Viral Diseases

With the exception of rabbit pox, and a herpesvirus infec tion, viral diseases in rabbits are restricted to the infectious fibromas and papillomatosis. The former are tumours com posed of connective tissue and consist largely of fibroblasts and their products. They are located under, rather than in the skin, in which respect they differ from the papillomas. There are 2 types of known infectious fibrotic tumours which occur under natural conditions, the tumour of infectious myxomato sis and the Shope fibroma. Both are viral and restricted to rabbits, the former to the domesticated species only, in the USA, and the Shope fibroma to the cottontail.

Infectious myxomatosis is a fatal disease of the ordinary domestic rabbit, Angoras, Belgian hares, Flemish Giants and the European wild rabbit. The cottontail and the jack rabbit are quite resistant, as are man, dog and other animal species tested. The virus causing the disease is transmitted by mos quitoes, biting flies and direct contact.

The first characteristic sign observed is a conjunctivitis that rapidly becomes more marked and is accompanied by a milky discharge from the inflamed eyes. The animal appears listless, is anorectic and the temperature frequently reaches 108 F. In severe acute outbreaks, some of the animals may die within 48 hours after showing signs. Those that do not die at this stage become progressively depressed, develop a rough coat, and the eyelids, nose, lips and ears become edematous, giving a swollen appearance to the head. The vent becomes inflamed and edematous and, in the male, swelling of the scrotum occurs. A very characteristic sign at this stage is the drooping of the edematous ears. A purulent nasal discharge invariably appears, the breathing becomes laboured and the animal goes into a coma just before death, which usually occurs within 1 to 2 weeks after the appearance of clinical signs.

The seasonal incidence of the disease, the clinical appear ance of the infected animals and the high mortality are all of diagnostic significance.

A live vaccine prepared from an attenuated myxomatosis virus has been shown to protect both field- and laboratory- infected animals, and .is available commercially.

Rabbit pox is an acute, generalised disease of laboratory rabbits and is characterised by pyrexia, nasal and conjunctival discharge and skin rash. The causative virus is closely relat ed to vaccinia virus and some outbreaks may have been caused by a virulent strain of vaccinia. The virus may be isolated and identified by methods appropriate to vaccinia.

Spread of this disease through a rabbitry or an animal house is very rapid, but rabbits which have been inoculated with smallpox vaccine are immune.

Bacterial and Fungus Diseases

Pasteurellosis is a highly contagious disease, common in domestic rabbits, transmitted either by direct or indirect contact. An indirect fluorescent-antibody test for use on nasal swabs has been found effective in identifying carriers, which may constitute up to 90 per cent of apparently healthy rabbits in conventional colonies. Pasteurella multocida in fections may be manifested in the following conditions:

Snuffles or nasal catarrh. An acute, subacute or chronic inflammation of the mucous membranes of the air passages and lungs. The signs are a thin or purulent exudate from the nose and eyes. The fur on the inside of the front legs just above the paws will be matted and caked with dried exudates from the rabbits pawing at their noses. The infected animal usually sneezes and coughs. Snuffles, in general, occurs when the resistance of the rabbit is low or at kindling time. Those animals that recover may become carriers.

Abscesses caused by Pasteurella may be found in any part of the body or head. Rabbits of all ages are susceptible. When bucks are penned together, their' fight wounds frequently develop into abscesses. In most instances, it is advisable to eliminate rather than to treat the affected rabbit. The condi tion may terminate in a septicemia, the animal dying within 48 hours. Necropsy reveals bronchial congestion, tracheitis, splenomegaly and subcut hemorrhages.

A troublesome genital infection is often caused by Pas teurella but several other organisms also may be involved. It is manifested by an acute or subacute inflammation of the reproductive tract. This condition most frequently is found in adults, more often in does than bucks. If the condition is bilateral, the does often become sterile, but if only one horn is infected, a normal litter may develop in the other. It is best to eliminate the animal as a source of infection. The infected hutch and its equipment should be thoroughly disinfected. For a valuable breeder, antibiotics may be used in combating the infection; however, a poor prognosis should be given.

Pneumonia is not uncommon in domestic rabbits. It may occur in adult animals or may infect the young while they are in the nest box. Frequently, it is a secondary and com plicating factor in the enteritis complex. The cause is bacte rial with Pasteurella accounting for the greatest number of cases. Drafty, damp, unsanitary hutches and inadequate bedding are predisposing causes. The animals usually suc cumb within 4 days after the first signs have been noted. Affected rabbits are off feed and show elevated temperature (104 F), dyspnea, diarrhea and lassitude. Necropsy reveals a bronchopneumonia, pleuritis, or pericardial petechial hemorr hages. Treatment consists of a course of oxytetracycline, chlortetracycline or penicillin. Combinations of penicillin and streptomycin are also useful and effective for such mixed infections.

