Vector species composition and malaria infectivity rates in Mkuzi, Muheza District, north-eastern Tanzania.

Entomological surveys were conducted in Mkuzi village in Muheza District, north-east Tanzania from April to September 2003. The objectives were to determine the species composition and infectivity rates of mosquitoes in Mkuzi village. Mosquito collection was done using CDC light trap and pyrethrum spray catch (PSC) techniques. The light trap: spray catch ratio was 2.2:1. A total of 2157 mosquitoes were collected (light trap = 1483; PSC = 674). Anopheles gambiae s.s. accounted for 56.7% (N = 1224) of all mosquitoes collected. Other species were An. funestus complex (19.2%) and Culex quinquefasciatus (24.1%).The mosquito density per room was 74.15 and 33.7 for light trap and PSC techniques, respectively. A total of 1637 Anopheles mosquitoes were tested for circumsporozoite protein by Enzyme linked Immunosobent Assay (ELISA). The overall infectivity rate for circumsporozoite protein for P. falciparum in Anopheles mosquitoes was 21.14% (346/1637). Species-specific infectivity rates were 22.7% (278/1224) in An. gambiae s.s. and 24.0% (68/283) in An. funestus funestus, 0% (0/80) for An. rivulorum and 0% (0/50) for An. parensis. Blood meal analysis indicated that 92.3% of An. gambiae s.s, 88.9% of An. funestus s.s., 64.5% of An. rivulorum and 67.7% of An. parensis had taken blood meal from human hosts. In conclusion, malaria transmission in Mkuzi area of Muheza district is mainly by the highly anthropophagic An. gambiae s.s. and An. funestus s.s. More studies are needed to identify the seasonal variation of species composition and transmission dynamics in this village.

Association of transmission intensity and age with clinical manifestations and case fatality of severe Plasmodium falciparum malaria.

CONTEXT: There are concerns that malaria control measures such as use of insecticide-treated bed nets, by delaying acquisition of immunity, might result in an increase in the more severe manifestations of malaria. An understanding of the relationships among the level of exposure to Plasmodium falciparum, age, and severity of malaria can provide evidence of whether this is likely. OBJECTIVE: To describe the clinical manifestations and case fatality of severe P falciparum malaria at varying altitudes resulting in varying levels of transmission. DESIGN, SETTING, AND PATIENTS: A total of 1984 patients admitted for severe malaria to 10 hospitals serving populations living at levels of transmission varying from very low (altitude >1200 m) to very high (altitude <600 m) in a defined area of northeastern Tanzania, studied prospectively from February 2002 to February 2003. Data were analyzed in a logistic regression model and adjusted for potential clustering within hospitals. MAIN OUTCOME MEASURES: Specific syndromes of severe malaria; mortality. RESULTS: The median age of patients was 1 year in high transmission, 3 years in moderate transmission, and 5 years in low transmission areas. The odds of severe malarial anemia (hemoglobin <5 g/dL) peaked at 1 year of age at high transmission and at 2 years at moderate and low transmission intensities and then decreased with increasing age (P = .002). Odds were highest in infants (0-1 year: referent; 2-4 years: odds ratio [OR], 0.83; 95% confidence interval [CI], 0.72-0.96), 5 to <15 years: OR, 0.44; 95% CI, 0.27-0.72; > or =15 years: OR, 0.44; 95% CI, 0.27-0.73; P<.001) and high transmission intensity areas (altitude <600 m: referent; 600 m to 1200 m: OR, 0.55; 95% CI, 0.35-0.84; >1200 m: OR, 0.55; 95% CI, 0.26-1.15; P for trend = .03). The odds of cerebral malaria were significantly higher in low transmission intensity areas (altitude of residence <600 m: referent; 600 m to 1200 m: OR, 3.17; 95% CI, 1.32-7.60; >1200 m: OR, 3.76; 95% CI, 1.96-7.18; P for trend = .003) and with age 5 years and older (0-1 year: referent; 2-4 years: OR, 1.57; 95% CI, 0.82-2.99; 5 to <15 years: OR, 6.07; 95% CI, 2.98-12.38; > or =15 years: OR, 6.24; 95% CI, 3.47-11.21; P<.001). The overall case-fatality rate of 7% (139 deaths) was similar at high and moderate levels of transmission but increased to 13% in low transmission areas (P = .03), an increase explained by the increase in the proportion of cases with cerebral malaria. CONCLUSIONS: Age and level of exposure independently influence the clinical presentation of severe malaria. Our study suggests that an increase in the proportion of cases with more fatal manifestations of severe malaria is likely to occur only after transmission has been reduced to low levels where the overall incidence is likely to be low.

Estimating medium- and long-term trends in malaria transmission by using serological markers of malaria exposure.

The implementation and evaluation of malaria control programs would be greatly facilitated by new tools for the rapid assessment of malaria transmission intensity. Because acquisition and maintenance of antimalarial antibodies depend on exposure to malaria infection, such antibodies might be used as proxy measures of transmission intensity. We have compared the prevalence of IgG antibodies with three Plasmodium falciparum asexual stage antigens in individuals of all ages living at varying altitudes encompassing a range of transmission intensities from hyper- to hypoendemic in northeastern Tanzania, with alternative measures of transmission intensity. The prevalence of antibodies to merozoite surface protein-1(19) was significantly more closely correlated with altitude than either point-prevalence malaria parasitemia or single measures of hemoglobin concentration. Analysis of age-specific seroprevalence rates enabled differentiation of recent (seasonal) changes in transmission intensity from longer-term transmission trends and, using a mathematical model of the annual rate of seroconversion, estimation of the longevity of the antibody response. Thus, serological tools allow us to detect variations in malaria transmission over time. Such tools will be invaluable for monitoring trends in malaria endemicity and the effectiveness of malaria control programs.