Symptoms and ailments 
We'll focus this discussion on symptoms, since that is where most people begin when they suspect that their guinea pig is ill. Again, this is not intended to be a replacement for competent veterinary care, but rather as an introduction to common afflictions.
Sneezing, nasal discharge
Some sneezing is actually normal for guinea pigs, though excessive sneezing could be the sign of a respiratory complaint. Certainly, any time you see discharges from the nose, or the guinea pig regularly wiping its nose, it is most likely related to a respiratory or sinus infection.
Contrary to popular belief, guinea pigs do not catch colds; the cold and flu in humans are caused by viruses, but in guinea pigs, most respiratory problems are caused by bacteria. It is also possible to have a fungal infection in the nasal passages, but this is more rare.
Some sneezing and nasal discharges are merely allergic reactions that can be caused by soft wood beddings (such as cedar and pine) or dusty hay. Some guinea pigs are even allergic to certain hays, including timothy.
Coughing
Like sneezing, some coughing is normal in guinea pigs. Most of the time, coughing is brought about by a minor irritation in the windpipe, possibly caused by inhaling dusty hay or something similar. More serious would be constant coughing, which could be the sign of an infection or illness. Kennel Cough, in particular, is a rather serious illness in guinea pigs, and can actually be transmitted between species, including dogs, rabbits and guinea pigs. If any coughing is accompanied by other respiratory problems, particularly wheezing, then it is most likely a sign of a respiratory infection.
Wheezing, labored breathing
Wheezing and labored breathing are usually a symptom of a respiratory infection, and should be treated very seriously. Typically, they are indicators of congestion (phlegm or fluids) in the respiratory system that could easily develop into pneumonia. If your guinea pig has these symptoms, you should take him or her to a competent vet right away.
Scratching
Scratching is also normal for guinea pigs, though excessive scratching can be a sign of a parasitic infection, such as lice or mites. Less common are fungal infections, which can also cause hair loss.
Lice are fairly easy to kill; a bath in a pyrethrin shampoo will almost always solve the problem, though it should be noted that lice eggs don't go away so easily. Often times, it will take two baths, about a week or two apart, to completely eradicate lice from a guinea pig. The first bath kills the existing lice, and the second kills the lice that hatch from the first batch's eggs. You can obtain a pyrethrin shampoo from your vet, who will instruct you in its use. Lice are also fairly easy to spot: they resemble tiny, brownish worms that crawl around through the hair near the surface of the skin.
Mites are more difficult to kill. They are also hard to spot initially, as they can't be seen with the naked eye. There are some home-remedies for eliminating mites, but most people opt for veterinary care, which usually involves injections of Ivermectin.
Contrary to popular belief, fleas are not a big problem with guinea pigs. For some reason, fleas don't care much for the species, and usually aren't present for very long if they do take up residence.
The hutch should always be cleaned and disinfected when dealing with parasites.
Diarrhea, soft stool
Diarrhea is an extremely serious condition in guinea pigs, as they can dehydrate and die quickly if the diarrhea persists. If you recently fed your pet a large amount of vegetables, or a new vegetable, that can be the cause. Try backing off the wet foods for a day or two to see if the problem clears up. Feeding lots of grass hay, such as timothy, can help keep your guinea pig's digestive system in balance.
If your guinea pig is on antibiotics, then the diarrhea could be caused by enteritis. Antibiotics work by killing bacteria, and can and do kill off the good, digestive bacteria in the stomach. If this happens, then it becomes more difficult for the guinea pig to properly digest its food. No matter the cause of diarrhea in your guinea pig, you can provide some basic treatment immediately that will help him or her recover more quickly. Take a half-capsule of lactobacillus acidophilus (available at any pharmacy or health-food store), and dissolve the powder in 1 cc of water. Using an open syringe (a syringe without the needle), feed the resulting liquid to the guinea pig by inserting the end of the syringe into its mouth, behind the incisors and from the side. Be sure to feed the acidophilus slowly, so they don't accidentally choke on it and send the fluid into their lungs.
The lactobacillus acidophilus is a bacteria-growing culture that will accelerate the growth of the good, digestive bacteria in the guinea pig's stomach. Although many people suggest feeding yogurt for the same reasons, it is important to note that acidophilus as less is needed for the same results.
If your guinea pig is put on antibiotics, you should always give supplements of acidophilus as a preventative measure.
Milky-white urine, bladder sludge 
The urine of guinea pigs typically has a slightly milky appearance to it, but if the urine is very white, and leaves white deposits after it dries, then it can be an indicator that your guinea pig is getting too much calcium in its diet. This can lead to bladder stones in some pigs.
Pink urine (blood in urine)
This can be an indicator of uroliths (bladder stones), which is a very serious condition. Get the guinea pig to a vet right away, and reduce the calcium in his or her diet. Lots of water can help prevent the formation of stones, and cranberry juice can actually help break down stones that have already formed. Cranberry juice is often times prescribed for humans who are suffereing from stones for thie very reason. Cranberry juice also kills off the bacteria that cause urinary tract infections, as an added bonus.
It is believed that the formation of bladder stones is not caused by dietary factors alone. In other words, high calcium levels in a guinea pig's diet will not automatically cause bladder stones. Rather, there is evidence to suggest that there are genetic factors that make guinea pigs more susceptible to stones, and that high calcium levels in these pigs' diets can cause their formation very easily. If your guinea pig is prone to forming stones, then you will need to carefully monitor the calcium that is in their diet, and avoid foods that supply calcium in significant amounts. The biggest offender of high calcium levels is pelleted feed, which is alfalfa-based. In these cases, it may be necessary to eliminate pellets completely from the guinea pig's diet. Your vet will be able to provide you with more information.
Hair loss
Hair loss can be caused by a variety of problems. Mites are once source: they burrow under the skin, and hair will fall out around the resulting sores as the guinea pig furiously scratches the afflicted region. Also, if your guinea pig is bitten, cut or otherwise hurt such that a scab forms, the hair will typically fall out in the vicinity of the wound as the skin heals. Some pregnant sows may lose patches of hair during the period of gestation. Far more serious are ovarian cysts in sows, and fungal infections such as ringworm, both of which can cause massive hair loss across the body.
Fungal infection ring worm

