Reproduction, structure and host specificity of Trypanosoma (Herpetosoms) tamiasi sp. n. from the eastern chipmunk, Tamias striatus

Morphological polymorphism of Trypanosoma copemani and description of the genetically diverse T. vegrandis sp. nov. from the critically endangered Australian potoroid, the brush-tailed bettong (Bettongia penicillata (Gray, 1837))

Background

The trypanosome diversity of the Brush-tailed Bettong (Bettongia penicillata), known locally as the woylie, has been further investigated. At a species level, woylies are critically endangered and have declined by 90% since 1999. The predation of individuals made more vulnerable by disease is thought to be the primary cause of this decline, but remains to be proven.

Methods

Woylies were sampled from three locations in southern Western Australia. Blood samples were collected and analysed using fluorescence in situ hybridization, conventional staining techniques and microscopy. Molecular techniques were also used to confirm morphological observations.

Results

The trypanosomes in the blood of woylies were grouped into three morphologically distinct trypomastigote forms, encompassing two separate species. The larger of the two species, Trypanosoma copemani exhibited polymorphic trypomastigote forms, with morphological phenotypes being distinguishable, primarily by the distance between the kinetoplast and nucleus. The second trypanosome species was only 20% of the length of T. copemani and is believed to be one of the smallest recorded trypanosome species from mammals. No morphological polymorphism was identified for this genetically diverse second species. We described the trypomastigote morphology of this new, smaller species from the peripheral blood of the woylie and proposed the name T. vegrandis sp. nov. Temporal results indicate that during T. copemani Phenotype 1 infections, the blood forms remain numerous and are continuously detectable by molecular methodology. In contrast, the trypomastigote forms of T. copemani Phenotype 2 appear to decrease in prevalence in the blood to below molecular detectable levels.

Conclusions

Here we report for the first time on the morphological diversity of trypanosomes infecting the woylie and provide the first visual evidence of a mixed infection of both T. vegrandis sp. nov and T. copemani. We also provide supporting evidence that over time, the intracellular T. copemani Phenotype 2 may become localised in the tissues of woylies as the infection progresses from the active acute to chronic phase. As evidence grows, further research will be necessary to investigate whether the morphologically diverse trypanosomes of woylies have impacted on the health of their hosts during recent population declines.

Trypanosoma (Herpetosoma) kuseli sp. n. (Protozoa: Kinetoplastida) in Siberian flying squirrels (Pteromys volans)

All trypanosome species classified in the subgenus Herpetosoma in sciurid hosts have been recorded from ground and tree squirrels to date, but not from any flying squirrels. We describe in this paper a novel trypanosome species, Trypanosoma (Herpetosoma) kuseli sp. n., from Siberian flying squirrels (Pteromys volans) imported from China, and compare it with T. (H.) otospermophili in Richardson's ground squirrels (Spermophilus richardsonii) and Columbian ground squirrels (Spermophilus columbianus) from the USA. Due to a short free flagellum, the new species appeared stumpy compared with T. otospermophili (length of free flagellum 7.0 +/- 0.8 microm, total length 32.1 +/- 0.8 microm, n = 13 and length of free flagellum 15.5 +/- 1.6 microm, total length 35.9 +/- 1.0 microm, n = 13, respectively). Another conspicuous morphological feature of the new species was an anteriorly positioned kinetoplast, found approximately at the midpoint between the nucleus and the posterior end. These characters have not been recorded from any squirrel Herpetosoma trypanosome species. Comparison of the nucleotide sequences of the small and large subunit rRNA genes indicated that T. kuseli sp. n. was more homologous to T. otospermophili than murid Herpetosoma species, such as T. grosi, T. lewisi, T. musculi, T. microti and T. evotomys.

Trypanosoma acomys (Wenyon, 1909): reproductive forms and course of parasitemia in the natural host Acomys cahirinus (Desmarest, 1819)

Trypanosoma acomys (Stercoraria, Trypanosomatidae) was studied in the laboratory-bred spiny mouse Acomys cahirinus. Only trypomastigotes were found in peripheral blood, whereas the thymus of experimentally infected A. cahirinus showed amastigote syncytial reproductive forms whose nuclei of nuclei ranged from 2 to 128. These reproductive forms were detected 9-10 days after the i.p. injection of spiny mice with trypanosomes obtained from primary lung cultures. Transitional trypomastigote-like forms were observed in the thymus; no reproductive or diving forms were encountered in any other tissue, including blood. The course of the parasitemia in spiny mice inoculated i.p. with 1.2 x 10(6) parasites from 26- to 32-day-old cultures initiated from infected lungs was studied. A similar, characteristic pattern was observed in both male and female hosts. Four phases were recognized: latent, logarithmic, stationary, and decline. These phases ended on days 2, 14, 98, and 154 postinoculation, respectively. The decline phase was gradual and the parasites could not be detected by day 154 postinoculation. In contrast, inoculation from older cultures (35-50 days old) showed longer latent and logarithmic phases, a shorter stationary phase, and a sharp drop in parasite density during the decline phase; the parasites were not detected in the peripheral blood by 120 days postinoculation.

In vitro cultivation of Herpetosoma trypanosomes in insect cell tissue culture media

The cultivation of Herpetosoma trypanosomes in insect tissue culture media supplemented with foetal calf serum is described. Trypanosoma lewisi and T. musculi, which can be grown in blood agar media, were compared with four other species of Herpetosoma trypanosomes, T. microti, T. evotomys, T. grosi and T. nabiasi, in their growth in Schneider's Drosophila medium, Grace's, Mitsuhashi-Maramorosch, RPMI 1640, TCM 199 and nutrient blood agar media. Schneider's Drosophila and Grace's media supplemented with 20% foetal calf serum proved the most suitable media for growth of all parasites except T. nabiasi from rabbits which was not successfully established. Primary cultures were passaged after approximately 3 weeks and were maintained to continuously produce metacyclic trypomastigotes which produced less virulent infections although they maintained their infectivity to their respective hosts. The growth patterns in culture and morphology of the parasites are described.