Distemper, Other Infectious Dog Diseases

By Johnny D. Hoskins and John D. Rhoades.

The most important infectious diseases affecting dogs are canine distemper, infectious canine hepatitis, leptospirosis, parvovirus infection, kennel cough, and rabies. Other infectious diseases that affect dogs do not occur as frequently.

Canine Distemper

Canine distemper is a severe, highly contagious, worldwide viral disease of dogs and other carnivores. It is caused by a virus closely related to but not the same as measles virus. All forms of the disease are caused by the same virus but the duration and type of diseases produced by different canine distemper strains vary greatly.

In the early stages it is characterized by discharges from eyes and nose and signs referable to digestive and respiratory involvement. In later stages there are signs referable to nervous system involvement.

The disease's incidence is highest in young dogs, but susceptible dogs of all ages may become infected. Young dogs become susceptible to canine distemper when they lose colostral antibody, usually between 6 and 12 weeks of age. Young dogs between 3 and 6 months of age are affected most often by the disease.

Infection of susceptible animals usually occurs by inhalation of airborne organisms, and the virus spreads throughout the body. These animals develop fever, depression, eye and nose discharges, and coughing. Diarrhea and occasional vomiting frequently occur simultaneously.

The animal's condition deteriorates with accompanying weight loss and dehydration. Animals eventually become moribund with or without nervous system signs.

Some dogs may show improvement after the first signs are seen, but weeks or months later develop nervous system disturbances that terminate in death or lifelong impairment of the nervous system.

Chewing Gum Fit. Convulsions, chomping the jaws (chewing gum fit), incoordination, pacing, circling, and psychic changes are common in early disease states. Rhythmic movements of the jaws, ears, or legs, caused by twitching muscles and usually called chorea, may occur after other signs subside. Blindness, hardpad disease, and reproductive failures are other problems that can occur because of canine distemper.

With the use of vaccines and antibiotics, canine distemper disease has changed. Use of vaccines has controlled viral strains that induce early disease better than strains causing delayed disease. Use of antibiotics has reduced the incidence of digestive and respiratory involvement due to bacterial infections that accompany the viral infection.

Diagnosis can be difficult to make in dogs that have a delayed form. Laboratory tests, such as fluorescent antibody tests, virus isolation and neutralization test, frequently are required to diagnose canine distemper.

Immunization is the preferred method of preventing canine distemper. Potent and safe modified live-virus vaccines are available and induce good immunity in dogs.

Because colostral antibody interferes with vaccination, dogs should be vaccinated repeatedly. In most cases, 3 vaccinations are given, at 8 weeks, 12 weeks, and 16 weeks of age.

Because of antibody loss, vaccinated dogs can develop canine distemper several years later after receiving vaccinations as puppies. Annual revaccinations throughout the dog's life are recommended because of loss of their antibody protection.

Infectious Canine Hepatitis also is a severe, highly contagious, viral disease of dogs. It is caused by an adenovirus and is related to the large group of adenoviruses that cause a variety of diseases in humans and lower animals.

The virus that causes infectious canine hepatitis is not infectious for people. The virus is spread from dog to dog through the urine, and a dog may shed the virus from the kidneys in the urine for long periods of time after apparent recovery. Infection usually is acquired by contact of infective material such as urine or saliva in the mouth.

This disease is seen most frequently in young dogs, but can be seen in all ages of dogs. The affected animal becomes apathetic and loses its appetite and may frequently have an intense thirst. At this time the body temperature increases and swelling of the head, neck, and lower portion of the abdomen may occur.

Vomiting and diarrhea are common. Many animals manifest pain by moaning, especially when pressure is brought to bear on the abdominal wall.

Only rarely does jaundice occur. The gums usually are pale and sometimes hemorrhages appear on them. The tonsils frequently are enlarged and painful.

Progression of this disease is much more rapid than distemper. Most dogs have either recovered or are dead within 2 weeks. Many die within a few days.

