Current and cumulative malaria infections in a setting embarking on elimination: Amhara, Ethiopia

Abstract

Background: Since 2005, Ethiopia has aggressively scaled up malaria prevention and case management. As a result, the number of malaria cases and deaths has significantly declined. In order to track progress towards the elimination of malaria in Amhara Region, coverage of malaria control tools and current malaria transmission need to be documented.

Methods: A cross-sectional household survey oversampling children under 5 years of age was conducted during the dry season in 2013. A bivalent rapid diagnostic test (RDT) detecting both Plasmodium falciparum and Plasmodium vivax and serology assays using merozoite antigens from both these species were used to assess the prevalence of malaria infections and exposure to malaria parasites in 16 woredas (districts) in Amhara Region.

Results: 7878 participants were included, with a mean age of 16.8 years (range 0.5-102.8 years) and 42.0% being children under 5 years of age. The age-adjusted RDT-positivity for P. falciparum and P. vivax infection was 1.5 and 0.4%, respectively, of which 0.05% presented as co-infections. Overall age-adjusted seroprevalence was 30.0% for P. falciparum, 21.8% for P. vivax, and seroprevalence for any malaria species was 39.4%. The prevalence of RDT-positive infections varied by woreda, ranging from 0.0 to 8.3% and by altitude with rates of 3.2, 0.7, and 0.4% at under 2000, 2000-2500, and >2500 m, respectively. Serological analysis showed heterogeneity in transmission intensity by area and altitude and evidence for a change in the force of infection in the mid-2000s.

Conclusions: Current and historic malaria transmission across Amhara Region show substantial variation by age and altitude with some settings showing very low or near-zero transmission. Plasmodium vivax infections appear to be lower but relatively more stable across geography and altitude, while P. falciparum is the dominant infection in the higher transmission, low-altitude areas. Age-dependent seroprevalence analyses indicates a drop in transmission occurred in the mid-2000s, coinciding with malaria control scale-up efforts. As malaria parasitaemia rates get very low with elimination efforts, serological evaluation may help track progress to elimination.

Keywords: Malaria; Malaria transmission; Plasmodium falciparum; Plasmodium vivax; Seroconversion; Seroprevalence.

Fig. 1

a Amhara Region, Ethiopia, b survey areas (woredas) selected for the Malaria Elimination, colour-coded light to dark from lowest to highest for altitude, c Plasmodium falciparum RDT prevalence, d Plasmodium vivax RDT prevalence, e Plasmodium falciparum seroprevalence, and f Plasmodium vivax seroprevalence

Fig. 2

Plasmodium falciparum and P. vivax RDT-positivity and seroprevalence by woreda. The woredas are arranged from highest to lowest altitude

Fig. 3

Plasmodium falciparum and P. vivax RDT-positivity and seroprevalence by a altitude and b age group

Fig. 4

Plasmodium falciparum and P. vivax RDT-positivity and seroprevalence by altitude and age group

Fig. 5

Age-seroconversion plots for antibody responses to Plasmodium falciparum antigens (left) and P. vivax antigens (right). Triangles represent deciles of observed data, solid lines represent the fit to the data of a reverse catalytic conversion model and broken blue lines provide the 95% confidence interval for this fit