Host determinants of reinfection with schistosomes in humans: a systematic review and meta-analysis.

BACKGROUND: Schistosomiasis is still a major public health burden in the tropics and subtropics. Although there is an effective chemotherapy (Praziquantel) for this disease, reinfection occurs rapidly after mass drug administration (MDA). Because the entire population do not get reinfected at the same rate, it is possible that host factors may play a dominant role in determining resistance or susceptibility to reinfection with schistosomes. Here, we systematically reviewed and meta-analyzed studies that reported associations between reinfection with the principal human-infecting species (S. mansoni, S. japonicum and S. haematobium) and host socio-demographic, epidemiological, immunological and genetic factors. METHODOLOGY/PRINCIPAL FINDINGS: PubMed, Scopus, Google Scholar, Cochrane Review Library and African Journals Online public databases were searched in October 2013 to retrieve studies assessing association of host factors with reinfection with schistosomes. Meta-analysis was performed to generate pooled odds ratios and standardized mean differences as overall effect estimates for dichotomous and continuous variables, respectively. Quality assessment of included studies, heterogeneity between studies and publication bias were also assessed. Out of the initial 2739 records, 109 studies were included in the analyses, of which only 32 studies with 37 data sets were eligible for quantitative data synthesis. Among several host factors identified, strong positive association was found with age and pre-treatment intensity, and only slightly for gender. These factors are major determinants of exposure and disease transmission. Significant positive association was found with anti-SWA IgG4 level, and a negative overall effect for association with IgE levels. This reconfirmed the concept that IgE/IgG4 balance is a major determinant of protective immunity against schistosomiasis. Other identified determinants were reported by a small number of studies to enable interpretation. CONCLUSIONS: Our data contribute to the understanding of host-parasite interaction as it affects reinfection, and is a potential tool to guide planning and tailoring of community interventions to target high-risk groups.

Onchocerciasis in Anambra State, Southeast Nigeria: endemicity and clinical manifestations.

BACKGROUND: A cross-sectional study was performed to determine the current endemicity of onchocerciasis in Ayamelum Local Council, Anambra State, Southeast Nigeria, where community-directed treatment with ivermectin has been implemented for over a decade. METHODS: An estimate of the endemicity of onchocerciasis was obtained using the rapid assessment method in 894 subjects from 13 communities selected by multistage sampling. Dermatological and ocular manifestations were analysed and classified using standard criteria. RESULTS: Onchocerca volvulus nodules were recorded in 86 (9.6 ± 1.9%) of the subjects, and 186 (20.8 ± 3.7%) had one or more of the various classes of onchocercal skin diseases (OSD). Prevalence was dependent on age (p = 0.001), but not on sex (p = 0.31). There was a total absence of symptoms in the youngest age group and a low prevalence among subjects in their second decade of life. Pearson's correlation showed a strong positive correlation between nodular rate and prevalence of chronic papular onchodermatitis (r = 0.943) and a poor correlation with acute papular onchodermatitis (r = 0.259). Age-dependent analysis of various classes of OSDs showed that the rate of acute papular onchodermatitis increased with age up to the third decade of life and decreased steadily thereafter, while the chronic forms of OSD increased with age for both sexes. Infection was dependent on occupation and proximity of the village to the vector breeding sites. CONCLUSIONS: Generally low prevalence in the population and absence of symptoms among the youngest age group emphasise the success of the intervention, but the persistent occurrence of acute disease may suggest a shortfall due to low coverage or non-compliance with the mass chemotherapeutic regimen.