Al Serouri, Abdel Wahed Abdel Gabar; (1999) Impact of asymptomatic malaria parasitaemia on cognitive function and school achievement of schoolchildren in the Yemen Republic. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Asymptomatic malaria parasitaemia is highly prevalent among schoolchildren especially in hyperendemic and holoenedemic areas where up to 90% of schoolchildren are affected. We hypothesized that parasitaemia may have a direct but transient effect on cognition through cytokine production. The impact of asymptomatic parasitaemia on cognitive functions and school achievement was examined in two separate studies, with different designs, that were conducted in two hyperendemic areas in Yemen. We first conducted a randomized controlled trial of the effect of treatment of asymptomatic parasitaemia on cognitive functions of schoolchildren. Due to unforeseen rapid clearance of parasitaemia among the placebo group we abandoned the trial after half the children had been enrolled and ran a second study designed to be a natural trial. A group (n= 445) of asymptomatic parasitaemic boys and a group of non-parasitaemic boys (n=142) matched for grade and school were first compared on their performance on a battery of cognitive and school achievement tests. Two weeks later the parasitaemic children were re-screened and 150 children of those who remained parasitaemic were matched for grade and school with 150 children who were previously parasitaemic but no longer parasitaemic. These children were then retested and compared on their performance on the cognitive tests. The results showed a high prevalence of anaemia and malnutrition among school-children. The parasitaemic children were significantly more anaemic, had a higher prevalence of splenomegaly, were more likely to come from fathers who were illiterate and farmers. After controlling for age, socioeconomic background and nutritional status it was found that the parasitaemic children performed worse than the non-parasitaemic children in fine motor function tests, but not on the other cognitive tests. The parasitaemic children in the clinical trial also had worse performance only in these tests. The results from the natural experiment showed no difference in performance in cognitive tests between those who naturally cured and those who remained parasitaemic. However, children who initially had the highest parasite density improved the most in a fine motor tests and a picture memory test. C-reactive proteins (CRP) concentrations were determined on enrollment and at follow-up. On both occasions they were significantly higher among parasitaemic children than non-parasitaemic children. The CRP concentrations at follow-up of those who were parasitaemic on enrollment and became non-parasitaemic at follow-up returned to normal concentration, while the CRP concentrations of children who remained parasitaemic remained high. The CRP concentaration was highly positively correlated with parasite density and splenomegaly, and negatively correlated with haemoglobin and picture memory test. In both the clinical trial and natural trial, parasitaemia was associated with low performance in fine motor function. In addition, initial parasite density predicted changes in scores of the same tests and picture memory. Therefore there is limited evidence that parasitaemia may affect performance in these tests. However, we were unable to show a benefit from loosing parasitaemia over a two weeks period. The need for more research in this area and the ideas for future studies are highlighted.

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