Urban schistosomiasis in Itamaracá Island, Pernambuco, Brazil: epidemiological factors involved in the recent endemic process.

Abstract

Schistosomiasis has been considered as a rural endemic disease. In the State of Pernambuco, migratory human movements from endemic areas to urban ones with precarious sanitary and environmental conditions, is being pointed out as responsible for expansion and transmission of schistosomiasis (CS Barbosa et al. 1996 Rev Saude Publica 14: 693-700). The possibility that schistosomiasis mansoni could reach urban populations of high socio/economic background levels have been negleg. In 1991, four autochthonous cases from accidental exposure were detected near the Fort Orange beach, in Itamaraca Island, Pernambuco (JF Goncalves et al. 1992 Cad Saude Publica 7: 424-425). All cases occured in individuals from medium/high classes, that were in vacation in the island. After the detection of these accidental cases our major objective was to search for factors involved in schistosomiasis transmission in this area: a condominium composed by 560 houses of vacationists or tourists, built upon a destroyed mangrove ecosystem. An epidemiological quantitative study was conducted through demographic, sanitary, parasitological, social/economic and malacological surveys. Information about previous morbidity were also provided by the individuals that were temporary visitors in the area. The malacology survey identified 19 breading sites of Biomphalaria glabrata and 27 capture stations were set up. Snails were collected and examined each month during a year. The results show sazonal variation in mollusc populational density, associated with infection rates. The concentration of snails in water collections during the period from September to December 1997 were the highest observed, with infection rates of 18.2% (CS Barbosa et al. 1998 unpublished data). So, it is possible to imagine the potencial environmental risk of infection for human population in summer vacation on this beach. In the coproscopical survey, fecal samples of 349 vacationists and 91 local inhabitants were collected. Among vacationists, 10 cases of Schistosoma mansoni infection were detected (Table I). Moreover, 12 additional confirmed and autochthonous cases of schistosomiasis, in the last three years, were detected by refered morbidity survey (Table II). The prevalence of infection among local residents (fisherman and civil construction laborers) was 41.8%. Either, vacationist and local residents showed very few eggs of S. mansoni, indicating low levels of exposure. However, vacationists showed clinical acute forms, with characteristic exacerbated symptoms. The autochthony of cases was confirmed by personal interviews. We can conclude that the urban transmission of schistosomiasis in Itamaraca Island have dis-