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Neosporosis: Introduction |  |
| Neosporosis has been recognized in dogs, cattle, sheep, goats, deer, horses, and experimentally rodents, pigs, monkeys, and cats. It is a major cause of abortion in dairy cattle. |
| Etiology and Transmission: |
|
Neospora
caninum
is an obligate intracellular protozoan parasite that has been confused previously with
Toxoplasma
gondii
. The dog is the definitive host. Infection can be acquired by ingesting food and water contaminated with oocysts excreted in feces of dogs, by ingesting infected tissues, or transplacentally. Vertical transmission is a major route of transmission in cattle and dogs. Tachyzoites are 5-7 × 1-5 µm, depending on the stage of division. They divide by endodyogeny. Tachyzoites are found in myocytes, neural cells, dermal cells, macrophages, and other cells. Tissue cysts up to
100 µm in diameter are found in neural cells; the cyst wall is amorphous and up to 4 µm thick. Cysts have no septa and enclose slender bradyzoites (7 × 1.5 µm). Oocysts are ~10-12 m in diameter. |
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| Clinical Findings and Lesions: |
| In dogs, both pups and older dogs are affected. Not all littermates are affected. Most severe infections are in young pups, which typically develop an ascending paralysis of the limbs, particularly the hindlimbs. The paralysis is often progressive and results in rigid contracture of the muscles of affected limbs. In some dogs, only neural signs are seen. The syndrome of polyradiculoneuromyositis appears typical of neosporosis. Ulcerative dermatitis, hepatitis,
pneumonia, and encephalitis may also occur. |
| In dairy cattle,
N
caninum
is a major cause of abortion in many countries. Calves may be aborted; stillborn; born underweight, weak, or paralyzed; or they may become paralyzed within 4 wk of birth. Nonsuppurative encephalitis is the main lesion in aborted fetal tissues. Abortion can occur throughout gestation, and some cows may abort again; dams of these calves are clinically normal. |
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| Diagnosis: |
| An immunoperoxidase test using specific antibodies can identify
N
caninum
in tissue sections or biopsy specimens. An indirect fluorescent antibody test and several ELISA can be used to detect antibodies. |
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| Treatment and Control: |
| Drugs used to treat toxoplasmosis (sulfadiazine, daraprim, clindamycin) show some success in treating neosporosis. Dogs should not be allowed to defecate in cattle feed. There is no proven vaccine. |
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