A progressive declining in the burden of malaria in north-eastern Tanzania

Abstract

Background: The planning and assessment of malaria interventions is complicated due to fluctuations in the burden of malaria over time. Recently, it has been reported that the burden of malaria in some parts of Africa has declined. However, community-based longitudinal data are sparse and the reasons for the apparent decline are not well understood.

Methods: Malaria prevalence and morbidity have been monitored in two villages in north-eastern Tanzania; a lowland village and a highland village from 2003 to 2008. Trained village health workers treated presumptive malaria with the Tanzanian first-line anti-malarial drug and collected blood smears that were examined later. The prevalence of malaria parasitaemia across years was monitored through cross-sectional surveys.

Results: The prevalence of malaria parasitaemia in the lowland village decreased from 78.4% in 2003 to 13.0% in 2008, whereas in the highland village, the prevalence of parasitaemia dropped from 24.7% to 3.1% in the same period. Similarly, the incidence of febrile malaria episodes in the two villages dropped by almost 85% during the same period and there was a marked reduction in the number of young children who suffered from anaemia in the lowland village.

Conclusion: There has been a marked decline in malaria in the study villages during the past few years. This decline is likely to be due to a combination of factors that include improved access to malaria treatment provided by the trained village helpers, protection from mosquitoes by increased availability of insecticide-impregnated bed nets and a reduced vector density. If this decline in malaria morbidity is sustained, it will have a marked effect on the disease burden in this part of Tanzania.

Figure 1

Proportion of Plasmodium falciparum parasitaemia and reported use of insecticide treated or non-treated nets obtained during cross-sectional surveys. Filled circles connected with solid lines for the proportion of Plasmodium falciparum and filled circles with dotted lines for proportion of reported use of insecticide treated or non-treated nets. Panel A for lowland village and Panel B for highland village.

Figure 2

Odds ratio of Plasmodium falciparum parasite adjusted for age, bed nets use and season of survey from 2003-2008, with 2003 as a baseline. Filled and open bars are for lowland and highland villages, respectively.

Figure 3

Age-specific point prevalence of Plasmodium falciparum and 95% CI (line segments) obtained during cross-sectional surveys between 2003 and 2008 in lowland village (panel A) and highland village (panel B). Symbol representing the year of the survey, open circles (2003), open squares (2004), open triangles (2005), open diamond (2006), filled circles (2007) and filled triangles (2008).

Figure 4

The incidence of febrile malaria episodes among residents of lowland village (filled circles and triangles) and highland village (filled squares and diamonds) between 2003 and 2008. Full lines represent children < 5 years, while dashed lines are individuals aged ≥ 5 years.

Figure 5

Age-specific mean haemoglobin concentration (g/dl) measured during cross-sectional surveys between 2003 and 2008 in lowland (A) and highland (B) villages, respectively. Graduated grey colour shows year of survey and line segments represent 95% CI.