Nectomys squamipes (Rodentia: Cricetidae) as an experimental model for schistosomiasis mansoni

Twenty specimens of Nectomys squamipes born in captivity, were infected with 500 cercariae by the transcutaneous route. Coprologic examinations were carried out from the 5th to 23rd week after infection. On the 7th, 8th, 12th, 16th, and 23rd weeks the animals were sacrificed and perfused. The oogram was performed in segments of the small intestine (proximal, medial and distal portions) and the large intestine. The average pre-patent period was of 42 days. The average number of eggs varied from 350 on 6th week, to 800 on the 13th. From the 14th week on, the average number of eggs eliminated was lower than 50 per gram of feces. The recovery of worms kept steady on the 7th, 8th, and 12th week (16.85%; 15.45% and 11.95%), decreasing to 7.70% on the 16th week and 8.45% on the 23rd week. The proportion of male/female worms was about the same on the first two weeks, but from the 12th week on, the proportion was: 1,4/1 on the 12th week; 2,5/1 on the 16thweek and 1,8/1 on the 23rd weekThese observations suggest that N. squamipes may used as an experimental model for schistosomiasis mansoni, to wich it develops resistance mechanism, useful for immunity studies.

Evaluation of the resistance to Schistosoma mansoni infection in Nectomys squamipes (Rodentia: Cricetidae), a natural host of infection in Brazil

The development of resistance in three stages throughout an active infection (pre-ovular, acute and initial chronic stages) was studied, comparing the total number of adult worms recovered from the reinfected group and the control groups. It was shown that Nectomys squamipes was unable to develop resistance in the tested conditions and, on the other hand, reinfection in the pre-ovular period of the parasite led the rodent to present the phenomenonacilitation, with reduction of natural resistance and an increase in the parasite load. These results suggest the existence of other forms of immunity diverse from the concomitant immunity in the host-parasite relationship, according to the employed model.

Biological implications of the phenotypic plasticity in the Schistosoma mansoni - Nectomys squamipes model

The water-rat Nectomys squamipes is mostly important non-human host in schistosomiasis mansoni transmission in Brazil, due to its susceptibility, high abundance and water-contact pattern. During experimental infection of N. squamipes with Schistosoma mansoni, adult worms show phenotypic plasticity. This finding led us to investigate whether biological behavior is also affected. This was assessed comparing the biological characteristics of four S. mansoni strains: BE (State of Belém do Pará), CE (State of Pernambuco), CMO (State of Rio Grande do Norte) and SJ (State of São Paulo) using laboratory-bred N. squamipes. The infection was monitored by determination of the pre-patent period, fecal egg output, egg viability, intestinal egg count and, infectivity rate. No biological modification was observed in these parameters. Overall results highlight that N. squamipes was susceptible to several S. mansoni strains, suggesting that it might contribute to the maintenance of schistosomiasis mansoni in Brazil.

Maritremopsis mariettavogeae sp. n. (Trematoda, Microphallidae) and Amphimerus lancea (Diesing, 1850) (Trematoda, Opisthorchiidae) parasites of Nectomys Squamipes (Rodenta) in Brazil

In this paper two species of trematodes recovered from nectomys squamipes from Goiás State, Brazil, are presented. Maritremopsis mariettavogeae sp. n. is compared to M. proxilum (Caballero & Montero-Gei, 1961) and M. belopolskaiae (Caballero, 1964). Amphimerus lancea originally described from a cetacean host, is for the first time referred in a rodent.

Helmintos parasitos de Nectomys squamipes (Brants) do município de Sumidouro, RJ

Os helmintos encontrados em setenta e uma necrópsias de Nectomys squamipes, capturados no Município de Sumidouro, Estado do Rio de janeiro, São analisados qualitativamente e quantitativamente. Foram estudadas as seguintes espécies: Pseudechinostomum caballeroi, Raillietina sp., Hassalstrongylus epsilon, Syphacia venteli, Aspidodera raillieti, Physaloptera getula e Litomosoides carinii.

Holochilus brasiliensis and nectomys squamipes (Rodentia-Cricetidae) natural hosts of Schistosoma mansoni

After several Brazilian researches, the author examines the capacity of two species of rodents Cricetidae, Holochilus brasiliensis and Nectomys squamipes, to maintain the biological cycle of Schistosoma mansoni in the field and to be parasite reservoir: (a) the role they are able to play in human endemy; (b) the methods necessary to characterize the population of Schistosoma mansoni related either to man, either to rodents, either to both.

Amphimerus bragai N. Sp. (Digenea: Opisthorchiidae), a Parasite of the Rodent Nectomys squamipes (Cricetidae) from Minas Gerais, Brazil

Amphimerus bragai n.sp. (Digenea, Opisthorchiidae) from the bile ducts of a rodent from the State of Minas Gerais, Brazil, Nectomys squamipes (Cricetidae), is described. The new species was studied by both light and scanning electron microscopy. A table is presented comparing the measurements of the new species with those of A. lancea (Diesing, 1850) and A. vallecaucensis Thatcher, 1970, parasites of dolphins and marsupials, respectively. The new species is similar in size and body form to A. vallecaucensis from which it differs in having a vitellarium that extends to the acetabulum while that of the former species are limited to the posterior one-third of the body. Additionally, the new species is from a rodent.

