Canine distemper is a serious, often fatal viral disease of dogs, and unvaccinated puppies are hit hardest. The virus can attack the airways, the gut and the nervous system, and the nerve damage it leaves in some survivors can be permanent. No drug kills the virus once a dog is infected, so prevention matters most. Distemper is one of the core vaccines every dog should get.
The illness also hides well early on. The first fever is easy to miss, and a dog that looks healthy can still shed the virus, which is why knowing the course of the disease matters as much as knowing the signs.
What is Canine Distemper Virus?
Canine distemper virus (CDV) is a morbillivirus in the family Paramyxoviridae. Its close relatives include the measles virus of people and the rinderpest virus of cattle. CDV is an enveloped, single-stranded RNA virus, which means its genetic material sits inside a fragile outer coat. That fragile coat is a big part of why the virus does not last long outside the body and is killed by most common disinfectants (Merck Veterinary Manual).
The envelope carries the hemagglutinin (H) and fusion (F) glycoproteins the virus uses to enter cells. Antibodies against H are what protect a dog that recovers.
How Distemper Spreads
Most dogs catch distemper by breathing in virus droplets when an infected animal coughs or sneezes, or through direct contact with its eye, nose and mouth discharges. Infected dogs shed the virus in respiratory secretions, saliva, urine and feces. Food and water bowls, bedding and other objects can carry the virus too, but only for a short time.
The main threat to a pet dog is contact with an infected dog or wild animal. Outdoor food and water bowls are an easy route to miss: they attract raccoons and other wildlife, and a sick raccoon can contaminate a bowl your dog drinks from later (LA County Veterinary Public Health).
Two things make CDV hard to contain. Some dogs keep shedding the virus for weeks to months after they seem to have recovered. And infection can be mild or produce no obvious signs, so a dog that looks healthy can still pass the virus on. Domestic dogs are considered the main reservoir of CDV.
Outside the host the virus is fragile. It breaks down fairly quickly in warm conditions but can survive long periods in freezing temperatures. Dogs that recover usually develop long-lasting immunity.
Clinical Signs and Symptoms of Distemper in Dogs
Signs vary with how severe the infection is and how the dog's immune system responds. Distemper often moves through phases, but not every dog shows every phase. Nervous system signs can appear together with the other signs, after them, or on their own.
Which dogs are most at risk
Puppies and unvaccinated dogs are the most likely to catch distemper and to develop the severe forms. Veterinarians suspect distemper in any sick dog with compatible signs whose vaccination history is missing or unknown.
Early and later signs
- Early, systemic phase. A short fever often appears 3 to 6 days after infection, sometimes with a low white blood cell count (lymphopenia) and mild appetite loss. It is easy to miss. The virus multiplies first in the lymphatic tissue of the respiratory tract, then travels through the bloodstream inside white blood cells to the rest of the body.
- Second fever with respiratory and digestive signs. After a brief improvement, many dogs develop a second fever with watery nasal discharge, thick pus-like eye discharge, tiredness and loss of appetite. Coughing, sneezing, breathing difficulty, vomiting, diarrhea and dehydration can follow. Because the virus suppresses the immune system, secondary bacterial infections such as pneumonia are common. Cornell's Wildlife Health Lab notes that clear signs usually show 10 to 14 days after infection.
- Neurologic phase. Signs include muscle twitching, often in a leg or the face (myoclonus); seizures, often with drooling and chewing motions of the jaw ("chewing-gum fits"); circling, head tilt and rapid involuntary eye movements; poor coordination; and weakness or paralysis that often starts in the back legs. They come from inflammation of the brain and spinal cord and damage to the protective coating of nerve fibers (demyelination). Neurologic signs can start weeks or months after the first illness and usually get worse over time.
Distemper can also leave visible marks. The skin of the footpads and nose may thicken and harden (hyperkeratosis), which is where the old name "hardpad disease" comes from. The virus can infect the optic nerve and affect vision, and dogs that survive may have damaged tooth enamel (enamel hypoplasia). A pustular skin rash is a rare sign.
When to call your veterinarian: call promptly if a puppy or unvaccinated dog has a fever, eye or nose discharge, a cough, vomiting or diarrhea, or any twitching or seizures. Tell the clinic you are worried about distemper so the team can keep your dog away from other patients.
Distemper in Wildlife and Other Animals
CDV occurs worldwide. It mainly infects carnivores: dogs, ferrets, foxes, wolves, coyotes, raccoons, skunks, and big cats such as lions and tigers. It has also been found in animals outside that group, including Asian elephants and Japanese monkeys, and researchers have recorded it in at least six orders of mammals.
