Female BALB/c mice weighing 18-20 g were immunized by three injections of 1 x 10(6) Naegleria fowleri trophozoites intraperitoneally at the interval of one week 6 times for the pregnant mice and 3 times for the offspring mice. One week after immunization the mice were challenged intranasally with N. fowleri trophozoites 5 x 10(4) under secobarbital anesthesia. Experimental primary amoebic meningoencephalitis developed between day 7 and 16 after infection. All mice were dead due to amoebic meningoencephalitis in all experimental groups except in the offspring born to non-immune mothers. Mean of survival time, which is the duration of survival of mice from infection to death, was delayed in the groups of mice born to immune mothers, immune mice born to immune mothers. Active or passive protective immunity against N. fowleri infection was demonstrated in the immunized mice and mice born to immune mothers. But the effectiveness of immunization was greatly impaired in terms of mortality in the immune mice born to immune mothers when N. fowleri was infected intranasally.
