Human Antibody Test Gives New Hope for Canine Encephalitis

Analysis by Dr. Karen Shaw Becker

encephalitis in dogs

Story at-a-glance -

  • Recent research from North Carolina State University suggests that dogs can develop the same type of autoimmune encephalitis that humans do
  • Encephalitis means inflammation of the brain, and it may be accompanied by inflammation of the spinal cord (myelitis) and/or inflammation of the membranes that cover the brain and spinal cord (meningitis)
  • There are two primary types of encephalitis — infectious and idiopathic; idiopathic (non-infectious) encephalitis often has an immune-mediated cause
  • NC State researchers successfully employed an antibody test designed to detect human autoimmune encephalitis on dogs
  • These study results could lead to better screening methods for diagnosis and perhaps more effective treatments for canine encephalitis

A recent study conducted by researchers at North Carolina State University and published in the Journal of Veterinary Internal Medicine finds that dogs can develop the same type of autoimmune encephalitis that people do.1 According to NC State University News this finding, revealed through antibody testing, could lead to better screening methods for diagnosis and possibly more effective treatments for canine encephalitis.2

Encephalitis is the medical term for inflammation of the brain. The brain and spinal cord make up the central nervous system (CNS), and inflammatory disease of the CNS is one of the most common causes of neurologic disease in animals.

There can also be inflammation of the spinal cord, which is called myelitis, and/or meningitis, which is inflammation of the membranes that cover the brain and spinal cord, along with encephalitis. Certain dog breeds are predisposed to encephalitis, including German Shorthaired Pointers, the Maltese, and Yorkshire Terriers.

Infectious Encephalitis

There are two primary categories of encephalitis: infectious and idiopathic. The infectious form of the disease can be caused by a bacterial, viral, or fungal infection, parasites, immune-mediated disorders, tick-borne disease, and foreign bodies. We diagnose the disorder of idiopathic encephalitis when we can’t find an infectious cause for the disease.

Where a pet lives often plays a role in the cause of encephalitis. In areas of the U.S. where ticks are a problem, tick-borne infections such as Rocky Mountain spotted fever, ehrlichia, and Lyme disease are common causes. In the southwest U.S., a fungal infection known as valley fever can also be a cause.

Bacterial infections are a relatively rare cause of encephalitis in companion animals, but they do occur from time to time. Viral causes include canine distemper and feline infectious peritonitis. When a parasite is involved, Toxoplasma gondii is often the culprit.

Idiopathic Encephalitis Is Often the Result of an Autoimmune Disorder

When no infectious cause for the disease can be found, idiopathic encephalitis often has an underlying immune-mediated cause, meaning the animal’s immune system attacks its own brain or spinal cord.

Types of immune-mediated disease seen in dogs with encephalitis include granulomatous meningoencephalitis (GME), which is seen most often in middle-aged small breed dogs and can be linked to vaccine reactions, in some cases. Another is necrotizing meningoencephalitis (NME). Predisposed breeds include young to middle-aged Pugs, Maltese, Chihuahuas, Papillons, Shih Tzus, and Boston Terriers.

A third type of immune disorder that can cause encephalitis is called necrotizing leukoencephalitis (NLE), which affects Yorkies, Chihuahuas, and Shih Tzus most commonly. Autoimmune forms of encephalitis are not only challenging to treat, but difficult to differentiate. In fact, veterinary neurologists often refer to them as "meningoencephalitis of unknown etiology,” which has become an umbrella term for autoimmune encephalitis.

"In reality, there are likely to be many different forms of autoimmune encephalitis in which the immune system is reacting to different targets within the brain,” says Natasha Olby, study co-author and professor of veterinary neurology and neurosurgery at NC State.

“Currently we are unable to distinguish these in the living patient. While we treat all the cases with immunosuppression, better categorization of the different forms of encephalitis might enable us to predict prognosis better and fine-tune treatment for different diseases."3

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Encephalitis Symptoms

Clinical signs of encephalitis depend on the area of the brain that is affected. Symptoms typically appear suddenly and are rapidly progressive.

If the forebrain is involved, there can be seizures, blindness, behavior changes, depression, and circling. With brainstem disease, there can be loss of coordination, head tilting, tremors, and facial paralysis. Other signs can include fever, decreased responsiveness, unequal size of the pupils, or smaller-sized “pinpoint” pupils.

A dog or cat with encephalitis may have neurologic abnormalities that come from a single or focal area of the brain, or multiple (multifocal) areas of the brain. However, whereas many other diseases such as a stroke or brain tumor can cause focal neurologic signs, when the symptoms are multifocal, encephalitis is most often the cause.

Diagnosing Encephalitis

While it’s important for your veterinarian to run the usual diagnostic tests on your pet, including blood tests, urinalysis, chest X-rays, etc., it’s possible for animals with encephalitis to show no abnormalities on those tests because what’s happening in the central nervous system can be entirely separate from the rest of the body.

That’s why a definitive diagnosis of the disease often involves a spinal tap. The cerebrospinal fluid that surrounds the brain and spinal cord gives direct evidence of what is going on inside the CNS. A significant increase in white blood cells in the spinal fluid usually indicates encephalitis.

A spinal tap does carry some risk for certain animals. Your pet may require a magnetic resonance imaging (MRI) or computerized tomography (CT) scan of the brain prior to a spinal tap to look for signs of elevated intracranial pressure that can increase the risk for the procedure. Brain imaging can also be helpful in ruling out other causes of neurologic disease like a brain tumor.

For the just-released NC State study, the researchers used an antibody test developed to detect cases of human autoimmune encephalitis that screens for antibodies against six different neuronal surface targets known to be involved in the disease. Human and canine genes for these targets are nearly identical, so a human test works effectively for dogs.

The researchers used the antibody test to screen cerebrospinal fluid from 32 dogs with neurological disease, both inflammatory and non-inflammatory. Nineteen of the dogs had been diagnosed with inflammatory disease. Of the 19, three were positive for antibodies to the target.

"Being able to show that dogs suffer from a specific autoimmune encephalitis is really a paradigm shift," said Olby. "But what causes this immune response is a slightly different question. We haven't found a trigger, but our findings suggest that dogs and humans suffer from the same condition.

While treatment options will remain the same, we can now look for more antibody targets and perhaps be able to change the diagnosis from 'unknown etiology' to a diagnosis by neuronal cell surface target. Being able to categorize the disease more accurately may give both dogs and humans more options for treatments in the future."

Treatment Options

Treatment of encephalitis focuses on reducing the severity of symptoms. Typically, antibiotics or antifungals will be given if an infection is present. If the pet is having seizures, anticonvulsant medications may be recommended. Low-dose steroid therapy may also be started to treat significant inflammation in the spinal fluid or severe clinical signs.

Traditional treatments for autoimmune encephalitis usually involve the intentional suppression of the immune system with high doses of drugs for three to six months, and sometimes longer.

Many integrative veterinarians, myself included, have found that incorporating adjunctive therapies such as homotoxicology, ozone therapy, and traditional Chinese herbal protocols have been very beneficial for reducing symptoms and shortening the course of the disease for many patients.

I firmly believe that all pets who have recovered from idiopathic or immune-mediated encephalitis should never be vaccinated again for any reason. These animals should have titer tests performed in lieu re-vaccination.

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