ON THE SURVIVAL OF HIGH VIRULENT STRAIN OF TOXOPLASMA GONDII INOCULATED INTRAVENOUSLY INTO IMMUNE MICE

Abstract

Observations were made on the survival of high virulent RH strain inoculated intravenously into immune mice which had been infected with the low virulent Beverley or S-273 strain previously. Following results were obtained.
1) Trophozoites penetrated into tissue cells in 85% of immune mice within 2 hours and 59% within 6 hours after the challenge. Even within 2 minutes many trophozoites were already found in tissues of lung. At this stage, however, only a few parasites were found in liver and spleen. The invaded parasites multiplied in tissues and no difference was seen as regards the invasion and subsequent multiplication between immune and control mice in this period.
2) In immune mice, the trophozoites once multiplied in tissues began to decrease in number on the 3rd day from challenge and most of them suddenly disappeared on the 4th and 5th day, only a few being found in lung, spleen and liver. This state of infection continued up to 2 weeks after the challenge. Between 3 and 8 weeks after the challenge, only a few parasites were found in tissue preparations on rare occasions. On the contrary, a large number of parasites were found in tissues of control animals until one week after the challenge and they died of the infection within 10 days.
3) It was demonstrated that organisms inoculated into immune mice were able to multiply in tissues at the early stage of challenge infection, but most of them were soon destroyed. A small number of parasites, however, were able to survive in tissues for a very long time.