Susceptibility of Nectomys rattus (Pelzen, 1883) to experimental infection with Schistosoma mansoni (Sambon, 1907): a potential reservoir in Brazil

The aim of the present research was to evaluate the potential of Nectomys rattus, the "water rat", to develop Schistosoma mansoni infection. Comparison with N. squamipes was carried out. Both species of rodents were submitted to transcutaneous infection using different infective cercariae loads: 50, 100 or 500. N. rattus showed high susceptibility to S. mansoni, with an infection rate of 71%. Rodents were able to excrete viable eggs of S. mansoni in the feaces during all infection period. For both species, the small intestine, followed by the liver and the large intestine, presented the highest concentration of eggs among the surveyed organs. Infection caused no animal death. Moreover, N. rattus accomplished the parasite's life cycle, by infecting the snails Biomphalaria glabrata and later Mus musculus. These evidences indicate that both N. rattus, as for N. squamipes are potential reservoirs for schistosomiasis in Brazil. Considering the fact that N. rattus and N. squamipes exist in the same natural ecosystems of S. mansoni, we suggest that these rodents must be regarded as influential factors in epidemiology surveys.

Changes on Schistosoma mansoni (Digenea: Schistosomatidae) worm load in Nectomys squamipes (Rodentia: Sigmodontinae) concurrently infected with Echinostoma paraensei (Digenea: Echinostomatidae)

The water rat, Nectomys squamipes, closely involved in schistosomiasis transmission in Brazil, has been found naturally infected simultaneously by Schistosoma mansoni and Echinostoma paraensei. Laboratory experiments were conducted to verify parasitic interaction in concurrent infection. It was replicated four times with a total of 42 water rats and essayed two times with 90 mice pre-infected with E. paraensei. Rodents were divided into three groups in each replication. A wild strain recently isolated from Sumidouro, RJ, and a laboratory strain of S. mansoni from Belo Horizonte (BH) was used. Rats infected with E. paraensei were challenged 4 weeks later with S. mansoni and mice 2 or 6 weeks after the infection with S. mansoni. Necropsy took place 8 weeks following S. mansoni infection. The N. squamipes treatment groups challenged with S. mansoni RJ strain showed a significant decrease (80 and 65%) in the S. mansoni parasite load when compared with their respective control groups. There was a significant change or no change in the hosts challenged with the BH strain. The persistence time of E. paraensei within host was extended in relation to control groups, with a consequent enhancement of the number of recovered worm. An E. paraensei strain-specific influence on S. mansoni parasitism is reported. This paper presents some experimental data about this interaction in N. squamipes and Mus musculus.

Cercarial Chaetotaxy and Sex Differentiation of Schistosoma mansoni Deriving from Humans and Nectomys squamipes (Muridae: Sigmondontinae) in Brazil

A comparative study was made between sympatric isolates of Schistosoma mansoni: one from a wild rodent (R) Nectomys squamipes and another one from humans (H) isolated from a low endemic schistosomiasis transmission area in Brazil. Our purpose was to detect differences between them concerning chaetotaxy (number and pattern of distribution of the argentophilic papillae) of the cercariae by means of silver impregnation. No significant difference (x > 0.05) between isolates was noted. Nevertheless, a significant difference (x < 0.05) was observed in the cercarial index (ratio of the distance between the first and the second preacetabular papillae and the distance between the first and the second dorsal preacetabular papillae) of male and female cercariae in both isolates. Males presented a greater cercarial index than females. By means of multivariate analysis, male cercariae were distinguished from female cercariae through the following characteristics: average number of dorsal papillae on the right quadrant, average number of ventral middle papillae on the right quadrant (H isolate) and average number of dorsal middle papillae on the left quadrant (R isolate). The results suggest that R and H isolates belong to the same population that could complete its life cycle in rodent-snail-rodent fashion.

Experimental evidence and ecological perspectives for the adaptation of Schistosoma mansoni Sambon, 1907 (Digenea: Schistosomatidae) to a wild host, the water-rat, Nectomys squamipes Brants, 1827 (Rodentia: Sigmodontinae)

Due to the semi aquatic habits and the overlap of the geographical distribution of the water-rat, Nectomys spp., with schistosomiasis endemic areas, these wild rodents are very likely to acquire Schistosoma mansoni infection in their daily activities. The role of the water-rat in the S. mansoni cycle would be substantiated if one could prove that these rodents acquire the parasite during their own activity time, a completely independent time schedule of human activities. To pursue this goal, we performed two field experiments in the municipality of Sumidouro, State of Rio de Janeiro, Brazil, a schistosomiasis endemic area where N. squamipes is found naturally infected. One experiment was devised as a series of observations of activity time of the water-rat. The other experiment was a test of the occurrence of late transmission of S. mansoni to the water-rat. The daily activity pattern showed that the water-rat is active chiefly just after sunset. At both diurnal and late exposition essays the water-rat sentinels got infected by S. mansoni. These findings clarify ecological and behavioral components necessary to the adaptation of S. mansoni to the water-rat as a non human definitive host and the existence of a transmission cycle involving this animals as a reservoir.

