Toxoplasmosis: i. a study of the fluctuation in antibody titre to Toxoplasma gondii in a flock of sheep; ii. a comparison between the three serological tests used in the study

Abstract

A review of toxoplasmosis is presented in the dissertation.

A flock of 40 sheep, were bled weekly for a period of 6 - 7 months (Nov. 1976 - May/june 1977). At least one of three serological tests were carried out on each serurn sample.

The results showed a good degree of association between the three tests especially between the l.H.A.T. and the I.F.A.T. These two tests were considered to be easier to perform than the C.F.T., although the specificity of the l.H.A.T. was doubted. A titre of 1:8 or less was considered to be negative and the 1:16 as inconclusive for the l.H.A.T. and I.F.A.T.

Antibody titres showed little change over the.period of study, a slight decrease perhaps. A similar state of decrease or of no change was noted when comparing titres before and after parturition.

In one ewe and lamo that showed serological evidence of infection around parturition it took four weeks for the antibody titres to rise four-fold.

Minor j. luctuations in the results were put down to experimental variation, but larger fluctuations were considered to indicate reinfection or possible reactivation of latent infection. Periods of cold weather appeared to have no effect on titres, and vaccination had no apparent effect, except for one case of abortion which was not due to toxoplasma.

Ewes showed a higher reactor rate compared with gimmers but there was very little evidence of lateral transmission of infection within the flock although about five ewes showed a transient seroconversion shortly after tupping. The absence of disease transmission to seronegative ewes at lambing time was considered to be possibly due to genetic factors within the host, or to low excretion rates of infection with a mild strain of the parasite.

Ewes with high antibody titres produced less lambs than the group with low or negative titres, and finally there was passive transfer of antibody between ewe and lamb.