Experimentally-induced toxoplasmosis in Scottish Blackface rams

Abstract

The work was carried out in an attempt to characterise certain of the clinical changes occurring in young male sheep during experimental infections with Toxoplasma gondii, and to ascertain the frequency with which the organism could be recovered from the semen and blood of these animals and the period over which such isolations might be made.

Ten young Scottish Blackface tups were used. Six received inoculations of mouse brain containing T. gondii cysts, three received non-infected brain and one tup remained uninoculated and was allowed to run with the infected group. Before, and at intervals following these inoculations for approximately three months, clinical examinations were carried out, rectal temperatures and haematological changes recorded, indirect-haemagglutinating antibodies were monitored and semen quality assessed. The presence of T. gondii was tested for by inoculation of mice with tup blood and semen and subsequent examination of mouse brains for the presence of T. gondii cysts.

There was a marked clinical and serological response in those tups receiving infected material with the exception of one tup which began the trial with a moderate indirect-haemagglutination test (l.H.A.T.) titre. With the possible exception of a leucocytosis during the first four weeks post-inoculation in those tups receiving non-infected mouse brain and a moderate leucocytosis in infected and control tups towards the end of the sampling period, haematological changes were unremarkable. Variability in sperm motility and semen density on an apparently random basis in both groups made it impossible to draw conclusions concerning the effect of toxoplasmosis, if any, on these parameters.

T. gondii was recovered from the semen of three animals on two occasions and from the blood of two animals on one occasion. All isolations occurred on or between days 11| and 26 post-inoculation.

These findings support the conclusions of other workers that semen transmission of T. gondii is a possibility in sheep, although this work suggests grounds for suspecting that this would be only a rare occurrence, if it occurs at all, due to the transient and variable nature of semen infection.

Clinically in young Blackface tups, the acute disease was evidenced by a pyrexia. There were no apparently characteristic signs.

There was no evidence of contact transmission of infection between the tups, a finding which is consistent with the results of previous work in sheep.