Canine distemper is a viral infection which is contagious, incurable, affects multiple systems, and can be fatal. The disease affects the digestive, respiratory, and the central nervous sytem. The disease is caused by the Canine Distemper Virus (CDV), a paramyxovirus.
CDV is common in dogs, skunks, racoons, foxes, ferrets, coyotes, wolves, and other carnivores. Cats also are subject to distemper; however, the causative agent is different from that of CDV. Feline distemper is caused by parvovirus. This virus has succeeded in jumping cross species and is responsible for the canine disease parvo. The disease is worldwide in its distribution and was once the leading cause of fatality in unvaccinated puppies. Creation of an effective vaccine has greatly reduced the ravages of the disease among domestic dogs. Introduction of the vaccine in the 1960s has reduced the disease from being endemic to a status of sporadic occurrance.
Animals at risk are primarily young pups from 3-6 months old and unvaccinated older dogs. Pups of vaccinated females possess the mother's immunity, an effect which lasts until about 12-16 weeks of age. This is the proper time to immunize. Nonimmunized dogs exposed to other nonimmunized dogs and wild carnivores run an elevated risk of exposure to the disease.
CDV is transmitted by infected animals via bodily secretions, especially respiratory secretions. The virus travels by cough, sneezing, runny noses and other means. These methods are usually airborne, making infection of other animals quite prevalent. Dogs who are in recovery still shed the virus for several weeks after symptoms abate. Dogs who are fully recovered no longer shed the virus.
The virus enters the body of the host where it is engulfed by macrophages (immune system cells whose mission it is to absorb and wall off infection, then to destroy it through enzyme action). Instead of eliminating the virus, the macrophages transport the virus into the lymph tissue of the lungs. The virus rapidly replicates itself and spreads to the surface tissues lining the gastro-intestinal tract, respiratory system, and central nervous system. The liver and spleen are also involved as sites for infection. This phase of disease developemtn is called the mucosal phase.
The next phase is called the neuroligic phase, in which involvement of the central nervous system becomes pronounced.
It is possible for humans to contract CDV in a subclinical form. The virus is capable of replicating inside the human host but causes no symptoms. Humans vaccinated for measles are immune to CDV, as the measles virus is related to the virus which causes CDV.
The disease manifests through the following symptoms:
- lack of appetite
- mild eye inflammation which may last just 1-2 days
- nasal discharge
Fever can be from 103-106, and may go unnoticed, usually peaking within 3-6 days following infection, then subsiding only to reappear later. As the disease progresses, other more serious symptoms occur, to include:
These symptoms are often accompanied by secondary viral or bacterial infections. Dogs characteristically develop inflammation of the brain and spinal cord. Most dogs who die of distemper succumb due to neuro-muscular effects which include:
- ataxia (muscle incoordination)
- hyperesthesia (heightened sensitivity to sensory input such as temperature, touch, pain)
- Muscle twitching or spasm, (myoclonus), which can become disabling
- partial or complete paralysis
- progressive deterioration of mental ability
- progressive loss of motor skills
- seizure which may affect any portion of the body
Many dogs contract other conditions affecting the eye. These conditions include inflammation, lesion, and optic neuritis (inflammation of the optic nerve, leading to blindness). Other conditions which may develop are hyperkeratosis (hardening of the foot pads and nose), and enamel hypoplasia, a condition in which tooth enamel erodes. The virus kills the cells responsible for depositing enamel.
Diagnosis is difficult, relying on many indirect indicators. These include vaccination history, exposure to known infected animals, symptomology, and lab tests.
Since there is no cure for the disease, treatment is supportive. Treatments include:
- Provide a clean, warm, and draft-free environment.
- keep eye/nasal discharges cleaned.
- For vomiting administer antiemetic drugs (anti-nausea and anti-vomiting drugs)
- For diarrhea provide anti-diarrheal medications.
- provide adequate rehydration including intravenous rehydration
- antibiotics and/or bronchodilators for pneumonia
The myoclonus, (muscle twitching/spasm), is not treatable. Treatment exists to replace eroded tooth enamel and prevent further enamel erosion. Glucocorticoid therapy may help reverse blindness from optic neuritis, but it weakens the immune system and over time may exacerbate symptoms.
Diseases such as distemper, which are so destructive, are best avoided. The best method available to prevent the disease is vaccination of puppies at 8-12 weeks of age. Puppies require a series of vaccinations as the carryover immunity from the mother can interfere with the efficacy of the vaccine. It is important to give the vaccine early enough to bridge the period between the inherited immunity and the immunity imparted via the vaccine. Vaccination of dogs who are infected is still effective as long as vaccination occurs within 4 days of infection.
There are several vaccines currently available. One type utilizes virus obtained from infected animals and is virtually 100% effective, though it possesses a risk of fatal encephalitis developing, especially in dogs with compromised immune systems. The condition is rare, but should be considered when using infective tissue culture vaccine.
The second type commonly used is made from chick embryo cultured virus. It does not pose a risk of encephalitis, however it is not as effective as the infective tissue culture variety. Embryo cultured vaccine provides an 80% immunity. Vaccinate puppies by 12 weeks of age and yearly afterwards to maintain protection.
Dogs who are infective or who have been exposed to infected animals should be isolated from other dogs in the household or kennel. Other dogs should be immediately innoculated.
In households or kennels where a dog has died of distemper, a waiting period of at least 1 month should be observed to allow the virus to perish before a new dog or puppy is introduced into the environment. The CDV virus doesn't fare well outside of a host animal. Heat, sunlight, as well as many disinfectants, chemicals, and soaps cause the virus to become inactive. Disinfection of the living area and any objects contacted by the infected animal with a 1:30 solution of bleach/water is recommended.
Distemper progresses depending on the strain of the disease as well as the health of the infected animal's immune system. Following subsidence of the initial fever the disease can progress in various ways. More than half of infected dogs will die within 2 weeks to 3 months. Surviving animals may experience debilitating symptoms even if they do not die. Dogs with severe and progressive central nervous system disorder are often recommended for euthanasia by veterinarians. Dogs who recover may have lingering symptoms for months.
It is possible for dogs with very strong immune systems to have the disease and display no symptomology whatsoever. Animals who have fully recovered from distemper are no longer infective and are incapable of spreading the virus.