Schistosomiasis is a health problem in Brazil and the role of rodents in maintaining the schistosome life-cycle requires further clarification. The influence of Schistosoma mansoni on a population of Nectomys squamipes was studied by capture-recapture (1st phase, from June 1991 to November 1995) and removal (2nd phase, from April 1997 to March 1999) studies at Sumidouro, Rio de Janeiro, Brazil. During both phases coproscopic examinations were performed. At the 2nd phase the rodents were perfused and worms were counted. The population dynamics of parasites was studied. During the 1st phase, female reproductive parameters, longevity, recruitment and survivorship rates and migration patterns were studied in relation to schistosome prevalence. Water contamination (source of miracidia), abundance intermediate host and rodent migration were related to prevalence. The N. squamipes population was not obviously influenced by the infection, as shown by the high number of reproductive infected females, high longevity of infected individuals and the absence of a relationship between recruitment or survivorship rates and the intensity of schistosome infection. The data indicate that N. squamipes can increase transmission of S. mansoni in endemic areas and carry it to non-infected areas. Furthermore, this rodent can be used as an indicator of a transmission focus.
The water rat, Nectomys squamipes, is reported as a natural host of Schistosoma mansoni in Brazil. This paper presents some reproductive, growth and developmental data, and laboratory management of a breeding programme for N. squamipes. The colony was derived from animals captured at Sumidouro, Rio de Janeiro state. The animals' diploid number was 56, conception rate was 66.7% and gestation period was 30 days. Litter size ranged from 1 to 6, with a mean of 4.1 (SD +/- 1.2) and a mode of 4 and 5. Sex ratio at birth and at weaning was not significantly different from the expected ratio of 1:1. There were no significant differences between mean body weights at birth for males and females. The minimum age for weaning was between 20-25 days. The growth curves of body weight, head-body length and tail length, for both sexes, comprise at least three linear segments representing different phases of approximately constant growth rates. Facilities for colony maintenance and its potential for use as experimental model are reported.
Echinostoma paraensei Lie and Basch, 1967 (Echinostomatidae:Platyhelminthes), a 37 collar spine echinostome of the "revolutum group", has been used extensively as a model organism to study the interactions of digenetic trematodes with both their snail and vertebrate hosts. This worm was first isolated from the snail Biomphalaria glabrata from Belo Horizonte (BH isolate), Minas Gerais State, Brazil, by Lie and Basch [J Parasitol (1967) 53:1192-1199]. The natural definitive host for the BH isolate was never determined, and it has been maintained in the laboratory since 1967 in B. glabrata and hamsters. In this study, using light and scanning electron microscopy and molecular analysis, we describe an echinostome recently obtained from its natural vertebrate host, the wild rodent Nectomys squamipes (Rodentia: Sigmodontinae) from Sumidouro, Rio de Janeiro State, Brazil (RJ isolate). This echinostome was also compared to the laboratory-maintained BH isolate of E. paraensei. We observed that adult worms of both BH and RJ isolates could be differentiated from other echinostome species by the relatively small size of the dorsal collar spines relative to lateral and corner collar spines. SEM confirmed the similarity of this morphological character between the two isolates. As additional diagnostic features, the tegumentary spines are scale-like and the region between the genital pore and the acetabulum lacks scales. There is a folded protuberance with a pore just posterior to the genital pore. The tegument of the acetabulum is unspined and radially wrinkled, and there are numerous randomly distributed small, domed, ciliated papillae. The sequences of the internal transcribed spacers of the nuclear rDNA complex of the RJ and BH isolates are identical. Together these shared features provide strong evidence that both isolates are the same and can be referred to as E. paraensei. In conclusion, we have identified, for the first time, one of the natural definitive hosts for E. paraensei, the rodent N. squamipes, and have extended the known geographical distribution of this species to include Sumidouro in Rio de Janeiro State, Brazil.
The water rat Nectomys squamipes is endemic in Brazil and found naturally infected with Schistosoma mansoni. Helminth communities, their prevalences, intensity of infection and abundance in N. squamipes in an endemic area of schistosomiasis in the state of Rio de Janeiro, Brazil were studied. Four species of nematodes (Physaloptera bispiculata, Syphacia venteli, Hassalstrongylus epsilon and Litomosoides chagasfilhoi) were recovered in 85.3%, two trematodes (Schistosoma mansoni and Echinostoma paraensei) in 38.8% and one cestode species (Raillietina sp.) in 1.7% of rats examined. Rats were infected with up to five helminth species each, and these were highly aggregated in distribution. For H. epsilon and S. venteli, intensities and abundances were higher in adult male and subadult female hosts, respectively. Hassaltrongylus epsilon, P. bispiculata, S. venteli and S. mansoni were classified as dominant species, L. chagasfilhoi and E. paraensei as co-dominant and Raillietina sp. as subordinated. No significant correlation was found in the intensity of infecton between each pair of helminth species. Schistosoma mansoni was not related to any other helminth species according to their infection rates, althougth S. mansoni was well established in the natural helminth comunity of the water rat.
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