Canine Distemper Virus is a highly contagious virus, which is mainly transmitted between dogs via close contact. This virus is a Morbillivirus, closely related to the measles virus in humans. Various species of animals are susceptible to the virus, such as dogs, jackals, hyenas, ferrets, civets, genets, seals, dolphins, whales and even lions. The domestic cat is not affected by this virus.
1. Signs of disease
The Canine Distemper Virus attacks the gastrointestinal, respiratory, and central nervous systems of the dog. The infection rate is much higher than the disease rate. Between 25-75% of the dogs will not show clinical signs and will clear the disease within two weeks. However, dogs with a poor immune response will show clinical symptoms.
Clinical signs are initially listlessness, fever, discharge from the nose and eyes, depression, lack of appetite, conjunctivitis, coughing, vomiting, diarrhoea, weight loss and sometimes hardening of the footpads. Neurological symptoms follow two to three weeks after infection. Clinical signs for the neurological form are ataxia (drunken appearing movements), inflammation of the optic nerve, tremors, myoclonus (twitching or contraction of a muscle group), seizures, moribund and even death. Secondary bacterial infections often develop during the acute phase of the disease.
Diagnosis of the disease is normally made based on clinical symptoms and history. The dog can be tested with a snap test in the veterinary clinic. This test will show an immediate result. The more invasive test is the testing of cerebrospinal fluid, which must be sent to a laboratory.
The virus is shed by the dog from seven days after first being infected and it can be shed for up to 90 days after exposure. The virus is shed in saliva, conjunctival (from the eye) and nasal exudates, faeces, and urine. It is spread from dog to dog mainly via aerosol droplets, via coughing or sneezing. The virus multiplies in the upper respiratory tract and spreads via the lymphatic system to the rest of the body.
The virus only has a short life span outside the dog and is easily inactivated by disinfectants. Ultraviolet light, heat and desiccation will kill the virus that contaminates the environment. Research showed that the virus can survive in the environment at room temperature for up to three hours.
In South Africa, most outbreaks occur during spring and early summer.
The most important prevention method is regular vaccination. Only 25% of the dogs in South Africa receive their annual vaccination. The other 75% of the dog population is therefore highly susceptible to the Canine Distemper Virus. This Virus is always included in the so-called five in one vaccination given by the veterinarian. Puppies should be vaccinated at the age of six to eight weeks followed by a booster three weeks later (at the age of nine to eleven weeks). A second booster will be given three weeks later at the age of 12 to 14 weeks. Thereafter dogs should be vaccinated on a yearly basis. In most European countries, dogs are vaccinated on a three-yearly basis. However, due to the small number of vaccinated dogs in South Africa, yearly vaccination is advised.
No treatment for this viral disease is available, while no antiviral drugs are known to be effective in treating Canine Distemper Virus. Only supportive treatment for secondary bacterial infections can be given to the dogs. Supportive treatment includes a broad-spectrum antibiotic, fluid therapy and nutritional support. Most veterinarians will not admit a dog with distemper virus and will only treat these patients through home treatment. Admitting dogs with distemper into the hospital will result in contamination of all sick patients. Dogs that show central nervous systems symptoms will often die from this virus, therefore dogs showing these symptoms should be euthanised.
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Written by Dr Tessa Brouwer, BVSc, MSc, BSc