two more ring worm
Stiff joints, difficulty walking
If your guinea pig is having trouble walking, it could be a symptom of scurvy, which is caused by a vitamin C deficiency. You should make sure that your guinea pig is getting at least 10 mg of vitamin C a day to prevent scurvy. If the condition develops, you will need to go see your vet; the guinea pig may need an immediate source of vitamin C, possibly by injection.
Watery eyes
This can be caused by allergies or by irritants in the eye. Contact your vet for directions on bathing the eye to remove the irritant. More serious are eye sores caused by cysts on the eyelids, which will need to be removed by a veterinary surgeon.
Discharge
Fatty eye
Pea Eye
Pea eye (or fatty eye) is a permanent protrusion of the conjunctival sac, thought to be inherited. Pea eye and fatty eye are frequently grouped together by vets as conjunctival swelling. These conjunctival protrusions can be removed by laser if they are interfering with vision. Cavies with pea eye generally do not seem to be uncomfortable and treatment is usually not necessary.
Micropthalmia is a congenital condition where the eye is either very small or non-existent, rendering the guinea pig blind.
According to VC Richardson, it is generally the result of breeding a roan X roan or dalmatian X dalmatian. These white guinea pigs are known as "lethals". They may also have disorders of the digestive system and the animal may be missing one or more teeth. In a roan X roan or dalmatian X dalmatian mating, there is a one in four chance of breeding a lethal. Severely affected guinea pigs will die. Responsible breeders will never intentionally mate these breeds.
BLINDNESS
Guinea pigs seem to have poor eyesight to begin with. Some guinea pigs are blind due to age, injury or genetics. A guinea pig born blind may have other genetic defects Observing your pig's behavior in an unfamiliar environment can help determine if your guinea pig is blind. A blind pig will often startle more easily. A light shown into the eye of a blind pig may reflect white rather than the typical red reflected by a normal eye.
Blindness does not seem to bother most pigs, who readily adapt to loss of sight. Provide your vision impaired pig with a familiar environment so he/she can find food, water, and hay easily.

