Abstract
ObjectivesTo study the manifestations of Plasmodium infection, and its relations with the malaria disease, especially when comparing dry and rainy seasons in a hyperendemic area of West Africa.MethodsThe study was carried out in an area where malaria transmission is high, showing important seasonal variations. One thousand children, representing the total child population (1–12 year old), were observed transversally at the end of three consecutive seasons (dry/rainy/dry). The usual indicators, such as parasite density, splenomegaly, anaemia, or febrile disease were recorded and analysed.ResultsThe prevalence of Plasmodium falciparum was high in all age groups and seasons, constantly around 60%. The high transmission season (rainy) showed higher rates of anaemia and spleen enlargement and, in the youngest children only, higher parasite densities. There were also differences between the two dry seasons: in the first one, there was a higher rate of fever than in the second one (p < 0.001). Low parasite density (<2,000 p/μl) was never associated with fever during any season, raising some concern with regard to the usefulness of parasite detection. The possible origins of fever are discussed, together with the potential usefulness of analyzing these indices on a population sample, at a time when fever incidence rises and malaria is one potential cause among others. The distinction to be made between the Plasmodium infection and the malaria disease is highlighted.ConclusionsThese data confirm previous hypotheses of a strong difference in malaria infection and disease between dry and rainy seasons. The most relevant seasonal indicator was not mainly parasite rate and density but anaemia, spleen enlargement, prevalence and possible origin of fever.RecommendationsIn any situation (i.e. fever or not) and especially during the dry season, one must consider that detection of parasites in the blood is only evidence of a Plasmodium infection and not necessarily of a malaria disease. In such a situation, it seems suitable to obtain, through national malaria teams, a well-defined situation of transmission and prevalence of Plasmodium infection following zones and seasons, in order to adapt control strategies. For researchers, a systematic management of data separately for dry and rainy season appears mandatory.
Highlights
In regions where malaria is highly prevalent, malariarelated morbidity and mortality are high and mainly affect subjects whose immunity is considered to be low, mostly young children and pregnant women, especially during their first pregnancy [1,2]
Recommendations: In any situation and especially during the dry season, one must consider that detection of parasites in the blood is only evidence of a Plasmodium infection and not necessarily of a malaria disease
The prevalence of P. falciparum was high in all age groups and seasons, constantly around 60%
Summary
In regions where malaria is highly prevalent, malariarelated morbidity and mortality are high and mainly affect subjects whose immunity is considered to be low, mostly young children (clinical signs going from simple febrile episodes to severe malaria with its complications) and pregnant women, especially during their first pregnancy [1,2]. Many factors may affect the pathophysiology of malaria: transmission intensity, prevalence of Plasmodium infection in the population, prevalence of other diseases, genetic background, age, season, or nutrition [3,4]. Where parasites are widespread (i.e. moderate to high endemicity), its usefulness as the “gold standard” for the diagnosis of the malaria disease is questionable. A previous work estimated that above a prevalence of 20% in the general population, the detection of parasites in the blood becomes useless for confirming that a febrile patient suffers from malaria [5]. In high transmission areas, the specificity of either technique is low to determine a malaria disease because the prevalence of Plasmodium infection is high [7]
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