The detection of Toxoplasma gondii by comparing cytology, histopathology, bioassay in mice, and the polymerase chain reaction (PCR)

The objective of this study was to compare the different methods of detecting Toxoplasma gondii in sheep tissue, tested serologically positive by the indirect immunofluorescent antibody test (IFAT). Brain, diaphragm, and blood samples were collected from 522 sheep slaughtered at the São Manuel abattoir, São Paulo State, Brazil. Brain and diaphragm samples from IFAT seropositive animals were digested by both trypsin and pepsin and then injected into mice. Part of the digested samples was used to prepare slides for Giemsa staining and in the polymerase chain reaction (PCR). Tissue fragments were fixed in formalin and examined using hematoxilin-eosin (HE). Forty of the sheep (7.7%) were IFAT positive. T. gondii was isolated in 23 (59.0%) of the 39 mice with pepsin-digested brain samples and in 27 (69.0%) of the 39 with trypsin-digested brain samples. Injection of diaphragm samples led to T. gondii isolation in 26 (66.7%) of the 39 pepsin-digested samples and 21 (53.8%) of the 39 trypsin-digested samples. Cytological and hystopathological examination of both brains and diaphragms was negative in all examined sheep. PCR was positive in 7 (17.9%) of the trypsin and 2 (5.1%) of the pepsin-digested samples, while 9 (23.1%) of the trypsin and 3 (7.7%) of the pepsin-digested samples showed T. gondii DNA. T. gondii isolation rate in mice (n = 34; 85.0%) was significantly higher than detection by PCR (n = 15; 37.5%). © 2001 Elsevier Science B.V.