Detection of T-gondii in tissues of sheep and cattle following oral infection

It has been reported in the literature that cattle are more resistant to to xoplasmosis than sheep. Congenital disease due to I gondii infection is rar ely reported in cattle whereas the parasite is a major cause of abortion an d neonatal mortality in sheep. It is believed that sheep remain chronically infected for life. Undercooked meat from infected sheep is an important so urce of infection for man. In contrast cattle are thought to harbour fewer parasite tissue cysts which may not persist for the lifetime of the host. T herefore, cattle are believed to pose less of a risk for human infection. I n this study we examined the presence of I gondii within a range of tissues in sheep and cattle at 6 weeks and 6 months following oral infection with 10(3) or 10(5) sporulated oocysts of I: gondii. The presence of parasite wa s determined by bioassay in mice and using polymerase chain reaction (PCR). The results from this study show that I gondii was more frequently and con sistently detected in sheep, in particular within brain and heart tissues, whereas parasites were not detected in the samples of tissues taken from ca ttle. I: gondii was more frequently detected in sheep given the higher dose of I gondii. Examination of tissues at either 6 weeks or 6 months after in fection did not appear to affect the distribution of I: gondii. The polymer ase chain reaction has more specificity and sensitivity when detecting the presence of T. gondii in large animals than histological detection. (C) 199 9 Elsevier Science B.V. All rights reserved.