New Procedure Speeds Detection of Livestock Parasite

July 10, 1996

New Procedure Speeds Detection of Livestock Parasite
USDA Agricultural Research Service
Information Staff, 6303 Ivy Lane, Greenbelt MD 20770
Sandy Miller Hays, (301) 344-2764


WASHINGTON, July 8 -- A new diagnostic test trims time and expense in pinpointing whether aborting cattle are infested with the newly discovered parasite Neospora caninum, according to a U.S. Department of Agriculture scientist who helped develop the test.

Parasitologist Nicola C. Lally said the new test is based on specific purified proteins--called antigens--produced by the parasite itself that cause an infected animal's immune system to make antibodies. The antigens are mass-reproduced in fast-growing E. coli bacteria and the final diagnostic procedure can be automated to check dozens of samples per minute. Previous diagnostic procedures required growing the entire parasite in culture and individual evaluation of samples.

"Ours isn't the first diagnostic test for neosporosis, the disease caused by N. caninum, but it is an improvement over existing tests," explained Lally, who worked on the project with fellow parasitologists Mark C. Jenkins and J.P. Dubey. Lally and Jenkins work at the ARS Immunology and Disease Resistance Laboratory operated by USDA's Agricultural Research Service at Beltsville, Md. Dubey is at the ARS Parasite Biology and Epidemiology Laboratory, also at Beltsville.

Dubey discovered and named N. caninum in 1988, finding it first in tissues from paralyzed dogs. A subsequent collaborative study by ARS and the University of California at Davis in 1990 indicated as many as half of cattle abortions could be caused by infection with N. caninum. The parasite has since been identified in livestock all across the United States as well as in New Zealand, Australia, Africa, Israel, Japan and Europe.

The new test mixes blood samples from suspected infected animals with the purified N. caninum antigens. If the blood sample contains antibodies to N. caninum--an indication of infection with the parasite--the purified antigens will bind to the blood sample. A second antibody is added that contains an enzyme that changes color if the animal's blood shows signs of infection. The samples can be checked mechanically using a diagnostic method called indirect enzyme-linked immunosorbent assay (ELISA).

Lally, Jenkins and Dubey cloned genes from N. caninum to produce two separate antigens for reproduction in E. coli. ARS has applied for a patent on the recombinant antigens and diagnostic method. The new diagnostic test could be available commercially within the next two to three years, Lally said.
NOTE TO EDITORS: Contact for details Mark C. Jenkins, Immunology and Disease Resistance Laboratory, Agricultural Research Service, USDA, Beltsville, Md. 20705.
Telephone: (301) 504-8054.

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United States Department of Agriculture, Agricultural Research Service

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