The most common pet and research hamster is the golden or Syrian hamster (Mesocricetus auratus). Most Syrian hamsters in captivity appear to have originated from a single litter collected near Aleppo in Syria in 1930.
Syrian hamsters have a head and body length of 170–180 mm and tail length of 12 mm. Body weight is 110–140 g, with females larger than males. Wild Syrian hamsters have a light, reddish brown dorsal coat and white underparts. The skin of Syrian hamsters is very loose.
Two other species of hamsters, the common or European hamster (Cricetus cricetus) and the ratlike Chinese hamster (Cricetulus griseus) are used in research. They do not make good pets because of their aggressive nature. However, dwarf hamsters such as the Djungarian (Phodopus sungorus) and Roborovsky's (P roborovskii) have a docile disposition, do not attempt to bite or run away, thrive in captivity, and make good pets. This section discusses the diseases of the Syrian hamster.
At least 20 mutations affecting coat color in Syrian hamsters are known. Most are simple recessive traits, 4 are dominant and 2 are sex-linked. Five mutations affect the fur, giving rise to long hair (also known as teddy bear hamsters), rex, and satin coats. Length of hair in the longhaired Syrian hamster is influenced by testosterone. Longhaired males from the age of sexual maturity have significantly longer hair than females or castrated males, which display fluffy, shorter hair.
Syrian hamsters possess androgen-dependent, paired flank organs in the costovertebral area that consist of sebaceous glands, pigmented cells, and terminal hairs. They are larger and heavily pigmented in males and used for territorial marking. All hamsters have large cheek pouches that extend well past the shoulders; when filled with food, these pouches more than double the width of the animal's head and shoulders.
Adult male Syrian hamsters develop large adrenal glands due to enlargement of the zona reticularis, which is 3× the size of that in female hamsters. Like gerbils, Syrian hamsters have a high proportion of erythrocytes with polychromasia.
Female Syrian hamsters are heavier than males and generally are aggressive toward other hamsters. Nonestrous females can be especially aggressive toward young males and may kill them. The 4-day estrous cycle is characterized by a copious postovulatory discharge on the last day. The discharge is creamy white and has a distinctive odor; it fills the vagina and usually extrudes from the vaginal orifice. Its stringy nature is distinctive, and if touched it can be drawn out as a 4- to 6-in. thread. Estrus lasts ∼1 day, and the gestation period is 16–19 days. Litter size ranges from 2–16, with an average of 9. Cannibalism of young accounts for nearly all preweaning mortality. Cold ambient temperatures (<10°C), lean diets, and low body weight during pregnancy increase cannibalism. Disturbing the mother by handling the young or nest, and not providing adequate nesting material, warmth, food, or water, often results in cannibalism. Syrian hamsters are prolific breeders and can produce 3–5 litters/yr. The young are weaned at 20 days and capable of reproducing at 7–8 wk. The lifespan of Syrian hamsters is 2–3 yr.
In the wild, Syrian hamsters live in shallow burrows on dry rocky steppes or brushy slopes. Deep bedding that is appropriate for burrowing is recommended. Cages with at least 40 cm of bedding enhance the welfare of Syrian hamsters.
Wild Syrian hamsters are omnivorous, eating green vegetation, seeds, fruit, and meat. Exposure to cold stimulates the hamster to gather food, and it will often hibernate at temperatures <5°C. Syrian hamsters do not fatten before hibernation and will starve unless they waken periodically to eat. Hibernating animals remain sensitive to external stimuli and are usually aroused if handled. Syrian hamsters have prominent deposits of brown fat beneath and between the shoulder blades, in the axilla, and in the neck and perirenal areas.
Syrian hamsters are active chewers and are skillful at escaping from their cages. Glass water tubes are contraindicated for Syrian hamsters, as they readily bite through glass. Stainless steel sipper tubes close to the floor are recommended. As Syrian hamsters have broad muzzles that often prevent them from accessing feed hoppers, feed pellets should be placed on the floor of their cage. Hamsters are naturally coprophagic.
The animal's overall appearance and behavior, particularly in relation to its cagemates, should be noted. Sick animals are often isolated from others and may show weight loss, hunched posture, lethargy, rough fur, labored breathing, and a loss of exploratory behavior. Early signs of disease involve changes in the color, consistency, odor, and volume of urine and feces. The perineal area should be checked for fecal or urine stains or discharges from the vulva in females. Fecal samples may be taken for parasite detection and bacterial culture. The fur and skin should be examined for alopecia, fight wounds or other trauma, and ectoparasites. The oral cavity should be checked for overgrown teeth or impacted cheek pouches. Ears should be examined for discharges or inflammation and eyes for discharges or conjunctivitis. Feet should be examined for sores and overgrown or broken nails. The abdomen should be palpated for masses.
Syrian hamsters are not normally aggressive, but can be provoked if startled, awakened, or roughly handled. It may be easier to scoop Syrian hamsters up in a small container rather than pick them up directly. Their highly elastic skin should be grasped sufficiently to prevent the animal from biting.
