Abstract
Published and unpublished observations on geographical distribution of Biomphalaria snails in the State of Minas Gerais, Brazil, were compiled. This work is aimed at knowing the present occurrence of Biomphalaria species in this region, and at contributing to the elaboration of the planorbid chart of Minas Gerais. In malacological surveys, performed by several researchers, the presence of seven species of this genus was recorded. Those planorbids were found in 12 mesoregions, in 283 (33.1%) municipalities out of 853 with the following distribution: B. glabrata (185 municipalities), B. straminea (125), B. tenagophila (58), B. peregrina (57), B. schrammi (26), B. intermedia (20) and B. occidentalis (2). B. glabrata and B. tenagophila are found naturally infected by Schistosoma mansoni in Minas Gerais. In 24 municipalities the three snail hosts of S. mansoni in Brazil, B. glabrata, B. tenagophila and B. straminea, are present.
Biomphalaria; planorbids; geographic distribution; Minas Gerais; Brazil
Geographical Distribution of Biomphalaria Snails in the State of Minas Gerais, Brazil
Vol.96(3): 293-302, April 2001
Cecília Pereira de Souza/+ + Corresponding author. Fax: +55-31-3295.3115. E-mail: souzacp@cpqrr.fiocruz.br Received 11 July 2000 Accepted 14 November 2000 , Roberta Lima Caldeira*, Sandra Costa Drummond**,Alan Lane Melo***, Carlos Tito Guimarães, Delza de Moura Soares, Omar dos Santos Carvalho*
Laboratório de Malacologia *Laboratório de Helmintoses Intestinais, Centro de Pesquisas René Rachou-Fiocruz, Av. Augusto de Lima 1715, 30190-002 Belo Horizonte, MG, Brasil **Fundação Nacional de Saúde, Belo Horizonte, MG, Brasil ***Departamento de Parasitologia, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil
Published and unpublished observations on geographical distribution of Biomphalaria snails in the State of Minas Gerais, Brazil, were compiled. This work is aimed at knowing the present occurrence of Biomphalaria species in this region, and at contributing to the elaboration of the planorbid chart of Minas Gerais. In malacological surveys, performed by several researchers, the presence of seven species of this genus was recorded. Those planorbids were found in 12 mesoregions, in 283 (33.1%) municipalities out of 853 with the following distribution: B. glabrata (185 municipalities), B. straminea (125), B. tenagophila (58), B. peregrina (57), B. schrammi (26), B. intermedia (20) and B. occidentalis (2). B. glabrata and B. tenagophila are found naturally infected by Schistosoma mansoni in Minas Gerais. In 24 municipalities the three snail hosts of S. mansoni in Brazil, B. glabrata, B. tenagophila and B. straminea, are present.
Key words: Biomphalaria - planorbids - geographic distribution - Minas Gerais - Brazil
Brazil is an endemic focus of schistosomiasis mansoni with over 6 million people infected (Rey 1991). The current national prevalence of schistosomiasis in Brazil indicates that it is still considered an important endemic parasitosis (Katz & Peixoto 2000). The endemic areas are located in the states of Maranhão, Pará, Rio Grande do Norte, Paraíba, Pernambuco, Alagoas, Sergipe, Bahia, Minas Gerais, Espírito Santo and in the city of Rio de Janeiro. In Minas Gerais, the endemic areas are located in the mesoregions of Norte de Minas, Campo das Vertentes, Oeste de Minas, Je-quitinhonha, Vale do Mucuri, Vale do Rio Doce, Metropolitana de Belo Horizonte, Zona da Mata and Central Mineira.
Among neotropical Biomphalaria, ten species and one subspecies are found in Brazil. Some species are widely distributed while others are restricted to some specific regions. The intermediate hosts of Schistosoma mansoni in Brazil are Biomphalaria glabrata (Say, 1818), Biomphalaria tenagophila (Orbigny, 1835) and Biomphalaria straminea (Dunker, 1848). B. glabrata is epidemiologically the most important host regarding its wide geographic distribution and high susceptibility to infection by the trematode (Souza et al. 1995). Furthermore, its distribution is nearly always related to the presence of schistosomiasis. Two other species, Biomphalaria amazonica Paraense, 1966 and Biomphalaria peregrina (Orbigny, 1835) can be infected with S. mansoni under experimental conditions (Corrêa & Paraense 1971, Paraense 1973).
Malacological surveys and isolated captures, undertaken by several researchers, have already recorded the presence of seven Biomphalaria species in Minas Gerais. The three snail hosts of S. mansoni occur in some municipalities, having been found naturally infected with S. mansoni and other trematode larvae, which do not infect man (Ruiz 1952, Souza et al. 1998b).
The present work was aimed to update the knowledge of the distribution of Biomphalaria species and to contribute to the elaboration of the planorbid chart of Minas Gerais.
The list of municipalities of Minas Gerais where Biomphalaria (=Australorbis; Tropicorbis; Platytaphius; Taphius, Paraense 1958) occurs was organized with data of the literature and unpublished observations. The list is presented by mesoregions and municipalities (IGA 1995). Snails were collected in breeding places from different municipalities in Minas Gerais at different periods, using scoops and tweezers, and then packed to be transported to the laboratory (Souza & Lima 1990). Specific identification was performed according to the morphology of the shells, reproductive system and renal ridge of the snails (Deslandes 1951, Paraense & Deslandes 1955a,b, 1959, Paraense 1975, 1981), or recently through low stringency polymerase chain reaction and restriction fragment lenght polymorphism (Vidigal et al. 2000). Different researchers, whose works are quoted in the references, collected and identified the snails. In the last 40 years, great part of identification was undertaken by Dr Wladimir Lobato Paraense, Departamento de Malacologia, Instituto Oswaldo Cruz, Rio de Janeiro. In the last two decades technicians and researchers, mainly from Centro de Pesquisas René Rachou, Fiocruz, Belo Horizonte, Fundação Nacional de Saúde, Belo Horizonte and Universidade Federal de Minas Gerais, Belo Horizonte, have done their utmost to collect and classify the planorbid snails from this state (Souza et al. 1981a, 1998b, Souza 1986, Souza & Lima 1997, Carvalho et al. 1989, 1994, 1997, 1998a, FNS 1995, 1998). A great deal of information was also obtained from materials sent by health officials of municipalities in the state, urban and rural state owners, researchers and technicians from several institutions.
