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Fall 1999 Newsletter


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NeosporaCaninum

Neosporacaninum is an organism that is capable of causing abortions in cattle, horses, goats, and possibly others. The organism was first reported in dogs in 1988 and has been since identified as a major cause of bovine abortion in California. The organism is very similar to Toxoplasmagondi. The definitive host was recently reported to be the dog. The intermediate hosts include cattle, goats, sheep, horses, and deer. The dog ingests Neospora infected tissues from an intermediate host and develops a subclinical to mild intestinal infection. The organism undergoes sexual replication and is shed as oocysts in the dog’s feces. The intermediate host ingests these oocysts in contaminated feed. A systemic infection develops and the parasite localizes and becomes dormant in specific tissues, especially the brain. The infection is life long and latent unless the animal is pregnant. The fetus is nearly always infected when the mother is infected.

There are three consequences of fetal infection. The first is fetal death and mid-gestational abortions. The second is congenital CNS disease ranging from mild to severe. The third is a latent infection in the fetus (vertical transmission.)

Cow to cow transmission (horizontal transmission) does not appear to occur at this time. Cows throughout the U.S. and the world have antibodies to Neosporacaninum. The biggest problem area in the U.S. is the California dairy industry, however, abortions do occur in beef cattle as well.

A highly sensitive and specific ELISA isavailable to identify those cows that havebeen exposed. However a positive result doesnot indicate the cow will abort. The majority of latently infected cows do not abort and pass the infection on to their fetuses. The risk of abortion is highest in first calf heifers and cows that are stressed or sick. Most of the abortion storms seem to occur in nave cows that are exposed to oocyst-contaminated feed during pregnancy.The list of differential diagnoses for abortions and abortion storms in ruminants includes Leptospirosis, Bovine Viral Diarrhea, Infectious Bovine Rhinotracheitis, Campylobacter, and Neospora. To confirm a Neospora-associated abortion the organism must be demonstrated in the fetal tissues. This is often difficult because the fetal infection can occur up to one month prior to the abortion and the fetal tissues are often very autolyzed. Fetal serology and immunohistologic examination of fetal tissues (particularly brain and spinal cord) are the best method of diagnosis. In addition, other causes such as IBR, BVD and Leptospirosis need to be ruled out. Paired sera from the cows do not appear to be diagnostic because the cows do not have an increased antibody titer at the time of abortion.

At the present time there are no vaccines available. There are suggested control measures. The first is to protect the feed and water sources from canid fecal contamination, the second is to buy seronegative replacements. Finally, one should promptly remove aborted fetuses and placentas.

Neospora is estimated to cost the California dairy industry $35 million dollars per year. This can be a very costly disease and considered part of a differential list of abortions in ruminants in other states besides California.

-by Bryan Wolfe, Class of 1999

-edited by Brad Njaa, DVM, MVSc

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