GASTROINTESTINAL DISEASE

Compared to the rabbit, much less is known about the digestive mechanisms of the guinea pig. The guinea pig is is most closely related to another South American rodent, the chinchilla.

The guinea pig is a monogastric herbivorous rodent with a large, thin-walled sacculated cecum. The cecum is 15-20 cm long and can contain more than 50% of the entire gastrointestinal contents. There are 3 longitudinal bands, the taeniae coli, that run the length of the large intestine and form the lateral pouches of the cecum. Normal gastric emptying time is reportedly about 2 hours, however, guinea pigs are prone to gastric reflux under anesthesia and should be fasted at least 3 hours prior to induction for surgery.

Like rabbits, guinea pigs perform coprophagy or cecotrophy on a daily basis and usually ingest the pellets directly from the rectum. They will often excrete cecotropes throughout the day as opposed to the rabbit and chinchilla who produce cecotropes at regular, daily intervals. The exact nutritional role of coprophagy in guinea pigs has not been identified but it is thought to provide vitamins and protein as it does in rabbits. Guinea pigs digest fiber more efficiently than rabbits and do not increase feed intake when fiber is added to the diet as rabbits do.

Dietary Recommendations

The dietary needs of guinea pigs (and chinchillas) have not been studied as extensively as rabbits. Wild cavies consume a variety of vegetation. Domestically bred guinea pigs are also herbivores and can be fed a large amount of fresh vegetables once they are gradually added to the diet. A high fiber diet is recommended: guinea pig pellets, and ad lib alfalfa or grass hay. Guinea pigs have a dietary requirement for Vitamin C (ascorbic acid) and need approximately 5-10 mg/day and more during stress, illness and pregnancy (25-50 mg). Although the pellets generally contain ascorbic acid when milled, the 90-day shelf life of this vitamin makes the content of some pellets negligable. Diets supplemented with produce high in ascorbic acid is recommended: spinach, kale, parsley, chickory, bell peppers, and oranges. Vitamin C supplementation may be necessary in those pets that do not obtain enough ascorbic acid from the diet.

Anorexia

Anorexia is a common presenting complaint from guinea pig owners. There are many causes of anorexia, from metabolic diseases to systemic infections. There are some specific conditions that should be considered in the work-up of the inappetant pig.

Guinea pigs are very sensitive to changes in diet; a new brand of pellet may be enough to create inappetance. Guinea pigs can also develop gastrointestinal tract stasis from food impactions and bezoars. Dietary lack of vitamin C can result in painful joints and mastications (see dental disease below). Pain in general, from pododermatitis to urolithiasis, can induce inappetance.

It is not always possible to detect the true cause of anorexia and weight loss in the ante-mortem guinea pig. All anorexic patients should have full body radiographs, blood tests (CBC/chemistry), and skull (dental) films if all else is normal.

Dental Disease

See lecture on rabbit and rodent dentistry for details.

Gastrointestinal Bloat/Impactions

Guinea pigs are susceptible to acute abdomens characterized by gaseous distension ("bloat"), painful abdomen, anorexia, and profound weakness. Onset appears to be sudden, and the owner may visualize a distended abdomen. Radiographically these individuals have large sections of stomach or cecum distended by gas and sometimes fluid.

Etiology may not always be identifiable but considerations include impactions from hairballs or dietary indiscretion, bacterial gastroenteritis, and gut adhesions from prior abdominal surgeries. Although poorly documented, gastrointestinal hypomotility may result from inappropriate diets (low fiber, high carbohydrates). Treatment consists of decompression by stomach tube or trocharization with a fine needle. Pediatric anti-gas formulations like Phazyme^® and oral antibiotics should be administered. Prognosis is guarded. Some of these individuals probably require surgical intervention but prognosis for surgical success is poor.

Diarrhea

Diarrhea is not a common condition in clinical practice. Individuals with severe enteritis often die acutely before the development of diarrhea. The normal gastrointestinal flora of the guinea pig consists of mostly gram-positive bacteria. Overgrowth of coliforms (particularly E.coli) and clostridial organisms can result in diarrhea and death. Inappropriate antibiotic use may predispose enteric flora imbalances. Avoid antibiotics with a gram-positive spectrum, e.g., the beta-lactams and the macrolides. Parenteral ampicillin has been shown to be toxic at doses above 6 mg/kg. Safe antibiotics include chloramphenicol, trimethoprim-sulfa, ciprofloxacin, and enrofloxacin. In the author's experience, an occasional guinea pig has become transiently inappetant and "gassy" on oral enrofloxacin or ciprofloxacin.

