Faculty of Veterinary Science
Department of Veterinary Tropical Diseases
Selected Highlights from Research Findings
The aim of this study was to assess the existence of possible cross-protection between Trypanosoma congolense strains of low and extreme virulence circulating in the same trypanosomosis focus. Groups of six mice were infected using one of three strains of low virulence and challenged with one of three strains of adverse effects of extremely virulent T. congolense strains. Results indicated that mice infected with one of the strains of extreme virulence developed high parasitaemia and a significant drop of the packed cell volume, compared to mice infected with a strain of low virulence and challenged with one of the strains of extreme virulence. With an exception of one strain of extreme virulence, the survival time of mice infected with the strains of extreme virulence was shorter compared to mice infected with strains of low virulence and subsequently challenged with a strain of extreme virulence. These results suggest that in an area where trypanosomes of various virulence profiles circulate, livestock infected with T. congolense strains of low virulence can be protected against the adverse effects of extremely virulent T. congolense strains.
Contact person: Dr JM Masumu.
Babesia rossi, an intraerythrocytic protozoan, causes a severe, often life-threatening disease in domestic dogs. Dogs infected with B. rossi have varied clinical manifestations, ranging from uncomplicated (with a good prognosis) to complicated (with a poor prognosis). Blood samples from Babesia-infected dogs were screened by polymerase chain reaction (PCR) targeting the Babesia rossi erythrocyte membrane antigen gene (BrEMA1) and by sequencing of the polymorphic region (that is, the region with a variable number of hexapeptide repeats). Analysis of PCR products revealed 11 different gene profiles, visualised by gel electrophoresis. Twelve distinct BrEMA1 genotypes – identified by sequencing – were retrospectively compared to the clinical case data. The most frequently encountered genotypes were also the ones associated with the poorest prognosis. This preliminary finding suggests clinically important differences between the various manifestations of the disease.
Contact person: Dr PT Matjila.
Blood specimens were received from five cases in which young adult giraffe, from different geographic origins in South Africa, showed sudden onset of disease and subsequently died. Additional specimens from two translocated giraffe were also included in the study. Blood slides from some of these animals showed the presence of piroplasms. DNA was extracted, the V4 hypervariable region of the 18S rRNA gene amplified and analysed using the reverse line blot hybridisation assay. PCR products failed to hybridise with any of the Babesia or Theileria species-specific probes, and only hybridised with the Babesia/Theileria genus-specific probe, suggesting the presence of a novel species or variants of a species. Full-length 18S rDNA was amplified, cloned and the recombinants were sequenced. The 18S rRNA gene sequence similarity analysis revealed the presence of novel piroplasm species in both healthy and clinically sick or dead giraffes. Phylogenetic analysis grouped five of these organisms in the Babesia sensu stricto clade and three in the Theileria sensu stricto clade. Although parasites were observed in blood smears, there is no direct evidence that the five giraffes died of piroplasmosis, although it seems likely.
Contact person: Dr MC Oosthuizen.
A molecular epidemiological survey of the protozoal parasites that cause equine piroplasmosis revealed the existence of as many as 25 distinct 18S rRNA sequences for Theileria equi, which belonged to three main groups, and six different Babesia caballi 18S sequences, which formed two distinct genetic groups. The researchers developed a TaqMan minor groove binder (MGB™) qPCR assay, targeting the 18S rRNA gene, for the detection of B. caballi infections in equine blood samples, and evaluated the ability of a recently developed T. equi-specific qPCR assay to detect all T. equi 18S rRNA variants identified in South Africa. Both tests were sensitive and specific and could detect the parasites in field samples.
Contact person: Dr NE Collins.
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