Helminth Infections of Children: Prospects for Control

Abstract

The major soil-transmitted helminth (STH) infections, ascariasis, trichuriasis, and hookworm infection, together with schistosomiasis, occur in an estimated 2 billion people in the developing countries (de Silva et al., 2003; Hotez et al., 2006). It has been suggested that the STHs and schistosomes are among the most common human pathogens, and it is not unusual for a single individual, especially a child, to harbor several different species at the same time. According to the World Health Organization (WHO), these infections account for more than 40% of the disease burden due to tropical diseases, exclusive of malaria (WHO, 2002a). A characteristic feature of STH and schistosome infections is that their morbidity is non-linearly related to the number of adult worms an individual harbors (sometimes referred to as the “worm burden”) (Anderson and May, 1992; Hotez et al., 2005). Usually, only individuals with medium and heavy worm burdens suffer severe morbidity. The WHO estimates that of the approximately 300 million people who harbor heavy worm burdens, most are school-aged children (WHO, 2002a). Data collected over the past two decades indicate that heavy worm burdens in children result not only in adverse health effects, but also in cognitive and educational impairments (Drake et al., 2000). In contrast, other important helminth infections such as lymphatic filariasis and onchocerciasis exert their major effects on adult populations; the major approaches to their control have been reviewed elsewhere (Hoerauf, 2003). Because of the emerging importance of pediatric helminthiases, the WHO and World Bank have focused international attention on identifying and implementing cost-effective methods for helminth control. To date, the major approach has been to reduce the worm burdens and their corresponding morbidity through the periodic