Other causes of enteritis include Salmonella, Yersinia pseudotuberculosis, Listeria monocytogenes, and Pseudomonas aeruginosa. Tyzzer's disease (Clostridium piliforme) has been reported in guinea pigs.

Parasitic diarrheas are uncommon in guinea pigs. Cryptosporidium has been associated with diarrhea and mortality in immunosuppressed individuals. Guinea pigs can also harbor coccidia, and Balantidium, but nematodes and cestodes are rare. Viral causes of enteritis and diarrhea is rarely identified.

Fecal evaluations should be done on any individual with diarrhea: fecal direct wet mounts, gram-stains to check for coliforms and clostridia, and culture and sensitivity. Clostridium spp can be difficult to culture and treatment should be based on history (inappropriate antibiotics) and clinical signs.

Rectal Impactions

Rectal impactions with soft, malodorous feces is common in older guinea pigs. The cause is conjectured to be from loss of rectal tone, from the build-up of soft stools during stress and illness, or from lack of coprophagy. It is not a disease in itself, but owners will complain of odor and constipation. There is no prevention but owners can be instructed on the gentle manual extraction of feces using wet gauze, q-tips, or with a gloved finger.

INTEGUMENTARY CONDITIONS

Alopecia

Alopecia can be self-induced or spontaneous. Self-induced fur loss can be seen in stressed or bored individuals (behavioral barbering) or secondary to a pruritic dermatitis (see below). Spontaneous fur loss is most commonly seen in female pigs with cystic ovaries or other reproductive tract condition that results in hormone elevations. Some breeding sows will loss fur at the end of gestation, either spontanously or from fur-pulling for nesting.

Dermatophytosis ("Ringworm")

Guinea pigs can be clinically or subclinically infected with Trichophyton mentagrophytes most commonly. Microsporum canis has also been identified. Lesions usually begin as patches of alopecia and crusts. Lesions may or not be pruritic. Diagnosis is with culture of the affected hair samples; Trichophyton species do not fluoresce with a Wood's lamp. Treatment can be topical if confined to small areas; antifungal creams (miconazole or butenafine) are used for 2-4 weeks following local fur clipping. Oral griseofulvin (15-25 mg/kg/day for 2-4 weeks) can be used if lesions are extensive.

Ectoparasites

Mites are occasionally seen in the pet guinea pig. The fur mite (Chirodiscoides caviae) rarely causes clinical signs but the sarcoptid mite (Trixacarus caviae) can result in intense pruritus and self-trauma. Diagnosis is through skin scrapings (which can be negative) and response to treatment. Topical carbaryl flea powders can generally be used safely at weekly intervals. Ivermectin (.4 mg/kg/SQ) is the drug of choice for sarcoptic mange and may need to be used 2-3 times at 2 week intervals.

Lice can be identified in guinea pigs and rarely cause clinical signs. Small white nits are easily seen on dark fur in the neck and back region. Topical carbaryl powder can be used.

Pododermatitis

Pododermatitis is common in guinea pigs. Obese individuals with sedentary lifestyles are most at risk, however, sick guinea pigs often develop "bumblefoot" as a secondary condition. Hypovitaminosis C may be an underlying factor; individuals with painful joints may develop pressure sores from a reluctance to move.

Severely affected individuals have swollen feet that may progress to osteomyelitis. Radiographs are recommended in severe cases. Treatment can be long term and may be palliative in some pigs. Affected individuals are treated with padded bandages, antibiotics (topical and/or oral), and a soft, clean environment.

"Lumps and Bumps"

The most common skin mass in the guinea pig is trichofolliculoma or benign basal cell epithelioma. These are solitary masses, sometimes cystic, that can grow to be quite large. They are most common along the back and flanks and are treated with surgical excision. Lipomas, and sebaceous adenomas are also seen. Mammary gland tumors occur in both males and females (see below).

