Characteristics of the Human Host Have Little Influence on Which Local Schistosoma mansoni Populations Are Acquired

Abstract

BackgroundBrazil remains the country in the Americas with the highest prevalence of schistosomiasis. A combination of control efforts and development, however, has sharply reduced its intensity and distribution. The acquisition of specific schistosome populations may be dependent on host characteristics such as sex, age, geography, work, habits and culture. How these and other host characteristics align with parasite subpopulations may guide approaches to improve control.MethodologyA cohort of more than 90% of the residents in two rural communities in Brazil participated in an epidemiologic survey of demographic, socio-economic and behavioral characteristics. The variables sex, age, intensity of infection, socio-economic index, % lifetime spent on site, previous infection, and trips outside the district were used to group parasites infecting individuals. Schistosoma mansoni infection status was determined by examination of stools submitted on 3 different days. The aggregate of eggs collected from the whole stool was used to determine degree of population differentiation from allele frequencies for 15 microsatellites.Conclusions/SignificanceInfection prevalence was 41% for these communities, and the epidemiologic characteristics were similar to many of the endemic areas of Brazil and the world. Parasite population structuring was observed between the two communities (Jost's D 0.046, CI95% 0.042–0.051), although separated by only 8 km and connected by a highway. No structuring was observed when infected individuals were stratified by host's biologic, demographic or epidemiologic characteristics. Those most heavily infected best reflected the communities' overall parasite diversity. The lack of differentiation within villages suggests that individuals are likely to get infected at the same sites or that the same parasite multilocus genotypes can be found at most sites. The geographic structuring between villages and the lack of structuring by age of the host further supports the impression of a population little affected by migration or drift.

Repeated praziquantel treatments remodel the genetic and spatial landscape of schistosomiasis risk and transmission

“…In 2009 the two villages differed in population (Jenipapo 482, Volta do Rio 368), and the percentage of the population with access to a septic tank at home (Jenipapo 44%, Volta do Rio 91% (Barbosa et al, 2013)), but were similar for other characteristics (Table 1). There also were no significant demographic changes over the 2009 – 2013 period.…”

“…This relative isolation, together with the prevalence of schistosomiasis in the area, were the main reasons for choosing these sites. The two communities have been described previously (Blanton et al, 2011; Barbosa et al, 2013). …”

“…Epidemiologic and parasitologic surveys were conducted in both communities for all inhabitants ≥ 1 year old who agreed to participate in 2009 and 2012 (Blanton et al, 2011; Barbosa et al, 2013). Only Jenipapo was studied in 2013 (Fig.…”

“…All procedures and primers were previously described (Blank et al, 2009; Barbosa et al, 2013). Briefly, S. mansoni eggs were concentrated from the whole stool by selective sieving and sedimentation, and extracted DNA was PCR-amplified with a panel of primers for 11 microsatellites (Supplementary Table S1).…”

“…We registered host epidemiologic characteristics and parasite allele frequencies, and treated all of those infected (Barbosa et al, 2013). This population was then followed for two additional rounds of treatment over a 4 year period, and the longitudinal effects of treatment on parasite population dynamics and structure were analyzed.…”