Canine Distemper

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Overview
Canine distemper is a contagious, incurable, often fatal, multisystemic viral disease that affects the respiratory, gastrointestinal, and central nervous systems. Distemper is caused by the canine distemper virus (CDV).

Incidence
Canine distemper occurs worldwide, and once was the leading cause of death in unvaccinated puppies. Widespread vaccination programs have dramatically reduced its incidence.

CDV occurs among domestic dogs and many other carnivores, including raccoons, skunks, and foxes. CDV is fairly common in wildlife. The development of a vaccine in the early 1960s led to a dramatic reduction in the number of infected domestic dogs. It tends to occur now only as sporadic outbreaks.

Young puppies between 3 and 6 months old are most susceptible to infection and disease and are more likely to die than infected adults. Nonimmunized older dogs are also highly susceptible to infection and disease. Nonimmunized dogs that have contact with other nonimmunized dogs or with wild carnivores have a greater risk of developing canine distemper.

Transmission
Infected dogs shed the virus through bodily secretions and excretions, especially respiratory secretions. The primary mode of transmission is airborne viral particles that dogs breathe in. Dogs in recovery may continue to shed the virus for several weeks after symptoms disappear, but they no longer shed the virus once they are fully recovered.

It is possible for humans to contract an asymptomatic (subclinical) CDV infection. Anyone who has been immunized against measles (a related virus) is protected against CDV as well.

Symptoms
Macrophages (cells that ingest foreign disease-carrying organisms, like viruses and bacteria) carry the inhaled virus to nearby lymph nodes where it begins replicating (reproducing). It spreads rapidly through the lymphatic tissue and infects all the lymphoid organs within 2 to 5 days. By days six to nine, the virus spreads to the blood (viremia). It then spreads to the surface epithelium (lining) of the respiratory, gastrointestinal, urogenital, and central nervous systems, where it begins doing the damage that causes the symptoms.

Early symptoms include fever, loss of appetite, and mild eye inflammation that may only last a day or two. Symptoms become more serious and noticeable as the disease progresses.

The initial symptom is fever (103°F to 106°F), which usually peaks 3 to 6 days after infection. The fever often goes unnoticed and may peak again a few days later. Dogs may experience eye and nose discharge, depression, and loss of appetite (anorexia). After the fever, symptoms vary considerably, depending on the strain of the virus and the dog's immunity.

Many dogs experience gastrointestinal and respiratory symptoms, such as:

• Conjunctivitis (discharge from the eye)
• Diarrhea
• Fever (usually present but unnoticed)
• Pneumonia (cough, labored breathing)
• Rhinitis (runny nose)
• Vomiting

These symptoms are often exacerbated by secondary bacterial infections. Dogs almost always develop encephalomyelitis (an inflammation of the brain and spinal cord), the symptoms of which are variable and progressive. Most dogs that die from distemper, die from neurological complications such as the following:

• Ataxia (muscle incoordination)
• Depression
• Hyperesthesia (increased sensitivity to sensory stimuli, such as pain or touch)
• Myoclonus (muscle twitching or spasm), which can become disabling
• Paralysis
• Paresis (partial or incomplete paralysis)
• Progressive deterioration of mental abilities
• Progressive deterioration of motor skills
• Seizures that can affect any part of the body (One type of seizure that affects the head, and is unique to distemper, is sometimes referred to as a "chewing gum fit" because the dog appears to be chewing gum.)

Many dogs experience symptoms of the eye:

• Inflammation of the eye (either keratoconjunctivitis, inflammation of the cornea and conjunctiva, or chorioretinitis, inflammation of the choroid and retina)
• Lesions on the retina (the innermost layer of the eye)
• Optic neuritis (inflammation of the optic nerve which leads to blindness)

Two relatively minor conditions that often become chronic, even in dogs that recover are:

• Enamel hypoplasia (unenameled teeth that erode quickly in puppies whose permanent teeth haven't erupted yet—the virus kills all the cells that make teeth enamel)
• Hyperkeratosis (hardening of the foot pads and nose)

In utero infection of fetuses is rare, but can happen. This can lead to spontaneous abortion, persistent infection in newborn puppies, or the birth of normal looking puppies that rapidly develop symptoms and die within 4 to 6 weeks.

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