Experimental toxoplasmosis in pregnant sows. I. Clinical, parasitological and serological observations.

Six sows in the 3rd month of gestation were infected with Toxoplasma gondii, four intravenously with the RH strain, two perorally with a porcine strain. Severe disease, characterized by fever, anorexia and dyspnoea, was seen in the animals infected with the RH strain and one sow died on day 4. Mild febrile disease was seen in the porcine strain infections. Parasitaemia and Toxoplasma antibodies became demonstrable in all sows, and at term the sows delivered dead and/or live piglets, the mortality being 50–100 per cent in three RH strain infected litters and 30 per cent in one porcine strain infected litter. At sacrifice, Toxoplasma was found in the sows infected with the porcine strain but in none of those infected with the RH strain. Non-viable Toxoplasma was demonstrated histologically in 17 of 35 dead piglets and viable Toxoplasma was isolated from the cord blood of three liveborn piglets. At sacrifice 3–4 weeks after birth, Toxoplasma was demonstrable in several piglets from both sows infected with the porcine strain but in none of the piglets from sows infected with the RH strain. It is concluded that toxoplasmosis during the 3rd month of pregnancy in swine may cause fetal infection, resulting in death and congenital toxoplasmosis of liveborn piglets. Infection of the fetuses occurs probably during the maternal parasitaemia but horizontal infection i. e. from one litter mate to another, may also take place. There is little chance of isolating viable Toxoplasma from mummified or macerated fetuses, but non-viable Toxoplasma may be demonstrated by histological examination.