1. HAMSTERS
BIOLOGY, CARE, DISEASES & MODELS
I. INTRODUCTION/HISTORY
A. Approximately 1,000,000 hamsters are used in research
annually in the united states. Of these, 90% are Syrian
(Golden), Mesocrictus auratus, and the remainder are primarily
the Chinese(striped back), Cricetus griseus; the Armenian(gray),
Cricetulus migratorius; and the European, Cricetus cricetus. By
1971, the hamster had become the third most commonly used
laboratory animal in the United States, exceeded only by mice and
rats.
B. Syrian hamsters, utilized as laboratory animals,
originated from one litter captured in Syria in 1930. Only three
menbers of this litter were retained in captivity, and it is the
progeny of these that were first imported to the United States in
1938. The four main reasons given for selection of the Syrian
Hamster for research are (1) availability and ease of
reproduction,(2) relative freedom from spontaneous diseases
coupled with susceptibility to many introduced pathogenic agents,
(3) anatomical and physiological features with unique potential
for study, and (4) rapid development with short life cycles.
C. The Chinese hamster was first used as a laboratory
animal in 1949. Since that time it has been used in several
aspects of infectious disease,radiobiological,endocrine,
carcinogenic, and mutagenic research. Since the Chinese hamster
has the lowest chromosome number of any other placental nurtured
lab animal it is useful for cytogenesis research.
D. The European hamster developed some laboratory
importance when several wild animals caught in a West German
industrial area were found to have had bronchogenic squamous cell
carcinoma. This hamster has since been found to be susceptible
to N-diethylnitrosamine with the resultant development of
respiratory tumors. It was concluded that the European hamster
is a more suitable model than the Syrian hamster for highly
concentrated and prolonged smoke inhalation studies. Also the
Europeon hamster is much larger than other hamster
species(300-400 gm).
E. The Armenian hamster was first introduced as a
laboratory animal in 1963. It was selected because of its
susceptibility to mutagenic and carcinogenic agents and for
studying meiosis. Their diploid chromosome number is 22.
II. SYRIAN HAMSTERS
A. ORIGIN- The Syrian, hamster is native to the arid,
temperate regions of Southeast Europe and Asia Minor. In their
natural environment, hamsters live in deep tunnels that ensure a
cooler temperature and higher humidity than the general desert
environment.
B. GENETICS/ANATOMY
1. Taxonomy
ORDER: Rodentia
FAMILY: Cricetidae

2. GENUS: Mesocricetus
SPECIE: auratus
2. Common names: Golden or Syrian hamster,Symbol(SYR)
3. Strains
a. Inbred Strain (i.e.,20 or more successive
generations of brother x sister matings)
Nomenclature of more common types (All
developed by Billingham and Silvers at Univ Pa)
(1) MHA/SsLak -White--pink eyes;Mill Hill
Albino- susceptible to dental caries
(2) LSH/SsLak -Brown & white; London School
of Hygiene
(3) CB/SsLak -Brown & white; Chester Beatty
Instutite
(4) PD4/Lak -White--pink eyes;
(5) LHC/Lak -Cream; Lakeview Hamster Colony
b. Outbred Strain
Nomenclature
(1) Lak:LVG(SYR) -Golden Syrian
4. Genotype- Diploid (2N) chromosome number: 44
5. Phenotypic Characteristics- The adult Syrian
hamster is larger than a mouse, usually growing to 6 to
8 inches in length and weighing from 110 to 140 gm. It
virtually tailless, and has smooth, short hair. Normal
coloration is reddish-gold, with grayish-white ventral
portion, however, color can range from albino to dark
brown (Other pertinent anatomical features as follows)
a. Dentition:
(1) Dental formula
1 0 0 3
I- C- PM- M- = 16
1 0 0 3
(2) Incissors
(a) Erupted at birth
(b) Grow continuously
(3) Molars
(a) Erupted at birth
(b) Cuspidate and do not continue to grow
(4) Dental caries is easily induced by
altering diet
b. Cheek pouches- Evaginations of the lateral

3. buccal wall are devoid of glands and lymphatic
drainage. These sites are priviledged for foreign
tissue transplant due to this lack of lymph
drainage.
c. Stomach- Two compartments
(a) Non-glandular-similar to ruminants
-cardia region
(b) Glandulary -acid
-pyloric region
(c) The two compartments are joined by a
narrow passageway with the esophagus entering
just proximal to the dividing stricture.
d. Sebaceous scent glands
(a) costovertebral area
(b) larger in male than female
(c) function controled by androgens
(d) thought to serve as olfactory ID marker
e. Pulmonary system
(a) Limited numbers of gland in upper airways
(b) Left lung- single lobe
(c) Right lung-3 lobes(apical,middle,caudal)
f. Kidney- The renal papilla extends out into the
ureter making it possible to collect urine from
tubules in a living hamster.
g. Mammary Gland- 14-22 mammae.
h. External Genitalia/Sexing
(a) Males-greater urogenital distance and
only one urogenital opening
(b) Females- Separate vaginal,urinary,and
anal openings
C. PHYSIOLOGY
1. Neonatal Development
a. Teeth present at birth,eyes & ears closed, and
pups are hairless.
b. Ears open at 4-5 days
c. Eyes open at 15 days
d. Eat solid food at 7-10 days
e. Weaned at 21-28 days
2. Normative Data
PARAMETER VALUE
Adult weight

