Canine Distemper Virus
Overview of Canine Distemper Virus
Canine distemper virus (CDV) is a highly contagious disease that affects dogs, foxes, coyotes, wolves, ferrets, skunks, Asian elephants, large felines, and raccoons. The incidence of disease is greatest seen in juvenile unvaccinated dogs. Younger dogs are most susceptible due to a decrease in protection against distemper, which is passed on from mother to a newborn, but disappears between 9 and 12 weeks of age.
Distemper is caused by a virus similar to the one that causes measles in humans. It is a single-stranded RNA paramyxovirus transmitted through the air via droplets, which originates from the bodily fluids of an infected animal. The virus does not affect humans, therefore, it is not zoonotic and can’t be transmitted to people. The mammals most susceptible to the disease are Mustelids (ferrets, mink), and many cases are fatal in these species.
The virus replicates in the lymphatic tissue of the respiratory tract, where it then spreads through the lymphatic system to the respiratory, gastrointestinal, and neurologic systems. It is transmitted through the bodily fluids of infected animals (including urine and mucus), so your dog may become infected without coming into contact with an infected dog.
Different stages of the disease are associated with various clinical signs, usually involving some combination of the respiratory and/or gastrointestinal tract symptoms in the early stages, and the nervous system several weeks later. Dogs can have any or all systems involved.
Distemper is much less prevalent now due to the presence of the distemper vaccine. Once a dog has been fully vaccinated, their chances of contracting the disease are very low. The prognosis for dogs with distemper ranges from good to guarded. Some patients recover, while others have additional manifestations of the disease later in life, or have such severe, persistent signs that they have to be euthanized or die from the disease. Once dogs develop neurological signs, recovery is an uphill battle. Rate of fatality is 50% in adult dogs and as high as 80% in puppies.
Clinical Signs of Distemper
While some affected individuals only have mild clinical signs, others may exhibit severe signs. The first noticeable signs are discharge from the eyes and nose, mild cough, and mild lethargy.
Other common signs are:
- Depression or malaise
- Gastrointestinal signs
- Respiratory signs
- Nasal discharge
- Labored breathing
- Difficulty breathing
- Neurological signs
- Seizures. A “chewing gum” seizure is one of the classic signs of distemper.
- Lack of coordination
- Involuntary muscle tremors or tics
- Paralysis or weakness
- Hardening of the footpads
- Enamel defects on the teeth
There is a rare chronic encephalitis form of distemper that has also been called old dog encephalitis (ODE). This is characterized in older dogs that are vaccinated for distemper who may not show signs of infection. The pathophysiology of ODE is still not completely understood, but it is thought to be secondary to the inflammatory reaction of a persistent distemper infection in the central nervous system.
Clinical signs associated with ODE include:
- Ataxia (wobbly, uncoordinated movements)
- Compulsive movements, such as head pressing, circling, pacing
Diagnosis of Canine Distemper Virus
Diagnosis can be difficult to determine, but is usually based on the animal’s history and current clinical signs. It requires exclusion of other diseases with indistinguishable symptoms.
A physical examination can reveal specific characteristics that indicate distemper.
These characteristics are:
- Discoloration of tooth enamel
- Muscular tics or myoclonus
- Thick and hardened foot pads (hyperkeratosis)
Your veterinarian may recommend completing blood work, including a complete blood count, chemistry panel, and urinalysis, as well as tests to exclude similar conditions. These tests are not always necessary in every case, however, they may be of benefit in certain individuals and are selected on a case-by-case basis.
On the complete blood count (CBC), a lymphopenia (decreased numbers of lymphocytes) may be seen secondary to the virus. Occasionally, viral inclusion bodies can be found in circulating leukocytes (white blood cells) in the beginning stages of the disease.
Cerebrospinal Fluid Analysis
A respiratory PCR panel is available to test for distemper, and respiratory swab samples are submitted for this test. More invasive testing includes cerebrospinal fluid (CSF) samples and conjunctival scrapings to look for inclusion bodies.
