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.
Two species of Paragonimus lung flukes can accidentally migrate to the nervous system and produce cysts in the brain and spinal cord of cats, dogs, 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.
Several types of intestinal worms (nematodes) are found in domestic animals.
The larvae of some roundworms, including Toxocara species, can invade the central nervous system and cause localized damage in cats. 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 more commonly known as the canine heartworm, but it can also affect cats. In addition to the heart and lungs, other parts of the body, including the central nervous system and the eye, can be infected.
Gurltia paralysans is found in the spinal veins of cats and has reportedly produced a high incidence of paralysis.
Myiasis is the development of certain types of larval flies (maggots, 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. Treatment of myiasis in the central nervous system is experimental. Antiparasitic drugs may be recommended to eliminate certain insect larvae from the nervous system. Corticosteroid drugs are often recommended to prevent additional inflammatory damage and pressure on the brain during treatment. (Also see Flies and Mosquitoes.)
Tick paralysis is a sudden, progressive motor paralysis caused by a salivary toxin that attacks the nervous system. Certain species of ticks are known to cause tick paralysis. People (especially children) and many other animals may be affected. Human cases of tick paralysis caused by the genera Ixodes, Dermacentor, and Amblyomma have been reported in Australia, North America, Europe, and South Africa. These 3 genera plus Rhipicephalus, Haemaphysalis, Otobius, and Argas have been associated with paralysis in animals. Cats seem to be resistant to the disease caused by these ticks, except in Australia where Ixodes holocyclus causes a severe and sometimes fatal paralysis in cats.
Signs typically appear 3 to 5 days after attachment of the Ixodes holocyclus female tick, but the timing can vary. Early signs include a change in voice, weakness of the rear limbs, breathing abnormalities, gagging, coughing, vomiting, and dilated pupils. As the toxicity progresses, weakness or paralysis of the breathing muscles becomes life threatening. Cats are also prone to "asthma-like" constriction of the airways and often breathe with increased focus and effort. Cats with moderate or severe toxicities can also be anxious. If stressed or handled too roughly, these cats can deteriorate quickly and die.
The presence of a tick along with the sudden (within 12 to 24 hours) appearance of leg weakness and/or difficulty breathing is diagnostic. If the tick is not still attached, the presence of a tick “crater” (a small hole surrounded by a slightly raised and red area) can help confirm the diagnosis. Other diseases and disorders can have the same signs as tick paralysis, but in areas where ticks are prevalent, tick paralysis is a strong possibility.
Treatment involves removing all ticks. If all ticks are not removed, death can occur due to paralysis of the muscles responsible for breathing. Cases of tick paralysis not caused by Ixodes holocyclus typically improve within 24 hours, with complete recovery in 72 hours. Unfortunately, removal of Ixodes holocyclus ticks does not stop the disease. Topical treatment with any product to kill attached ticks must only be done with chemicals that are safe for use in cats. In Australia, treatment for Ixodes holocyclus paralysis involves a specific antiserum (tick hyperimmune serum), in addition to treatment to minimize stress and support respiration. Severely fatigued animals may require anesthesia to improve breathing and oxygenation, allow muscles to rest, and overcome exhaustion. Asthma-like signs in cats can be difficult to treat because routine medications often do not work.
With early treatment, most animals recover from tick paralysis. However, approximately 5% of affected animals will die despite appropriate treatment. In general, cats tend to be less severely affected and have better outcomes than dogs. Applying pesticides that prevent tick infestations (that are safe for use in cats) can help protect cats, but they cannot completely prevent disease. If you live in an area where ticks are prevalent, it is important to thoroughly search your pets' coats for ticks on a daily basis. Vaccines are not available to prevent tick paralysis.
Also see professional content regarding CNS diseases caused by parasites.