The importance of trophozoites in transmission of toxoplasmosis: survival and pathogenity of Toxoplasma gondii trophozoites in liquid media.

It has been generally assumed that Toxoplasma gondii trophozoites cannot survive long outside the body, and that toxoplasmosis is transmitted by transplacental infection, cysts and oocysts. We tested the survival and pathogenicity of separated Toxoplasma trophozoites in saline, colostrum, and solutions of albumen and serum, and the penetration of Toxoplasma trophozoites from infected secretions through mucous membranes of nose, conjunctiva, and mouth. The trophozoites survived 24 h in saline, 3 days in 3.5% serum albumen, 3 days in colostrum, and 17-43 days in serum solutions. The infectivity of the trophozoites was highest after nasal instillation, second highest after instillation into conjunctiva, and lowest after instillation into the mouth. The infective dose was calculated. The results show that Toxoplasma trophozoites survive and remain infectious for a relatively long time in biological liquid media and can easily penetrate mucous membranes, and suggest a revised hypothesis for the transmission of Toxoplasmosis with the trophozoites as one important source of infection.