4. Male 85-140 gm
Female 95-120 gm
Life span
Average 2 years
maximum expected 3 years
Chromosome number (diploid) 44
Water consumption 30 ml/day
Food consumption 10-15 gm/day (adult)
Body temperature 36.2-37.5 C (rectal)
Heart rate 280-412/min
Respiratory frequency 74(33-127)
HEMOTOLOGY
RBC 7,500,000/mm
WBC 7,600/mm
Segmented Neutrophils 21.9%
Non-segmented Neutrophils 8.0%
Lymphocytes 73.5%
Monocyte 2.5%
Eosinophils 1.1%
Basophils 1.1%
3.Reproduction and mating
PARAMETERS VALUE
Puberty
Male 6-8 weeks (90 gm)
Female 6-8 weeks (90-100gm)
Estrous cycle (1) 4 days
Estrus (2) 6-10 hours(night)
Gestation (3) 15-18 days
Litter size 4-12 pups
Birth weight 2-3 gm
Weaning (4) 21 days(35-40gm)
Optimum breeding life 14 months
FOOTNOTES
(1) Stage of cycle can be determined by the tenacity
and opacity of vaginal discharges-- The discharge is
thick and opaque at the time of and after ovulation.
(2) Heat generally begins approximately 1-2 hours after
dusk on the third day of the estrous cycle and
ovulation is completed 6-10 hours after onset of
psychic estrus. The female should be placed in the cage
with the male at the begining of the dark cycle. If
the female is receptive she will quickly assume a
lordotic position with hindlegs spread and tail erect.
If copulation does not occur within 5 minutes or if the
female becomes aggressive, she is removed. If
copulation occurs, the pair can be left together until
the following light cycle. (3) A copulation plug will
be visible for a few hours after copulation. Colony
raised females can be returned to the colony until day
14 of gestation if they don't fight. Pregnant animals
should be separated and undisturbed for at least 2 days
prior to and 7 day after parturition to avoid litter
cannibolism.
(4) Estrous cycle will not resume for the mother until
a few days after her young are weaned. Young from
different litters can usually be housed together until
50 days of age.

5. 4. Behavior
a. Docile unless surprised or awaken.
b. Nocturnal o
c. Hibernate when temperature drops below 5 C,
however, animal is responsive to external stimuli.
d. Curious by nature
D. COLONY CARE & HUSBANDRY
1. Housing
a. Caging
(1) Plastic shoebox solid bottoms/latchable
lid to prevent excape.
(2) Space requirements
(a) Hamster < 60gm - 10sq.in.
(b) Hamster > 60gm - 11/20 sq.in.
(c) Female with litter - 150 sq.in.
b. Bedding
(1) Routine types include: hardwood chips,
sawdust, shavings, corn cobs, and beet pulp.
(2) Pregnant animals will use soft paper for
nest building.
(3) Bedding should be replaced 1 or 2 times
weekly and can be left as long as 2 weeks when
is is desirable to leave a litter undisturbed.
c. Temperature/Relative Humidity
(1) Adults should be maintained at
approximately 65 to 70 degrees F with 40-60%
relative humidity.
(2) Breeding rooms should be kept slightly
warmer (71-75 degrees F).
(3) Hamsters are more adaptable to cold
extremes than to warm extremes.
d. Photoperiod: 12-14 hour light period daily
with 14 hours required for breeding colonies.
2. Feeding
a. Nutritional requirements: Since the hamster's
first stage of digestion is a fermentation
process their nutrient utilization is slightly
different than that of other rodents. Often
times rat feed is used as a basic diet and is
then supplemented with rabbit chow or other
similar diets.
(1) Soybean meal provides a better protein
supplement than fishmeal at about 16% of the
ration. Protein levels of 18-24% promote more
rapid growth, but at the cost of higher
incidences of nephritis.

