The importance of platynosomiasis has increased in feline veterinary practice, but aspects related to the specificity of Platynosomum spp. in definitive hosts requires further study. Although morphological traits suggest that the same species, P. illiciens, may infect both birds and mammals, the synonymies previously proposed have not been widely accepted, likely because host specificity is assumed. In addition, the name P. fastosum has frequently been used for parasites recovered from mammals. In the present study, metacercariae (n= 100/animal) of P. illiciens recovered from lizards (Hemidactylus mabouia) in Brazil were fed to Australian parakeets (Melopsittacus undulatus) and mice. Two parasites were recovered from the liver of one M. undulatus specimen during a necropsy that was performed 105 days after infection, and all mice were found to be infected with 37 ± 12 (18-48) parasites. The morphology of the P. illiciens obtained from the parakeet was similar to that of parasites obtained from mice and those described previously from naturally infected birds and mammals. Non-specificity of P. illiciens in hosts is discussed briefly, based on the parasitological and morphological results obtained during the avian experimental platynosomiasis and the epidemiology and geographical distribution of this parasite.
Recently, the transformation of Schistosoma mansoni cercaria into schistosomulum have been investigated by several workers, mainly in relation to the immunological and biochemical aspects. A t first glance a logical conclusion from the facts available is that various modification steps occur during the transformation of a cercaria (a free living larva adapted to a freshwater environment) to a schistosomulum (an organism newly adapted to the host conditions).Various methods for collecting living schisto somula have been described and the larvae have been recovered both in vitro and in vivo. The basic differences between cercaria and schistosomulum were established by Stirewalt1** 20 Additional differences were subsequently reported^ 3 9 11 12 22 23 24 These differences are the standard criteria by which the organisms recovered by in vitro methods can be considered to be schistosomula.
Belostoma anurum was reared under laboratory conditions. Specimens were exposed to semi-natural conditions of photo period. The mortality rate was 26.3% during the post embryonic period (38.6 ± 0.7 days). During this time the average predation of Biomphalaria glabrata was of 99.0 ± 9.4 snails. The mean increment ratio of length and dry weight per instar was of 1.4 ± 0.1 and 2.8 ± 0.5, respectively. The predation by B. anurum adults can be divided into two different periods: phase I (4.8 ± 1.4 snails/day) and phase II (1.8 ± 0.5 snails/day). The higher predation in phase I suggested the sexual maturation of the belostomatid.
Treatment with dexamethasone (DMS) in the early phases of the experimental Schistosoma mansoni infection causes an indirect effect on the cercaria-schistosomulum transformation process. This is observed when naive albino mice are treated with that drug (50 mg/Kg, subcutaneously) and infected intraperitonealy 01 hour later with about 500 S. mansoni cercariae (LE strain). An inhibition in the host cell adhesion to the larvae, with a simultaneous delay in the cercaria-schistosomulum transformation, is observed. This effect is probably due to a blockade of the neutrophil migration to the peritoneal cavity of mice, by an impairment of the release of chemotactic substances. Such delay probably favors the killing of S. mansoni larvae, still in the transformation process, by the vertebrate host defenses, as the complement system.
In Brazil, when prevalence data were examined using simple summary statistics, there is a negative association between prevalence of Taenia spp. infection and Schistosoma mansoni or soil-transmitted helminths (STH) irrespective to routes of infection. That does not occur in African data. However, they vary considerably when plotted. So, in data collected on Brazilian area, it to show in ordered (smallest first) scores prevalence of STH infections both long lag phase in prevalence of STH infecting by oral route (Ascaris and Trichuris), and into STH infecting by skin route (hookworm and Strongyloides). To the other side, African study it show smaller lag phase in prevalence of STH infecting by oral route or into STH infecting by skin route. Darwinian, it was suggested Taenia spp. and STH, inhabiting a nonhuman environment which became so suitable for them according to their biological needs, their develop by means of natural selection.
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