What I Learned About Hamsters After I Graduated From Vet School

Tiny and adorable, the hamster’s health mysteries are gradually being revealed.

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Diarrhea usually has different causes in young hamsters than in adult hamsters. Via Marcin/Flickr
Dr. Jerry Murray

When I was in the College of Veterinary Medicine at Texas A&M University, I had a brief “everything you need to know about hamsters” lecture. Needless to say the professor could only cover a few topics in his 50-minute presentation, and it was clearly not everything I needed to know about pet hamsters. Unfortunately there were very few articles on pet hamsters in the veterinary journals back then, and the only textbook at that time was The Biology and Medicine of Rabbits and Rodents, which was focused on lab animal hamsters. It would be six more years before the pink book (Ferrets, Rabbits and Rodents: Clinical Medicine and Surgery) would come out. The pink book was a giant step forward for pet hamsters.

Wet Tail

The most common problem seen in pet hamsters is diarrhea. This is frequently called “wet tail” by hamster owners. Wet tail is a vague term, but it is typically used by veterinarians to just describe diarrhea in very young hamsters. I learned very little about diarrhea in baby hamsters when I was in vet school. The disease is more accurately called proliferative ileitis, and it is caused by the bacterium Lawsonia intracellularis. Lawsonia also causes problems in piglets and ferret kits. This disease frequently causes severe diarrhea, dehydration and electrolyte imbalances. It can also cause a rectal prolapse from the frequent straining to defecate. It is often a fatal problem, and it requires aggressive treatment and some luck for the baby hamster to survive. Several antibiotics including tetracycline, Baytril, and trimethoprim-sulfa are effective against this bacterium, but it is difficult to correct the dehydration and electrolytes fast enough. Fluids can be administered orally, subcutaneously or intravenously.

A different diarrhea syndrome is seen in adult hamsters. This is usually an antibiotic-associated diarrhea. When hamsters are treated with certain antibiotics, such as amoxicillin, penicillin, ampicillin or lincomycin, they are prone to developing diarrhea three to five days later. This is because the antibiotic kills the “good bacteria” and allows the “bad bacteria” in the gastrointestinal tract to take over. The bad bacterium is Clostridium difficile (C. diff.). This bacterium actually produces toxins that cause severe diarrhea, dehydration, hypothermia and frequently death. There has been a lot of research on C. diff. and its associated toxins, because humans have a very similar syndrome from C. diff. This was one of the topics that were briefly covered in school, but treatment options were very limited back then. Now there are some safe antibiotics that are effective against C. diff. and some probiotics that can help restore the good bacteria to the intestinal tract.


Back in school respiratory infections were briefly covered, but respiratory infections and pneumonia were considered uncommon in hamsters. Actually, pneumonia seems to be quite common in pet hamsters. Bacterial and viral pneumonia are both possible, but strep pneumonia seems to be most common. It might be possible for the pet hamster to acquire the strep from people. Bacterial pneumonia can be treated with antibiotics and fluid therapy.

Heart Disease

Hamster heart disease was not covered in school, but pet hamsters are prone to heart disease. They can get either dilated cardiomyopathy where the walls of the heart are thin and stretched or hypertrophic cardiomyopathy where the walls are much thicker than normal. Both of these problems can cause congestive heart failure. Hamsters with congestive heart failure typically have labored breathing, exercise intolerance and coughing. Treatment of congestive heart failure is similar to what I use for dogs and ferrets, but hamsters do not do well even with heart medications. Most only survive for a few weeks.

Another heart problem seen in hamsters is atrial thrombosis. This is the fancy way of saying a clot forms in the upper chamber of the heart. This is a common cause of sudden death in hamsters aged 1 to 2 years old. This is very common in hamsters with hypertrophic cardiomyopathy. If hypertrophic cardiomyopathy is diagnosed, then heart medications and medications to try to prevent clots are needed. Unfortunately most hamsters die from the heart disease or atrial thrombosis despite treatment.


Cancer in hamsters was not covered in school, but lymphoma is common in pet hamsters. There are three different forms of lymphoma seen in pet hamsters. In adult hamsters lymphoma is usually spread throughout the body and is typically found in the lymph nodes, thymus, spleen and liver. This form causes weight loss, anorexia, diarrhea and eventually death.

The second form is called cutaneous lymphoma because it causes skin tumors. Hamsters with this form usually have weight loss along with hair loss and skin tumors.

The third form of lymphoma is from the hamster polyomavirus (HaPV). Hamsters with this form of lymphoma are usually thin and have tumors in the abdomen. Some hamsters with resistance to HaPV might develop only wartlike skin tumors. Some may also develop demodectic mange from the viral-induced immune suppression. The virus is spread to other hamsters through the urine from an infected hamster. There is no known cure for HaPV-induced lymphoma.

In hindsight, I did not know much about pet hamsters when I graduated from vet school. Since then, I have gradually learned a lot about these friendly little pet rodents.

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Critters · Hamsters