Molecular and serological diagnosis of Toxoplasma gondii infection in experimentally infected chickens

Little is known of the molecular detection of Toxoplasma gondii infection in chickens (Gallus domesticus). The objectives of the present study were to determine the suitable tissues of chickens infected with T. gondii for direct polymerase chain reaction (PCR) amplification of T. gondii DNA. Thirty, 35-day-old broiler chickens were divided into three groups of 10 birds (two replications of five chicks). Of these, two groups were experimentally inoculated intravenously with 4.3 × 106 or 4.3 × 107 tachyzoites of the low virulent T. gondii QHO strain. Two inoculated chickens from each of the two groups were killed on days 7, 14, 21, 28, and 35 post-inoculation, respectively, and two uninoculated chickens were also killed at the same time. Sera from chickens were collected for examination of anti-T. gondii antibodies by indirect hemagglutination test (IHAT) and the modified agglutination test (MAT). Brains, hearts, livers, lungs, spleens and eyes of chickens were sampled and DNA from each tissue was extracted as template for PCR assay. Specific anti-T. gondii antibodies were detected in all infected chickens from day 7 to day 35 p.i. with antibody titers between 1:5 and 1:640 by MAT. PCR assay can detect T. gondii DNA in tissues from the day 21 p.i. to day 28 p.i. This study demonstrates that MAT is more sensitive than IHAT for detecting antibodies to T. gondii in chickens, and PCR assay is a specific, speedy, sensitive and cost-effective method for detecting T. gondii DNA in chickens.