Abstract

Paratuberculosis (Johne's disease) is a chronic infectious disease of cattle and other domestic and wild ruminants caused by Mycobacterium avium ssp. paratuberculosis (Map) which is widespread throughout the world. The disease is characterized by persistent diarrhea, weight loss, and eventually death. In addition to interest in the economic losses, there has been an increasing interest in eradicating the disease due to the potential involvement of the causative microorganism in Crohn's disease, a debilitating chronic enteritis in man. Experiments were conducted to determine the possibility of transmission of Map by embryo transfer (ET) and the association of Map with in vivo-derived and in vitro-fertilized (IVF) embryos. These experiments involved (1) collection of embryos from naturally infected donors (n = 5) and transfer of those embryos to uninfected recipients (n = 12) and testing of others for Map by culture on Herrold's medium with mycobactin or by PCR; and (2) in vitro exposure of in vivo-derived and IVF embryos to Map and their subsequent transfer to uninfected recipients. Experiment 1 revealed the presence of Map in the uterine horns of all five subclinically infected donors, but it was not detected in association with sequentially washed in vivo-derived embryos by culture or by PCR. In Experiment 2, a high proportion of both in vivo-derived and IVF embryos exposed to Map in vitro tested positive for Map even after sequential washings as recommended by IETS. Transfer of in vivo-derived and IVF embryos that had been exposed to Map, and then washed, into 18 recipients resulted in 13 pregnancies and 8 calves born without evidence of disease transmission to either the recipients or the offspring over the following 5 year period. In conclusion, it is unlikely that Map will be transmitted by ET when the embryos have been processed according to the washing protocols recommended by the IETS.