Carlos Tito Guimarães

Possible competitive displacement of planorbids by Melanoides tuberculata in Minas Gerais, Brazil

Several species of snails, including Pomacea haustrum, Marisa cornuarietis and Helisoma duryi, have been identified as probable competitors and/or predators of planorbid intermediate hosts of Schistosoma. During the last few years, studies carried out in the Caribbean region have shown reductions and even disappearances of populations of Biomphalaria glabrata and B. straminea in breeding places where the snail Melanoides tuberculata was introduced. Observations made over a period of 10 years in two lakes close to Belo Horizonte, MG, showed that there were marked reductions in autochthonous populations of B. glabrata and B. straminea after the arrival of M. tuberculata, both Biomphalaria species disappearing completely after eight years.

Moluscos límnicos da microrregião de Belo Horizonte, MG, com ênfase nos vetores de parasitoses

A malacological survey to detect foci of transmission of schistosomiasis and other parasitic diseases was undertaken into water-courses from 13 municipalities of microregion of Belo Horizonte, MG, Brazil. From 1990 to 1996, 22,066 snails were collected. From those, 378 (1.7%) were found infected by trematodes: Biomphalaria glabrata (7,920), infected by Schistosoma mansoni (1.9%), Echinostomatidae (1.2%), Strigeidae (0.6%), Cercaria minense (0.1%) and Derogenidae (-0.1%); B. straminea (4,093) infected by Strigeidae (0.6%), Echinostomatidae (0.2%), Clinostomatidae (-0.1%) and two unidentified cercariae; B. tenagophila (1,338), infected by Strigeidae (0.1%) and Physa marmorata (1,776) by Echinostomatidae (1.6%). The snails Biomphalaria peregrina, B. occidentalis, B. schrammi, Drepanotrema depressissimum, D. lucidum, D. cimex, Physa cubensis, Lymnaea columella, Melania tuberculata, Idiopyrgus souleyetianus, Pomacea sp, Anodontites sp and Ancylidae were found noninfected. Snails from 9 municipalities were infected by S. mansoni and from 11 by other trematodes.

Geographical distribution of Biomphalaria snails in the State of Minas Gerais, Brazil

Published and unpublished observations on geographical distribution of Biomphalaria snails in the State of Minas Gerais, Brazil, were compiled.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.

Situação atual da esquistossomose mansoni no Lago da Pampulha, Belo Horizonte, MG, Brasil

Descreve-se a atual distribuicao dos planorbideos hospedeiros intermediarios do Schistosoma mansoni no Lago da Pampulha, Belo Horizonte, MG (Brasil) e a rapida dispersao de Biomphalaria tenagophila por todo o perimetro lacustre. Relata-se o primeiro encontro de B. tenagophila naturalmente infectada por S. mansoni, naquela colecao hidrica. Discute-se, a importância epidemiologica destas observacoes e a possibilidade da B. tenagophila vir a substituir a primitiva populacao de B. glabrata no Lago da Pampulha.Descreve-se a atual distribuicao dos planorbideos hospedeiros intermediarios do Schistosoma mansoni no Lago da Pampulha, Belo Horizonte, MG (Brasil) e a rapida dispersao de Biomphalaria tenagophila por todo o perimetro lacustre. Relata-se o primeiro encontro de B. tenagophila naturalmente infectada por S. mansoni, naquela colecao hidrica. Discute-se, a importância epidemiologica destas observacoes e a possibilidade da B. tenagophila vir a substituir a primitiva populacao de B. glabrata no Lago da Pampulha.

Production of Shistosoma mansoni cercariae by Biomphalaria glabrata from a focus in Belo Horizonte, Minas Gerais

The snail density, levels of infection and the monthly production of Schistosoma mansoni cercariae by Biomphalaria glabrata were determined in a focus of Barreiro de Baixo (Belo Horizonte, MG, Brazil). During a period of 38 months (1984 to 1987) 5,366 snails were collected of which 324 (6.03%) were infected with S. mansoni. The total number of cercariae shed was 5,667,312. Each snail shed an average of 17,422 cercariae during the time that it was under study in the laboratory. The greatest longevity of infected snails was 218 days. Natural cure was observed in 42 (12.9%) of the infected specimens about 130 days after collection. The average snail density in the focus during the period of study was 16.3 snails per scoop. The shedding of cercariae by snails collected from the field was compared with laboratory bred specimens infected in mass with the LE strain of S. mansoni from Belo Horizonte. The laboratory infected snails shed an average of 6,061 cercariae each, a value 2.8 times less than the field specimens due to a shorter life span. The prevalence of schistosomiasis in the focus was 14.3%.

Algumas observações de campo sobre biologia e ecologia de Pomacea haustrum (Reeve, 1856) (Mollusca, Pilidae)

Some field observations on the pilid Pomacea haustrum (Reeve, 1856), predator-competitor of schistosomiasis mansoni planorbid intermediate hosts have shown that: Copula and oviposition are preferably carried out at night or at dawn. Eggmasses - whose dimension and shape depend on the number of eggs and types of supports - are often laid from 6 to 10 com above the water level and hatched 9 to 30 days after incubation; the average number of eggs/egg-mass was 236. Habitual food consist of confervoid algae, besides natant and submerged aquatic vegetation; it is common, however, the utilization of the other material as food. Its habitat is the shallower marginal zone of hidric collections, predominatly in lentic surrounding. Its spacial distribution is conditioned to the biotipe special characteristics. Some aquatic birds - anatid, ralid, etc. - reveal important natural enemies, attacking both young and adult specimens, besides the egg-masses; under certain conditions they may be an impedictive factor to the establishment and colonization of this pilid in new biotopes.

