Canine Distemper

Signs usually appear 5-7 days after infection: fever, lethargy and poor appetite, conjunctivitis with eye discharge, nasal discharge and sneezing, and a dry cough that can become moist as secondary pneumonia develops. Vomiting and diarrhoea follow. Seizures, incoordination and muscle tremors from encephalitis may appear weeks later. Some dogs lose sight. Infected puppies may grow pitted, discoloured adult teeth, and infection in pregnancy can cause abortion, stillbirth or weak pups.

Canine distemper is caused by canine distemper virus, now named Canine morbillivirus, family Paramyxoviridae. It uses SLAM (CD150) on immune cells and nectin-4 on epithelial cells as receptors. After inhalation the virus infects lymphoid tissue via dendritic cells, produces a primary viraemia and spreads to secondary lymphoid organs, then infected lymphocytes carry it to the respiratory and other epithelia. Loss of lymphoid cells causes marked leukopenia and immunosuppression, which lets secondary infections take hold. Epithelial infection explains respiratory, digestive, urinary and skin disease, and in later stages the virus reaches the central nervous system, where demyelinating leukoencephalitis is common.

Hosts are mainly carnivores: domestic dogs plus wild canids, felids and mustelids such as foxes, coyotes, wolves, ferrets, raccoons, skunks and otters. Puppies of 2-6 months and unvaccinated dogs older than 6 weeks are most often affected, but unprotected dogs of any age can fall ill. Sick dogs shed virus in coughs, sneezes, tears, saliva, urine and faeces, and dogs recovered within the past 1-2 weeks remain a risk. Transmission is by aerosol, close contact or contaminated objects, and is greatest in kennels, shelters and large dog gatherings. The virus occurs worldwide, survives only a few days outside the host, and does not infect people.

Early distemper resembles kennel cough and canine influenza; suspicion rises with fever, eye and nose discharge, cough and pneumonia in a young, unvaccinated or incompletely vaccinated dog with likely contact, and with later gastrointestinal or neurological signs. Laboratory tests help confirm it, but a negative result does not rule distemper out.

Lymphoid tissue and white blood cells, respiratory tract and lungs, eyes and conjunctiva, gastrointestinal tract, urinary tract, skin, central nervous system, developing teeth

Core vaccination of all dogs: puppy series, first booster a year later, then periodic boosters. Isolate suspect cases, clean and disinfect (the enveloped virus is easily destroyed), and avoid mixing puppies with dogs of unknown vaccine status.

No specific antiviral treatment exists. Supportive nursing care and control of secondary infections improve outcome, but once neurological signs appear the prognosis is worse and death more likely.