Diagnosis and Treatment of Schistosomiasis in Children in the Era of Intensified Control

Stefanie Knopp; Sören L Becker; Katrin J Ingram; Jennifer Keiser; Jürg Utzinger

Disclosures

Expert Rev Anti Infect Ther. 2013;11(11):1237-1258. 

In This Article

Epidemiology of Schistosoma Infections

Schistosomiasis is a water-based parasitic disease, and the causative agents are blood flukes of the genus Schistosoma.[2,13–15] There are six Schistosoma species that can infect humans. However, of particular public health importance are only three species, namely S. haematobium, S. japonicum and S. mansoni. Schistosomiasis has a fairly complex life cycle. In brief, the adult female and male worms live in permanent pairs in the perivesical (S. haematobium) or portal veins and mesenteric blood vessels (other species). Eggs produced by the female worms reach the bladder or intestine, respectively, from where they can be excreted with urine or feces.[3] In case the eggs get in contact with freshwater, the parasitic first-stage larva, the miracidium, hatches. Miracidia infect species-specific intermediate hosts, freshwater snails of the genus Bulinus (S. haematobium, S. intercalatum and S. guineensis), Biomphalaria (S. mansoni), Oncomelania (S. japonicum) and Neotricula (S. mekongi), in which they multiply asexually. Snails shed hundreds to thousands of cercariae (4–6 weeks after infection), and this larval stage is infective for humans. If humans get in contact with natural freshwater, cercariae are able to penetrate their skin, are transported with the blood stream via the lungs to the liver, mature into adult worms in the portal veins and finally mate and migrate to their final destination. Although most Schistosoma species have humans as the only definitive host, S. japonicum also infects a large range of domestic and wild animals, including cattle, dogs, pigs, water buffaloes and rodents, thus contributing to disease transmission.[13,16]

High schistosomiasis transmission areas are located in sub-Saharan Africa (mainly S. haematobium and S. mansoni), Brazil (S. mansoni) and the Philippines (S. japonicum). A low risk of acquiring Schistosoma infections occurs in the Middle East (S. haematobium and S. mansoni), Surinam, Venezuela and some of the Caribbean islands (S. mansoni), Indonesia and the People's Republic of China (S. japonicum), Lao People's Democratic Republic and Cambodia (S. mekongi).[2,10]

Age prevalence curves for Schistosoma infection typically rise from early childhood, peak in SAC or adolescents and decline to reach low levels in adulthood.[13,17,18] There is evidence that, depending on exposure history, resistance to infection can be acquired over time, resulting in lower infection rates and intensities in adults.[19,20] However, data obtained from a cross-sectional survey done in western Côte d'Ivoire suggest that a second peak in prevalence occurs in individuals aged 45 years and above.[21] People living in endemic areas, who are using unprotected open water bodies as domestic sources or are exposed to natural freshwater due to occupational or recreational activities, have an elevated risk of infection or reinfection.[14,22,23] Living in close proximity to natural freshwater bodies constitutes an important risk factor for children and other community members, as it leads to frequent exposure to open water bodies (e.g., while washing clothes or fetching water, or during recreational activities such as swimming, bathing, playing or fishing).[23–26]

Discussion Point

Several studies have explored ways to change the behavior of children to reduce their risk of becoming infected with schistosomiasis. For example, health education through active teaching and learning, using songs, poetic dramas, short plays and peer discussions result in increased knowledge of how to prevent schistosomiasis and reduce risky behavior in schoolchildren.[27] A study carried out in Mwanza, United Republic of Tanzania found that participatory hygiene and sanitation transformation (PHAST) interventions increased peoples' knowledge about schistosomiasis transmission and succeeded in changes in their perceptions and attitudes toward water contacts.[28] Children below the age of 15 years had less water contact after the PHAST activities. Alternative play areas and safe play options, or water recreation areas such as artificial pools, are considered as effective means for reducing the infection risk for children, particularly when used in combination with health education and treatment.[29,30]

Comments

3090D553-9492-4563-8681-AD288FA52ACE

processing....