small eyes and normal
Tilted head, difficulty walking
If your guinea pig is tilting its head to one side and is having difficulty walking, it could be an indicator of a middle ear infection. This is a very serious condition, and you should get your guinea pig to a competent vet right away.
Seizures
Generally speaking, there are two "styles" of seizures in guinea pigs. If your guinea pig's seizures involve them lifting their head straight up in the air (without a "tilt" to one side), then the seizures could be caused by mites. Some varieties of mites burrow deep into the skin, and can affect the nervous system, causing these seizures.
If the seizure causes the guinea pig to "tilt" their head to one side, and/or curl their body, then it is most likely not related to parasites. These seizures can be caused by a variety of factors: everything from genetic seizure disorders to dietary problems. Start off by taking your guinea pig to a vet to have a blood test done. Abnormal levels of sugar, calcium, phosphorus or potassium can all be responsible, as can other blood-related factors. Some guinea pigs, however, do have seizure disorders, and they can be genetic or idiopathic (ie, having no known cause). Brain tumors are also a possible cause, though these are very rare. The frequency and severity of the seizures will determine whether or not they will need to be treated with anti-seizure medication.
Most seizures involve, in addition to the head lift or tilt, twitching of the muscles and eyes. The eye twitching can last for several minutes after the seizure has passed, as can some of the head tilt. Some guinea pigs will also vocalize during or after the seizure, with load squeals or screeches.
Eating poop
This is actually not a sign of illness at all, but some inexperienced owners may not realize that it is, in reality, an essential part of guinea pig nutrition. Guinea pigs create special, moist droppings that are stored in a small "sack" just inside the anus. These droppings are rich in vitamins and proteins that are essential for the cavy's health.
Other health concerns
There are some health concerns that you will want to be aware of that aren't necessarily related to an illness or an infection. Some of these are described below.
Broken toenails
Toenail breaks typically happen when the toenails have grown too long and brittle, but can also be caused by accidents even if kept trimmed to the proper length. If the toenail breaks such that the quick is cut, you should treat the wound with some quick-stop, if available, and dab some iodine or hydrogen peroxide on it periodically to prevent infection.
Sometimes, the toenail can break off completely, exposing the bone of the toe. In these cases, it is important to go see a vet to have the wound inspected, as it is likely that an abscess may form due to bacterial infections, requiring antibiotics.
Cavy Teeth

Guinea pigs have 20 teeth:

A pair of upper and lower incisors

No canines (instead, a gap called the
diastema)

A pair of upper and lower premolars

Three pairs of upper and lower molars
A guinea pig's teeth are "open rooted" and grow continuously.
The enamel is white in color and the front teeth can be sharp. Fat pads in the cheeks make examination of the molars difficult.
Buccal pad separators are designed to hold the cheeks back, aiding examination.
Good teeth are essential to your pet's health. A nutritious diet and adequate vitamin C will help them grow strong. In a healthy guinea pig, the biting, chewing and grinding of food (especially hays, grasses, and abrasive foods) will normally keep the teeth at the proper length -- a length which varies somewhat from one guinea pig to another. Routine
tooth trimming is not necessary and may interfere with your guinea pig's ability to eat.
Broken teeth can be the result of a fall, injury or accident. A cavy living on a poor diet can be vulnerable to broken teeth, especially if the diet is deficient in vitamin C, which is essential for bone and tooth growth.
The teeth of a normal healthy guinea pig should grow back just fine. Watch to make sure the remaining teeth do not get so long that they touch the gums or skin of the mouth. If the tooth has broken far down, leaving a hole, and the gum is bloody, periodically flush any food out of the hole and keep it clean with a luke-warm mild saline solution (a teaspoon of common salt dissolved in a pint of warm water will work fine).
WHAT YOU CAN DO Food: Make absolutely sure your cavy is still able to eat. Cutting food into smaller pieces or feeding by hand may be necessary. If your cavy is unable to use a water bottle, offer liquids by syringe and adequate vegetables and fruits to insure he gets enough water.
Do not arbitrarily clip a cavy's remaining teeth too early or too severely as it can make eating on his own very difficult. Clipping teeth will interfere with his ability to "rip, tear and grasp" food.
Vitamin C: Tooth loss can be aggravated by vitamin C deficiency (scurvy). Ensure that your cavy is getting enough vitamin C by providing a quarter of a 100mg chewable tablet or 25 to 30 mg liquid vitamin C. Vitamin C promotes good bone growth, strong teeth, and healing.
WHEN TO SEE A VET You may wish to contact a veterinarian if:

The break is ragged.

