Virulence in Trypanosoma congolense Savannah subgroup. A comparison between strains and transmission cycles.

Trypanosoma congolense strains have been shown to differ in their virulence both between subgroups and within the Savannah subgroup between strains. This review revisits these findings and complements them with information on the virulence of T. congolense Savannah subgroup strains isolated from cattle (domestic transmission cycle) in different geographical areas and of strains isolated in protected areas where trypanotolerant wildlife species are the reservoir of the trypanosomes (sylvatic transmission cycle). The virulence of a total of 62 T. congolense Savannah subgroup strains (50 domestic and 12 sylvatic), determined using a standard protocol in mice, was compared. Virulence varied substantially between strains with, depending on the strain, the median survival time of infected mice varying from five to more than sixty days. The proportion of highly virulent strains (median survival time <10 days) was significantly (P = 0·005) higher in strains from the sylvatic transmission cycle. The analysis highlights repercussions of the domestication of the trypanosomiasis transmission cycle that may have to be taken in consideration in the development of trypanosomiasis control strategies.

Combination therapy using intratumoral bacillus Calmette-Guerin (BCG) and vincristine in dogs with transmissible venereal tumours: therapeutic efficacy and histological changes.

Therapeutic efficacy and histological changes after bacillus Calmette-Guerin (BCG), vincristine and BCG/vincristine combination therapy of canine transmissible venereal tumours (CTVT) were studied. Twenty dogs with naturally occurring CTVT in the progression stage were divided into 4 groups and treated with intratumoral BCG, vincristine, BCG/vincristine combination therapy or intratumoral buffered saline (control group). Tumour sizes were determined weekly and tumour response to therapy was assessed. Tumour biopsies were taken weekly to evaluate histological changes. Complete tumour regression was observed in all the dogs treated with BCG, vincristine and BCG/vincristine combination therapy. BCG/vincristine combination therapy had a statistically significantly shorter regression time than BCG or vincristine therapy. No tumour regression was observed in the control group. Intratumoral BCG treatment resulted in the appearance of macrophages and increased numbers of tumour infiltrating lymphocytes (TILs) followed by tumour cell apoptosis and necrosis. Treatment with vincristine resulted in increased tumour cell apoptosis, reduction in the mitotic index and a decrease in the number of TILs. Tumours from dogs on BCG/vincristine combination were characterised by reduction in the mitotic index, and appearance of numerous TILs and macrophages followed by marked tumour cell apoptosis and necrosis. This study indicates that combined BCG and vincristine therapy is more effective than vincristine in treating CTVT, suggesting that the clinical course of this disease may be altered by immunochemotherapy.

SSCP analysis of the P2 purine transporter TcoAT1 gene of Trypanosoma congolense leads to a simple PCR-RFLP test allowing the rapid identification of diminazene resistant stocks.

Analyses were made on a Trypanosoma congolense contig coding a putative P2-like nucleoside transporter (the contig was named in this study TcoAT1). The sequence includes a start and stop codon and presents a high similarity with the gene TbAT1 of T. brucei (Smallest Sum Probability 2.8e-136). To investigate a possible link between point mutations and diminazene aceturate (DA) resistance in mice, the TcoAT1 putative genes of 26 T. congolense strains, characterised for DA sensitivity in the single dose mouse test, were screened by means of the Single Strand Conformation Polymorphism technique (SSCP). Results showed that the SSCP profiles of 23 out of 26 (88.5%) T. congolense strains were confirmed by the sensitivity test in mice with the commonly accepted criterion for sensitivity to diminazene being a CD80 of 20mg/kg in the mouse test. The remaining T. congolense strains showed a resistant SSCP profile and relapsed in mice after treatment at doses lower than 20mg/kg indicating that the SSCP is more sensitive than the single dose mouse test for the detection of resistance to diminazene. However, none of the strains used in this study showed a sensitive SSCP profile while they were resistant in the single dose mouse test. The sequencing of the TcoAT1 gene of two sensitive, two intermediate and two resistant strains allowed the set up of a PCR-RFLP test for the discrimination between sensitive and resistant strains confirming the SSCP results for the 26 strains of this study.

Canine transmissible venereal tumour: assessment of mast cell numbers as indicators of the growth phase.

Mast cells are immune cells that are involved mainly in type 1 hypersensitivity reactions, and they have been implicated in tumour angiogenesis. In this study we assessed the presence of mast cell numbers and microvessel density during the progression and regression stages of natural spontaneous canine transmissible venereal tumours (CTVT). Mast cells were demonstrated by histochemical staining with toluidine blue, alcian blue and safranin O. Microvessel counts were demonstrated by immunohistochemical labelling with an antibody against the endothelial cell marker factor VIII. Mitotic cells, apoptotic cells and tumour infiltrating lymphocytes were counted from haematoxylin-eosin-stained sections. Tumour fibrosis was evaluated on Masson's trichome-stained sections. The results showed that progressing tumours had significantly higher mast cell counts and microvessel counts at the invasive edges of the tumours than did regressing tumours. In both the progressing and regressing tumours, microvessel counts were significantly positively correlated with mast cell counts. Regressing tumours had significantly higher mast cell counts of the whole tumour than progressing tumours. The results also showed that progressing tumours had significantly higher mitotic rate than regressing tumours, and fibrosis and apoptosis were significantly higher in regressing tumours than progressing tumours. There were no significant differences between the biochemical and haematological values of dogs with progressing and regressing tumours. These results suggests that mast cells play a role in CTVT progression probably by promoting vascularization at the invasion front during the progression phase, and that mast cell count could be used as one of the histological factors to indicate growth stage of CTVT.

Canine cutaneous neoplasms: prevalence and influence of age, sex and site on the presence and potential malignancy of cutaneous neoplasms in dogs from Zimbabwe.

Histopathological examination was performed on cutaneous biopsies from 900 dogs with skin lesions from Zimbabwe, collected from 1996 to 2000. Clinical data were collected from medical records. Sixty per cent (540/900) of the cases were tumours and 40% (360/900) were non-neoplastic inflammatory or degenerative diseases. Thirty different histological types of tumour were diagnosed. The prevalence of epithelial, mesenchymal, lymphohistiocytic and melanocytic tumours was 39.4%, 44.4%, 7.4% and 8.7%, respectively. The 10 most common tumours, comprising 73.7% of all cutaneous neoplasms, were mast cell tumours, squamous cell carcinomas, perianal gland adenomas, lymphomas, benign melanomas, haemangiosarcomas, sebaceous gland adenomas, fibrosarcomas, lipomas and malignant melanomas. The prevalence of various neoplasms, age of affected dogs and sites of occurrence were similar to surveys in other countries, except that in Zimbabwe there was a greater prevalence of lymphomas and of tumours associated with increased exposure to ultraviolet light (squamous cell carcinomas, haemangiosarcomas and melanomas). For all classes of tumours the sex of the dog did not have any significant influence on the likelihood of developing a tumour. For a dog diagnosed with a tumour located on the trunk, the tumour was significantly more likely to be an epithelial tumour than a non-epithelial tumour The occurrence of melanocytic tumours on the trunk was significantly lower than at other sites. Lymphohistiocytic tumours were 10 times more likely to occur at multiple locations as opposed to single locations.