Effects of Trypanosoma congolense on pituitary and adrenocortical function in sheep: changes in the adrenal gland and cortisol secretion.

The effect of trypanosomiasis on adrenal function was studied in 10 pubertal Scottish blackface rams infected with Trypanosoma congolense and nine uninfected controls. Plasma cortisol concentration was measured by radioimmunoassay in samples obtained twice a week for three weeks before infection and three times a week for 79 days after infection. There was a significant (P < 0.001) increase in cortisol concentration in all the infected rams after the onset of parasitaemia nine to 16 days after infection. This was followed by a transient non-significant decrease in cortisol levels between 19 and 41 days and a variable and parasitaemia-dependent increase in cortisol levels between 44 and 79 days after infection. Marked hypertrophy of the zona fasciculata-reticularis, infiltration of mononuclear cells into the cortical and medullary zones, hyperaemia and focal coagulative necrosis were evident in the adrenal glands of infected rams killed at the end of the study. Trypanosome infection induced a low grade persistent pyrexia, marked anaemia, reduced growth rates and general loss of body condition. These results demonstrate that T congolense infection in sheep causes marked pathological changes in the adrenal cortex and changes in the secretion of cortisol.