Relationship between the intensity of exposure to malaria parasites and infection in the Usambara mountains, Tanzania

The relationship between exposure to Plasmodium falciparum malaria and parasite density and prevalence was studied in six communities along an altitude transect. Prevalence of parasitemia in children decreased by 5% for every 100 meter increase in altitude from 82% in the lowlands at 300 meters to 12% in the highlands at 1,700 meters. This decrease in prevalence corresponded to a 1,000-fold reduction in transmission intensity. The ability to suppress parasite density and prevalence with age increased proportionally with increasing transmission intensity when transmission rates were higher than 0.1 infective bites per year, but developed after 2–3 years of age, regardless of transmission intensity. However, at transmission rates less than 0.1 infective bites per year, prevalence remained similar in all age groups. We propose that both exposure-dependent acquired immunity and age-dependent acquired immunity regulate parasite prevalence and density and suggest that transmission control will not hinder the development of protective anti-parasite immunity

Exploratory Study of Malaria Situation in Hanang and Babati Districts after Reported Malaria Epidemic: IV: Assessment of Malaria Parasitaemia, Anaemia and Sulfadoxine/Pyrimethamine (sp) and Chloroquine Efficacy

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Exploratory study of Malaria situation in Hanang and Babati districts after reported Malaria epidemic: Health facility based information on Malaria morbidity and mortality

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Effect of topography on the risk of malaria infection in the Usambara Mountains, Tanzania

We investigated whether the risk of infection with malaria parasites was related to topography in the Usambara Mountains, Tanzania. Clinical surveys were carried out in seven villages, situated at altitudes from 300 m to 1650 m. Each village was mapped and incorporated into a Digital Terrain Model. Univariate analysis showed that the risk of splenomegaly declined with increasing altitude and with decreasing potential for water to accumulate. Logistic regression showed that altitude alone could correctly predict 73% of households where an occupant had an enlarged spleen or not. The inclusion of land where water is likely to accumulate within 400 m of each household increased the accuracy of the overall model slightly to 76%, but significantly improved predictions between 1000 m and 1200 m, where malaria is unstable, and likely to be epidemic. This novel approach illustrates how topography could help identify local areas prone to epidemics in the African highlands

Relationship between altitude and intensity of malaria transmission in the Usambara Mountains, Tanzania

There is a consensus that malaria is a growing problem in African highlands. This is g because many parts of the highlands were considered too cold to support transmission. In this report, we examined how transmission of Plasmodium falciparum in six villages changed along an altitude transect in the Usambara Mountains, Tanzania, from 300 m to 1700 m. Routine entomological collections were made using spray catches and light traps for 15 mo. Direct estimates of entomological inoculation rates and indirect estimates of vectorial capacity suggested a >1000-fold reduction in transmission intensity between the holoendemic lowland and the hypoendemic highland plateau. Lowland transmission was perennial with a significant peak in the cool season after the long rains in May, when vectors densities were high. In the highlands, low temperatures prevented parasite development in mosquitoes during the cool season rains, and highland transmission was therefore limited to the warm dry season when vector densities were low. The primary effect of increasing altitude was a log-linear reduction in vector abundance and, to a lesser extent, a reduction in the proportion of infective mosquitoes. Highland malaria transmission was maintained at extraordinarily low vector densities. We discuss herein the implications of these findings for modeling malaria and suggest that process-based models of malaria transmission risk should be improved by considering the direct effect of temperature on vector densities. Our findings suggest that variation in the short rains in November and changes in agricultural practices are likely to be important generators of epidemics in the Usambaras

Exploratory Study of Malaria Situation in Hanang and Babati Districts after Reported Malaria Epidemic: II. Community Perception and Treatment Seeking and Prevention for Malaria

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Prevalence of glucose-6-phosphate dehydrogenase deficiency and haemoglobin S in high and moderate malaria transmission areas of Muheza, north-eastern Tanzania

