In malaria endemic regions, a certain percentage of the population will harbour parasites in their blood without succumbing to symptoms. These asymptomatic malaria parasite carriers do not seek anti-malarial treatment, and so infections are likely to persist for long periods. This is detrimental for two reasons; firstly, these individuals constitute a reservoir for the transmission of parasites within a population, and secondly, there may be underlying health risks to the individual associated with long term parasite carriage.
In order to gauge the level of asymptomatic carriage amongst adolescents in a highly endemic area, and to identify the risk factors associated with such carriage, we conducted a cross sectional survey of 1032 adolescents from eight schools located in Akinyele and Ibadan North Local Government Areas, a collection of semi-urban densely populated and urban communities, respectively, in the southwest of Nigeria. Blood film and filter paper samples were prepared for microscopic examination for DNA extraction, respectively. The prevalence of asymptomatic malaria was determined using microscopy, rapid diagnostic test (RDT) and PCR.
A total of 530 asymptomatic and 101 symptomatic malaria positive samples were parasite-species typed. Of the asymptomatic infections, 330 (62%) had mixed infections, comprising of 187 (35%), P. falciparum with P. malariae; 34 (6%) P. falciparum with P. ovale; and 109 (21%) P. falciparum with P. malariae and P. ovale. The unusually high prevalence of P. malariae and P. ovale in these asymptomatic infections prompted us to ask whether a similar prevalence of these species would be observed in symptomatic malaria cases. We found that symptomatic infections from the same region and of the same population demographic were predominantly (90%) single infections of P. falciparum, suggesting a link between malaria parasite species co-infection and the development of malaria symptoms.