Advocacy, policies and practicalities of preventive chemotherapy campaigns for African children with schistosomiasis

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From: Expert Review of Anti-infective Therapy(Vol. 11, Issue 7)
Publisher: Expert Reviews Ltd.
Document Type: Report
Length: 13,654 words
Lexile Measure: 1650L

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Author(s): J Russell Stothard [*] 4 , José C Sousa-Figueiredo 1 2 , Annalan MD Navaratnam 3

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cure rate; egg reduction rate; intestinal schistosomiasis; praziquantel; preventive chemotherapy; Schistosoma; urogenital schistosomiasis

Background on epidemiology & treatment

Schistosomiasis is a waterborne parasitic infection which typically gives rise to a chronic inflammatory disease, as typified by immunopathological lesions around schistosome eggs trapped inside host tissues [1,2] . In Africa, there are two forms of schistosomiasis, intestinal and urogenital, which are caused by different species, Schistosoma mansoni and Schistosoma haematobium , respectively [3-5] . Other schistosome species able to infect man include Schistosoma intercalatum and Schistosoma guineensis but these are of minor public health importance [3] . Although widespread, the geographical distribution of schistosomiasis across Africa is often focalized and difficult to predict locally. This is due to interdependence (as part of the schistosome's lifecycle) with aquatic snails and site-specific conditions of impoverished sanitation and water hygiene. As schistosome larvae (i.e., cercariae) can penetrate skin directly, and infection with schistosomes takes place upon exposure to water containing viable larvae [5] . This can be from contact with either domestic water drawn from environmental bodies or from activities within these water bodies themselves in passive- or active-like water contact mechanisms, respectively, see Figure 1 [6] . Accurate mapping of schistosomiasis is an ongoing challenge but fundamental for effective control by targeting resources [3,7] .

Schistosomiasis is not restricted to humans, with several other schistosome species infecting livestock and wildlife, although these have limited medical importance [8-10] . Nonetheless in West Africa, recent detection of novel hybrids between S. haematobium and Schistosoma bovis and Schistosoma curassoni has revealed an unexpected zoonosis thereby challenging conventional wisdom both on epidemiology and control [11,12] . Equally important has been the detection of schistosomiasis in infants and preschool-aged children that highlights other shortcomings in present control tools for example, in diagnostics and of suitable drug formulations [13] . These instances, although important, should not distract attention from the more obvious disease burden and need for control within school-aged children [14] . In resource-limited settings, typically school-aged children are given prioritization which is in-keeping with their higher burden of parasitemia (i.e., infection prevalence and intensity both peak in childhood), their greater vulnerability to disease (but with better reversibility of morbidity if given prompt treatment), as well as their easier accessibility within educational infrastructure (i.e., by attending primary school) as supported by universal primary education (UPE) [4,14] .

In endemic areas, interventions are thus targeted towards mass treatment of school children by large-scale administration of single standard dose praziquantel (PZQ) given out at 40 mg/kg bodyweight dosing following international guidelines for preventive chemotherapy (PC) [4] . Although the exact killing mechanism of PZQ against schistosome worms is still unknown (see section below), its efficacy is typically judged by the cessation of parasite egg excretion in stool or urine samples [14,15] . The specimens are processed by routine parasitological methods and parasitological cure (i.e., the percentage of those children who stop shedding eggs) is judged by inspection of a cohort of children before and after PZQ treatment, as shown in...

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Gale Document Number: GALE|A337663389