria transmission (7,8). In those same areas, 90% of the female mosquitoes die within 12 days (7) and are therefore unlikely to contribute to malaria transmission.…”

Rapid assessment of malaria risk using entomological techniques: taking an epidemiological snapshot

“…Oocysts on the dissected midgut of unfed and gravid females can be observed through a compound microscope or, with care, a good dissecting microscope. The proportion of parous mosquitoes with oocysts provides an indication of the proportion of feeds infective to mosquitoes (the infectious reservoir) (Haji et al 1996;Charlwood et al 1997;Graves et al 1988;Muirhead-Thomson 1954). Sporozoite identification by microscopy is labour-intensive, and does not identify Plasmodium species, although this is not a problem where only one parasite species is present, and ELISA or PCR on stored mosquitoes requires time and cost investment.…”