A microscopic parasite believed to be responsible for hundreds of California dairy cattle abortions each year has been identified, isolated in the laboratory and transmitted to cows, report researchers at the University of California, Davis, School of Veterinary Medicine and the California Veterinary Diagnostic Laboratory Systems. Currently known simply as bovine Neospora, the one-celled protozoal parasite is passed from an infected mother cow to her fetus, causing the fetus to be aborted or to be born infected and in some cases partially paralyzed. The symptoms and process of infection parallel that of a protozoal parasite called Toxoplasma, which infects a wide range of mammals. "Spontaneous abortions are a serious problem for the dairy industry, because cows that abort either do not produce milk or have reduced milk production," said Dr. Patricia A. Conrad, a bovine Neospora researcher and parasitologist in the UC Davis School of Veterinary Medicine, who in early winter presented the latest research developments on bovine Neospora at the American Society of Parasitologists conference. "This disease is so common in California that it has been conservatively estimated to cost the state's dairy industry $35 million annually," said colleague Dr. Bradd C. Barr, a pathologist at the California Veterinary Diagnostic Laboratory Systems. Conrad, Barr and Dr. Mark L. Anderson, a pathologist at the diagnostic laboratory, have been collaborating on Neospora research since 1988. Last April the team reported in the scientific journal Parasitology that it had successfully isolated Neospora from the brains of two aborted calves and cultivated the parasite in the laboratory. Using these samples of Neospora, the UC Davis researchers have since experimentally infected pregnant cows and found that the parasites passed through the placentas, infecting the fetuses and causing brain tissue damage similar to that observed in the brains of the naturally infected fetuses. "It's logical that Neospora ultimately attacks the tissue of the brain and spinal cord, because it is very difficult for the immune system to destroy the parasite in those locations," Conrad said. Although Neospora also invades the skeletal muscles, heart, liver and other organs, it appears that the parasite may prefer neurological tissues, she said. Since identifying bovine Neospora, the research team has found the parasite in the tissues of more than 600 dairy cow fetuses collected since 1985. During that time period, there was no noticeable increase in the number of abortions among dairy cattle, leading the researchers to believe that this protozoal disease has been present for quite some time. The parasite may cause just a few abortions each month in a dairy herd or a major outbreak of abortions. Infected cows show no other physical symptoms of the infection, and currently no medicinal treatments exist that can be used in food animals such as dairy cattle. The method of transmitting Neospora -- other than from the mother cow through the placenta to the fetus -- is unknown. UC Davis researchers are continuing to investigate where the infection originates and how it is spread, why cows get repeated infections and the importance of the timing of the infection during pregnancy. In addition, they are working to develop tests that identify the presence of the parasite in the blood or tissues of an infected animal. "We're interested in learning more about the biology of Neospora so that we can propose better recommendations for control and possible vaccines," Conrad said. "The dairy industry needs to know how to prevent cattle from becoming infected with this parasite and how to stimulate cows to produce an immune response that will prevent the fetus from becoming infected." The bovine Neospora research is funded in part by the Livestock Diseases Research Laboratory of the UC Davis School of Veterinary Medicine and by the California Milk Advisory Board.