Distemper is caused by the canine distemper virus (CDV). Canine distemper is caused by a paramyxovirus. Canine distemper is a contagious, incurable, and often fatal, multi-systemic (i.e. affects many internal systems) viral disease. It generally affects the respiratory, gastrointestinal, and central nervous systems. CDV occurs among domestic dogs and many other carnivores (for example, raccoons, skunks, binturong, ferret, and foxes). CDV is fairly common in wildlife. Young puppies between 3 and 6 months old are most susceptible to infection and disease and are more likely to die than infected adults. Non-immunized older dogs are also highly susceptible to infection and disease.

Clinical features

It is characterized by fever, leucopoenia, Gastro-intestinal and respiratory catarrh, and frequently pneumonic and neurologic complications. Early symptoms include fever, loss of appetite, and mild eye inflammation that may only last a day or two. Symptoms become more serious and noticeable as the disease progresses. The initial symptom is fever (103°F to 106°F), which usually peaks 3 to 6 days after infection. The fever often goes unnoticed and may peak again a few days later. Dogs may experience eye and nose discharge, depression, and loss of appetite (anorexia). After the fever, symptoms vary considerably, depending on the strain of the virus and the dog's immunity.

Pathogenesis and Lesions

Thymic atrophy is a consistent post-mortem finding in infected young puppies.

Diagnosis

Diagnosis can be difficult and is based on the dog's vaccination history, clinical symptoms, and laboratory tests. Diagnosis (after necropsy) is usually confirmed by histological lesions or immunofluorescent assay for viral antigen in tissues (or both). Immunofluorescence involves using special proteins labelled with a fluorescent chemical that bind to the antigens and make them visible.

Differential Diagnosis

Distemper is sometimes confused with other systemic infections such as leptospirosis, infectious canine hepatitis, or Rocky Mountain spotted fever.  Symptoms can also be confused with those of Rabies, especially in advanced cases due to the neurological effects of the virus.

Treatment
 
Treatments are directed at limiting secondary bacterial invasion, supporting fluid balance, and controlling nervous manifestations. Antibiotics, balanced electrolyte solutions, parenteral nutrition (providing nutrition via the veins), dietary supplements, antipyretics (to reduce fever), nasal preparations, analgesics, and anticonvulsants are used. No single treatment is specific or uniformly successful.

Prevention and control

Vaccination program - The vaccine usually consists of a modified form of the live virus, which causes the immune system to respond to the weakened virus and develop immunity.

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