Diarrheas, which comprise one of the most important disease complexes of rabbits, are often referred to as bloat, scours, or diarrhea. Not only do many rabbits die, but the young animals that have been affected fail to regain lost weight by weaning time. The disease may occur sporadically or as an epizootic. The greatest mortality occurs in the age group between 5 and 9 weeks, just before or after weaning.

An attack of the disease does not confer immunity. The cause is unknown.

The signs, which may be acute in onset, include anorexia, lassitude and a rough hair coat; the ears droop and the eyes have a squinty appearance. The temperature may be subnor mal. Affected individuals sit in a “humped” position and grind their teeth. They may be constipated or exhibit a pro fuse diarrhea. The feces may consist of clear, viscid, mucoid material. Occasionally there is great thirst, but at other times the rabbits refuse to drink. There are no significant findings at necropsy. The stomach and anterior part of the intestine may contain liquid, gas and some undigested food; the colon usually is filled with a jelly-like mucous material. The mu cous membrance of the cecum and intestine may be reddened. Ulcers are not uncommon. Pellets containing antibiotics, such as the tetracyclines, may lower the mortality during the sucking period. However, the results are unpredictable.

Diseases of the guinea pig

Antibiotic toxicity. Guinea pigs and hamsters are highly susceptible to the toxic effects of many of the commonly used antibiotics. Toxicity results from overgrowth of the normal gram-positive cecal flora by gram-negative rods. This causes fatal enterocolitis, with diarrhea and death in 3 to 7 days. Antibiotics with an activity spectrum directed primarily against gram-positive organisms (e. g., penicillin, lincomycin, eryth romycin, tylosin) should not be used in guinea pigs and hamsters. Broad-spectrum antibiotics should not be used oral ly because of their direct effect on the intestinal flora, but may be used parenterally with caution.

Metastatic calcification occurs most often in male guinea pigs over a year or age. Signs include slow weight gains, stiff joints and high mortality. At necropsy, calcium deposits are seebn in the lung, liver, heart, aorta, stomach, colon, kidney, joints and skeletal muscles. There are conflicting reports concerning the etiology; however, most investiga tors agree that when animals are fed diets low in magnesi um and potassium, the calcificlesions increase with the phos phorus content of the ration. It is believed that hyperphos phatemia results from the inability of the guinea pig to conserve fixed bases by excreting ammonia in the urine; thus, the low-base reserve impairs normal urinary excretion of phosphorus. The condition may be aggravated by increas ing the vitamin D content of the ration beyond 6 IU/gm. The condition may be minimized or prevented by feeding diets that contain adequate magnesium (0.35 per cent), a calcium:phosphorus ratio of 1.3 to 1.5:1, and not more than 6 IU of vitamin D per gram.

Scurvy. (Vitamin С deficiency): Guinea pigs require a dietary supply of ascorbic acid (vitamin C) because they lack the enzymes necessary for conversion of L-gulonolactone to L-ascorbic acid. Signs of vitamin С deficiency are unsteady gait, painful locomotion, hemorrhage from gums, swelling of costochondral junctions and emaciation. Lesions include hemorrhages in the subcutis, around joints and on all serosal surfaces. The condition may be prevented by providing 1 to

2. mg ascorbic acid per 100 gm body wt daily. Commercial guinea pig diets contain vitamin С which is stable for 3 months after milling. Marginal diets should be supplemented with greens or vegetables high in vitamin C.

Muscular dystrophy. Guinea pigs are exquisitely sensi tive to dietary deficiency of vitamin E.

Signs are stiffness, lameness and refusal to move* Micro scopic lesions include coagulative necrosis, inflammation and proliferation of sarcolemmal nuclei in skeletal muscle. Diets should contain 3 to 5 mg of vitamin E per 100 mg.

Ringworm is a common mycotic infection in guinea pigs, usually caused by Trychophyton mentagrophytes or Microsporum gypseum. It causes characteristic, crusty, flak ing lesions on the skin. Facial lesions are usually prominent. Diagnosis is based on characteristic lesions and cultural and microscopic identification of the causative organism. The disease is usually self-limiting if good husbandry and sanita tion are maintained. Long-term feeding of griseofulvin is effective. Isolated skin lesions may be treated effectively with tolnaftate cream. The disease is contagious to man.

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