BACKGROUND AND OBJECTIVESToxoplasma gondii is an important zoonotic intracellular protozoan parasite, which can affect all warm-blooded mammals and birds throughout the world, including humans. The cat is the definitive host but other warm-blooded animals such as humans and dogs are considered intermediate hosts.Dogs can be a transport host for T. gondii oocysts, and can become infected by the ingestion of T. gondii oocysts from cat feces or by the feeding habit of uncooked mutton, however there are little information about venereal transmission of disease. Little information has been presented about placental transmission of toxoplasmosis in dogs, although it appears to be less common than in species such as cats, humans, and sheep, but congenital toxoplasmosis also occurs naturally in dogs.In different studies T. gondii detected in the semen and reproductive organs of experimentally infected male rat, rabbit, goat, sheep, cattle, pig and dogs and there is some evidence propose that T. gondii can transmit with semen to female animals.In this study, at the first step serological surveillance was done by MAT method in dogs which is selected from kennels with reproductive disorders compliant from the southeast of Iran and the overall infection rate was %۴۳.۵. At the second step, by using the most sensitive detection method "RE-based nested
PCR assay" the probability of the presence of T. gondii were detected in the semen of ۴۸ male seropositive dogs which ۳ positive dogs (۶.۲۵%) was detected. The results of this project confirmed the venereal risk of toxoplasmosis transmission in dogs.For the first time, tachyzoites were isolated from seminal fluid of experimentally infected male dogs and it has clearly showed that T. gondii is transmitted through semen to female dog. Vertical transmission of T. gondii, fetal reabsorption and congenial toxoplasmosis with cerebral cysts in puppies were also reported.Venereal transmission can cause abortion and still birth in female dog and severe health problems for survived infected puppies. Hypothalamic–pituitary axis dysfunction was reported in murine toxoplasmosis in male rats, so further investigation must be done in infected male dogs to evaluate the effect of toxoplamosis on the spermatogenesis and hormonal impairment.