FURTHER OBSERVATIONS ON THE EPIDEMIOLOGY OF OVINE <i>TOXOPLASMA</i> INFECTION

Abstract

Summary This paper records a seven year follow‐up epidemiological investigation in the surviving offspring of a flock of ewes which had experienced an outbreak of overt congenital toxoplasmosis. The following observations were made: Fifty‐one percent of the offspring of dye test (D.T.) positive ewes developed antibodies to Toxoplasma. The duration and level of this antibody response varied considerably: in some sheep it was persistent and in others it fluctuated between negativity and positivity, and in one year there was a general and pronounced rise in D.T. titres. Fourteen percent of the offspring of dams with a D.T. titre of 1:64 became sero‐positive, whereas 90% of the offspring of ewes with D.T. titres of 1:1,024 or greater became sero‐positive. No congenital transmission of Toxoplasma occurred when the D.T. positive offspring were mated. All offspring born from D.T. negative ewes and running in contact with D.T. positive sheep remained sero‐negative over a 6 year period. Latent congenital Toxoplasma infection persisted in 93% of D.T. positive offspring for up to 7 years.