Comparative haematological changes following Trypanosoma vivax and T. congolense infections in Zebu bulls

Abstract

A comparative study of haematological changes subsequent to Trypanosoma vivax and Trypanosoma congolense infections was carried out using 24 Zebu bulls during a period of 12 weeks. Eight bulls were infected with T. vivax, another eight with T. congolense and eight served as controls. Infected bulls developed chronic trypanosomiasis which was characterized by many clinical manifestations including intermittent pyrexia. Elevated rectal temperatures of up to 105 and 106°F were recorded, respectively, in all bulls infected with T. vivax or T. congolense. Mean parasitaemia was higher and more chronic in T. congolense-infected bulls and ranged between means of 0 and 3.06 in all infected bulls. There was a slight and transient drop in packed cell volume (PCV) of T. vivax-infected bulls as against a marked and more chronic drop in T. congolense-infected bulls. mean PCV of T. vivax- and T. congolense-infected bulls and controls ranged between 28 and 38, 17 and 38, and 31 and 38%, respectively. Haemoglobin (Hb) concentrations also decreased in infected bulls. The decrease was greater and more chronic in the T. congolense-infected bulls. Values ranged between means of 10.47 and 13.84, 5.44 and 14.16, and 10.24 and 14.12 g dl −1 in T. vivax- and T. congolense-infected and control bulls, respectively. Total plasma proteins also decreased in infected bulls; this was more marked in the T. congolense-infected group. Values for T. vivax-infected, T. congolense-infected and control bulls ranged between means of 7.66 and 8.99, 6.26 and 8.81, and 7.94 and 8.78 g dl −1, respectively. The results indicate that T. congolense was more pathogenic than T. vivax and caused more severe and chronic pyrexia, parasitaemia, and anaemia (as indicated by a greater decline of PCV and Hb concentrations and total plasma proteins). For all parameters studied, the T. vivax-infected bulls differed significantly from the control group ( P<0.05), whereas the T. congolense-infected bulls differed very significantly from the control group ( P<0.001). The T. congolense-infected bulls also differed significantly ( P<0.001) from the T. vivax-infected bulls. The results from this investigation tend to contradict the general belief in West Africa that the indigenous T. vivax strains are more pathogenic than the T. congolense strains.