Natural Schistosoma mansoni infection in Nectomys squamipes: histopathological and morphometric analysis in comparison to experimentally infected N. squamipes and C3H/He mice

Histopathologic and morphometric (area, perimeter, major and minor diameters) analysis of hepatic granulomas isolated from twelve naturally infected Nectomys squamipes were compared to four experimentally infected ones and six C3H/He mice. Liver paraffin sections were stained for cells and extracellular matrix. Both groups of N. squamipes presented peculiar granulomas consisting predominantly of large macrophages, full of schistosome pigment, characterizing an exudative-macrophage granuloma type, smaller than the equivalent granuloma type in mouse. Naturally infected animals exhibited granulomas in different stages of development, including large number of involutional types. Morphometric analysis showed that all measurements were smaller in naturally infected animals than in other groups. The results demonstrated that both N. squamipes groups reproduced, with small variations, the hepatic granuloma aspects already described in cricetidium (Calomys callosus), showing a genetic tendency to set up strong macrophage responses and small granulomas. Unexpectedly, natural infection did not engender distinguished histopathological characteristics distinct from those derived from experimental single infection, showing changes predominantly secondary to the duration of infection. It appears that the variability of the inocula (and the number of infections?) interfere more with the quantity than with the quality of the pathological changes, denoting some morpho-functional determinism in the response to schistosomal infection dependent on the animal species.

Reproductive system abnormalities in Schistosoma mansoni adult worms isolated from Nectomys squamipes (Muridae: Sigmodontinae): brightfield and confocal laser scanning microscopy analysis

Schistosoma mansoni adult worms with genital anomalies isolated from Nectomys squamipes (Muridae: Sigmodontinae) were studied by confocal laser scanning microscopy under the reflected mode. One male without testicular lobes (testicular agenesia/anorchism) and two females, one with an atrophied ovary and another with 17 uterine eggs, were identified. The absence of testicular lobes occurred in a worm presenting otherwise normal male adult characteristics: tegument, tubercles and a gynaecophoric canal with spines. In both female specimens the digestive tube showed a vacuolated appearance, and the specimen with supernumerary uterine eggs exhibited a developing miracidium and an egg with a formed shell. The area of the ventral sucker was similar in both specimens however the tegument thickness, ovary and vitelline glands of the specimen with the atrophied ovary were smaller than those of the one with supernumerary eggs. These reported anomalies in the reproductive system call attention to the need to improve our understanding of genetic regulation and the possible role of environmental influences upon trematode development.

An ecological field study of the water-rat Nectomys squamipes as a wild reservoir indicator of Schistosoma mansoni transmission in an endemic area

Small mammals are found naturally infected by Schistosoma mansoni, becoming a confounding factor for control programs of schistosomiasis in endemic areas. The aims of this study were: to investigate the infection rates by S. mansoni on the water-rat Nectomys squamipes during four years in endemic areas of Sumidouro, state of Rio de Janeiro, using mark-recapture technique; to compare two diagnostic methods for schistosomiasis; and to evaluate the effects of the chemotherapy in the human infected population on the rodent infection rates. The rodent infection rates of S. mansoni increased when rodent population sizes were lower. Coprology and serology results presented the same trends along time and were correlated. Serology could detect recent infection, including the false negatives in the coprology. The chemotherapy in the humans could not interrupt the rodent infection. Rodents can increase the schistosomiaisis transmission where it already exists, they probably maintain the transmission cycle in the nature and can be considered as biological indicators of the transmission sites of this parasite since they are highly susceptible to infection. The water-rats may present different levels of importance in the transmission dynamics of S. mansoni infection cycle for each area, and can be considered important wild-reservoirs of this human disease.

Nests and nesting sites of Brazilian forest rodents (Nectomys squamipes and Oryzomys intermedius) as revealed by a spool-and-line device

Patterns of nest construction and nest site selection of two murid rodents of the Brazilian Atlantic rainforest were described. The animals were captured in an area of about 1.5 ha of primary forest, marked, equipped with a spool-and-line device and released at the capture point. The next day we followed the thread to find their nests. In total 11 nests of Nectomys squamipes (Brants, 1827) and 13 of Oryzomys intermedius (Leche, 1886) were found. They were all egg-shaped, about 15 cm long and 10 cm wide, without any apparent entrance and consisted of dry leaves and grass. The two species differed in the selection of nest sites. The nests of N. squamipes were close to streams and built inside decomposed fallen logs or using natural entrances between the soil and tangled roots or rocky crevices. Nests of O. intermedius were built under or inside fallen logs and inside aerial root systems of palms. The spool-and-line technique used here is useful to provide detailed information on several aspects of the ecology and natural history of small mammals.