Parasites of the Domestic Rabbit

EVERETT E. LUND.

DOMESTIC RABBITS raised commercially in this country are usually maintained in individual hutches, each of which contains at most a doe and her litter of unweaned young. The degree of isolation secured by this practice, together with the employment of reasonable measures of sanitation, has been effective in controlling parasitism in our domestic rabbits. There are, however, a few parasitic diseases that still become troublesome.

Coccidiosis is the most prevalent of all parasitic diseases of domestic rabbits. It is caused by microscopic one-celled parasites that invade the lining of the intestine, multiply prolifically, and eventually leave the body of the rabbit in the droppings. At this stage they are in a resistant form and are called oocysts. When conditions of temperature and moisture are favorable, the minute oocysts develop to an infectious stage within a few days. They are then ready to attack another rabbit, if taken in with feed or water or as the animal washes itself.

At least four species of coccidia live entirely in the lining of the intestine of domestic rabbits, save for their passage from one animal to another. Not all are equally harmful. Rabbits tolerate moderate numbers of any of these species without suffering measurable damage. Excessive numbers of the larger species produce soft droppings or diarrhea, indisposition to feed, a consequent loss in rate of gain, and at times death.

There is no positive means of diagnosing intestinal coccidiosis without a microscopic examination of the droppings, the intestinal or cecal (blind pouch) content, or the intestinal wall. Even then, experience is needed to judge whether the number of parasites present is great enough to account for the symptoms, because other disorders, particularly mucoid enteritis, may produce similar symptoms and be present at the same time.

The control of intestinal coccidiosis in domestic rabbits rests largely on the employment of management practices that minimize the danger of fecal contamination of feed, water, hutch floors, and other equipment. Self-cleaning floors that permit droppings to fall through, out of reach of the animals, reduce to about one-tenth the hazard that is presented by soil or floors on which manure accumulates. Feeders about 4 inches above floor level, provided with guards to keep animals from perching in them, also are necessary. If watering cannot be accomplished with automatic valves placed 8 to 9 inches above floor level, the water containers must also be provided with guards.

Handling of animals must be reduced to a minimum. Equipment brushes, scrapers, pails, and other utensils should never come in contact with one hutch after another. The oocysts are quite resistant to all usual disinfectants but are susceptible to drying. If the hutch floors and other equipment are kept clean and dry, infections heavy enough to be of economic significance are unlikely.

Even the best substances used for treatment have only transitory effects on the intestinal coccidia, but sometimes they may be useful in subduing severe outbreaks. A pelleted ration containing one-half pound of sulfaquinoxaline per ton of feed (0.025 percent concentration) may be offered in place of the regular ration for 2 or 3 weeks to reduce the incidence of intestinal coccidiosis to a point at which control by suitable management practices is sufficient. The intestinal coccidia develop a tolerance when the drug is used continuously.

One species of coccidium, Eimeria stiedae, multiplies in the liver of domestic rabbits. Like the other species, it enters the intestinal wall but lodges in the liver before reproducing. Infections more than 16 days old are easily recognized by the creamy-white, circular nodules produced on the liver. Because infections of any degree disfigure the liver, making it unmarketable, and prejudice the marketing of the entire carcass, liver coccidiosis is always of economic significance.

Liver coccidiosis by itself does not produce diarrhea or any other external symptoms, except in the most extreme cases. Then the liver may be so greatly enlarged as to distort the body of the animal. Some animals affected to this extent die; usually ruptured livers, peritonitis (body cavity inflammation), or pneumonia are complications. A technician with experience can diagnose some cases of liver coccidiosis by a microscopic examination of the droppings, but the disfiguring lesions remain on the liver several weeks after the last evidence of oocysts in the fecal pellets, so only internal symptoms can be entirely trustworthy.

Liver coccidiosis is acquired in the same way as intestinal coccidiosis. The control measures also are the same. Liver coccidiosis can be held to much lower incidences than can intestinal coccidiosis with the same control measures. In well maintained commercial rabbitries, 2 to 10 percent of the animals may have light cases of intestinal coccidiosis, while liver coccidiosis is either absent or present in less than 0.5 percent of the herd.

A ration containing 0.025 percent of sulfaquinoxaline is more than 90 percent effective against the liver coccidium. Its effectiveness continues, so the ration can be fed indefinitely. But this is not necessary, and if the drug is used at all, it should be used only as an emergency measure, until management control can be effected.

EAR MANGE is probably the second most important parasitic disease of domestic rabbits. It is caused by a small mite, usually Psoroptes communis cuniculi, which is just visible to the naked eye. Studies conducted in California in 1948 and 1949 revealed that 45 to 80 percent of the commercial rabbitries visited had been troubled with ear mange. The incidence among mature animals was found to range as high as 84 percent, but averaged ii percent.

Ear mange is usually contracted by close or prolonged contact with animals already infected or by placing animals in quarters recently occupied by affected ones.

The tiny mites that are able to find their way into the auditory canal at the base of the ear pierce the skin with their sharp mouth parts, feed, and permit the escape of the clear serum.

The serum hardens into scales, beneath which the mites continue their activity, feeding, mating, laying eggs, producing more layers of scales, and spreading. Finally thick crusts are formed, and the area involved extends far up the inner surface of the ear and occasionally even to the head and neck near the ear.

Intense itching is provoked by all this activity. Affected rabbits shake their heads, rub their ears with their front feet, and scratch vigorously at the base of their ears with their hind feet. Parallel scratches one-fourth to three-eighths inch apart at the base of the skull or on the neck are self-inflicted by the nails of the hind feet and are indicative of ear mange. By looking into the ear, one can see yellow crusts of dried serum, sometimes tinged with blood. Their presence can be accepted as almost certain evidence of ear mange.

Treatment consists of cleaning the ear first with a bland oil, such as ordinary vegetable oil used in cooking, and then swabbing the entire inner surface of the ear with medicated oil. Enough oil should be applied so that it runs into the auditory canal and wets all surfaces thoroughly. Cases of long standing have such heavy encrustations that it is necessary to extend the cleaning over a period of 2 or 3 days, so that the heavy cakes can soften before one attempts to extract all of them. A mixture of 1 part of iodoform, 10 parts of ether, and 25 parts of vegetable oil is effective. It may be prepared by any druggist. A second application of this mixture should be made 7 to 10 days after the first, to kill recently hatched mites, or ones having strayed from the area. A 0.25-percent solution of lindane in vegetable oil is effective and inexpensive, but should not be used unless the operator wears rubber gloves or can otherwise avoid prolonged contact with the solution while it is being applied. The drug is harmful when absorbed through the skin.