Infectious Diseases of Dogs and Cats

J. E. GREENE.

DISTEMPER in dogs, like influenza of the human family, is an acute, infective disease caused by a filterable virus usually complicated by many bacterial secondary invaders.

Distemper occurs throughout the world even in Iceland and Greenland.

Few unimmunized dogs reach 1 year without having contracted distemper. It is most common at about 7 months of age, less common after 2 years, and practically unknown in suckling pups. Unconfirmed diagnoses have been reported in dogs as old as 9 years.

A young dog usually begins to show the first symptoms about 5 days after it is exposed to the disease. The eyes become sensitive to light, as shown by squinting and the presence of a clear discharge. The rectal temperature usually rises to about 103 or 105 F. Swelling usually can be detected at that time in the lymph nodes of the throat. Death can occur during convulsions within a few days.

The fever reaches a peak in about 5 to 7 days and begins to drop to nearly normal until the 7th to 10th day. Then it begins to rise again. The temperature chart is irregular throughout the rest of the disease.

The animals become languid. The coat roughens. Loss of appetite develops. Usually rhinitis inflammation of the lining of the nasal cavities begins 1 to 2 days after the first fever, as shown by sneezing, rubbing the nose with the forepaws, and a nasal discharge, which at first is watery but later becomes thicker and whitish and sometimes streaked with blood.

Catarrh of the respiratory tract, as manifested by a short, soft, spasmodic cough and rapid breathing, inflammation of the eyes, a discharge of tears mixed with pus, and a tendency to avoid light, develops almost simultaneously with the rhinitis.

Digestive symptoms begin early. Loss of appetite, vomiting, constipation, diarrhea, extreme thirst, dehydration, and coating of the tongue are signs of that.

Nervous symptoms may begin with the other initial symptoms, or they may occur as late as the fifth or sixth week. They occur as rhythmic, brief spasms of the muscles that control the lips, cheeks, ears, and the fore or hind limbs, or in any group of skeletal muscles.

Early nervous symptoms often are manifested by epileptiform fits. Paresis (partial paralysis) usually begins in the hind limbs and progresses forward. Death occurs when any group of vital muscles is affected by the paralysis.

Some cases are affected by eruption of the skin, which begins as small pimples, which may contain pus and later become encrusted and emit a repulsive odor. The urine may contain bile pigment, indican, acetone, and albumen. Significant changes usually occur in the white blood cells. The disease usually lasts 10 days to 6 weeks.

Exposure to cold, parasites, inbreeding, malnutrition, and unhygienic conditions are believed to make dogs more susceptible to distemper.

From 30 to 80 percent of the dogs that develop distemper die.

As is true of most virus diseases, present-day antibiotics, biologicals, and drugs seem limited in their ability to alter the course of the disease once it has become well established. Careful nursing is necessary. Particular attention should be paid to forced oral or intravenous feeding of the essential, food elements.

A number of different methods have been developed through the years for protecting dogs from this disease by vaccination. They include formolized tissue vaccine, followed by attenuated or unattenuated virus, serum and live or unattenuated virus, and modified live virus.

The vaccine and virus method is based on increasing the animal's resistance to the virus by one or more injections of the formolized (formalintreated) vaccine before one introduces the live virus.

The simultaneous use of immune serum and unmodified virus, a method that was popular in the early 193o's, is not widely used today because of the apparent instability of the virus.

The modified-virus methods are based on cultivating the virus in an unusual host, such as ferrets or egg yolk, in order to render it incapable of producing the disease in dogs while maintaining its ability to stimulate resistance to disease.

It seems advisable to use occasional booster injections to maintain immunity regardless of the method of vaccination used.

INFECTIOUS CANINE HEPATITIS is one of the specific viral diseases of dogs. It affects primarily the endothelial and liver cells. It often includes symptoms of acute shock, followed by coma and death.

Infectious canine hepatitis has been miscalled fox encephalitis and infectious canine encephalitis.

Since most of the investigators credit Sven Rhubarth, of Sweden, with the original observations and differentiations, the virus usually is known as the virus of Rhubarth.

Transmission is usually by means of virus-carrying urine, which is passed by healthy carriers or by nonclinical cases. The disease usually is transmitted from dog to dog, although it may be carried indirectly by the hands, clothing, and implements of the handlers. James A. Baker, of Ithaca, N. Y., has shown that the disease is not carried across enclosures as narrow as 2 feet.

The virus withstands heat of 133 F., is stable at 4 F., and will withstand repeated thawing and refreezing. H. B. Parry and N. M. Larin, of the Canine Research Station, Newmarket, England, detected the virus in lice collected from sick dogs and were able to transmit a mild infection with inoculations of suspensions of such lice. This is not conclusive proof that the dog louse is a vector, but it may be accepted as circumstantial evidence that such a possibility exists.

Some investigators believe that the best way to destroy the virus is to use plenty of hot water, soap, and detergents and to follow that with a harsh disinfectant, such as the phenols (carbolic acid) and phenol-containing products, and a very caustic one, such as sodium hydroxide (caustic soda).

According to the studies of Parry and Larin, when the disease is introduced into a susceptible kennel or community, the percentage of sick dogs usually approaches 70, but the mortality rate usually is 12 percent or even less.

The more susceptible animals are apt to die within the first 24 hours.

Others may run a very mild course for 2 weeks or longer and show only hemorrhage of the urinary mucous membranes and the membranes of the eye and mouth, severe tonsillitis, and some loss of weight. They usually maintain their appetite throughout the course of the disease. Most of the affected animals will recover with supportive treatment.

A hyperimmune serum is available that seems to be effective in preventing the disease and slightly effective in treating the disease. A vaccine for immunizing dogs has been available since 1952. Statistics on the effectiveness of this vaccine are limited, but evidence does indicate its effectiveness in controlling the hepatitis.

Some investigators believe that the incubation period is 5 to 10 days, at the end of which time a rise in temperature can be expected, the white blood count may decline, and the development of tonsillitis and hemorrhagin visible mucous membranes occur. However, the appetite is rarely affected as is the case in canine distemper.

The more susceptible animals develop severe and rapid enteritis (inflammation of the intestines) which may be accompanied by massive bleeding from the rectum and end in sudden death.

The least susceptible animals develop tonsillitis and lesions of the mucous membrane, usually become jaundiced, have a loss of energy and sometimes soreness over the area of the gallbladder, and may develop opacity of the cornea (white eye).

Infectious canine hepatitis is difficult to differentiate from leptospirosis and canine distemper. Differentiation often is possible only by examination of tissues microscopically for inclusion bodies (tiny bodies that are in cells).