Encephalitis Secondary to Parasitic Migration in Dogs
Brain inflammation, also known as encephalitis, may be due to a variety of factors. For instance, parasites can migrate into the dog’s central nervous system (CNS), gain entry via blood or through adjacent tissues, including the middle ear, natural opening in the skull, nasal cavities and cribriform plate (part of the skull), or open fontanelles, also called “soft spots.”
These parasites may normally 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). Dirofilaria immitis is most often seen in adult dogs, while the other parasites generally infect younger pups that are exposed to the outdoors.
Symptoms and Types
Symptoms associated with this type of encephalitis will vary depending on the portion of CNS affected. Cuterebriasis, for example, occurs mainly between July and October in the U.S. and is characterized by the sudden onset of behavior changes, seizures, and vision issues. Meanwhile, a common rat parasite in Australia, Angiostrongylus cantonensis, may cause lumbosacral syndrome in puppies, which can lead to paralysis or paresis of the hindlimbs, tail, and bladder. In addition, parasite infections are often asymmetrical, affecting one side but not the other.
The most common way a dog acquires this type of encephalitis is by being housed in a cage that has been previously occupied by an infected host; e.g., raccoons, skunks.
You will need to give a thorough history of your dog’s health, including the onset and nature of the symptoms, to the veterinarian. He or she will then perform a complete physical examination as well as a biochemistry profile, urinalysis, complete blood count (CBC) — the results of which are typically normal unless the parasites have also migrated into other organs.
Computed tomography (CT) or magnetic resonance imaging (MRI) of the brain may reveal a focal lesion and/or cerebral tissue death from blockage of cerebral blood vessels, both of which are consistent with parasitic infections. A cerebrospinal fluid tap is another common diagnostic method used to confirm parasitic infection; however, the tap may yield normal results despite encephalitis.
Medication such as anthelmintics (dewormers) may be used to kill off the parasites, but they may also lead to other complications. Consult your veterinarian for the best course of treatment. Puppies with a mild form of angiostrongylosis may even recover fully with just supportive care and corticosteroid therapy. In other cases, surgical removal of intercranial parasites (e.g., Cuterebra) may be necessary.
Most parasitic infections of the central nervous system are incurable and progress in severity. To prevent your dog from contracting such infections keep it indoors and away from wild animals. Dewormers, anthelmintics, and dirofilaricides can also prevent infection.
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