Analysis and testing CSF obtained from individuals exhibiting neurologic signs may be useful in diagnosing distemper. Microscopic analysis of CSF may show increased numbers of lymphocytes and protein. Detection of high antibody titers for distemper in the CSF can provide supportive evidence of an active infection. Comparing the antibody titers found in the CSF to antibody titers found in the serum (blood) may also help support the diagnosis of distemper.
The measurement of antibodies to the distemper virus in blood may be helpful. Dogs that are able to mount an antibody response to the virus usually have titers that increase over a 2- to 4-week period. A single elevated antibody titer taken at the beginning of the illness may be difficult to interpret, because it could represent antibodies produced by prior vaccination.
Comparing distemper antibody titers in the CSF to peripheral blood has also been helpful in the diagnosis of this disease.
The ultimate diagnosis is based on demonstration of viral antigens (proteins) in scrapings and body fluids such as conjunctival smears, transtracheal washings, urine sediment, buffy coat (layer of white blood cells formed after blood is spun down), and cerebrospinal fluid (CSF). However, their absence does not rule out infection.
Treatment of Canine Distemper
There aren’t treatment measures available to specifically target the distemper virus. Instead, the treatment relies on supportive care and prevention of secondary bacterial infections. The disease is often progressive despite therapy. Therapy is supportive and aims to strengthen and nourish the body, allowing the dog time to personally fight off the infection. Dogs with distemper may need to be hospitalized and must be kept in isolation, so as not to infect other dogs.
Therapy usually includes:
- IV fluids to maintain hydration
- Antibiotics to prevent secondary bacterial infections
- Anti-nausea medications
- Nutritional support
- Oxygen support for dogs with respiratory signs
- Anticonvulsant medications if seizures are present
Prevention of Distemper in Dogs
Fortunately, canine distemper is preventable. Puppies should receive a series of vaccinations beginning when they are six to eight weeks old and repeated at three to four week intervals until a high state of immunity is achieved (usually around 16 to 20 weeks of age). The distemper vaccine is part of the core puppy vaccine known as DA2PP, which includes canine distemper, canine adenovirus type 2, canine parvovirus, and canine parainfluenza.
Puppies are not fully vaccinated until after their third set of booster shots. Caution should be taken when exposing a dog that isn’t fully vaccinated to other dogs, since they are still susceptible to the virus.
In addition, if your dog is exhibiting signs of the distemper virus, they should be isolated and prevented from interacting with other animals. All exposed surfaces should be thoroughly cleaned with bleach.
Several diseases and disorders can appear similar to canine distemper, though few diseases mimic all of the clinical signs.
Diseases that have similar respiratory clinical signs, but lack the gastrointestinal and neurological signs, include:
- Kennel cough, or infectious tracheobronchitis, which is a contagious respiratory disease that is manifested by coughing. This is a transient disease, and most dogs recover without severe complications.
- Canine influenza or canine flu. This is an infectious disease that spreads in dog populations of all ages. Like the human flu, it is hardest on young and geriatric dog populations.
- Pneumonia. Puppies tend to contract infectious bacterial pneumonia. They can recover with supportive care and may need hospitalization.
Other diseases in young dogs that have similar gastrointestinal signs to canine distemper, but lack the respiratory and neurological clinical signs, include:
- Parvovirus. This is a highly contagious disease that affects any age of unvaccinated dog and causes severe vomiting and diarrhea. It can be fatal if untreated.
- Coronavirus. Enteric coronavirus (CCov) causes vomiting, diarrhea, and inappetence. Luckily, there is a vaccine available for this disease. Please note, this is different from respiratory coronavirus, and is not the same virus as SARS-CoV-2.
- Gastrointestinal Parasites, including giardia.
- Bacterial Enteritis, including Campylobacter, Salmonella and Clostridia.
Other differential diseases that have similar neurological clinical symptoms as canine distemper, but lack the gastrointestinal and respiratory signs, include:
- Rabies Virus. A fatal neurological virus.
- Encephalitis. This can be bacterial, protozoal (neosporosis, toxoplasmosis), or inflammation.