A low-cost mesocosm for the study of behaviour and reproductive potential in Afrotropical mosquito (Diptera: Culicidae) vectors of malaria.

A large-scale mesocosm was constructed and tested for its effectiveness for use in experiments on behaviour, reproduction and adult survivorship in the Afrotropical malaria vector Anopheles gambiae s.s. Giles (Diptera: Culicidae) in temperate climates. The large space (82.69 m(3) ) allowed for semi-natural experiments that increased demand on a mosquito's energetic reserves in an environment of widely distributed resources. A one-piece prefabricated enclosure, made with white netting and vinyl, prevented the ingress of predators and the egress of mosquitoes. Daylight and white materials prompted the mosquitoes to seclude themselves in restricted daytime resting sites and allowed the easy collection of dead bodies so that daily mortality could be assessed accurately using a method that accounts for the loss of a proportion of bodies. Here, daily, age-dependent mortality rates of males and females were estimated using Bayesian Markov chain Monte Carlo simulation. In overnight experiments, mosquitoes successfully located plants and took sugar meals. A 3-week survival trial with a single cohort demonstrated successful mating, blood feeding, oviposition and long life. The relatively low cost of the mesocosm and the performance of the mosquitoes in it make it a viable option for any behavioural or ecological study of tropical mosquitoes in which space and seasonal cold are constraining factors.

Prevalence of geohelminths in savana and forest areas of Côte d'Ivoire.

BACKGROUND: Côte d'Ivoire has large regional variation in intestinal helminth prevalence. STUDY DESIGN: In a large cross-sectional study conducted from 1997 to 1999, stool samples from 6952 children aged 4-15 years were examined for helminth eggs by the Kato/ Katz technique from 24 villages in the savanna (North) and from 21 villages in the forest (West) in Côte d'Ivoire. RESULTS AND CONCLUSION: Ascariasis lumbricoides (0.7%) was the only species present in the savana area. In the forest area, ascariasis occurred most frequently (18.9%), followed by trichuriasis (2%), Strongyloidiasis (0.1%) and oxyuriasis (0.03%). Ascariasis prevalence was not significantly associated with age within each ecological zone, but was significantly higher in boys in the forest zone. This study confirms that in the more arid savanna, the conditions are less suitable for helminth transmission than in the forest zone.

Rice irrigation and schistosomiasis in savannah and forest areas of Côte d'Ivoire.

Prevalence and intensity of infection of Schistosoma haematobium and Schistosoma mansoni were studied in relation to irrigated rice cultivation in Côte d'Ivoire. Urine and stool samples were collected from 4 to 15-year-old children in 24 villages in the savannah zone and 21 villages in the forest zone. Villages were classified according to surrounding inland valleys into three agro-ecosystems: (R2) full or partial water control allowing two rice cycles per year; (R1) no or partial water control allowing one harvest per year and (R0) absence of rice growing. In the savannah zone, S. haematobium prevalence was 4.8%, 2.3% and 0.7% and S. mansoni prevalence was 16.1%, 11.9% and 2.1% in R2, R1 and R0, respectively. In the forest zone, S. haematobium prevalence was 0.9%, 4.4% and 1.7% and S. mansoni prevalence was 61.3%, 46.6% and 17.5% in R2, in R1 and R0, respectively. Prevalences of S. mansoni adjusted for village effects were significantly different between agro-ecosystems in both zones. Significance of differences between agro-ecosystems of S. haematobium infection were strongly influenced by outlying villages. In savannah rice growing villages, negative binomial regression on infection intensity of each species showed significant positive relations to the surface of rice cultivated inland valleys, whereas uncultivated inland valleys showed no significant relation. However, in forest rice growing villages, S. mansoni infection intensity showed significant positive relations to the surface of uncultivated inland valleys, whereas surface water on rice cultivated land showed significant negative relations with infection intensity of each schistosomiasis species.

A simple method for calculating mosquito mortality rates, correcting for seasonal variations in recruitment.

A simple age-structured exponential growth model is presented for the analysis of the population dynamics of mosquitoes (Diptera: Culicidae). In this model, the proportion of parous mosquitoes R depends on the birth rate beta, and the length of the first gonotrophic cycle g, but not on the mortality rate. If the age structure is fairly constant, R = exp(- betag). Extensions of the model correcting for feeding patterns are given. A simple method is applied to an example of Anopheles gambiae Giles biting density and parity ratio in Cjte d'Ivoire (fortnightly sampled longitudinal data set), for calculation of the seasonally fluctuating mortality rate, correcting for effects of recruitment. The seasonal variations in birth rate and mortality rate are discussed in relation to variations in density and rainfall.