Algumas observações de laboratório sobre biologia e ecologia de Pomacea haustrum (Reeve, 1856)

Laboratory observation on the pilid Pomacea haustrum (Reeve, 1856), competitor and predator of Mansons schistosomiasis intermediate hosts, have shown that: Males and females reach sexual maturity after one year, copulating preferably in the morning and laying eggs at night. The time spent in these acts is variable; in the case of egglaying it depends on the number of eggs to be laid. The eggs are round, about 3mm in diameter, and have a pink color that changes with the development of the embryos. With an average incubation time of 15 to 23 days and conditioned by the temperature of the environment, they resist for 5 to 6 days immersed in water without damage to th embryos and they do not need light to hatch. The newly-hatched specimens have about 2.4 x 1,7 mm of height and diameter, respectively. The specimens bred alone grow more and survive better that when in a group. They resist for at least 90 days when left dry, remaining during this period enclosed in the shell, with the operculum hermetically closed, in hydrobiosis. In this phase, death by attack of diptera-larvae may occur.

Alguns dados bioecológicos de Pomacea haustrum (Reeve, 1856), predador-competidor de hospedeiros intermediários de Schistosoma mansoni Sambon, 1907

Foram feitas observacoes no laboratorio e no campo, em Belo Horizonte, MG, Brasil, com a finalidade de se obter informacoes biologicas e ecologicas sobre Pomacea haustrum (Reeve, 1856), molusco pilideo, competidor-predador de hospedeiros intermediarios de Schistosoma mansoni Sambon 1907.Foram feitas observacoes no laboratorio e no campo, em Belo Horizonte, MG, Brasil, com a finalidade de se obter informacoes biologicas e ecologicas sobre Pomacea haustrum (Reeve, 1856), molusco pilideo, competidor-predador de hospedeiros intermediarios de Schistosoma mansoni Sambon 1907.

Esquistossomose: nova ocorrência de Biomphalaria straminea em Belo Horizonte, Minas Gerais

In Belo Horizonte, Minas Gerais, Brazil, the snail Biomphalaria straminea was found in the Pampulha region. Recently the snail was found in ditches in the old Santa Lúcia Reservoir, a now-extinct focus of schistosomiasis transmission by B. glabrata. The snails were collected and examined to verify whether they were naturally infected with Schistosoma mansoni. Negative specimens were used for breeding or infection with the LE strain of S. mansoni from the laboratory and another strain obtained from eggs found in the feces of a schoolchild (VGS) from Belo Horizonte. Among the 1890 snails collected from 1994 to 1995, none were infected with S. mansoni. Among 87 snails collected and exposed to the LE strain, 9 (10.3%) shed cercariae; among 83 snails from F1, and exposed to LE, 10 (12.0%) shed cercariae. Among 88 snails exposed to VGS, 10 (11.3%) shed cercariae. In Belo Horizonte, schistosomiasis is transmitted by B. glabrata and B. tenagophila. However, currently there exists the risk of appearance of a focus in which B. straminea could be the host if prophylactic measures are not taken by the authorities responsible for the construction of a park and lake at that site.

Controle biológico: Pomacea haustrum Reeve, 1856 (Mollusca, pilidae) sobre planorbíneos, em laboratório

Foi acompanhado em laboratorio o controle de planorbineos (Biomphalaria straminea Dunker, 1848; B. tenagophila Orbigny, 1835 e B. glabrata Say, 1818), hospedeiros intermediarios da esquistossomose mansoni, atraves da predacao de suas desovas pelo pilideo Pomacea haustrum Reeve, 1856. De 829 desovas ovipostas por B. straminea, 203 (24,5%) foram expostas a 10 exemplares de P. haustrum; destas, 200 (98,3%) foram predadas. De 892 desovas ovipostas por B. tenagophia, 201 (22,5%) foram expostas a 10 exemplares de P. haustrum; destas, 194 (97,0%) foram predadas. De 1.300 desovas ovipostas por B. glabrata, 657 (50,5%) foram expostas a 10 exemplares de P. haustrum sendo totalmente predadas. Paralelamente, procurou-se observar as possiveis interacoes ocorridas entre pomaceas e planorbineos quando da coabitacao do mesmo aquario.Foi acompanhado em laboratorio o controle de planorbineos (Biomphalaria straminea Dunker, 1848; B. tenagophila Orbigny, 1835 e B. glabrata Say, 1818), hospedeiros intermediarios da esquistossomose mansoni, atraves da predacao de suas desovas pelo pilideo Pomacea haustrum Reeve, 1856. De 829 desovas ovipostas por B. straminea, 203 (24,5%) foram expostas a 10 exemplares de P. haustrum; destas, 200 (98,3%) foram predadas. De 892 desovas ovipostas por B. tenagophia, 201 (22,5%) foram expostas a 10 exemplares de P. haustrum; destas, 194 (97,0%) foram predadas. De 1.300 desovas ovipostas por B. glabrata, 657 (50,5%) foram expostas a 10 exemplares de P. haustrum sendo totalmente predadas. Paralelamente, procurou-se observar as possiveis interacoes ocorridas entre pomaceas e planorbineos quando da coabitacao do mesmo aquario.