6. (2) More complex carbohydrates,such as, corn
starch are more highly tolerated energy
sources. 30-40% corn starch in the ration is
ideal
(3) Compared to the rat, the hamster has a
higher requirement for zinc, copper, and
potassium.
b. Feed delivery- If food hoppers are used, the
feed pellets must be able to fall through the
slots to the floor of the cage. This is
required because the hamster's muzzle is so
broad as they would be forced to chew food from
both sides of the metal strips of the feeder
resulting in broken teeth and starvation.
c. Water- A continuous supply of fresh clean
water is required. Water delivered via
Stainless steel siper tubes is most desirable.
3. Handling
a. Physical restraint- Insure that the hamster is
aware of your presence and is not asleep.
(1) Container or cupped palms are often
adequate for transfer or weighing.
(2) One-hand hold (thumb and 3rd finger around
the thorax stablizing the hindquarters with the
1st & 2nd fingers.)
b. Chemical restraint/preanesthesia/anesthesia
AGENT DOSAGE
Ketamine HCL 40-150mg/kg IM
100-200mg/kg IP
Xylazine(with ketamine) 10mg/kg IM Improves
degree of relaxation
Pentobarbital(10mg/ml) 50-90mg/kg IP
Pentobarbital(60mg/ml) 90mg/kg IP
30mg/kg IV
Thiopental 20mg/kg IV
Morphine up to 150mg/kg IM;IP;SC
analgesia w/o narcosis
Inhalant anesthetics cone;chamber;mask
Atropine sulfate 0.2-0.5mg/kg SC
c. IV injection site: saphenous vein
d. Common bleeding sites:
(1) Cardiac puncture (requires anesthesia
2 ml/100gm animal safely)
(2) Tail clip (no anesthesia,small quantities)

7. (3) Orbital sinus (requires anesthesia,small
quantities)
e. Euthanasia
(1) Physical methods
(a) Cervical dislocation
(b) Decapitation
(2) Parenteral methods
(a) Pentobarbital 135-150mg/kg IV
minimum
(b) T-61 : not to be used when histo-
pathology is anticipated.
(3) Inhalant methods
(a) Carbon dioxide
(b) Halothane
(c) Methoxyflurane
(d) Ether(explosive)
E. SPONTANEOUS DISEASES
1. Hamsters are generally very resistant to diseases
and have few health care problems. This, coupled with
the fact that diseases can be readily induced, make the
hamster ideal as a model for many human diseases. Some
disease conditions have been propagated by inbreeding
to maintain specific models for human disease which are
not common for the species as a whole.
2. Common diseases listed in decending order of
occurrance (below)
a. Enteritis
b. Pneumonia
c. Neoplasia
d. Amyloidosis (old animals)
e. Polycystic disease
3. Enteritis is the most common type of spontaneous
hamster disease. The condition may occur due to a
broad number of factors from infectious agents to
management practices.
a. Common names- Wet tail, proliferative ileitis,
regional enteritis, and ileal hyperplasia.
b. Agents routinely associated with disease.

8. (1) Clostridium difficile is often isolated
subsequent to enteric disease associated with
antibiotic therapy(i.e. clindamycin ampicillin,
lincomycin) which could indicate that this
bacterium may play some role in the
pathogenisis.
(2) Campylobacter Fetus ssp jejuni has been
incriminated of late as having a contributing
role in the clinical symptoms of enteric
disease. Although it is cultured on occassion
from clinically normal animals it was reported
by Lentsch in almost 100% of the hamsters with
symptoms of proliferative ileopathy.
c. Predisposing factors
(1) Young age.
(2) Stress (shipping overcrowding lack of
fresh water.)
(3) Poor diet.
(4) Antibiotic therapy.
d. Clinical signs
(1) Acute - lethargy, anorexia, ruffled hair
diarrhea, dehydration, and death within 48
hours. Intussuceptions may occur.
(2) Subacute-diarrhea, retarded growth and
eventual death.
(3) Chronic-palpable abdominal masses with
emaciation or even normal appearance with
occassional deaths.
e. Histopathology - Hyperplasia of the ileal
absorptive epithelium is the primary lesion.
f. Treatment - Erythromycin 20mg/kg is most
desirable.
g. Differential diagnosis.
(1) Salmonella spp.- rare spontaneous disease
of hamster; Dx culture.
(2) Tyzers
(a) Clinical signs may include all those
listed in regards to proliferative
ileitis or animals may just be found
dead.
(b) Etiology - Bacillus piliformis.
(c) Transmission fecal - oral.
(d) Pathology - focal necrosis of
viseral organs.