Wild animals show the same mix of respiratory and neurologic signs as dogs, and sick wildlife can look disoriented or act strangely (Cornell Wildlife Health Lab). In Los Angeles County, for example, outbreaks recur in raccoons, gray foxes have been hit too, and canine distemper is a reportable condition there. Because domestic dogs are the main reservoir, the virus can move from dogs to wildlife and back again. If you see a raccoon or fox that looks sick, keep your dog away from it.
Diagnosis
You cannot tell for sure that a dog has distemper just by looking. The signs overlap with other infections, so your veterinarian combines the dog's history (especially vaccination history), a physical exam and lab tests.
For the pros: lymphopenia supports the suspicion but is not specific. Confirmation relies on RT-PCR (a test that detects the virus's genetic material) and antibody tests such as ELISA and IFA, run on samples like conjunctival swabs, blood, urine or cerebrospinal fluid. Recent vaccination with a modified-live vaccine can complicate results, because RT-PCR may not tell vaccine virus from field virus. Differentials include canine parvovirus, kennel cough, infectious canine hepatitis, and lead or organophosphate poisoning in dogs with neurologic signs.
Treatment
There is no medicine that kills the distemper virus inside the body. Treatment is supportive care, meaning the veterinary team treats the signs and complications while the dog's own immune system fights the virus. Depending on the case, that can include fluids for dehydration, nutritional support, antibiotics for secondary bacterial infections such as pneumonia, and medications to control fever, pain and seizures. Your veterinarian chooses the treatments and doses for each dog.
Some dogs can be cared for as outpatients. Dogs with severe signs may need hospitalization in an isolation ward so they do not infect other dogs. Any dog with distemper should be kept away from other dogs. When neurologic disease is severe and getting worse, euthanasia may be discussed.
Prognosis
The outlook depends on the dog's immune response, any other health problems and how far the infection has progressed. Distemper is often fatal, and the risk is highest in unvaccinated puppies. Pneumonia and brain involvement make death more likely.
Dogs that survive usually recover fully from the respiratory and digestive signs. The neurologic outcome is harder to predict, and nerve damage can be permanent.
Old dog encephalitis is a separate form of chronic brain inflammation linked to CDV. It shows up in adult dogs, including vaccinated ones and dogs that never showed distemper signs, causes poor coordination, head pressing and constant pacing, and worsens over time. Dogs with this form are not considered contagious.
Prevention and Vaccination
Vaccination is the best protection. Both the AAHA Canine Vaccination Guidelines and the WSAVA vaccination guidelines list distemper as a core vaccine, meaning one recommended for every dog wherever it lives.
A "distemper shot" is usually a combination vaccine that protects against distemper, hepatitis (adenovirus), parainfluenza and parvovirus, often called DHPP or DAPP.
Puppies need a series of shots rather than one. A mother passes antibodies to her puppies (maternal antibodies), and puppies become susceptible to distemper as those antibodies fade. The series is spaced to cover that gap. Your veterinarian sets the schedule for your dog based on its health, how common the disease is locally and other risk factors, so follow it and avoid gaps. Whether to vaccinate a pregnant or nursing dog is also a decision for your veterinarian.
Practical steps that lower the risk:
- Keep puppies that have not finished their vaccine series at home, away from unfamiliar dogs and wildlife.
- Do not let your dog share food or water bowls with sick dogs.
- Keep pet food and water indoors so it does not draw raccoons and other wildlife.
- Clean bowls, bedding and kennels a sick dog has used. The virus is easily killed by most common disinfectants.
Can Cats or People Get Distemper?
Cats cannot get distemper from dogs. A disease called feline panleukopenia, also known as feline parvovirus or feline distemper, should not be confused with canine distemper. They are not the same condition and are caused by different viruses. Large wild cats such as lions and tigers are the exception: they can be infected with CDV.
CDV is not known to cause disease in people. Researchers have discussed whether the virus could ever adapt to humans, but that remains a theoretical question based on laboratory studies, not something seen in people.
Sources
- Merck Veterinary Manual: Canine Distemper (professional version)
- Merck Veterinary Manual: Canine Distemper (Hardpad Disease), Dog Owners
- Cornell Wildlife Health Lab: Canine Distemper
- AAHA: 2022 AAHA Canine Vaccination Guidelines
- WSAVA: 2024 Guidelines for the Vaccination of Dogs and Cats
- Viruses: Evolution and Interspecies Transmission of Canine Distemper Virus (Duque-Valencia et al., 2019)
- LA County Veterinary Public Health: Distemper in Dogs and Wildlife
- Merck Animal Health: Q&A: Distemper in Dogs and Cats
This article is for general information and is not a substitute for advice from your veterinarian.
