Lapis ISSN 2398-2969

Cerebrospinal nematodiasis

Contributor(s): Molly Varga, Lesa Longley, Alana Shrubsole-Cockwill, Lesa Thompson


  • Cerebrospinal nematodiasis is a leading cause of neurological disease in free-living rabbits.
  • CauseToxacara canisand Baylisascarisspp - while Toxocara canishas a wide geographic range, Baylisascarisspp are restricted to areas where free living raccoons and skunk are found, or where they are kept as pets or exhibits in zoos. Raccoons ( Procyon lotor), skunks ( Mephitis mephitis) and canines are sources of disease.
  • It occurs when a rabbit accidentally ingests material that is contaminated with Baylisascaris eggs.
  • When the larval forms of Baylisascaris migrate through the central nervous system they damage surrounding tissues and can cause an encephalomalacia.
  • Signs: ataxia, behavioral changes, head tilt, circling, torticollis, seizures.
  • Diagnosis: serology, toxoplasma serology, blood lead levels, fecal flotation.
  • Treatment: anti-inflammatory agents, albendazole or fenbendazole.
  • Prognosis: poor.

Presenting signs

  • Signs vary depending on the route of larval migration, magnitude of infection and the damage done.
  • They can be non-specific such as ataxia and behavioral change, or more circumscribed localized such as head tilt/torticollis   Head tilt   and circling.
  • Neurological (CNS) signs (which are often progressive):
    • Tremors.
    • Vertical nystagmus.
    • Ataxia.
    • Circling.
    • Head tilt/torticollis   Head tilt  .
    • Swaying.
    • Falling.
    • Flipping.
    • Lateral +/- dorsal recumbency.
    • Paralysis   Paresis / paralysis: limb  .
    • Seizures   Seizures   - can occur in the later stages of disease.

Acute presentation

  • Often severe neurological signs such as head tilt/torticollis   Head tilt  +/- vertical nystagmus.
  • Circling.
  • Difficulty standing.

Geographic incidence

  • Toxocara canis has a widespread distribution on most continents.
  • Found in areas where rabbits are housed outdoors and follows the distribution of Baylisascaris procyonisBaylisascaris columnarisor Baylisascaris melis
  •  Baylisascarisspp are restricted to those geographic areas where skunks and raccoons are indigenous, namely North America. However, Baylisascaris procyonishas been reported in both Germany and Japan where raccoons had either been kept as pets or within zoological collections.
  • Definitive host of B. procyonisis the raccoon ( Procyon lotor), the definitive host of B. columnarisare skunks ( Mephitisspp) and American badgers ( Taxideaspp) and the definitive host of B. melisis the European badger ( Meles meles), with the former being the most common cause of cerebral larva migrans in rabbits.
  • Occurs in wild, feral and pet rabbits.

Age predisposition

  • None known.

Sex predisposition

  • None.

Breed predisposition

  • None known.

Public health considerations

  • Baylisascaris is a zoonotic parasite.
  • Oral intake of infected feces from skunks and raccoons can cause human infection, particularly in children or developmentally challenged adults, however contact with infected rabbits is not a public health risk.
  • Can cause visceral and neural larva migrans in infants and young children and ocular larva migrans in adults.
  • Most human cases are acquired from raccoons as rabbits acts as dead end hosts and therefore do not shed the eggs in their feces.
  • Preventative measures can be put into place to greatly decreased risk.

Cost considerations

  • Diagnostics tests are often performed to rule out a variety of other causes for various diseases that cause the similar CNS signs, the combined cost of some of these tests can be considerable.
  • Treatment may be intensive and chronic, which engenders significant financial cost. 
  • Exposure of a colony of rabbits, whether breeding, for display or within a laboratory setting can result in significant losses due to the poor long-term prognosis.
  • Supportive care can be costly if the animal has progressed to seizuring.

Special risks

  • Depending on migration route, effects on the lung, pulmonary vessels and left side of the heart may be seen.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Gavin P J, Kazacos K R & Shulman S T (2005) Baylisascariasis. Clin Microbiol Rev 18 (4), 703-718 PubMed.
  • Furuoka H, Sato H, Kubo M et al (2003) Neuropathological observations of rabbits (Oryctolagus cuniculus) affected with raccoon roundworm (Baylisascaris procyonis) larva migrans in Japan. J Vet Med Sci 65 (6), 695-699 PubMed.
  • Sorvillo F, Ash L R, Berlin O G et al (2002) Baylisascaris procyonis: An emerging helminthic zoonoosis. Emerg Infect Dis (4), 355-359 PubMed.
  • Deeb B J & DiGiacomo R F (1994) Cerebral larva migrans caused by Baylisascaris sp in pet rabbits. JAVMA 205 (12), 1744-1747 PubMed.
  • Kazacos K R, Reed W M, Kazacos E A et al (1983) Fatal cerebrospinal disease caused by Baylisascaris procyonis in domestic rabbits. JAVMA 183 (9), 967-971 PubMed.
  • Jacobson H A, Scanlon P F, Nettles V F et al (1976) Epizootiology of an outbreak of cerebrospinal nematodiasis in cottontail rabbits and woodchucks. J Wildlife Dis 12 (3), 357-360 PubMed.

Other sources of information

  • Percy D H & Barthold S W (2007) Pathology of Laboratory Rabbits and Rodents. 3rd edn. Blackwell Publishing, Iowa, USA. pp 294295. ISBN-13: 978-0813821016/2007.
  • Deeb B J & Carpenter J W (2004) Neurologic and Musculoskeletal diseases. In: Ferrets, Rabbits and Rodents: Clinical Medicine and Surgery. Includes sugar gliders and hedgehogs. 2nd edn. Eds: Quesenberry K E & Carpenter J W. W B Saunders, St, Louis, USA. pp 206. ISBN: 0721693776.
  • Samuels W M, Pybus M J & Kocan A A (2001) Parasitic diseases of Wild Mammals. 2nd edn. Manson Publishing, London.