Glucose-6-phosphate dehydrogenase (G6PD) deficiency and haemoglobin S (HbS) are very common genetic disorders in sub Saharan Africa, where malaria is endemic. These genetic disorders have been associated with protection against malaria and are therefore under strong selection pressure by the disease. In November-December 2003, we conducted a cross-sectional survey to determine the prevalence of G6PD deficiency and HbS in the population and relate these to malaria infection and haemoglobin levels in lowland and highland areas of differing malaria transmission patterns of Muheza, Tanzania. Blood samples from 1959 individuals aged 6 months to 45 years were collected. A total of 415 (21%) and 1181 (60%) samples were analysed for G6PD deficiency and HbS, respectively. Malarial parasite prevalence was 17.2% (114/1959) in the highlands and 39.6% (49/1959) in the lowlands. Lowlands had higher prevalence of G6PD deficiency and HbS than highlands (G6PD deficiency = 11.32% (24/212) versus 4.43% (9/203), P = 0.01, and HbS = 16.04% (98/611) versus 6.32% (36/570), P = 0.0001). Logistic regression model showed an association between G6PD deficiency and altitude [lowlands] (Odds ratio [OR] 3.4, 95% CI=1.49; 7.90, P=0.004). In the lowlands, G6PD deficient individuals had lower mean haemoglobin (10.9g/dl) than normal ones (12.8g/dl), P = 0.01. These findings show that high malaria transmission in the lowlands might have selected for G6PD deficiency and HbS

Exploratory Study of Malaria Situation in Hanang and Babati Districts after Reported Malaria Epidemic: III. Socio-Economic Factors

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Malaria specific mortality in lowlands and highlands of Muheza district, north-eastern Tanzania

Vital registration of causes of death in Tanzania is incomplete and many deaths occur outside health care settings. Verbal autopsies (VA) are used to determine the underlying cause of death, and the probable diagnosis helps to estimate reasonably cause-specific mortality. In this paper, we report findings of a verbal autopsy survey which involved eight villages in both low and highlands of Muheza district, north-eastern Tanzania. The survey was conducted following a rapid census, which was done to identify households that had lost one or more members within a period of two years from the date of census. Trained research assistants administered VA questionnaires to parents/close relatives. Two physicians reviewed each report independently and a third opinion was sought where there was discordant report between the two. A total of 9,872 households were surveyed and 134 deaths were recorded. A total of 96 (71.6%) deaths were from lowland villages representing high malaria transmission. Majority (72.4%) of the reported deaths occurred at home whilst 32.1% occurred at heath facility settings. Overall, severe malaria was the leading cause accounting for 34.3% of all deaths. Infants were most affected and accounted for 43.5% of the total deaths. Pulmonary tuberculosis ranked second (8.2%) cause of deaths and was exclusively confined to individuals ≥15 years. Probable cause of death could not be determined in 13.4% of deaths. In conclusion, majority of deaths in rural north-eastern Tanzania occur at home and the immediate causes are usually unknown or not documented. These findings indicate that the verbal autopsy is a useful tool for detecting leading causes of death at community level in the absence of health facility-based data

Malaria specific mortality in lowlands and highlands of Muheza district, north-eastern Tanzania

Vital registration of causes of death in Tanzania is incomplete and many deaths occur outside health care settings. Verbal autopsies (VA) are used to determine the underlying cause of death, and the probable diagnosis helps to estimate reasonably cause-specific mortality. In this paper, we report findings of a verbal autopsy survey which involved eight villages in both low and highlands of Muheza district, north-eastern Tanzania. The survey was conducted following a rapid census, which was done to identify households that had lost one or more members within a period of two years from the date of census. Trained research assistants administered VA questionnaires to parents/close relatives. Two physicians reviewed each report independently and a third opinion was sought where there was discordant report between the two. A total of 9,872 households were surveyed and 134 deaths were recorded. A total of 96 (71.6%) deaths were from lowland villages representing high malaria transmission. Majority (72.4%) of the reported deaths occurred at home whilst 32.1% occurred at heath facility settings. Overall, severe malaria was the leading cause accounting for 34.3% of all deaths. Infants were most affected and accounted for 43.5% of the total deaths. Pulmonary tuberculosis ranked second (8.2%) cause of deaths and was exclusively confined to individuals ≥15 years. Probable cause of death could not be determined in 13.4% of deaths. In conclusion, majority of deaths in rural north-eastern Tanzania occur at home and the immediate causes are usually unknown or not documented. These findings indicate that the verbal autopsy is a useful tool for detecting leading causes of death at community level in the absence of health facility-based data