The malacological survey was performed in all municipalities belonging to mesoregions of Triângulo Mineiro/Alto Paranaíba and Norte de Minas (Carvalho et al. 1994, 1997, 1998a). The municipalities in which the presence of any Biomphalaria species was noticed are recorded in the Table.
Table
The occurrence of seven Biomphalaria species was recorded in Minas Gerais. The current distribution, per municipalities, in the twelve mesoregions in this state is shown in the Table and in the Figure. Snails were found in 283 (33.1%) municipalities, out of 853, with the following distribution: B. glabrata 65.3% (185) municipalities, B. straminea 43.8% (125), B. tenagophila 20.4% (58), B. peregrina 20.1% (57), B. schrammi 9.2% (26), B. intermedia 7% (20) and B. occidentalis 0.7% (2). The three snail hosts of S. mansoni in Brazil (B. glabrata, B. straminea and B. tenagophila) were found in 24 (8.4%) municipalities.
Figure
The need for updated information on geographic distribution of parasite vectors, in endemic regions, has led urban and rural communities up to seek institutions responsible for public health, aimed to know the transmission risks of diseases by those organisms. In the summer, mainly on vacation periods or prolonged holidays, the flow of people towards rural regions with lakes, rivers and waterfalls raises the dispersion risks of diseases caused by protozoa, helminths and viruses. In Brazil, schistosomiasis prevalence justifies the necessity of updated knowledge of the localization of intermediate hosts in risk regions (Souza et al. 1998a). Besides, the presence in a shorter scale of angiostrongyliasis and fascioliasis also play an important role, since these diseases are transmitted by snails.
Indeed, the real geographic distribution of schistosomiasis the transmitter snails in Brazil is not well known owing to the great territorial extension and the lack of human and economic resources (Paraense 1972). However, the number of studies aimed to better know the malacological fauna in some regions has increased in the last decades (Paraense 1983, 1986, Paraense et al. 1983, Souza 1986, Souza & Lima 1997, Souza et al. 1998a,b, Teles 1987, 1989, 1996, Teles et al. 1991, Carvalho et al. 1989, 1994, 1997, 1998a,b, FNS 1995, 1998, Schlemper Junior et al. 1996).
In the present study the distribution of Biomphalaria snails per municipality and mesoregion in Minas Gerais (Table, Figure) is presented, showing the higher concentration of S. mansoni intermediate hosts, mainly B. glabrata, in three mesoregions - IV Metropolitana de Belo Horizonte, VI Norte de Minas and XI Vale do Rio Doce - with quite significant schistosomiasis prevalence rates.
B. glabrata was found naturally infected with S. mansoni in several municipalities and there were focuses with snail infection rates of 85% (Souza et al. 1997). In the mesoregions of Noroeste de Minas (V), Sul/Sudoeste de Minas (VIII) and Triângulo Mineiro/Alto Paranaíba (IX), where B. glabrata is rarely found, the occurrence of the parasitosis is very low (Figure). Although B. tenagophila is not widely spread in Minas Gerais, it was found naturally infected with S. mansoni in the municipalities of Jaboticatubas, Itajubá, Belo Horizonte and Ouro Branco (Melo & Pereira 1985, Carvalho et al. 1985a,b, Silva et al. 1994), localized in the mesoregions Metropolitana de Belo Horizonte (IV) and Sul/Sudoeste de Minas (VIII). The natural infection rates of this species in those focuses are low, ranging from 0.03 to 17.5%. B. straminea was mainly found in three mesoregions, Metropolitana de Belo Horizonte (IV), Noroeste de Minas (V) and Norte de Minas (VI). This species has not been found naturally infected with S. mansoni in Minas Gerais, as well as B. peregrina, but they have been experimentally infected with S. mansoni (Paraense 1973, Souza et al. 1981a,b, 1983, Souza 1986). B. intermedia was found only in the Triângulo Mineiro/Alto Paranaíba (IX) mesoregion, in the boundaries with the states of Mato Grosso do Sul and São Paulo, where its occurrence had already been recorded. B. occidentalis, resistant to S. mansoni infection and very similar to B. tenagophila by the morphology of the shell, was found in two municipalities (Table).
The current geographic distribution shows a high concentration of Biomphalaria species up to six per mesoregions, in Minas Gerais (Figure).
Studies on the planorbid fauna in all states of Brazil, mainly in less investigated regions, should be motivated with the objective to better know the geographic distribution of snail vectors of schistosomiasis and other helminthiases, aiming to control the risk of transmission.
To Dr Frederico Carlos Carvalho Soares, Regional Coordinator of Fundação Nacional de Saúde in Minas Gerais, for bibliography on snails of epidemiological importance in the transmission of schistosomiasis in the State of Minas Gerais.
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Publication Dates
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Publication in this collection
11 Apr 2001 -
Date of issue
Apr 2001
History
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Accepted
14 Nov 2000 -
Received
11 July 2000