Longitudinal Study on the Natural Infection of Biomphalaria straminea and B. glabrata by Schistosoma mansoni in an Endemic Area of Schistosomiasis in Pernambuco, Brazil

Abstract

In the Brazilian state of Pernambuco, schistosomiasis exhibits an epidemiological profile of chronic infection and persistent reinfection in the rainforest area (Zona da Mata). Heavy infections are also frequent in the coastal area (Barbosa et al. , 2001. Despite the amount of data amassed over the years and the advances in immunological and therapeutic clinical research, control of schistosomiasis transmission still represents a challenge for government institutions (Barbosa & Coimbra 2000). Although morbidity indices remain low, the prevalence of infection and the rate of reinfection have remained high in rural areas despite repeated treatment with oxamniquine , Favre 1999.Longitudinal studies of infected snails in critical areas, in parallel with application of control measures may shed light on why control measures fail. Nevertheless, few have been carried out (Dazo et al. 1976, Gundersen et al. 1990).In Pernambuco, there are two intermediate host species of Schistosoma mansoni: Biomphalaria straminea and B. glabrata. The first species is widespread over the Agreste, a zone of transitional vegetation, and the Zona da Mata, where it maintains high endemicity levels despite the low rates of natural and experimental infection (Paraense & Corrêa 1989). The second species, with infection rates reaching up to 20%, is mainly found in coastal areas, and remains responsible for several active foci of transmission .The present study aims to assess, on a monthly basis over a period of four years, the relative abundance and the natural infection of B. straminea and B. glabrata by S. mansoni in two representative localities in an endemic area in the state of Pernambuco, where infected persons were treated periodically with oxamniquine. In addition, tests were carried out to ascertain the susceptibility of snail species found in these localities to local parasite strains. MATERIALS AND METHODSTwo rural localities sharing similar sociodemographic characteristics and displaying medium levels of endemicity in relation to schistosomiasis (prevalence ranging from 30% to 40%), populated by distinct intermediate host species, were chosen after a preliminary stool survey and the application of a home questionnaire as described by Moza et al. (1998). Nine stool surveys by the Kato-Katz method (Katz et al. 1972) were undertaken every three months in both localities and individuals who tested positive for S. mansoni were treated with oxamniquine ), in March 1995, June 1995, March 1997 and March 1998 Characterization of the study area -Ecological features relevant to schistosomiasis transmission were recorded, including water-contact habits and rainfall. As recommended by Olivier (1973), sketch maps were used to display the location of houses, land use and water resources of each locality.Malacological survey -Snail breeding sites regarded as potential of transmission foci were identified in both localities. Snails were collected monthly from predetermined stations over the four years of the follow-up sur-+ Corresponding

Distribution and Schistosoma mansoni infection of Biomphalaria glabrata in different habitats in a rural area in the Jequitinhonha Valley, Minas Gerais, Brazil: environmental and epidemiological aspects

“…However, this contrasts with a study in Pernambuco, Brazil, which reported no relationship between human infection and snail abundance and infection following chemotherapy (Favre et al 2002).…”

Malacological assessment and natural infestation of Biomphalaria straminea (Dunker, 1848) by Schistosoma mansoni (Sambon, 1907) and Chaetogaster limnaei (K. von Baer, 1827) in an urban eutrophic watershed

“…by S. mansoni oscillates in freshwater ecosystems from as high as 4% in Biomphalaria straminea, and up to 52% in Biomphalaria glabrata. The overall infestation rate is related to the abundance of Biomphalaria in the area (Favre et al, 2002).…”

Assessment of schistosomiasis, through school surveys, in the Forest Zone of Pernambuco, Brazil

“…The emphasis has been on the ecology and control of the mollusks that are the intermediate hosts (Barbosa 1992a,b, 1996, Barbosa & Barbosa 1994, 1996, Barbosa et al 1992, 1993, Bogéa et al 1996, Dannemann & Pieri 1989, 1991, 1993a, b, Favre et al 1995, 1997, Gazin et al 2000, Pieri 1995, Pieri & Dannemann 1996, Pieri & Thomas 1986, 1987, Randall et al 2001, Sarquis et al 1997, the ecological and epidemiological determinants of the disease (Barbosa 1992b, 1997, 1998a, b, Barbosa & Coimbra 2000, Barbosa & Gouveia 2000, Coutinho et al 1997, Gazin et al 2002, Gonçalves et al 1992, Simões-Barbosa et al 2001, and also the impact of chemotherapy treatment for infected individuals, in relation to the transmission dynamics of the disease , Favre et al 2002, Zani et al 2004). The knowledge resulting from these studies has made it possible to adapt the schistosomiasis evaluation and control strategies recommended by central health bodies -WHO at the worldwide level and the Health Surveillance Department of the Ministry of Health at the national level -to the regional characteristics and demands.…”