The opposing teeth begin to curve inward and contact the mouth (possible if most of the tooth and root was lost)
An experienced exotics veterinarian can trim a ragged tooth if needed or slightly clip the remaining teeth if they begin to grow inward. If you suspect any other problem (infection, apparent pain when eating) be sure to see your vet right away.
Broken teeth
If a tooth breaks, then you will need to make feeding arrangements for your guinea pig, as it will not be able to eat hard foods. Most owners will puree pellets, fresh greens and their soft poops and feed with an open syringe. Always consult your vet in these cases for assistance and advice.
If boars are not getting enough fiber in their diet, they may face impaction problems as they grow older. Impaction occurs when feces hardens just inside the anus, making it impossible for the boar to pull out the soft droppings that it needs to eat. This lump must be removed. Smear petroleum jelly inside the anus, wait an hour, and then squeeze the lump out. This will be somewhat painful for the boar at first.
There is some evidence to suggest that a regular diet that is high in fiber can prevent impaction. The best source of fiber is a grass hay, such as timothy.
Excessive tooth length
The guinea pig's teeth are usually worn down naturally by eating hard foods. If your guinea pig's diet is too soft, his or her teeth may grow to excessive lengths. It is best to take the guinea pig to a vet to have the teeth trimmed back. Until then, you may have to syringe feed if he or she can't eat on his or her own.

Heatstroke
Heatstroke typically occurs when a guinea pig is housed in a cage with insufficient ventilation, or when they are caught out in direct sunlight for too long. It can also occur on extremely hot summer days, even if the cavy isn't in the sun. Typically, a guinea pig with heatstroke will have a chest that is wet from saliva. It may also run excitedly back and forth, while panting and trembling all over.
Heatstroke can kill guinea pigs very quickly, but if you can get to them in time, they can recover. First, move them to a cooler location and offer them room temperature water (drinking cold water can cause a system shock that will kill them, just as it can in humans). Dip their limbs in cool, but not cold, water, and wrap cool, damp cloths closely around the body.

Cheilitis -- Inflammation of the Lips
Most frequently these lesions are caused by a bacterial infection (typically Staphylococcus aureus) but there can be other causes like Candida (a yeast infection). A pox virus has been found in the UK which reportedly can cause cheilitis.
Brown and Rosenthal recommend debridement, culturing (both microbial and fungal cultures), cleaning with a mild antiseptic solution and using topical and systemic antibiotics safe for guinea pigs. Check for dental disease and treat if present.
Also check the mouth for signs of fungal infection (thrush).
TREATMENT FOR A BACTERIAL INFECTION
Apply triple antibiotic ointment
sparingly twice daily. Ointment contains antibiotics that are not safe to ingest so use very carefully. Daily application may be required to keep the infection from returning.
Painful Urine Scald is Easily Treated

Ill guinea pigs sometimes develop painful urine scald.
This may be due to incontinence caused by:

Urinary tract infections

Bladder stones

Interstitial cystitis

Reproductive organ problems like pyometra
Urine scald can also be the result of injury or aging-related problems resulting in decreased mobility.
While urine scald is relatively easy to clear up, be sure to also treat the underlying condition.
Neutering your guinea pig
If you opt to neuter your male, then you will need to locate a veterinarian that has experience with guinea pigs. Guinea pigs, and other small mammals, are not as robust as cats and dogs, so your generic, run-of-the-mill vet will either "" you outrageous prices, claim the surgery can't be done safely or refer you to an experienced vet. But, not all vets are created equal; even vets that have worked on guinea pigs may not know how to properly perform this surgery.
It is also important to realize that there is a risk of loosing your guinea pig during the procedure. Any surgery involving anastesia carries the risk that your guinea pig's heart may stop, or that he or she will fail to wake up afterwards. Even experienced vets can have a guinea pig die during surgery, so it is important that you be aware of the possibility.
That being said, here are some tips and questions to ask when calling around for information, so that you can locate an experienced vet and. in turn, minimize your risks. Don't be afraid to drive a long distance to have this operation performed; it could very well mean your cavy's life.
- First and foremost, you need to locate a vet that works with "exotics". These are the vets that work with small mammals (including the guinea pig), birds, reptiles and other pets that aren't just cats or dogs.
- The vet should be able to tell you how many neuterings he or she has performed in the last year, and what their success rate was. The success rate should be well above 90%.
- Ask what kind of anesthesia is used; it should be isoflurine gas.
- There should be a heart monitor and an EKG during the surgery, with a technician monitoring them.
- Recovery should be in a heated compartment.
- The vet should not recommend that your guinea pig fast the night before the operation. It is okay, and recommended, to fast the morning of. The goal of fasting is to make the guinea pig's reaction to the anastesia predictable, as well as minimize the risk of regurgitating his or her stomach contents. However, fasting more than four hours before surgery is completely unnecessary. In fact, a long fasting period can cause stress in the guinea pig, and lead to a buildup of toxins in their body during and after the operation, as well as run the risk of stopping the GI system to the point where it might not start up again when the guinea pig wakes up.
- If the guinea pig is three years or older, the vet should perform a blood test beforehand, in order to look for any pre-existing medical conditions.
- The vet should not prescribe oral antibiotics afterwards. Antibiotics should never, ever be prescribed casually or as a precautionary measure, but rather only when a bacterial infection has, or is suspected to have, taken place. Antibiotics are a dangerous treatment for guinea pigs; they can cause severe diarrhea and even toxic reactions that can lead to death, and should only be used to treat existing conditions.

