Canine distemper (Proceedings)

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Canine distemper (Proceedings)

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Apr 01, 2009

Distemper occurs intermittently, especially in shelters located in communities with many unvaccinated dogs, and can appear identical to run-of-the-mill "kennel cough." It is not unusual to hear of shelters reporting having a particularly "bad" kennel-cough problem that eventually realize that the disease at fault is canine distemper. In fact, complacency about symptoms of respiratory illness can prove disastrous. Vaccination against distemper virus immediately on intake will help to significantly decrease a shelter's risk of disease outbreaks.

Canine distemper virus infects dogs and other mammals, including ferrets and raccoons. Dogs of all ages are susceptible if not previously immunized, although infection is most common in puppies less than 16 weeks of age. Domestic cats are not at risk of distemper, although some large felids such as lions appear to be. (Feline panleukopenia, which sometimes is referred to as feline distemper, is not related to canine distemper).

Transmission

Canine distemper virus is shed in all body secretions of acutely infected animals. It can be spread by direct contact, by aerosol or respiratory droplet exposure. Dogs are capable of aerosolizing droplets up to 20 feet meaning this disease can be considered an "air-borne" contagion. In addition, virus can be transmitted by fomites such as hands, feet, or instruments over a time/distance even though it is short lived in the environment. Virus can be shed by subclinically or mildly infected animals; such animals probably play an important role in maintaining the virus in a chronically infected shelter population. This means that once distemper has been diagnosed in the shelter ANY sign of respiratory or gastrointestinal disease must be considered suspect. Therefore, careful isolation of all dogs with upper respiratory signs and/or diarrhea, poor appetite and weight loss - always a good idea - are especially important in a shelter where distemper is a concern.

Incubation

The incubation period (the time from exposure to the appearance of symptoms) is usually 1-2 weeks but can be as long as 4-5 weeks or even more. The initial symptoms of fever and lethargy in the early incubation period are often missed. Therefore, quarantine of dogs possibly exposed to distemper should be a minimum of one month, and even then it is impossible to be sure of catching all cases. This lengthy quarantine is often impossible to accomplish effectively resulting in either difficult euthanasia decisions and/or creative solutions. Be advised, ALL exposed dogs must be included in a quarantine plan in order to control an outbreak.

Clinical signs

Distemper virus can invade the respiratory, gastrointestinal, skin, immune and nervous systems. Consequently, signs are highly variable and disease course depends on immune response and dose. Most commonly, early signs of clear to green nasal and ocular discharge, fever, loss of appetite and depression are seen 1-2 weeks after infection, possibly followed by lower respiratory and gastrointestinal involvement. The "classical" neurological signs usually appear 1-3 weeks after recovery from GI and respiratory disease, but may develop at the same time or months later, even without a prior history of systemic signs.

Clinical signs more suggestive of distemper but seen with less frequency include neurological signs, ocular signs and dermatological signs. The ocular signs are often a valuable hint that distemper may be the underlying cause of dogs' symptoms. These include: anterior uveitis (inflammation of the front chamber of the eye; may cause the cornea to appear cloudy and/or cause changes in the appearance of the virus); keratoconjunctivitis sicca (dry eye); and optic neuritis (inflammation of the optic nerve-may cause sudden blindness.

Distemper in shelters

Most often distemper in shelters is rarely an isolated case. Mild cases tend to go undiagnosed so that the virus is effectively transmitted to more dogs resulting in a full blown outbreak. Once a case has been identified (usually a dog that develops full blown disease), then it is likely that there have been other, unrecognized cases in exposed dogs. An important effect of distemper virus is its immunosuppressive ability. Infected dogs are therefore not only more susceptible to other infectious diseases but also more likely to get sicker from them. For this reason, shelters that commonly have relatively mild true "kennel-cough" (URI caused by Bordatella bronchiseptica/parainfluenza/adenovirus infections) may suddenly find themselves dealing with particularly severe cases including pneumonias. "Routine" kennel cough is generally a mild to moderate self limiting disease that responds to well to antibiotics; distemper is not. However, upper or lower respiratory infection and gastrointestinal disease are non-specific; a diagnosis of distemper should not be made based on these signs alone especially if only dealing with one dog.