Establishing the extent of malaria transmission and challenges facing pre-elimination in the Republic of Djibouti

Abstract

BackgroundCountries aiming for malaria elimination require a detailed understanding of the current intensity of malaria transmission within their national borders. National household sample surveys are now being used to define infection prevalence but these are less efficient in areas of exceptionally low endemicity. Here we present the results of a national malaria indicator survey in the Republic of Djibouti, the first in sub-Saharan Africa to combine parasitological and serological markers of malaria, to evaluate the extent of transmission in the country and explore the potential for elimination.MethodsA national cross-sectional household survey was undertaken from December 2008 to January 2009. A finger prick blood sample was taken from randomly selected participants of all ages to examine for parasitaemia using rapid diagnostic tests (RDTs) and confirmed using Polymerase Chain Reaction (PCR). Blood spots were also collected on filter paper and subsequently used to evaluate the presence of serological markers (combined AMA-1 and MSP-119) of Plasmodium falciparum exposure. Multivariate regression analysis was used to determine the risk factors for P. falciparum infection and/or exposure. The Getis-Ord G-statistic was used to assess spatial heterogeneity of combined infections and serological markers.ResultsA total of 7151 individuals were tested using RDTs of which only 42 (0.5%) were positive for P. falciparum infections and confirmed by PCR. Filter paper blood spots were collected for 5605 individuals. Of these 4769 showed concordant optical density results and were retained in subsequent analysis. Overall P. falciparum sero-prevalence was 9.9% (517/4769) for all ages; 6.9% (46/649) in children under the age of five years; and 14.2% (76/510) in the oldest age group (≥ 50 years). The combined infection and/or antibody prevalence was 10.5% (550/4769) and varied from 8.1% to 14.1% but overall regional differences were not statistically significant (χ2 = 33.98, p = 0.3144). Increasing age (p < 0.001) and decreasing household wealth status (p < 0.001) were significantly associated with increasing combined P. falciparum infection and/or antibody prevalence. Significant P. falciparum hot spots were observed in Dikhil region.ConclusionMalaria transmission in the Republic of Djibouti is very low across all regions with evidence of micro-epidemiological heterogeneity and limited recent transmission. It would seem that the Republic of Djibouti has a biologically feasible set of pre-conditions for elimination, however, the operational feasibility and the potential risks to elimination posed by P. vivax and human population movement across the sub-region remain to be properly established.

Plasmodium vivax and Plasmodium falciparum infections in the Republic of Djibouti: evaluation of their prevalence and potential determinants

“…These observations are in agreement with parasite genetic diversity studies [10,11], and one recent work has reported a low transmission level [14]. …”

“…observed a P . falciparum seroprevalence rate of 14.2% in adults above 50 years, 6.9% in children and an average of 9.9% when they tested the reactivity of 4769 sera to one or both serological markers PfMSP1 and PfAMA1 among Djiboutian population [14]. The same method was applied to the present work and produced a seroprevalence rate of 30.0%.…”

“…P . falciparum merozoite surface protein 1–19 (MSP1 19 ) and apical membrane antigen 1 (AMA1) were obtained using procedures previously described [14]. For P .…”

Cross-Border Malaria: A Major Obstacle for Malaria Elimination

“…Testing for malaria at entry points in Mauritius was shown to provide benefits for investment, by maintaining elimination despite large cyclones in 1994 and 2002 that caused costly damage and an increase in the number of travellers arriving from malaria-endemic countries (Tatarsky et al, 2011;Aboobakar et al, 2012). Screening arriving passengers for malaria at the border points and obtaining a detailed travel history have been deployed to assess the impact of human population movement on malaria in Djibouti (Noor et al, 2011). Proactive prevention programmes to screen all prospective immigrants for malaria infection in their home countries, rather than point of entry, significantly reduced the numbers of imported infections in Kuwait (Iqbal et al, 2003).…”

Acquisition of Antibodies against Plasmodium falciparum Merozoites and Malaria Immunity in Young Children and the Influence of Age, Force of Infection, and Magnitude of Response

“…There is increasing interest in using antibodies specific for merozoite antigens as serological biomarkers of Plasmodium exposure or as biomarkers of immunity to help monitor changes in malaria transmission over time, to evaluate the impact of malaria control interventions, and to identify populations at high risk of developing symptomatic malaria to inform malaria control programs (33)(34)(35)(36)(37). However, to achieve this, a greater knowledge of antibody responses to malaria antigens and how they are acquired relative to exposure, age, and immunity is needed (38).…”