Tests, Vaccines. Infectious canine hepatitis must be differentiated from canine distemper, leptospirosis, parvovirus infection, and the effects of certain poisons. Diagnosis is especially difficult in young puppies. Results of laboratory tests reflecting damage to liver and kidneys strengthen a presumptive diagnosis which has been based on history and physical examination.

Specific diagnosis depends on demonstration of the virus in blood or liver tissue. This is accomplished by using fluorescent antibody test or virus isolation in liver cell cultures.

Recovery from infectious canine hepatitis produces a long-lasting immunity.

Modified live-virus vaccine is mostly used for immunization. Vaccination will be ineffective until the puppy has lost essentially all of its colostral antibody.

Products currently available for immunization against infectious canine hepatitis are usually combined with canine distemper virus.

Blue Eye. The first modified live-virus vaccine for infectious canine hepatitis contained the virus called adenovirus-1 which occasionally caused an immune-mediated "blue eye" condition. The eye problem would disappear spontaneously and did not cause damage if managed conservatively.

Recently a modified live-virus called adenovirus-2 was approved to replace canine adenovirus-1 in vaccines and the "blue eye" condition is no longer a problem. This modification has been very helpful in improving the protection against infectious canine hepatitis.

Vaccination of puppies is given at the same time as canine distemper, 8 weeks, 12 weeks, and 16 weeks. Annual revaccination is also recommended for dogs of all ages.

Leptospirosis

This disease of dogs is caused by Leptospira canicola and Leptospira icterohemorrhagiae. Leptospirosis is significant from a public health aspect because dogs and other animals can act as reservoirs for human infections.

Leptospira organisms are easily killed by heat and disinfectants. They will survive for long periods outside the body in water or sewage. Alkalinity of urine or water favors their survival, and acidity will cause their death within a few hours.

Infected animals, such as wild rodents and livestock, can contaminate food and water. The most common method of spread is thought to be direct contact or ingestion of contaminated food and water.

Outbreaks have occurred in humans and dogs after floods, or after swimming in or drinking water contaminated by urine of rodents or other animals. Leptospira organisms enter the body through abrasions in the skin or mucous membranes.

Animals may carry the organisms and shed them in the urine for months or years after apparent recovery from the disease.

Signs of leptospirosis in dogs are quite varied in severity depending on an individual animal's response to the infection. The onset of signs generally is sudden with high fever, not eating, vomiting, and diarrhea. Dehydration and depression result if the preceding signs are severe.

Reddening of the membranes of the eyes and mouth is common. Jaundice usually occurs with infection caused by Leptospira icterohemorrhagiae.

Pain in the abdomen is evident when liver, kidney or gastrointestinal tract is severely affected. Ulcers in the mouth are seen in animals that develop kidney failure.

A positive diagnosis of leptospirosis is based on finding organisms in the urine or blood with a history of liver and kidney disease. Demonstration of a rising leptospira titer in paired blood serum samples when taken at least one week apart is evidence of active infection.

Antibiotics are very effective for treating leptospirosis in dogs.

Owners of infected dogs should be aware of the potential health hazard and efforts should be made to determine the source of the infection.

Death occurs frequently from severe damage to the liver and kidneys.

Leptospira) vaccine is available and effective in preventing the disease in dogs. Animals should be vaccinated for leptospirosis when they receive their distemper-hepatitis vaccine. Annual revaccination is recommended for effective immunity.

Canine Parvovirus Infection is a relatively new disease of dogs, which was first described in 1977. The disease is caused by a small DNA-containing virus that requires rapidly dividing cells for its growth to occur in the body. Therefore young, rapidly growing dogs are most susceptible to severe disease.

Susceptible dogs are rapidly infected and canine parvovirus is very contagious. The main source of infection is ingestion of materials contaminated with feces from infected dogs.

Two Forms of Disease. There are two distinct forms of the disease. One involves the intestines and the other the heart.

Severity of the disease depends primarily on the age and immune status of the dog. The most severe and often fatal disease occurs in puppies less than 12 weeks old.

In the intestinal form the parvovirus grows in epithelial cells of the small intestine and rapidly destroys them.