The survival of Toxoplasma gondii trophozoites in changes in osmotic pressure.

It has generally been assumed that the trophozoites of Toxoplasma gondii cannot survive long outside the body and they cannot resist even small changes in osmotic pressure, and that toxoplasmosis is transmitted by transplacental infection, cysts and oocysts. In an attempt to demonstrate that trophozoites can resist changes in osmotic pressure, some were preserved in ascitic fluid made hypertonic with 1%, 2%, 5%, and 10% salt excess of sodium chloride and in ascitic fluid made hypotonic by mixing it in the ratio 3 : 7, 1 : 9 and 1 : 49 with distilled water. The trophozoites remained infectious in 1% salt excess for 29 days, in 2% for 15 days, in 5% for 5 days and in 10% salt excess for 2 days and in ascitic fluid diluted 3 : 7 with distilled water for 15 days and in ascitic fluid diluted 1 : 9 with distilled water for 3 days. We suggest that trophozoites, being resistant to changes in osmotic pressure, may survive outside the body long enough to transmit the disease.