Evidence for an improvement in cognitive function following treatment of Schistosoma japonicum infection in Chinese primary schoolchildren.

Abstract

Abstract. A double-blind, placebo-controlled, treatment trial was conducted in Sichuan, China to investigate the unique and combined effects on the cognitive function (working memory) of children after treating geohelminth infections with albendazole and treating Schistosoma japonicum infection with praziquantel. One hundred eighty-one children 5-16 years of age participated. At baseline, the praziquantel and placebo groups were similar in all background characteristics. Three months after praziquantel treatment, there was a significant reduction in the prevalence and intensity of S. japonicum infection. There were significant age group by praziquantel treatment interaction effects in three of the five cognitive tests, Fluency, Picture Search, and Free Recall, with effects being strongest in the youngest children (5-7 years old). Exploratory analysis within the youngest children showed a significant positive main effect of treatment on Fluency (P Ͻ 0.001), after controlling for sex, anthropometric, and parasitic and iron status. There was also a treatment by height-for-age interaction (P ϭ 0.03) and a treatment by iron status interaction (P ϭ 0.024) on Fluency. There was a treatment by S. japonicum intensity interaction (P Ͻ 0.001) on Free Recall, but the main effect of treatment on Picture Search was not significant (P ϭ 0.058). Younger children and those who are physically the most vulnerable are likely to benefit the most from the treatment of S. japonicum infection in terms of improved performance on tests of working memory.Several studies have shown that moderate to heavy parasitic helminth infections of children are associated with lower scores on tests of cognitive function and of educational achievement than children who are uninfected or lightly infected.1-7 The specific effects on mental function are not clear and may depend not only on the duration and intensity of infection but also on the species of parasitic infection and whether or not the parasites are present as single or multiple species infections.The specific cognitive domains that are associated with parasitic infection have not been clearly defined but could be important for understanding the implications of the effects on children's educational achievement and development. For example, it was observed that performance on tests of reaction time was associated with Ascaris lumbricoides infection (Watkins WE, Pollitt E, unpublished data), whereas Levav and others 8 found that infection with A. lumbricoides was associated with poorer performance on tests of verbal ability.One cognitive domain that has been investigated in several studies with differing results is that of working memory. Working memory refers to a brain system that provides temporary storage and manipulation of the information necessary for more complex cognitive tasks such as language comprehension, learning, and reasoning. 9 The working memory model is composed of three main parts: an attentional controller/central executive supplemented by two subsidiary systems called the p...

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