INTRODUCTION
The subfamily Cricetinae contains approximately 25 different hamster species worldwide. They are found primarily in southeastern Europe and Asia. A number of different genera and species of hamsters are used in the research laboratory: the Syrian or golden hamster (Mesocricetus auratus); Chinese or gray hamster (Cricetu- lus griseus); European or black-bellied hamster (Cricetus cricetus); Armenian or migratory hamster (Cricetulus migratorius); Dzungarian, Siberian, dwarf, winter-white, or striped hairy-footed hamster (Phodopus sungorus); South African hamster or white-tailed rat (Mystromys albicaudatus); and others.
The majority of hamsters used in research are Syrian and Chinese hamsters. Syrian hamsters that are commonly used in research and kept as pets originated from a litter captured in Syria in 1930, and it is believed that subsequent progeny are descendants of a single sibling pairing. The original animals were bred in captivity at Hebrew University, and their offspring later served as the foundation stock for M. auratus in other countries. Although often referred to as outbred, Syrian hamsters are understandably genetically homozygous. It has been claimed that outbred Syrian hamsters are so inbred that they can accept tissue transplants among one another, evidence of which is provided in their unique susceptibility to a transmissible reticulum cell sarcoma. True inbred strains of Syrian hamsters have also been developed. Cricetulus griseus was first domesticated in Beijing, China, around 1920.Syrian hamsters are susceptible to several serious enteric microbial infections, are remarkably susceptible to a number of xenogeneic viruses, and are prone to the induction of tumors with many such viruses. This is likely due to a limited major histocompatibility complex (MHC) repertoire resulting from their highly inbred nature. This chapter deals primarily with diseases of the Syrian hamster.
Very little is known about diseases of other types of hamsters, and it must be kept in mind that generalizations cannot be made among hamster species, since hamsters represent different, distantly related genera.In their natural habitat, Syrian hamsters live individually in burrows in close proximity to other hamsters and communicate using ultrasonic signals. Burrows are complex, with separate chambers devoted to food storage, nesting, and urination/defecation. Females tolerate adult males only when in estrus, and will reject and often kill males after mating. This solitary lifestyle is also evident when litters reach weaning age, at which time pups attempt to disseminate. If not separated at weaning, females will cannibalize their pups. Indeed, maternal cannibalization of pups is a major management challenge. Syrian hamsters may undergo true hibernation in response to variables such as low environmental temperature, decreased access to food, and exposure to diminishing hours of light. During hibernation, their metabolic rate may be reduced to 5% of normal. Hamsters may also undergo shorter periods of torpor. Hamsters are crepuscular, gathering food within their cheek pouches and hording food in their burrows. Using exercise wheel revolutions as a measurement of activity, female Syrian hamsters have been shown to travel distances equal to several kilometers during a 24-hour period while in estrus. Olfactory cues play an essential role in mating behavior. They are active chewers and adept at escape. Hamsters enjoy a well-constructed and comfortable nest and endeavor to cache impressive stores of food.
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