Overview

• Neospora caninum-recently recognized coccidian protozoon previously confused with Toxoplasma gondii; tachyzoites and tissue cysts resemble T. gondii under light microscopy.
• Dogs (and coyotes)-definitive host: excrete oocysts in feces, are infective to other dogs and cattle by contaminating feed. Neosporosis is a major cause of abortion in cattle (intermediate host).
• Disease caused by necrosis associated with tissue damage from cyst rupture and tachyzoite invasion.
• Transmission-transplacental, resulting in congenital infection. Ingestion of sporulated oocysts passed in feces of dog, or tissue cysts in tissues from intermediate hosts.

Signalment

• Dogs-natural infections (mainly puppies); hunting dogs overrepresented.
• Cats-experimentally infected, although antibodies found in domestic and wild cats.

Signs

• Similar to those of toxoplasmosis, except neurologic and muscular abnormalities predominate and are often more severe.
• Young dogs (<6 months)-ascending lower motor neuron rigid paralysis to tetraparesis more common; distinguished from other forms of paralysis by gradual muscle atrophy; stiffness of pelvic limbs more affected than thoracic limbs; progresses to rigid contracture of limbs.
• Cervical weakness and dysphagia, trismus, glossal paralysis-gradually develop, respiratory muscle paralysis eventually leading to death.
• Ataxia secondary to atrophy of the cerebellum.
• Old dogs-usually CNS involvement (seizures, tremors, behavior changes, blindness), polymyositis (lower motor neuron flaccid paralysis), myocarditis, and dermatitis; as in toxoplasmosis, virtually any organ may be affected; head tremor; postural deficits from cerebellar disease; Horner's syndrome.
• Generalized ulcerative and pyogranulomatous dermatitis seen in dogs on immunosuppressive treatment for SLE and lymphoma.

Causes & Risk Factors

N. caninum: feeding of raw meat to dogs may be a risk factor and should be avoided.

Differential Diagnosis

• Young dogs-other causes of peripheral multifocal neurologic signs, mainly including infectious diseases (toxoplasmosis, distemper); progressive polyradiculomyositis; other causes of diffuse lower motor neuron muscular diseases rare.
• Old dogs with CNS disease-other infectious diseases (fungal, rabies, pseudorabies); toxicity (lead, organophosphorus, carbamate, chlorinated hydrocarbon, strychnine); nonsuppurative encephalitis; meningitis; granulomatous meningoencephalitis; metabolic disease (hypoglycemia, hepatic encephalopathy).

CBC/Biochemistry/Urinalysis

• Depending on the organ system involved.
• Muscle involvement-creatine phosphokinase and AST activities may be high.

Other Laboratory Tests

• Serologic testing (IFA, ELISA, and immunoprecipitation)-CSF or serum.
• Antibodies do not cross-react with T. gondii, but do with N. hughesi, a neospora affecting horses.
• Organism detection-oocysts in feces need to be distinguished from Hammondia spp.
• Tachyzoites in aspirates, smears, or tissue sections need to be differentiated from those of Toxoplasma (immunohistochemistry).
• PCR-used successfully as a diagnostic tool and distinguishes between other parasites.

Imaging

N/A

Diagnostic Procedures

CSF-slight increase in protein and nucleated cell number; cells mainly mononuclear; neutrophils may be seen, but some cases have high numbers of eosinophils.

Pathologic Findings

• Non-suppurative encephalomyelitis.
• Severe non-suppurative inflammation of cerebella leptomeninges and cortex.
• Myositis.
• Myofibrosis.
• Polyradiculoneuritis.
• Pneumonia, cerebella atrophy, multifocal necrotizing myocarditis, and nodular dermatitis-described.
• Ulcerative and pyogranulomatous dermatitis.
• N. caninum seems to induce more inflammation than does T. gondii.
• Histology-differentiation by location in host cell cytoplasm (not within a parasitophorous vacuole as T. gondii).
• Tissue cysts-those of N. caninum have thicker walls; differentiated from T. gondii by immunohistochemical staining.
• Electron microscopy-rhoptries of N. caninum tachyzoites electron dense; those of T. gondii honeycomb.

Drug(s)

• See Toxoplasmosis.
• Clindamycin 25–50 mg/kg PO or IM/day, divided into 2 doses; continue for at least 2 weeks after clinical signs cleared.

Contraindications/Possible Interactions

N/A

Zoonotic Potential

None identified (unlike T. gondii)

See Also

Toxoplasmosis

Abbreviations

• AST = aspartate aminotransferase
• CNS = central nervous system
• CSF = cerebrospinal fluid
• ELISA = enzyme linked immunosorbent assay
• IFA = immunofluorescent antibody
• PCR = polymerase chain reaction
• SLE = systemic lupus erythematosus

Author Stephen C. Barr

Consulting Editor Stephen C. Barr