Continuing intense malaria transmission in northern Uganda

Abstract

Recent reports of reductions in malaria transmission in several African countries have resulted in optimism that malaria can be eliminated in parts of Africa where it is currently endemic. It is not known whether these trends are global or whether they are also present in areas where political instability has hindered effective malaria control. We determined malaria parasite carriage and age-dependent antibody responses to Plasmodium falciparum antigens in cross-sectional surveys in Apac, northern Uganda that was affected by political unrest. Under-five parasite prevalence was 55.8% (115/206) by microscopy and 71.9% (41/57) by polymerase chain reaction. Plasmodium ovale alone, or as a co-infection, was detected in 8.6% (12/139) and Plasmodium malariae in 4.3% (6/139) of the infections. Age seroprevalence curves gave no indication of recent changes in malaria transmission intensity. Malaria control remains a tremendous challenge in areas that have not benefited from large-scale interventions, illustrated here by the district of Apac.

Figure 1.

Plasmodium falciparum parasite carriage by microscopy and polymerase chain reaction (PCR). The prevalence of P. falciparum infection by microscopy (dashed bars) and PCR (black bars) is given for individuals < 2 years (microscopy, N = 87/PCR, N = 24), 2–4 years (N = 122/N = 34), 5–9 years (N = 111/N = 33), 10–14 years (N = 108/N = 28), 15–24 years (N = 155/N = 61), 25–34 years (N = 124/N = 29), and ≥ 35 years (N = 144/N = 32). Error bars indicate the upper limit of the 95% confidence interval around the proportion. The dotted line indicates the proportion of infections that is below the microscopic threshold for detection.

Figure 2.

The occurrence of fever for different parasite densities in children < 10 years of age. The prevalence of fever (temperature ≥ 37.5°C) is given for children < 10 years of age with no parasites (N = 172), with < 400 parasites/μL (N = 50), 400–1,500 parasites/μL (N = 46), 1,500–5,000 parasites/μL, 5,000–15,000 parasites/μL (N = 39), 15,000–80,000 parasites/μL (N = 35), and ≥ 80,000 parasites/μL (N = 35). Error bars indicate the upper and lower limits of the 95% confidence interval around the proportion.

Figure 3.

Age-seroprevalence plots for circumsporozoite protein (CSP), merozoite surface protein-1₁₉, and apical membrane antigen-1. Dots indicate the observed antibody prevalence for different age groups, the solid line the best fit based on age as a continuous variable, the dotted line the upper and lower limit of the 95% confidence interval (CI). The serocoversion rate λ was estimated at 0.025 (95% CI = 0.019–0.033) for CSP, 0.056 (95% CI = 0.044–0.072) for MSP-1₁₉, and 0.260 (95% CI = 0.208–0.326) for AMA 1.