Submitted to: Journal of Parasitology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/19/2003
Publication Date: 6/20/2003
Citation: DUBEY, J.P., MITCHELL, S.M., MORROW, J.K., RHYAN, J.C., STEWART, L.M., GRANSTROM, D.E., ROMAND, S., THULLIEZ, P., LINDSDAY, D.S. 2003. PREVALENCE OF ANTIBODIES TO NEOSPORA CANINUM, SARCOCYSTIS NEURONA, AND TOXOPLASMA GONDII IN WILD HORSES FROM CENTRAL WYOMING. JOURNAL OF PARASITOLOGY 89:716-720. Interpretive Summary: Sarcocystis neurona is a single celled parasite that causes a fatal disease (equine protozoal myeloencephalitis, EPM) in horses in the United States. Its distribution follows the geographical range of its reservoir host, opossum (Didelphis virginiana). Scientists at the Beltsville Agricultural Research Center report for the first time antibodies to S. neurona in horses from central Wyoming, outside the range of D. virginiana. These findingss will be of interest to veterinarians, parasitologists, and pathologists.
Technical Abstract: Sarcocystis neurona, Neospora caninum, N. hughesi, and Toxoplasma gondii are 4 related coccidians considered to be associated with encephalomyelitis in horses. The source of infection for N. hughesi is unknown, whereas the opossums, dogs, and cats are the respective definitive hosts for S. neurona, N. caninum, and T. gondii, respectively. Seroprevalence of these coccidians in 284 wild horses from central Wyoming outside the known range of the opossum (Didelphis virginiana) was determined. Antibodies to T. gondii were found only in 1 of 284 horses tested with the modified agglutination test using 1:25, 1:50, and 500 dilutions. Antibodies to N. caninum were found in 86 (30.2%) of 284 horses tested with the Neospora agglutination test (NAT); the titers were 1:25 in 38, 1:50 in 15, 1:100 in 9, 1:200 in 8, 1:400 in 4, 1:800 in 2, 1:1,600 in 2, 1:3,200 in 2 and 1:12,800 in 1 horse. Antibodies to S. neurona were assessed with the serum immunoblot; of 276 tested, 18 horses had antibodies considered specific for S. neurona. Antibodies to S. neurona were also assessed with the S. neurona direct agglutination test (SAT). Thirty-nine of 265 horses tested had SAT antibodies; in titers of 1:50 in 26 and in 1:100 in 13 horses. The presence of S. neurona antibodies in horses in central Wyoming suggests that either there is cross reactivity between S. neurona and some other infection, or a definitive host other than opossum may be the source of infection. In a retrospective study, S. neurona antibodies were not found by immunoblot in the sera of 243 horses form western Canada outside the range of D. virginiana.