9. (e) Diagnosis - tissue smears (silver,
PAS or Giemsa stains.)
4 Pneumonias
a. Clinical signs - depression, anorexia, nasal
and ocular discharges, respiratory distress and
chattering.
b. Common eitiologies.
(1) Pasteurella pneumotropica.
(2) Streptococcus spp.
(3) Streptococcus pneumoniae.
c. Control/Treatment - eleminate stress,
depopulate or treat with an effective
antibiotic which does not cause fatal
enterocolitis.
5. Neoplasia.
a. Malignant tumors in (decreasing order of
ocurrance.
(1) Lymphosarcoma.
(a) Horizontally transmitted - no type
C or retrovirus identified.
(b) Epidemic outbreaks in various
breeding colonies have reach 50 -90%
mortality.
(c) Clinical signs - solid tumors
enteritis, pyelonephritis, warts, poor
breeding efficiency and intussusceptions.
(2) Reticulum cell sarcoma - lymphnodes.
(3) Carcinoma - intestines and adrenals.
b. Benign tumors (most common).
(1) Gastro - intestinal polyps.
(2) Adenomas of adrenal cortex.
6. Amyloidosis - principle cause of death in aged
hamsters. The incidence can reach or exceed 85% in
hamsters over 18 months of age: The kidney is the
most likely site of deposition, however, other
organs are often involved. The disease compares
with the nephotic syndrome described in humans.
7. Polycystic Disease - cyst occur in a high incidence
in hamsters over 1 year of age with the site most
frequently in the liver. The lesions generally are
of no clinical significants and are thought to be
due to developmental defects of ductal structures.
8. Spontaneous viral diseases

10. a. Clinical symptoms secondary to common rodent
virus (i.e. Sendae,LCM) are rare,however,
sero-conversion is common.
b. Even though little disease is noted in the
hamster lymphocytic choriomeningitis is important
because of it's zoonotic implications in humans.
9. Spontaneous parasitic diseases
a. Internal
(1) Protozoan- Several have been identified
but they have little clinical significants.
(2) Nematodes
Syphacia obvelata(mouse pin-worm)
Syphacia muris (rat pin-worm)
(3)Helminth
(a) Hymenolopsis nana (zoonotic)
(b) Hymenolopsis diminuta
(c) Can cause obstruction and enteritis
(4) Dx- Fecal exam
b. External
(1) Ornithonyssus bacotis(tropical rat mite)
(2) Notoedres spp.(ear mite)
(3) Demodex criceti
D. aurata-more pathogenic
(4) Dx-Skin scraping
III. CHINESE HAMSTER
A. Native to the Eastern shore of China near the Caspian
Sea. They were first successfully bred in 1958, after
illumination schedules were reversed.
B. Taxonomy
ORDER: Rodentia
FAMILY: Cricetidae
GENUS: Cricetus
SPECIE: griseus
C. Physiology
1. Mayor differences from Syrian hamsters
PARAMETER VALUE
Chromosome(2N) 22
Adult Weight 39-46 gm
Body Length 4 inches
Water Intake 11-13 ml/100gm

11. 2. Reproductive physiology
PARAMETER VALUE
_______________________________________________________
Incisors Erupted at birth
Eyes & ears open 10-14 days
Weaned 21-25 days
Sexually mature 8-12 weeks
Estrous cycle Polyestrus
Estrous cycle duration 4 days
Estrus 6-8 hours
Ovulation time Just before estrus
Copulation 2-4 hours after start
of dark period
Implantation 5-6 days
Gestation 20.5 days
Average litter size 4-5
Mammae numbers 8
Postpartum estrus 4 days
_______________________________________________________
2. Hemogram similar to Syrian hamster
D. Diseases
1. Very few spontaneous infectious diseases reported.
2. Metabolic
a. Diabetes mellitus
(1) insulin dependent
(2) similar to human
(3) clinical signs-polydypsia,polyuria,
dehydration, blindness and death especially
after stress
(4) recessive factor-propogated by inbreeding
3. Neoplasia-low incidence
4. Miscellaneous
a. Periodontitis-Epecially in those with diabetes
which resembles the same condition in humans with
diabetes.

12. b. Nephrosclerosis
c. Spondylosis- Higher incidence in hamsters with
diabetes.
IV. EXPERIMENTAL MODELS/USES
A. Spontaneous Models of Human Disease
1. Diabetes mellitus in the Chinese hamster was
recognized in 1957. The disease is associated with a
decrease of the pancreatic B cells. It is insulin
dependent, juvinile onset,and hypoinsulinemic similar to
the juvinile type in man.
2. Syrian hamster dystrophy
a. strains: BIO 1.50-original strain
BI0 4.6 -acromelanic,homozygous
affected
BIO 50.54-agoute,homozygous affected
BIO 82.62-acromelanic,homozygous
affected
BIO 53.58-homozygous affected
b. Autosomal recessive skeletal muscle
degeneration
c. Serum levels of phosphocreatine kinase parallel
the course of the disease and calcific tongue
lesions are pathognomonic of the disease.
d. also develop cardiomyopathy,
cardiohypertrophy, and congestive heart
failure-die by nine months of age
Comparison: Good model for physiology and pathogenesis
of Duchenne's dystrophy: variable size