Blood and intestinal parasites of squirrels (Rodentia: Sciuridae) in Amazonian Brazil

Abstract

During 2001-2002, a parasitological study was made of 12 specimens of the red squirrel Sciurus spadiceus captured along the AC 40 Highway, km 70, in the locality of Birroque, municipality of Plácido de Castro, state of Acre, North Brazil. Blood was obtained from the femoral vein of the animals for preparation of thin blood films and culture in Difco B45 medium blood-agar slants. Air-dried blood films were fixed in absolute methyl alcohol and stained by Giemsa's method. Cultures were checked at weekly intervals and only discarded if negative at one month.Faecal samples from the squirrels were lightly triturated in 2% aqueous potassium dichromate solution (K 2 Cr 2 O 7 ) and spread as a thin layer in covered Petri dishes kept at approximately 24-26ºC. They were examined at once for the presence of coccidial oocysts, using normal light microscopy at magnifications of x 160 and x 400 and then at daily intervals to follow development of any oocysts detected. Bile was removed from the gall bladder of autopsied animals and also examined for oocysts. Tissues for histology were fixed in 10% buffered formol-saline, embedded in paraffin wax and examined in sections cut at 4 µm and stained with haematoxylin and eosin. Photomicrographs were made with a Zeiss "Photomicroscope III" and Kodak TMX 100 film. No parasites were detected in the Giemsa-stained blood films of the squirrels, but growth of epimastigotes occurred in the cultures of blood from three of them. The culture forms of one isolate were morphologically quite different from those of the other two cultures, and when inoculated into laboratory mice produced trypomastigotes which were morphologically indistinguishable from T. cruzi (Fig. 1). The epimastigotes of the other two cultures were remarkably elongated (Fig. 2) and inoculation of parasites from 10 day-old cultures into mice and hamsters gave rise to infections with a Trypanosoma lewisi-like parasite (Fig. 3). These infections were of a fleeting nature, however, and by the 4th day post-inoculation the trypanosomes had disappeared from the peripheral blood: subsequent attempts to isolate the parasite from the mice following the culture of blood failed.Initially, morphology of the trypomastigotes led us to suspect that the T. lewisi-like parasite might be T. rangeli and so, on three occasions, batches of approximately 20 nymphs of the triatomine bug Rhodnius robustus were fed on mice which were showing trypomastigotes in their peripheral blood at two days p.i. Dissection of the bugs made at 1, 2, 4, and 6 weeks after the blood-meal showed no development of the parasite in the intestine or the haemolymph.The type host of T. rangeli Tejera, 1920 is the triatomine R. prolixus and natural and experimental infections have also been recorded in a wide variety of other triatomine species (D'Alessandro 1976). R. robustus is very closely related to R. prolixus (Lent & Wygodzinsky 1979), to the extent that doubts have been expressed that they represent two distinct species. Our failure to infect R. robustus with the T. le...

Insights into the Biology of Leucocytozoon Species (Haemosporida, Leucocytozoidae): Why Is There Slow Research Progress on Agents of Leucocytozoonosis?

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Spatio-temporal survey of small mammal-borne Trypanosoma lewisi in Cotonou, Benin, and the potential risk of human infection

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Trypanosome diversity in small mammals in Uganda and the spread of Trypanosoma lewisi to native species

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