Mem Inst Oswaldo Cruz, Rio de Janeiro, 97 (Suppl.I) October 2002
First Report on the Presence of Biomphalaria straminea in the Municipality of Jaboticatubas, State of Minas Gerais, Brazil
Laboratório de Helmintoses Intestinais
IILaboratório de Educação em Saúde, Centro de Pesquisas René Rachou-Fiocruz, Av. Augusto de Lima 1715, 30190-002 Belo Horizonte, MG, Brasil
This is the first report on occurrence ofu00a0Biomphalaria straminea in the district of São José de Almeida (municipality of Jaboticatubas) State of Minas Gerais, Brazil. The presence ofu00a0B. glabrata andu00a0B. tenagophilau00a0had already been reported in this area. Such municipality is part of the metropolitan region of Belo Horizonte and comprises 60% of the Tourist Complex of Serra do Cipó. Since the 1950s throughout the 1990s, a schistosomiasis prevalence ranging from 15 to 40% has been observed. Although nou00a0B. straminea specimen has been found naturally infected in the region, descendants of these snails collected in the area, showed to be experimentally susceptible tou00a0Schistosoma mansoni infection reaching rates from 14.6 to 28.6%. Even not being found naturally infected, in the State of Minas Gerais, the possibility that the speciesu00a0B. stramineau00a0may keep endemicity foci of schistosomiasis should be regarded, as in the Northeastern region of Brazil where the high density of this planorbid and the social-economic and sanitary conditions enable to the transmission.
In Brazil, ten species and one subspecies of the genus Biomphalaria are known. Among them, three species are intermediate hosts of Schistosoma mansoni: B. glabrata, B. tenagophila and B. straminea. Although B. straminea is less susceptible to S. mansoni infection, this species is regarded epidemiologically important in the Brazilian Northeastern region, in which it is the main responsible for schistosomiasis transmission (Paraense & Correa 1989).
Schistosomiasis is an endemic disease that has been reported in Jaboticatubas since 1950 (Pellon & Teixeira 1950), when this municipality had 1,018 inhabitants and prevalence of 36%. Since then, several investigations have been confirming high prevalence data of schistosomiasis such as 40.5% (Brener & Mourão 1956); 48.6% (Souza et al. 1988) and 15.4% (Cury et al. 1994). Massara et al. (2001) performed a parasitological survey, from feces samples, using the Kato-Katz method (Katz et al. 1972) for two slides per sample of 1180 students, from the district of São José de Almeida (municipality of Jaboticatubas), and a prevalence rate of 8.6% was observed. Further examinations on the positive students relatives showed a prevalence of 41.6%.
In 1976, Fundação Nacional de Saúde (Funasa) included Jaboticatubas in the Program of Schistosomiasis Special Control (Pece), when prevalence rates showed to be 33.5% (CDS 1976). Malacological surveys and treatment for positive schistosomiasis cases have been carried out since 1986 by Funasa. According this reports the prevalence rate of 8 communities showed to be 19.8% in 1996 and 25.5% for 35 communities in 1998. From 1999 to 2000, 59 localities were under study and a prevalence of 15.3% was found.
The current work is part of a project aimed at implanting and assessing an integrated model of schistosomiasis and intestinal helminthiasis control in Jaboticatubas. Such project includes epidemiological and malacological surveys, parasitological examinations of local students and their relatives, as well as clinical, educational and environmental control measures. This work is the first result from the malacologial survey and it is aimed at reporting the first presence of B. straminea inJaboticatubas municipality and at studying susceptibility of this species to S. mansoni.
MATERIAL AND METHODS
Locality under study - This study was carried out in the locality of São José de Almeida, municipality of Jaboticatubas (19s31/43w44), which is part of the metropolitan region of Belo Horizonte, Minas Gerais.
Malacological survey - These surveys were performed in areas, where local schools had been previously selected for parasitological examinations including residences of positive students to schistosomiasis. The streams in the region were also investigated.
Snails - After collection, the snails were taken to the laboratory where they were measured and examined under artificial light and submitted to squeezing between glass plates. Some specimens were separated to be kept in aquarium in order to obtain descendants (F1) for susceptibility assays. Another sample of specimens was separated for morphological identification (Paraense 1975) and molecular analysis (Vidigal et al. 1998).
