A number of parasites (including worms and insects) are associated with central nervous system disease. Diagnosis requires eliminating other possible causes of illness, such as rabies, and identifying the specific parasite responsible.

Tapeworms

Coenurosis (also called gid, sturdy, or staggers) is caused by Taenia multiceps, an intestinal tapeworm of dogs and people. Other animals, such as sheep, goats, deer, rabbits, horses, and cattle can carry and spread this parasite to dogs. The larval stage of the parasite can invade the nervous system and lead to swelling of the brain and spinal cord. The adult worm may grow to more than 2 inches in diameter and cause increased pressure on the brain, which results in loss of muscle control, blindness, head tilting, stumbling, and paralysis. Dogs that are around sheep and other livestock should not be fed body parts of infected animals and should be dewormed regularly.

Echinococcosis is caused by Echinococcus granulosus, a tapeworm found in the small intestine of dogs. Its eggs are ingested by intermediate hosts, including sheep, cattle, and moose. People can also serve as intermediate hosts. The larvae can form large, thick-walled cysts that spread to the nervous system and produce signs similar to those of a brain tumor. Surgery can sometimes remove the cysts, and the infection can be treated with appropriate medication.

Flukes

Two species of Paragonimus lung flukes can migrate to the nervous system and produce cysts in the brain and spinal cord of dogs, cats, and people.

Schistosomes, or blood flukes, normally deposit their eggs in the blood vessels of the gut and urinary bladder, from which they pass into the external environment via the feces or urine. Some eggs, however, may get into the bloodstream and reach the central nervous system, where they form capsules. This condition has been seen in people and domestic animals.

Roundworms

Several types of roundworms are found in domestic animals.

The larvae of some ascarid roundworms, including Toxocara species, can invade the central nervous system and cause localized damage in dogs. Toxocara larvae may also invade the eye and cause vision loss in people.

Baylisascaris procyonis is a roundworm found in the small intestine of raccoons. Its larvae can infect people and domesticated animals and migrate to the central nervous system. This parasite can also cause central nervous system and eye damage in people, particularly children.

Dirofilaria immitis is the canine heartworm. In addition to the heart, other parts of the body, including the central nervous system and the eye, can be infected.

Disease Caused by Insects

Myiasis is the development of larval dipteran flies (bots and warbles) within the body's tissues or organs. The larvae of Cuterebra, which are deposited under the skin in dogs or cats, have been known to wander into the central nervous system and affect the cerebrum or cerebellum. Organophosphate drugs can eliminate certain dipteran larvae from the nervous system, but they can also cause nervous system damage. Corticosteroid drugs are often recommended to prevent additional inflammatory damage and pressure on the brain during treatment (see Skin Disorders of Dogs: Flies and Mosquitoes of Dogs).

Last full review/revision July 2011 by William B. Thomas, DVM, MS, DACVIM (Neurology); Cheryl L. Chrisman, DVM, MS, EDS, DACVIM (Neurology); Charles E. Rupprecht, VMD, MS, PhD; Kyle G. Braund, BVSc, MVSc, PhD, FRCVS, DACVIM (Neurology); Caroline N. Hahn, DVM, MSc, PhD, DECEIM, DECVN, MRCVS; Charles M. Hendrix, DVM, PhD; Karen R. Munana, DVM, MS, DACVIM (Neurology); T. Mark Neer, DVM, DACVIM; Robert Wylie, BVSc, QDA