Vitamin C
Ascorbic acid is essential to good growth and health. Since guinea pigs cannot produce their own vitamin C, it must be supplied in the food they eat.
Certain biologic oxidation and reduction systems depend on it for proper functioning. In its absence, bone and blood vessel abnormalities develop, and enlarged adrenal glands, bleeding in the limb joints, rib muscles and intestines result. Young animals are more likely to exhibit bone deformities than older ones.
The average guinea pig needs between 10 and 30 mg/kg daily for good health.
Actual requirements can vary from one guinea pig to another. Young, pregnant, and ill pigs need more vitamin C than the average pig. Some sources suggest a minimum of 5 to 10 mg/kg of ascorbic acid to maintain good health. Other sources put it at 10-30 mg/kg daily for maintenance and up to 50 mg/kg for treatment of deficiency (Ferrets, Rabbits and Rodents - Clinical Medicine and Surgery).
A pregnant pig or one suffering from deficiency requires a minimum of 30 mg/kg (Harkness and Wagner). Vicki of JPGPR's vet recommended 30-50 mg vitamin C daily per adult cavy - depending on size, diet, conditions, and stress. Extremely high doses of ascorbic acid can cause poor growth and can result in a susceptibility to scurvy if the amount is dramatically reduced, even to doses considered adequate for a normal cavy.
signs of deficiency
Lethargy, weakness, unwillingness to move

Hopping instead of walking, enlarged or stiff limb joints

Not eating, loss of weight

Diarrhea

Eye and nose discharge

Rough coat

Tenderness to touch (may cry out in pain if restrained), poor flesh condition

Internal skeletal-muscular hemorrhage
Vitamin C deficiency can be secondary to other medical problems. For example, a guinea pig with malocclusion that is not eating and losing weight, may not be getting adequate vitamin C.
It is wise to routinely provide extra vitamin C to an ill guinea pig. Keep in mind, some of these signs such as eye and nose discharge may indicate other serious conditions like a respiratory infection. If your guinea pig is showing some of these signs, do
not assume this is "just" a lack of ascorbic acid and fail to provide critical veterinary care for a serious illness. See an experienced vet. Unknowledgeable vets too often diagnose an ill pig with a vitamin C deficiency and leave the underlying problem untreated. You are familiar with your guinea pig's diet. If you are providing adequate amounts of vitamin C, be sure to tell your vet.
impaction in boars:
Older boars may develop a condition called impaction. The muscles of these guinea pigs have weakened and they are no longer able to expel the soft caecal pellets that accumulate in the perineal sack. But you can help! Andrew's advice will guide you through the maintenance process.
bumble foot:
Pododermatitis (Bumblefoot) in Guinea Pigs
Ulcerative pododermatitis, also known as
bumblefoot, is an extremely painful infection of the footpad. The footpad is swollen and may be crusted and/or bleeding. In severe cases, the cavy may be reluctant to move, depressed, and anorexic. If the bone becomes infected, the leg may need to be surgically removed.
Left untreated, pododermatitis can result in death.
Cause: Pododermatitis is often attributed to abrasions caused by wire floors or rough bedding which allow infections (typically Staphylococcus aureus, a common environmental bacteria) to become established. Poor sanitation, wet bedding, lack of activity and obesity may be factors. Prevention focuses on avoiding these causes.
It has been suggested by one pet owner that guinea pigs with heart problems (and perhaps poorer circulation) may be prone to pododermatitis. Adequate exercise and treatment of heart problems may help these pigs.
Cavies are one of many animals that can suffer from this disease. In
chickings wet bedding is often blamed; in captive rapters, lack of activity and standing on a perch;rats and rabbits can also develop bumblefoot.
Treatment: Pododermatitis can be difficult to cure. The advice and experience of several pet owners appears on this page in hopes that one treatment will work for you. Examine your pet regularly to catch problems early. A vet can aid diagnosis and treatment.