Canine distemper is highly contagious and infects a broad range of species: dogs, coyotes, wolves, foxes, ferrets, jackals, hyenas, weasels, raccoons, minks, skunks, badgers, otters, among others.
The disease is caused by the canine distemper virus (CDV). It is excreted in the saliva, respiratory secretions, urine, and feces and can be transmitted from dog to dog by aerosol and direct contact. Since the virus does not survive for extensive periods in the environment, infected and susceptible animals usually must be in close proximity for the infection to spread efficiently.
Initially, within a day or two of exposure, CDV can be identified in the tonsils and lymph nodes. By the second or third day, the virus can be detected in the bloodstream (viremia). This allows the virus to be transported to distant sites in the body where it replicates rapidly. During this initial period of virus replication, a fever develops. Further, the developing immune response of the infected animal will ultimately determine the eventual outcome of the infection.
If a dog develops a sufficiently strong immune response by the 8th or 9th day after infection, it terminates further spread of the virus and clears it from most tissues.
If a dog develops an intermediate immune response, it will eliminate or suppress the spread of CDV to the respiratory and intestinal tracks, but not from other tissues. These dogs often develop neurological disease without manifesting respiratory or diarrheal symptoms.
Dogs that develop a poor immune response will be completely overcome by the infection as the virus spreads throughout the body unchecked. Most will exhibit varying degrees of pneumonia and diarrhea followed by neurological disease, if they survive.
Most infections with CDV appear to be asymptotic or very mild in nature, reflecting the variable virulence of different CDV strains and the immunity imparted by previous exposure to CDV(either through prior infection or routine vaccination). In general, distemper most often affects younger dogs but can also affect older dogs. The following subsections describe manifestations of this disease according to age.
Maternal immunity typical protects puppies from CDV for the first few weeks of life. However, by age 5 to 7 weeks, the maternal immunity is waning and puppies can become susceptible to distemper. Affected puppies often exhibit a low-grade fever, depression, coughing and a mild to moderately severe diarrhea. Severe CDV infection can produce an inflammation and bleeding in the intestinal tract that can have a rapidly fatal outcome in very young puppies.
This is a common age group in which to see distemper in dogs. This is often true of puppies obtained from humane shelters, pounds, or local pet stores. The puppies are often incubating the infection at the time of purchase and show signs of disease in several days or weeks after arrival in the new household.
A transient fever appears which is associated with the initial spread of the virus throughout the body. Lack of appetite, slight depression, discharges from the eyes and nose, and tonsillitis may be observed. Once this stage has passed, the disease may take one of three courses based on the immune response described above.
Spread of the virus to the lungs and upper respiratory tract will lead to pneumonia and inflamed nasal passages and eyes. Spread of the virus to the intestinal tract leads to diarrhea and fluid loss. Spread to the skin is manifested initially by measles-like eruption and later by a thickening of the skin (hyperkeratosis).
Neurological symptoms can include circling, head-tilt, rapid eye movements (nystagmus), partial paralysis (paresis), paralysis, convulsions, and dementia. Involuntary rapid, jerky twitching or contraction of muscles and convulsions preceded by chewing-gum movements of the mouth are considered virtually diagnostic for distemper.
Older dogs, even if they have been routinely vaccinated for distemper can occasionally develop distemper after severe exposure. The disease is atypical in that it manifests primarily as an inflammation of the spinal cord. This disease is often self-limiting after several weeks, although residual central nervous system impairment may be evident after resolution of the infection.
Sometimes, a distemperlike disease is occasionally seen in puppies following vaccination. This is caused by either being born with an immune system defect or have a selective lack of resistance to CDV.
CDV has a preference for the enamel-forming cells of the tooth bud. If infection occurs during the time that the enamel layer of the tooth is being layed down, the mature tooth will develop irregularities of the tooth surface characterized by underdevelopment or incomplete development of the enamel. Fortunately, the underlying dentin layer of the dogs' teeth is very hard and resistant to decay, and affected teeth usually function well.
These include chewing-gum movements, muscle twitching, intermittent seizure episodes, partial paralysis, or abnormalities of balance.
Treatment is aimed at supporting the patient and preventing secondary complications by using antibiotics for bacterial infections; fluid replacement for prolonged diarrhea, lack of appetite, and vomiting; antidiarrheal medications; and anticonvulsive therapy in the presence of seizures.
Vaccinate your dog! The vaccines available are quite effective and produce long lasting immunity. Annual booster vaccinations are usually recommended.
When dealing with puppies, proper hygiene is essential in preventing exposure of the puppies to the virus.