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Abstract

Clinico-haematological effects of single and mixed experimental infection of Trypanosoma congolense and Trypanosoma brucei on parvoviral vaccinated dogs were studied in mongrel dogs. Twenty dogs of mixed sexes and 4-6 months of age weighing an average of 6.3 kg were used for the experiment. The dogs were divided into five groups of four animals each. Group A were vaccinated and uninfected, group B were unvaccinated and uninfected, group C were vaccinated and infected with T. congolense, group D were vaccinated and infected with T. brucei and group E were vaccinated and infected with T. congolense and T. brucei. Clinical signs observed in the dogs were pyrexia, anorexia, emaciation, lethargy, rough hair coat, white ocular discharges and pale mucus membranes. Trypanosoma brucei and T. congolense had pre-patent period of 6 and 21 days respectively post infection while that of the mixed infection was 7 days post infection when T. brucei became evident. Although the clinical signs of infection due to both species were generally similar, pyrexia appeared to be more characteristic of T. brucei than of T. congolense infection. Significant decrease (P<0.05) in body weight of dogs was observed in the infected groups (C, D and E) which differed from the uninfected groups (A and B). There were significant decreases (P<0.05) in PCV, total RBC and haemoglobin concentration following infection in the infected groups compared to the uninfected groups. Early leukocytosis was observed in the group infected with only T. congolense. This increase was associated with increase in the absolute numbers of neutrophil and eosinophil counts. Leucopenia was generally observed in this study among the infected groups. Decreased absolute numbers of lymphocytes and neutrophils occurred later in the group infected with only T. congolense. Leukocytosis occurred only in dogs that were vaccinated. It was thus concluded that there were clinical and haematological changes associated with canine trypanosomosis in canine parvoviral vaccinated dogs that generally led to leucopenia leading to immunosuppression among the vaccinated dogs. Leukocytosis only occurred among dogs that were vaccinated.