Submitted to: Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 1, 1997
Publication Date: N/A
Interpretive Summary: Toxoplasma gondii is a single celled parasite of animals and man. It causes mental retardation and loss of vision in congenitally infected children and abortion in livestock. Humans become infected with T. gondii by ingesting food or water contaminated with resistant T. gondii (oocyst) passed in feces of infected cats or by ingesting uncooked meat infected with T. gondii. Pigs are considered an important meat source of T. gondii for humans. Rats are considered an important source of T. gondii infection for pigs. It is not known if T. gondii can be maintained in nature by repeat congenital infection. Scientists at the Beltsville Agricultural Research Center and the Institute of Puericulture, Paris, France have found that T. gondii is not transmitted congenitally in rats from chronically infected dams, which is similar to humans but different than mice. These results will be of interest to veterinarians, public health workers and scientists working on toxoplasmosis.
Technical Abstract: To study congenital transmission of Toxoplasma gondii during acute and chronic infection, pregnant Sprague-Dawley rats were each fed 10000 oocysts of the VEG strain. Toxoplasma gondii was recovered from 33%, 55%, 83%, and 57% of rat pups (F1) when dams were inoculated at 6, 9, 12, and 15 days of gestation, respectively. A total of 15 congenitally infected female rats from 4 litters were mated and their progeny 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 original 4 dams that had given birth to congenitally infected rat pups produced congenitally infected rat pups during the second pregnancy. Thus, 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 (<1:4) in the Sabin-Feldman dye test and 5 were seronegative (<1:20) in the modified agglutination test by the use of whole formalinized tachyzoites and mercaptoethanol.