Common Guinea Pig Health Problems: Signs, Causes, and When to See a Vet

Why guinea pigs hide illness until it is serious

Guinea pigs are prey animals. In the wild, showing weakness invites predation. Domestic guinea pigs retain this instinct: they maintain normal-looking behavior until their condition deteriorates past the point of masking. This means that by the time a guinea pig looks visibly sick, the disease has typically been progressing for days. Owners who know their guinea pig's normal behavior, weight, food consumption, and droppings baseline catch illness much earlier than owners who wait for visible symptoms.

Weigh your guinea pig weekly on a kitchen scale. A guinea pig that loses 10% of its body weight (typically 70-100 grams in a 700-1,000 gram animal) is clinically underweight and needs veterinary evaluation even if no other symptoms are apparent. Weight loss is often the first and earliest measurable sign of illness.

Scurvy (Vitamin C deficiency): the most preventable guinea pig disease

Guinea pigs, like humans and other primates, cannot synthesize vitamin C (ascorbic acid). They require dietary supplementation. A guinea pig receiving insufficient vitamin C develops scurvy within 2-4 weeks of deficiency onset. Symptoms: rough coat, hunched posture, swollen and painful joints, reluctance to move, dental problems, and bleeding from gums. If untreated, scurvy is fatal.

The correct approach: feed guinea pigs fresh vegetables high in vitamin C daily. Bell peppers (red, yellow, or orange) are the highest-vitamin-C vegetable option (95-190mg per 100g) and most guinea pigs eat them readily. Leafy greens (kale, romaine, parsley) provide additional vitamin C. The required daily dose is approximately 10-30mg per kg of body weight. A handful of fresh bell pepper daily reliably meets this requirement for most guinea pigs.

Vitamin C added to water bottles degrades rapidly -- it loses 50% of potency within hours of exposure to light and air. Water-additive vitamin C is not a reliable supplementation method. Fresh vegetables are far more dependable.

Respiratory infections

Bacterial respiratory infections (most commonly Bordetella bronchiseptica or Streptococcus pneumoniae) are among the most serious guinea pig illnesses. They progress rapidly -- a guinea pig that appears mildly lethargic in the morning may be in critical condition by evening. Symptoms: nasal discharge, labored breathing, audible wheezing, crusty eyes, loss of appetite, lethargy. Upper respiratory infection is a veterinary emergency. Antibiotics are effective if treatment begins early; the prognosis is poor in guinea pigs that have been severely ill for more than 24-48 hours before treatment.

Important drug safety note: guinea pigs cannot receive penicillin, ampicillin, amoxicillin, cephalosporins, lincomycin, clindamycin, or erythromycin. These antibiotics disrupt guinea pig gut flora and cause fatal enterotoxemia. Always inform a veterinarian that you are treating a guinea pig and verify that the antibiotic prescribed is safe for guinea pigs. Safe options include enrofloxacin, trimethoprim-sulfa, and chloramphenicol.

Dental disease (malocclusion)

Guinea pig teeth grow continuously throughout their lives. When upper and lower teeth do not meet properly (malocclusion), teeth overgrow, causing pain, inability to chew, and weight loss. Molar malocclusion (back teeth) is more common and harder to detect than incisor malocclusion -- guinea pigs with molar problems often chew on one side, drool, or drop food. Diagnosis requires examination under sedation or anesthesia. Treatment is dental trimming by an exotic-animal veterinarian; malocclusion is managed but rarely cured.

Prevent dental problems by providing adequate hay. Timothy hay should comprise 70-80% of the guinea pig's diet. Hay wears teeth evenly and provides the coarse fiber essential for proper gut motility. Guinea pigs that eat primarily pellets with little hay are at higher dental and GI disease risk.

Mites and lice

Trixacarus caviae (sarcoptic mites) cause intense, severe itching in guinea pigs -- affected animals scratch so intensely they cause wounds. Hair loss, crusty skin, and seizure-like scratching episodes are characteristic. Chirodiscoides caviae (fur mites) and lice cause milder itching with hair loss. Diagnosis is by skin scraping. Treatment is ivermectin or selamectin administered by a veterinarian. Both the animal and its environment must be treated.

Bladder stones

Urinary calcium carbonate deposits (stones or sludge) are common in guinea pigs. Signs include blood in urine, pain when urinating (crying out, hunched posture, reluctance to move), and reduced urination. Diagnosis by X-ray or ultrasound. Small stones may be managed with diet modification (reduced calcium); large stones require surgical removal. High-calcium foods (spinach, kale in excess, and most fruits) in the diet increase stone risk in predisposed individuals.