Internal parasites

1. Coccidia

Coccidiosis is the prevalent parasitic disease of domestic rabbits. It is caused by a microscopic parasite that invades the lining of the intestine or liver. In these locations, the parasite multiplies extensively, and then leaves the body in the feces. Rabbits that recover from this protozoan infection frequently become carriers. It is important to distinguish between liver coccidiosis and intestinal coccidiosis. At least 4 species of coccidia live in the intestine, and 1 species grows in the liver.

Not all species of coccidia are equally harmful, and rabbits tolerate moderate numbers of some without illness. The most dangerous of the intestinal forms are Eimeria magna and E. irresidua. These produce symptoms such as diarrhea, poor appetite, weight loss, and sometimes death. E. irresidua evokes the most severe tissue damage. In some cases, direct damage may occur to the intestinal wall. The clinical diagnosis of coccidiosis depends on finding the oocysts in the feces or intestinal contents. Field diagnosis depends on live and post-mortem identification of the symptoms. Diagnosis of live animals is often difficult because other diseases and disorders produce similar symptoms.

Control of intestinal coccidiosis depends largely on management practices that minimize the danger of fecal contamination of feed, water, and hutch floors. Wire bottom floors greatly reduce the hazard presented by solid floors or slots. Feeders should be designed so that fecal contamination is held to a minimum. This is best done by building a feeder that the rabbits cannot sit in. An automatic water system (bottle and can) is recommended. Oocysts passed in the feces require moisture and warmth to sporulate and become infective. Therefore, coccidia are more widespread in the humid tropics than in other climatic zones. Dry wire floors and automatic water systems hinder sporulation of the parasite.

Sulfaquinoxaline administered continuously in the drinking water (0.025% for 30 days) prevents the development of the clinical signs of hepatic (liver) coccidiosis in rabbits heavily exposed to E. stiedai. Sulfaquinoxaline may also be given in the feed at 0.025% for 20 days, or for 2 days out of every 8, until slaughter. The rabbits acquire an immunity to subsequent infections. Lower concentrations of the drug are not satisfactory. The maximum prophylactic effect is obtained by 3 weeks of administration. A concentration of 0.10% of sulfaquinoxaline in the feed, or 0.05% in the feed and 0.04% in the drinking water, given continuously for 2 weeks, is recommended for therapeutic control of naturally occurring outbreaks. The drug should not be given within 10 days of slaughter of the rabbits. Sulfametazine, sulfamerzaine, or succinyl-sulfathiazole in the feed at 0.5% concentration have also been used during outbreaks

Treatment has only a temporary effect on intestinal coccidiosis, but may be useful in controlling outbreaks. When needed, a ration containing 0.1% sulfaquinoxaline may be fed continuously for 2 weeks. Intestinal coccidia develop a tolerance to the drug if it is used continuously, so treatment is not suggested unless clinical symptoms appear.

E. stiedade, the one species of coccidia that multiplies in the liver, is considered to be the most pathogenic coccidia of rabbits. Like the other forms, it enters the intestinal wall, but migrates to the bile ducts, where it reproduces. Infections lasting more than 16 days can be recognized by the white, circular nodules of the liver. The coccidia multiplies in the epilthelial cells of the bile ducts, which become thickened and tortuous and contain a vast number of occysts. In the early stages of infection there are no unusual symptoms, then the appetite decreases, a potbelly develops, and sometimes death follows. In moderate infections, there is no mortality, but disfigurement of the liver will occur.

Liver coccidiosis is acquired in the same manner as intestinal coccidiosis. The control measures also similar; however, liver coccidiosis can be controlled more easily by proper management.

Life cycle of coccidia

2. Nosema

Nosema cuniculi is the cause of this mild but long standing disease in rabbits. Many apparently healthy animals may have kidney lesions related to this infection. These lesions include cortical scarring with multiple, indented gray areas on the surface of the kidney. The scars extend from the cortical surface to the medulla. Nosematosis is a contagious colony infection. The organisms are passed in the urine and transmitted when there is urinary contamination of feed or water. Transmission may also occur to unborn rabbits in the uterus when the doe has the disease. The disease can be controlled by providing good sanitation and preventing contamination of food and water by urine. No treatment is available.

3. Roundworms

Roundworms (ascarius) are slender and cylindrical. They are found in the digestive tract. The stomach worm is a very slender, reddish worm about 1/2 inch long. Trichuris strongylus-the whip worm-is about the same size but is found in the small intestine. Both have similar life cycles. Eggs are passed in the feces, and after a short period small infective larvae develop. Moisture and warmth favor larval development; larvae are ingested and pass to the stomach or small intestine where they grow into adults.

Signs of infection depend on the degree of infestation. Light infestations produce little effect; heavy infestation may cause diarrhea and emaciation. The stomach worm produces ulceration of the stomach wall. Rabbits kept on the ground are more apt to be exposed to parasites than those kept on wire. Control can be accomplished by proper sanitation.

4. Pinworm

The pinworm, Passalurus ambiguus, is a common parasite of rabbits. These worms are glistening, white, and 1/2 inch long. They are often seen on the surface of freshly passed feces or through the wall of the cecum when animals are slaughtered. Ordinarily, pinworms do little harm. As the mature worms become inactive, they are passed out of the cecum as fecal pellets are formed. These parasites are spread from animal to animal by ingesting feed and water contaminated by the droppings of infected animals. Management methods used to control coccidiosis are effective against pinworms. When treatment is necessary, piperazine citrate is effective when administered at 100 mg/100 ml drinking water for one day. Also, phenothiazine may be mixed in the feed at a 2% strength.

5. Tapeworm

Tapeworms occur in rabbits as adults in the intestine and as larval forms in the liver and abdominal cavity. The adult forms are very rare in hutch-raised rabbits (they are fairly common in tropical zones where rabbits are raised on dirt floors) but larval forms are more common.

The rabbit tapeworm, Cittotaenia ctenoides, is flat, ribbon shaped, and made up of numerous segments. It has a head with 4 suckers with which the worm attaches to the lining of the intestine. Rabbits harboring a few tape worms show no signs of disease. When many tapeworms are present, diarrhea and emaciation occur. Control is readily accomplished by good sanitation.

The most common larval forms of tapeworm are those of Taenia pisiformis. They are fond in the abdominal cavity and in the liver. Rabbits acquire these tapeworms infections by eating contaminated feed and drinking contaminated water containing tapeworm segments and eggs from the feces of dogs. The young larvae are then released from the eggs, penetrate the digestive tract, and migrate to the liver. They migrate within the liver, leaving white streaks behind, then leave the liver and enter the abdominal cavity. They then form small fluid-filled cysts (cysicerci), which may be attached to the membranes holding the intestinal tract or may exist free in the abdominal cavity. Each cyst contains an embryonic tapeworm, which, when eaten by a dog, will develop into a mature tapeworm. Dogs should not be allowed near rabbits nor allowed to eat any part of a raw rabbit carcass. Treatment for larval stages in the rabbit is not practical so control must be accomplished by management.