Diarrhea occurs in Syrian hamsters of any age and is known as “wet tail”, though this euphemism is frequently used to describe the disease in young hamsters. Proliferative ileitis is the most significant intestinal disease of 3- to 10-wk old Syrian hamsters and results in high mortality. It is caused by the intracellular bacterium Lawsonia intracellularis. Treatment involves the correction of life-threatening electrolyte imbalance, administration of antibiotics, and force feeding. Several antibiotic treatments are recommended, including tetracycline hydrochloride (400 mg/L of drinking water for 10 days), tetracycline (10 mg/kg, PO, bid for 5–7 days), enrofloxacin (10 mg/kg, PO or IM, bid for 5–7 days), and trimethoprim-sulfa (30 mg/kg, PO, bid for 5–7 days). Symptomatic treatment with bismuth subsalicylate may be given if diarrhea persists. Replacement electrolyte and glucose solutions should be given orally, and electrolyte fluid replacement such as saline or lactated Ringer's solution should be given at a dosage of 20 mL/100 g daily. Sequelae of proliferative ileitis in surviving Syrian hamsters may include eventual intestinal obstruction, intussusception, or rectal prolapse.
Diarrhea in adult Syrian hamsters is associated with Clostridium difficile enterotoxemia and, as in guinea pigs, may occur 3–5 days after the administration of antibiotics such as penicillin, lincomycin, or bacitracin.
Tyzzer's disease due to Clostridium piliforme (Bacillus piliformis) is seen in Syrian hamsters and is usually precipitated by stress such as overcrowding, high environmental temperature and humidity, heavy internal and external parasite load, and nutritionally inadequate diets. C piliforme is opportunistic in immunosupressed animals and not seen in immunocompetent animals.
Hamster polyoma virus (HaPV) is the cause of epizootic lymphoma in young Syrian hamsters and epitheliomas in older enzootically infected hamsters. When first introduced into a naive population of breeding Syrian hamsters, HaPV results in an epizootic of lymphoma, with an incidence as high as 80%. Lymphomas often arise in the mesentery but can arise in the axillary and cervical lymph nodes. Once HAPV has become enzootic in a hamster population, the occurrence of lymphoma declines to a much lower level. Enzootically infected Syrian hamsters develop HaPV skin tumors rather than lymphoma. HaPV lymphoma-affected Syrian hamsters appear thin and often have palpable abdominal masses. They may have demodectic mange due to either Demodex criceti or D aurati.
Fecal smears of Syrian hamsters have abundant protozoa. However, their role in enteric disease is speculative, as similar protozoa are found in comparable numbers in both healthy and diseased animals.
Spontaneously occurring dermatophytosis is extremely rare in the Syrian hamster.
In older Syrian hamsters, lymphoma is the most frequently observed neoplasm of the hematopoietic system. It is multicentric and commonly affects lymphatic organs. Cutaneous lymphoma, resembling mycosis fungoides (an epidermotropic T-cell lymphoma in humans), is seen occasionally in adult Syrian hamsters. Affected animals show anorexia, weight loss, and patchy alopecia. Cutaneous lymphoma can be misdiagnosed as hyperadrenocorticism (Cushing's disease) because affected hamsters initially show patchy alopecia and dermal hyperpigmentation. However, cutaneous lymphoma shows rapid progression of the disease—mean time from presentation to euthanasia is ∼10 wk. Adenomas of the adrenal gland are common in Syrian hamsters, but few reports exist of confirmed clinical Cushing's disease in hamsters.
Melanomas, not only of the flank organ but also of the skin, are frequently reported in Syrian hamsters. There is a striking 10:1 male-female melanoma ratio.
Atrial thrombosis has an incidence of up to 70% in aging Syrian hamsters. Most thromboses develop in the left atrium secondary to heart failure and lead to a consumptive coagulopathy. Although the incidence does not differ between the sexes near the end of their respective lifespans, atrial thrombosis occurs on average at a younger age in females (13.5 mo) than in males (21.5 mo). Aged Syrian hamsters present with clinical signs of cardiomyopathy such as hyperpnea, tachycardia, and cyanosis. If untreated, death usually follows within a week after these signs are evident. The incidence of atrial thrombosis is influenced by the endocrine status of the animal, and especially by the amount of circulating androgens. Castration of male Syrian hamsters increases the prevalence of atrial thrombosis.
Weight loss is seen in older Syrian hamsters and often is associated with hepatic and renal amyloidosis. It is the principal cause of death in longterm research studies. Females have a higher incidence (80% among hamsters >18 mo old), increased severity, and an earlier age of onset of amyloidosis than males. There is a correlation between social stress induced by crowding and amyloidosis in laboratory Syrian hamsters. It is infrequently reported in pet Syrian hamsters where overcrowding is not a problem.
Degenerative renal disease also occurs more often in older female Syrian hamsters. Affected kidneys are pale and granular. Microscopically, glomerular changes vary from thickening of the basement membrane to glomerular obliteration. Amyloid deposition occurs frequently as a concurrent event.
Polycystic liver disease is observed in Syrian hamsters >1 yr of age. The lesions are due to developmental defects of the bile duct and are not associated with clinical signs. At necropsy, numerous thin-walled cysts may be seen.
Last full review/revision July 2011 by Thomas M. Donnelly, BVSc, DACLAM