To study congenital transmission of Toxoplasma gondii
during acute and chronic infections, 4 pregnant Sprague-Dawley
rats were each fed 10000 oocysts of the VEG strain. Toxoplasma gondii
was recovered from 33, 55, 83 and 57% of rats
(F1) when dams were inoculated at 6, 9, 12 or 15 days of gestation,
respectively. Progeny of 15 congenitally infected female
rats were examined for T. gondii. Toxoplasma gondii was
recovered from tissues of 1 of 155 rats (F2) born to congenitally
infected dams. A total of 4 (F2) females were mated; 0 of 40 (F3) rats
born
to them were infected. None of the acutely
infected 4 dams that had given birth to congenitally infected litters
produced congenitally infected offspring during the
second pregnancy. Thus, unlike mice, evidence for repeated congenital
transmission of T. gondii in the rat was found in
<1% of cases. Of the 16 congenitally T. gondii infected pups
with demonstrable tissue cysts, 5 were seronegative (<1[ratio ]4)
in the Sabin-Feldman dye test and 5 were seronegative (<1[ratio ]20)
in the
modified agglutination test by the use of whole
formalinized tachyzoites and mercaptoethanol.