Canine distemper is a severe, multi-system viral disease caused by a morbillivirus that attacks the respiratory, gastrointestinal, and neurological systems in unvaccinated dogs. Early signs mimic a bad cold — nasal discharge, fever, coughing — but the disease progresses to seizures and permanent neurological damage in many survivors. Vaccination is virtually 100% preventive; in an unvaccinated dog showing these signs, this is an emergency.
Last reviewed: June 2026
What Is Canine Distemper?
Canine distemper virus (CDV) is a paramyxovirus closely related to the human measles virus. As described in Greene's Infectious Diseases of the Dog and Cat, CDV is transmitted via respiratory droplets and aerosols from infected animals (dogs, ferrets, raccoons, foxes, and other carnivores) and has a tropism for epithelial cells, lymphocytes, and neurons. The systemic nature of the infection explains its biphasic clinical course: an early respiratory/GI phase driven by viremia, followed — in dogs whose immune response is insufficient — by a neurological phase caused by direct viral invasion of the CNS.
Unvaccinated dogs of any age are susceptible, but puppies 3–6 months old are at highest risk, particularly when maternal antibodies have waned before vaccination is complete.
Symptoms by Phase
Phase 1 — Systemic/Respiratory (Days 1–14):
- Fever (39.5–41°C / 103–106°F), usually biphasic
- Mucopurulent (thick yellow-green) nasal discharge
- Eye discharge — starts serous, progresses to purulent
- Coughing, which may develop into pneumonia
- Vomiting and diarrhea
- Anorexia and lethargy
- Hyperkeratosis of nose ("hard pad") and footpads — a classic but late sign
Phase 2 — Neurological (Weeks 1–6+): Not all dogs develop neurological signs, but when they occur, they may include:
- Myoclonus (rhythmic muscle twitching, especially of the face or a limb)
- Seizures
- Ataxia (incoordination)
- Circling, head tilt, nystagmus (involuntary eye movement)
- Behavioral changes, aggression, apparent blindness
- Paralysis in severe cases
The neurological phase is the feature that most distinguishes distemper from other respiratory illnesses. Myoclonus in a dog that recently had a "bad cold" is essentially pathognomonic for distemper until proven otherwise.
Diagnosis
There is no single definitive in-clinic test. Diagnosis is clinical combined with supportive tests: CBC typically shows lymphopenia; CSF analysis may show elevated protein; distemper-specific inclusions (Lentz inclusion bodies) in conjunctival smears or blood smears are occasionally visible. PCR testing on conjunctival swabs, urine, or CSF is the most sensitive method. The AAHA Canine Vaccination Guidelines, 2022 classify CDV vaccination as a core requirement for all dogs, specifically because the disease is preventable and its unvaccinated prevalence remains significant in wildlife reservoirs.
Treatment
No antiviral drug targets CDV. Treatment is supportive: IV fluids for dehydration and anorexia, antibiotics to prevent secondary bacterial pneumonia, anticonvulsants (phenobarbital, levetiracetam) for seizures, and nutritional support. Prognosis is guarded once neurological signs develop. Some dogs with mild neurological involvement recover partially; those with severe seizures or progressive myelopathy typically do not recover to normal function. Dogs that survive neurological distemper may carry permanent deficits — myoclonus that never fully resolves is common.
When to See a Vet
Call your vet today if:
- Your unvaccinated dog has a fever, nasal discharge, and eye discharge simultaneously
- Your dog is coughing and has stopped eating after being around unknown dogs
- Your dog's nose or footpads appear thickened or crusty
Go to the ER immediately if:
- Your dog is having seizures or muscle twitching (myoclonus)
- Your dog is uncoordinated, circling, or appears blind suddenly
- Your dog has a fever above 40.5°C (105°F) and is unresponsive to calling
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Frequently Asked Questions
How does canine distemper spread? Distemper spreads primarily via respiratory droplets and aerosols — a dog doesn't need direct contact with an infected animal. Shared water bowls, contaminated bedding, and proximity to wildlife (raccoons, foxes) in areas with active distemper outbreaks are all exposure routes. The virus survives only briefly in the environment under normal conditions.
Can vaccinated dogs get distemper? Vaccine failure is extremely rare with modern MLV (modified live virus) distemper vaccines. The AAHA Canine Vaccination Guidelines, 2022 recommend the core DA2PP vaccine (which includes distemper) starting at 6–8 weeks of age with boosters every 3–4 weeks until 16 weeks, then at 1 year, then every 3 years. Gaps in this schedule leave puppies vulnerable.
How much does distemper treatment cost? Hospitalization for supportive care typically runs $800–$2,500 for the initial respiratory phase. If neurological signs develop and require intensive management (anticonvulsants, longer hospitalization), costs can reach $3,000–$6,000+. Diagnostic workup (CBC, PCR, CSF tap) adds $300–$800. The DA2PP vaccine that prevents all of this costs $25–$60 per dose.
Is canine distemper the same as kennel cough? No. Kennel cough (infectious tracheobronchitis) is a distinct multi-pathogen respiratory syndrome, most commonly caused by Bordetella bronchiseptica and canine parainfluenza virus. Distemper causes a more severe, systemic illness with fever, eye discharge, and potential neurological progression — kennel cough is primarily a cough without high fever and does not cause neurological signs.
Can distemper spread to cats or humans? CDV does not infect cats or humans. Ferrets are highly susceptible and can spread the virus to dogs and vice versa. Ferrets should also be vaccinated against distemper with a ferret-approved vaccine.
Still Not Sure if Your Dog Needs a Vet?
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