Snails infection - F1 specimens of B. straminea were exposed to miracidia of two S. mansoni strains isolated in Jaboticatubas (WM and LGM) and three other strains: LE, from Belo Horizonte, MG, isolated and maintained in B. glabrata snails under laboratory conditions for over 30 years; SJ, from São José dos Campos, SP, obtained from naturally infected B. tenagophila, maintained under laboratory conditions for over 20 years and AL, from Alagoas, obtained from naturally infected B. glabrata, maintained under laboratory conditions for over 15 years. The techniques for obtaining miracidia are in accordance with Souza et al. (1979).
Fifty specimens of B. straminea, measuring 4-7 mm diameter, were used. The snails were individually exposed to 50 miracidia of each S. mansoni strain. For infection control, groups of B. glabrata, reared under laboratory conditions, with 8-10 mm diameter, were exposed to 10 miracidia/snail of each strain.
Due to the low number of miracidia obtained from human feces, it was only possible to perform infection ofB. straminea using 10 miracidia/snail of LGM strain.
After a 30-day exposition, the snails were individually placed under artificial light and examined by stereomi-croscopy. After 60 days, negative specimens were examined and submitted to squeezing between glass slides.
Malacological survey - Out of 6,574 snails collected in the area, 3,841 were identified as B. straminea and showed to be negative to S. mansoni cercariae. The other 2,733 were B. glabrata and 17 (0.6%) showed to be positive to S. mansoni cercariae.
Snails infection - B. straminea infection rates ranged from 14.6 to 28.6%, whereas for B. glabrata the rates varied from 45.9 to 85% (Table).
In the present study, the presence of B. straminea in the municipality of Jaboticatubas is first reported. The infection rates obtained here ranged from 14.6 to 28.6%, which showed to be higher than those found in literature, quite often lower than 10%, with experimental infections using several snail populations from the State of Minas Gerais (Freitas et al. 1972, Gerken et al. 1975, Souza et al. 1981a, b, 1983, Souza 1986, 1993). Souza et. al (1996), studying a B. straminea population from Belo Horizonte, infected 87 snails with LE S. mansoni strain and other 88 with VGS strain, which provided infection rates of 10.3 and 11.3%, respectively. In addition, 83 descendents of this snails were exposed to LE strain and 12% showed to be positive. Carvalho et al. (1980) reported an experimental infection rate of 12.5% for a B. stramineapopulation, from Piripiri (State of Piauí), with a variable number of miracidia per snail, using S. mansoni SJ strain. Favre (1993) demonstrated an experimental infection rate of 0.4% in B. straminea, from Picos (Piauí) exposed to five miracidia/snail.
Upon analyzing available data on the snail fauna of the genus Biomphalaria, from the Minas Gerais, Souza et al. (2001) reported the presence of B. straminea in 125 among 853 municipalities, reaching the 12 mesoregions of the State. However, although no naturally infected B. straminea specimen has been found, up to the present moment, in Minas Gerais, this species was considered to be the main responsible for a schistosomiasis focus in Paracatu (Carvalho et al. 1987).
Even not being found naturally infected, in Minas Gerais, the possibility of the B. straminea may keep foci of schistosomiasis should be regarded, as in the Northeastern region of Brazil due to the social-economic and sanitary conditions, which enable transmission and a high planorbid density in water collections (Paraense & Corrêa 1989). The finding of susceptible B. straminea, in Jaboticatubas, mirrors its dissemination throughout Minas Gerais. Indeed, Paraense (1972, 1986) remarks that such species is widely spread in hydrographic Brazilian bays.
Thus, the finding of B. straminea in Jaboticatubas is an important alert, as this region is visited by tourists all over Brazil, mainly on weekends and prolonged holidays. The lack of sanitation in the area added to the fact that both tourists and local inhabitants have little information about transmission of S. mansoni makes the current situation worse.
Our work shows that the B. straminea population, from Jaboticatubas, is susceptible to S. mansoniinfection at high rates, which in favorable conditions may become the intermediate host of S. mansoni.
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