Neosporosis in cattle

During the past decade, Neospora caninum infection has emerged as an import ant reproductive disease in cattle throughout the world. Abortion, occurrin g during the middle of gestation, is the primary clinical sign of the infec tion in cattle. Surveys in several countries from three continents have ide ntified N. caninum infection as the major diagnosed cause of bovine abortio n. Both endemic and epidemic patterns of abortion may occur in herds. An im portant feature of this disease is that the protozoan parasite is maintaine d in cattle as a chronic infection which can be passed on to the fetus duri ng pregnancy. Two methods for the transmission of the infection in cattle h ave been proposed and are the subject of current investigations. Horizontal transmission utilizes a two-host life cycle whereby the cow is infected fr om ingestion of coccidial oocyst stages shed by the definitive host. Experi mental infections have confirmed that the dog is a definitive host for the parasite. There is epidemiological evidence that the dog has a role in the prevalence of the infection but, as yet, no confirmation that the dog is th e source for natural infections in cattle. Vertical transplacental transmis sion of the infection is an important route of infection in many herds. Ver tical transmission occurs because fetal infection frequently does not resul t in abortion but rather the fetus survives to be a persistently infected a nimal. A heifer calf that is born congenitally infected is capable of trans mitting the infection to the next generation when she becomes pregnant, thu s maintaining the infection in the herd. The clinical outcome of transplace ntal fetal infection with N. caninum is likely determined by maternal and f etal immune responses which involve humoral, and most importantly, cell-med iated immune factors. The diagnosis of the infection is assisted through hi stopathology and immunohistochemical examination of aborted fetuses and ser ologic testing of cattle for evidence of infection. Several types of serolo gic tests, based on the use of culture-derived organisms or recombinant N. caninum antigens are available. There are no proven control methods for the prevention or treatment of neosporosis. Suggested control measures focus o n programs to reduce the number of congenitally infected animals retained i n the herd and to minimize the opportunity for postnatal transmission from the environment. (C) 2000 Elsevier Science B.V. All rights reserved.