Pug Dog Encephalitis (PDE)
Pug Dog Encephalitis (PDE), also known as necrotizing meningoencephalitis (NME), is an inherited brain disease affecting pug dogs. It is described as an aggressive and fatal inflammatory disease of the central nervous system. First diagnosis of necrotizing meningoencephalitis (NME) in a dog was reported in 1960-ih, but the disorder was not understood until many years later. Due to sharing many similarities with meningitis in humans, viral cause was suspected. However, thorough molecular examinations have ruled out infectious causes and it is established that pug dog encephalitis is an immune-mediated disease, which occurs as a result of genetic susceptibility. Until today, necrotizing meningoencephalitis has been described in several toy breed dogs, such as the Brussels Griffon, Chihuahua, Coton de Tulear, Maltese, Papillon, Pekingese and shih tzu.
Characteristics and Symptoms
Pug dog encephalitis, unlike other forms of encephalitis, is hereditary and immune-mediated. Immune-mediated diseases are characterized by abnormal immune response, in which the body’s immune system recognizes healthy body tissues as dangerous and attacks them. In PDE case, the immune system is attacking the brain, causing its painful inflammation.
First symptoms usually occur between 2 and 3 years of age. Although symptoms most commonly appear around that age, there were reported cases of dogs affected already at 6 months of age but also 7 years of age. Symptoms include seizures, loss of muscle coordination, walking in circles, head tilt, and pressing head against walls or objects. Behavioral changes can be observed as well, such as lethargy, confusion, depression or aggression. Usually, after development of first symptoms, the disorder progresses rapidly, and affected dogs die within months after the onset of symptoms.
Although the disorder is deadly, there are some medications which can ease the symptoms. Seizures can be controlled with anti-convulsants, while painful brain inflammation can be reduced thanks to anti-inflammatory drugs, such as corticosteroids.
After development of symptoms, disease can be diagnosed by a veterinarian through tests such as CAT scans and MRI. Unfortunately, the disorder progresses so fast that sudden death onsets or euthanasia is required, which leaves little time for diagnostic tests.
Pug Dog Encephalitis (PDE) is associated with 3 specific dog leukocyte antigen (DLA) class II genes: DRB1, DQA1, and DQB1. Mode of PDE inheritance seems to be complex, however it has been observed that only dogs with two copies of the PDE susceptibility associated markers have high risk of developing the symptoms in their lifetime.
Researches have established that approximately 1.2% of Pug dogs die of encephalitis, whereas susceptibility markers in homozygous or heterozygous state is present in approximately 50% of the Pug population. Due to this high percentage, it is not advised to completely remove carries from breeding program, since it would lead to significant loss of genetic diversity. Considering homozygosity for specific allele greatly increases risk of developing symptoms, selective mating against homozygosity is preferred. PDE genetic testing allows identification of two heterozygous dogs, which can prevent their breeding and obtaining homozygous puppies.
Pederson, N. (2011): Dog leukocyte antigen class II-associated genetic risk testing for immune disorders of dogs: simplifies approaches using Pug dog necrotizing meningoencephalitis as a mode. J Vet DIagn Invest 23:68-76.
Schrauwen I, Barber RM, Schatzberg SJ, Siniard AL, Corneveaux JJ, Porter BF, et al. (2014) Identification of Novel Genetic Risk Loci in Maltese Dogs with Necrotizing Meningoencephalitis and Evidence of a Shared Genetic Risk across Toy Dog Breeds. PLoS ONE 9(11): e112755. doi:10.1371/journal.pone.0112755