Cervical lymphadenitis is a bacterial infection of the lymph nodes along the ventral neck. It is most commonly caused by Streptococcus zooepidemicus, although other bacteria are possible. Normal bacteria from the oral cavity become opportunists following abrasions to the oral cavity. Abscessation of the cervical lymph nodes is a secondary effect. Treatment is surgical excision, and antibiotics. Guinea pig pus can be quite caseous and these abscesses are not typically amenable to lance and drain techniques used in feline abscesses.

Peripheral lymphadenopathy can also be caused by lymphosarcoma in the guinea pig. This is the most common tumor type reported in guinea pigs and is caused by a Type C retrovirus. Lymph node enlargement, as well as hepatomegaly and splenomegaly is possible. Affected pigs are typically leukemic with total white cell counts > 25,000/ul, although aleukemic forms can occur. Treatment is supportive.

UROGENITAL CONDITIONS

Urolithiasis

Calculi are fairly common in the urinary tract of guinea pigs. The calculi are typically calcium salts (carbonate or oxalate) and can be found anywhere within the tract: kidneys, ureters, bladder, urethra. These calculi are radiodense and easy to identify radiographically. The cause is unknown and is not always related to bacterial infections. Crystalluria (calciuria) is common in normal guinea pigs. Cystitis can result without the formation of calculi.

Stone dissolution diets are ineffective. Treatment is surgical removal of calculi with a guarded prognosis for long-term cure. Recurrence of calculi is common. Post-operative management should include appropriate antibiotics, a low calcium diet (limit pellets and alfalfa), and follow-up radiographs in 1-2 months.

Cystic Ovaries

Cystic ovaries are fairly common in female guinea pigs. Diagnosis is usually through palpation, but radiographs and ultrasounds are helpful. Most cases are incidental findings, however, some cysts are associated with endocrine alopecia, endometritis, and endometrial hyperplasia. Intermittent hematuria is possible. Ovariohysterectomy is the treatment of choice. Cystic ovaries without hematuria can be monitored or in very large or growing cysts, hCG can be attempted (human chorionic gonadotropin @ 1000 USP IM). Large cysts can be drained per cutaneously with a small gauge needle.

Mammary Gland Tumors

Mammary gland tumors occur in both male and females. Tumors can be adenocarcinomas or benign fibroadenomas. Metastasis is uncommon. Wide surgical excision and biopsy is recommended. Consider pre-surgical thoracic radiographs are in long-standing cases or geriatric individuals.

Dystocia

Females bred after the age of 7 months are at risk for dystocia. The pubic symphysis fuses after 7 months but will remain open once the sow has delivered a litter. Gestation averages 68 days. Parturition is quick with pups delivered within 30 minutes. Oxytocin can be attempted with a dystocia if the pubic symphysis is open, but ceserean section is indicated if no response to parenteral calcium (100 mg/kg/IM) followed by oxytocin (1 unit IM 15 minutes after calcium).

RESPIRATORY DISEASE

Bacterial Pneumonia

Guinea pigs are susceptible to infections with Bordetella bronchiseptica and Streptococcus pneumoniae. Clinical signs include rhinitis, weight loss, and dyspnea. Severely affected individuals can develop pulmonary abscesses and consolidation. Prognosis is guarded once respiratory distress becomes evident.

Pulmonary Neoplasia

Pulmonary adenoma and adenocarcinoma are considered frequent in older guinea pigs. Radiographs may help to identify solitary masses. Differential diagnosis includes abscessation or consolidation of lung from bacterial causes.

Cardiac Disease

There is little published information on heart disease in guinea pigs. While murmurs are not uncommon, it is difficult to classify cardiac conditions. Post-mortem examination at the author's practice has revealed a "mixed bag" of conditions ranging from valvular disease to neoplasia.

RECOMMENDED READING

1.  Crossley, DA: Clinical aspects of rodent dental anatomy. J Vet Dent, 12(4):131-135, 1995.

2.  Johnson-Delaney CA: Exotic Companion Medicine Handbook. Wingers Publishing, Lake Worth, Florida, 1996.

3.  Schaeffer DO: Disease problems of guinea pigs and chinchillas. In Hillyer EV, Quesenberry KQ (eds.): Ferrets, Rabbits, and Rodents, Clinical Medicine and Surgery. Philadelphia, WB Saunders, 1997, pp 261-281.