Scientists Finger Accomplice of Calf-Killing Parasite

By Jan Suszkiw
August 14, 1998

Science is gaining ground in the battle against Neospora caninum, a single-celled parasite of cattle that causes pregnant cows to abort their fetuses. A research team led by University of Wyoming scientist Milton McAllister, and including scientists at USDA's Agricultural Research Service and Virginia Tech, has shown for the first time that dogs are a "definitive host" of Neospora. This describes an animal in which a parasite can complete its life cycle.

The research was funded by a grant from USDA's National Research Initiative.

The team draws its conclusion from experiments in which it recovered Neospora from the tissues of a special lab strain of mice that had been inoculated with oocysts (spore structures) collected from the feces of 8-week old beagles. The dogs passed the oocysts after being fed the tissues of a separate group of mice infected with Neospora from an aborted bovine fetus.

The study, published today in the International Journal for Parasitology (Volume 28:1473- 1478, 1998) suggests that farmers should try to keep pet dogs or strays from defecating in dairy feedlots or choice pasture. Fencing, for example, could help prevent a pregnant cow from ingesting feces-contaminated feed and then transmitting the parasite to her fetus via the placenta.

In California, the nation's leading dairy producer, Neospora is the chief culprit behind calf abortions costing $35 million annually in losses. It also inflicts heavy cattle losses in New Zealand, Australia, and The Netherlands. The parasite also plagues other ruminant livestock like goats, typically attacking their central nervous system. In young dogs, such attacks can cause death or paralysis.

N. caninum's discovery in 1988 and scientific naming stemmed from studies led by J.P. Dubey, a microbiologist at ARS' Parasite Biology and Epidemiology Laboratory in Beltsville, Maryland.

The journal study's authors are Milton McAllister, Department of Veterinary Sciences, UW, Laramie; J.P. Dubey, ARS; David Lindsay, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech, Blacksburg; William Jolley, Rebecca Wills, and Angela McGuire — all at UW.

Scientific Contact: J.P. Dubey, USDA-ARS Parasite Biology and Epidemiology Laboratory, Beltsville, Md. (301) 504-8300, fax (301) 504-6273, jdubey@lpsi.barc.usda.gov. Milton McAllister and William Jolley, Department of Veterinary Sciences, University of Wyoming, Laramie, (307) 742-6638, fax (307) 721-2051, milt@uwyo.edu, willjo@uwyo.edu. David Lindsay, Virginia Tech, Blacksburg, (540) 231-6302, fax (540) 231-3426, lindsayd@vt.edu.