Overview

• Aberrant parasitic migration into the CNS.
• Parasites usually affect another organ system of the same host (e.g., Dirofilaria immitis, Taenia, Ancylostoma caninum, Angiostrongylus, or Toxocara canis), or a different host species (e.g., raccoon roundworm, Baylisascaris procyonis; skunk roundworm, B. columnaris; Coenurus spp.; or Cysticercus cellulosae).
• Access to CNS-hematogenously (dirofilariasis) or through adjacent tissues, including the middle ear, skull foramina, cribriform plate through nasal cavities, or open fontanelles (cuterebraiasis).

Signalment

• Dirofilariasis-adult animals only.
• Other parasites-young dogs and cats with access to outdoors-rare and sporadic occurrence.

Signs

• Vary with the portion of CNS affected.
• Likely asymmetrical.
• May suggest a focal mass lesion or a multifocal disease process.
• Cuterebriasis-seasonal (July–October) acute or peracute onset of behavior changes, seizures, visual deficits, etc. A previous history of respiratory disease is common.
• Rat parasite, Angiostrongylus cantonensis (Australia)-lumbosacral syndrome (hind limbs, tail, and bladder paralysis/paresis) in puppies that may ascend to thoracic limbs and cranial nerves.

Causes & Risk Factors

Housing in a cage previously occupied by wildlife (raccoons, skunks).

Differential Diagnosis

• Rule out other causes of focal encephalopathy-infectious diseases (viral, bacterial, protozoan, or fungal); granulomatous meningoencephalomyelitis; brain tumor.
• Diagnosis often made on necropsy.

CBC/Biochemistry/Urinalysis

Normal unless the parasite also affects non-neural tissues.

Other Laboratory Tests

CSF-may show an eosinophilic, neutrophilic, or mononuclear pleocytosis (also found in protozoal, fungal, and prototheca encephalitides); may be normal (strictly parenchymal lesions).

Imaging

CT or MRI-brain; focal lesion and/or cerebral infarction from occlusion of cerebral vessels. Non-specific and often inconclusive but could lead to surgical exploration and removal of migrating parasite.

Pathologic Findings

• The parasite or its tracts may or may not be identified.
• Infarction, vascular rupture and hemorrhage or vascular emboli may cause local to extensive necrosis and malacia. There may be granulomatous proliferation or/and obstructive hydrocephalus.
• Dirofilaria immitis-intravascular or extravascular.
• Worms produce focal inflammation.
• Cuterebriasis is the suspected cause of feline ischemic encephalopathy.

Drug(s)

• Dirofilariasis and neural angiostrongylosis-anthelmintic treatment may cause worsening of signs and sometimes death.
• Mild neural angiostrongylosis-puppies may recover with supportive care and corticosteroid therapy.
• A single dose of ivermectin (400 mg/kg SC) may kill cuterebra larvae in cats with suspected cuterebriasis. Pretreatment with diphenhydramine (4 mg/kg) and intravenous dexamethasone (0.1 mg/kg) may mitigate allergic/anaphylactic reactions to dead or dying larvae.
• Treat inflammation and secondary infections: corticosteroids/NSAIDs, antibiotics.

Patient Monitoring

As necessary

Prevention/Avoidance

• Keep pets indoors or/and segregated from wildlife.
• Use preventive anthelmintics and dirofilaricides.

Possible Complications

N/A

Expected Course and Prognosis

Acute or insidious onset, then usually progressive.

See Also

• Encephalitis
• Microsporidiosis (Encephalitozoonosis)
• Feline Ischemic Encephalopathy
• Heartworm Disease-Cats
• Heartworm Disease-Dogs

Abbreviations

• CNS = central nervous system
• CSF = cerebrospinal fluid
• CT = computed tomography
• MRI = magnetic resonance imaging

Internet Resources

• Braund KG. Neurovascular disorders (updated 2003) In: Clinical Neurology in Small Animals-Localization, Diagnosis and Treatment. www.ivis.org.
• Vite CH. Inflammatory diseases of the central nervous system (updated 2005) In: Clinical Neurology in Small Animals-Localization, Diagnosis and Treatment. www.ivis.org.

Author Christine F. Berthelin-Baker

Consulting Editor Joane M. Parent