This fact sheet was updated on 12/9/20.
This fact sheet was updated on 12/9/20.
Canine distemper is one of the most significant diseases of domestic and wild carnivores. It is caused by the highly contagious canine distemper virus (CDV) and can infect a variety of species.
Wildlife that contract the disease have a very high mortality rate. CDV may have a significant impact on local or regional populations as well as endangered or threatened species. Unvaccinated domestic dogs are susceptible to CDV and the disease is often fatal, but vaccines provide excellent protection and long-lasting immunity. CDV is not known to infect humans however, it has been recently detected in primates raising concern that the virus may have the potential to mutate and become infective to humans.
Canine distemper virus can infect a wide range of domestic and wild carnivores and all mammals are thought to be susceptible. Canids affected include domestic dogs, coyotes, wolves, and foxes. Raccoons, skunks, mink, javelinas, and marine mammals such as seals and sea otters have also been diagnosed with CDV. Black-footed ferrets are highly susceptible to the disease, and as a result canine distemper played a major role in the near loss of this species. Recently, a black bear infected with CDV was found in Pennsylvania, which is the first incidence in this species. Domestic and wild felines, including African lions and Amur tigers, are also susceptible to the disease. In the last few years, several species of monkey, including the rhesus monkey, have been diagnosed with CDV.
Canine distemper occurs in wild, captive, and domestic carnivores worldwide. While the disease may occur at any time of year, CDV is more common in domestic dogs in the winter and is thought to be more common in juvenile wildlife in spring and summer.
Close contact between animals is necessary to spread the disease, so CDV presents more of a problem in dense populations. The virus is usually transmitted via inhalation of infected respiratory droplets or direct contact with secretions from the oral cavity or the eyes. The virus is fragile and under most environmental conditions it cannot survive very long, so while infection from contact with a contaminated environment can occur, it is rare. The virus is shed from the skin, feces, and urine, which are also sources of infection. At times, the disease is spread via ingestion of contaminated material. CDV is known to cross the placenta of pregnant domestic dogs and the same is likely true for wildlife. Animals will shed the virus for up to 90 days after infection and may also shed the virus while showing no clinical signs.
Clinical signs may vary depending on the strain of the virus, the environment, the host species, age, and several other variables. Some animals will only have a subclinical infection and will clear the virus with no signs of illness. In general, juveniles are considered more susceptible. For example, the death rate from CDV in domestic mink kits is 90%. Black-footed ferrets and gray foxes are highly susceptible and survival is rare at any age. The virus suppresses the immune system so other organ systems can be affected. Clinically ill animals usually exhibit respiratory and intestinal signs including cough, difficulty breathing, vomiting, diarrhea, and anorexia. They may also be depressed, have poor body condition, a fever and have thickened skin on the nose and footpads. Thick ocular and nasal discharge is a common clinical sign that often leads to crusting around the eyes and nose. The disease may also cause damage to the central nervous system leading to abnormal behavior, convulsions, paralysis, abnormal head and neck posture, and loss of coordination.
A presumptive diagnosis of CDV can be reached based on clinical signs along with the microscopic examination of white blood cells from a blood smear or from ocular discharge. Necropsy often reveals signs of pneumonia including fluid and dark firm areas in the lungs. The spleen is frequently enlarged. Laboratory tests are needed to make a definitive diagnosis. When animals are showing neurological signs, it is important to differentiate CDV from rabies virus and the two can occur at the same time.
Apart from supportive care, there is no treatment for canine distemper, but wild animals that survive the disease likely develop lifelong immunity.
Canine distemper is an important disease of wild carnivores and can be particularly devastating in threatened and endangered species. Due to the similarity of some clinical signs of CDV and rabies, affected animals should be handled with caution until a diagnosis is established. Transporting wildlife infected with CDV has led to its introduction to naïve populations. Reducing population densities of susceptible wildlife such as raccoons, foxes, and coyotes and removing any carcasses of animals that have died from the disease can help prevent the spread of CDV. Supplemental feeding of wildlife is strongly discouraged as congregation at feeding stations can potentiate the spread of the virus. There have been some attempts to vaccinate wildlife, but the usefulness of vaccines for wildlife is mostly unknown. However, vaccines have been used effectively in the reintroduction of extirpated black-footed ferrets, as well as with recovery efforts for the threatened southern sea otter. Highly effective vaccines are available for domestic animals.