Canine distemper typically starts with a fever and eye or nasal discharge, then progresses to respiratory, gastrointestinal, and potentially severe neurological symptoms over the course of several weeks. The disease kills about 50% of infected adult dogs and up to 80% of puppies, so recognizing the signs early can make a critical difference in your dog’s outcome.
The First Signs Are Easy to Miss
Distemper’s earliest symptom is a fever spike that occurs 3 to 6 days after infection. At this stage, your dog might seem slightly off, maybe eating less than usual, but many owners don’t notice anything wrong. The fever actually drops on its own after a day or two, which creates a false sense that nothing is happening.
Then, roughly one to two weeks after infection, a second wave of fever arrives. This time it brings more visible signs: watery or greenish nasal discharge, thick or crusty eye discharge, lethargy, and loss of appetite. These symptoms look a lot like a bad cold or kennel cough, which is one reason distemper is frequently mistaken for less serious illnesses in the early stages.
Respiratory and Digestive Symptoms
As the virus spreads, it targets both the respiratory and gastrointestinal systems. Dogs often develop a persistent cough, labored breathing, or pneumonia. Vomiting and diarrhea are common and can quickly lead to dehydration, especially in puppies. This combination of upper respiratory illness and digestive upset happening at the same time is one of the more telling patterns of distemper, since most routine infections tend to affect one system or the other.
Neurological Signs
The most alarming phase of distemper involves the nervous system. Neurological symptoms usually develop one to three weeks after the respiratory and digestive signs resolve, but they can also appear at the same time, or even months later with no prior visible illness. In rare cases, neurological signs can show up as late as three months after infection.
The hallmark neurological signs include:
- Muscle twitching: involuntary jerking or spasms in the legs, face, or other muscle groups
- “Chewing gum fits”: seizures where the dog drools and makes repetitive chewing motions with its jaw
- Lack of coordination: stumbling, wobbling, or difficulty walking, often most obvious in the hind legs
- Circling and head tilt: walking in circles instead of a straight line, or holding the head at an angle
- Partial or complete paralysis: starting in the hind legs and potentially progressing to all four
- Rapid eye movements: uncontrolled, rhythmic darting of the eyes
Seizures tend to become more frequent and severe as the disease progresses. In advanced cases, dogs may fall onto their sides and paddle their legs uncontrollably. A chronic form of brain inflammation, sometimes called “old dog encephalitis,” can develop in dogs that survive the acute phase. It causes compulsive behaviors like head pressing against walls and constant pacing.
Hardened Paw Pads and Nose
Distemper earned its old name, “hardpad disease,” from a distinctive skin change: the paw pads and nose become unusually thick, hard, and cracked. This happens because the virus damages the cells responsible for producing normal skin in those areas. Not every dog with distemper develops hardpad, but when it appears alongside other symptoms, it’s a strong indicator.
Permanent Effects in Survivors
Dogs that survive distemper can carry lasting damage. Chronic seizures or persistent muscle twitching are common long-term consequences, even in dogs that otherwise recover well. Puppies infected during the first few months of life face an additional risk: because enamel formation in dogs happens between about 2 weeks and 3 months of age, the virus can permanently damage developing teeth. This results in pitted, discolored, or irregularly shaped adult teeth, a condition called enamel hypoplasia. Veterinarians sometimes spot these characteristic dental defects in rescued or shelter dogs and recognize them as evidence of a past distemper infection.
Why Distemper Is Hard to Confirm
One frustrating reality is that distemper’s early symptoms overlap heavily with other common respiratory and digestive illnesses. A coughing, feverish dog with runny eyes could have dozens of things wrong. Clinical diagnosis based on symptoms alone is unreliable, so veterinarians rely on lab tests to confirm suspected cases.
The most accurate test uses a technique called RT-PCR, which detects the virus’s genetic material in samples from nasal swabs, blood, or urine. Older methods, like staining cells from eye or nasal swabs to look for viral proteins, only work within the first three weeks of infection and miss many cases. Blood antibody tests are not especially useful either, because a positive result could simply reflect a past vaccination rather than an active infection. Virus isolation (growing the virus in a lab) is definitive but takes days to weeks, making it impractical for guiding treatment decisions in real time.
Which Dogs Are Most at Risk
Puppies under four months old are the most vulnerable, both because their immune systems are immature and because they may not yet have completed their vaccination series. Unvaccinated dogs of any age are at high risk, as are dogs in crowded environments like shelters, boarding facilities, and rescue operations where the virus spreads through airborne droplets, shared bowls, and direct contact with infected animals. The incubation period ranges from one to two weeks but can stretch to four or five weeks, meaning an apparently healthy dog entering a shelter could already be carrying the virus.