What every veterinarian needs to know about Virginia opossums

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EXOTIC VOLUME 6.6
DVM
38
Cathy A. Johnson-Delaney,
DVM, Dipl ABVP-Avian
Avian & Exotic Advanced
Diagnostic Consulting
Bird & Exotic Clinic of Seattle
Edmonds, Washington
cajddvm@hotmail.com
For More Information
The private practitioner interested in
working with Virginia opossums is
referred to the National Opossum
Society (NOS), www.opossum.org.
Membership is not open to
laboratory animal veterinarians who
may use opossums in research.
Information on specific diets,
diseases and therapeutics written by
the late Dr. Anita Henness is
copyrighted by NOS and is not
included in this article. Information
used here is from the listed
references and personal experience.
Dr. Anita Henness should be
acknowledged for her pioneering
efforts to establish nutritional,
medical and surgical treatments and
procedures for the Virginia opossum.
EXOTIC
ANIMAL
CARE
WHAT EVERY VETERINARIAN NEEDS TO KNOW ABOUT
Virginia Opossums*
*Adapted from Marsupial Module. In
Johnson-Delaney C: Exotic Companion Medicine
Handbook. Lake Worth, Zoological Education
Network, 2005.
The Virginia (Didelphis virginiana)
opossum is the only native marsupial
of North America. (New World
“possums” are properly called “opos-
sums”; Old World “possums” are
“possums”). In most areas, they are
considered a pest species. Some states
and municipalities prohibit ownership
of native or wildlife species. The
veterinarian should consult with local
and state regulatory agencies for
information on the proper permits.
Most animals that become pets are
captured as pouch babies, often from
road kill of the parent female. Because
of this scenario, Virginia opossums are
generally thought of as unintelligent
and slow. In actuality, the Virginia
opossum is a successful marsupial and
has increased its habitat. It was intro-
duced into California and has since
ranged northward through British
Columbia.
Characteristics in Captivity
Opossums found as infants (furred,
beginning to spend time outside the
pouch) can be successfully hand reared
and bonded to their human caretakers.
Virginia opossums are inoffensive,
quiet, gentle and non-aggressive. They
learn to urinate/defecate on newspa-
pers in designated areas of a home and
even may come when called. They like
to cuddle and will curl up in one’s lap
or enjoy riding around on their care-
taker’s shoulders.
House opossums should be spayed
or neutered. In females, this decreases
the likelihood of chronic urogenital
tract infections. In males, neutering
decreases scent marking and odor.
As pets, the biggest challenge may be
to prevent obesity by providing
sufficient exercise, as opossums tend to
be rather lazy. They startle easily and
don’t usually interact or play with
other pets, so human supervision when
the opossum is out in the house is
recommended. A frightened pet
opossum tends to run back to its
cage/bed or other place of safety.
One deterrent to having opossums as
pets in the Eastern US and California is

the zoonotic potential of Sarcocystis,
which opossums may carry and which
can also cause major problems for
horses, sea otters and Old World
psittacines; therefore, one needs to
exercise caution when handling feces.
Stools should be examined frequently
for protozoa.
Anatomic Variations
Virginia opossums have five toes,
including an opposable thumb on both
the front and back feet. The dental
formula is 5/4, 1/1, 3/3, 4/4. The brain
size is one-fourth that of a cat of com-
parable weight. The female’s pouch has
a variable number of nipples. The
vagina is forked as with all marsupials,
and the opossum has two separate
uterine horns. Ovariohysterectomy
may incorporate the lateral vaginas,
but care must be taken to separate the
ureters that loop between the central
and lateral vaginas. Anal glands are
present in both sexes and secrete a
greenish-colored fluid.
The opossum’s fur is rather woolly
instead of smooth and can be found in
nearly any color from black to white
and, in some regions, nearly a cinna-
mon color. Cinnamon opossums have
shorter fur than normal-colored
opossums. True albinos with pink eyes,
ears, feet and tail are found. Another
mutant has white fur but normally
pigmented skin.
Behavior
Free-ranging Virginia opossums prefer
to be solitary. Males roam in the spring
seeking mates. Young opossums may
hang from tree branches with their
scaly, prehensile tail, although adults
are too heavy to do so. Adults may use
the tail to carry bundles of leaves or
bedding materials.
The Virginia opossum is nocturnal
but may adjust somewhat to a human
schedule, particularly if it is fed during
daylight. Opossums can run, climb
trees and dig under fences. They can
make four distinct vocalizations:
hissing, clicking, growling and screech-
ing, all of which may be used in
aggressive actions. When threatened,
the opossum may hiss and then freeze
in position with its mouth slightly open
showing the teeth. It can also go limp
and feign death, which is the classic
“playing ‘possum” pose.
Housing
Immature animals, pairs or individual
opossums may be housed in caging
45 cm x 75 cm with a sloping roof 80
cm at the highest point and 35 cm at
the lowest. Adults may fight if the
quarters are too small. Standard caging
for rabbits with a solid floor may also
be used. Large groups may be housed
in gang yards measuring 100 feet x
150 feet.
Appropriate bedding includes
recycled newspaper that has been
shredded or pelleted. A nest box (30 cm
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DVM 39
Vital Statistics
Average life span (captivity): 7 years
Life span (free ranging): May survive
only 2 winters
Body weight: Adult females 2 kg
Adult males 4-5 kg
Body length (including tail): Approx 91 cm
Cloacal body temperature: 32.2-35.0°C
(90-95°F)
Blood volume: 5.7% of body weight
Heart rate: 70-100 beats/min10
140-228 beats/min12
Respiratory rate: 25-40 breaths/min
Water consumption/day: 100-150 ml
Food consumption/day: 150-200 g
Environmental temperature: 10-30°C
(50-86°F)
Ideal relative humidity: >58%
Puberty: 6-8 mo
Sexual maturity: 12 mo
Breeding season:
Early spring: 6-7 weeks
Early summer: 1-2 months
Estrus: Polyestrous: 23- to 28-day cycle
Estrus lasts 1-2 days
Ovulation: Spontaneous
Litters per year: 1-2
Gestation period: 12-13 days, at which
time the fetus migrates
to the pouch and
attaches to a nipple
Litter size: 8-20 embryonic young
Birth weight: Approx 2 g
(size of a honeybee)
Vibrissae appear: 34 days
Hair on back: 43 days
Eyes open: 56-64 days
Weaning age: 10-12 weeks
Milk composition: 86% water, 4.7% fat,
4% protein, 4.5% sugar
The opossum has an opposable thumb on both
the front and back feet.
Opossums tend to be lazy and must be
encouraged to exercise.

x 45 cm x 40 cm) should be provided
and can be attached to the outside of
the cage.
Environmental temperature ranges of
10-30°C (50-86°F) are acceptable with
22°C (72°F) considered the most
appropriate. The environmental
humidity should be greater than 58%.
Diet
The diet eaten by free-ranging Virginia
opossums is truly omnivorous: any and
all green and yellow vegetables, grass,
fruit, carrion, snails, slugs, worms,
insects, flies, earwigs, roaches and other
insects, rats, mice, snakes, amphibians,
eggs, crayfish and fish. They may eat
birds but rarely will eat the entire
carcass.
In captivity, they can be fed a varied
diet that includes good quality dog
and/or cat foods, various vegetables,
fruits, an occasional egg, supplemental
calcium and vitamin A, live foods (such
as crickets, slugs, mealworms) and
yogurt. Exact formulations have been
developed for different life stages
(www.opossum.org).
■ Suggested Diet #1: Commercial dry
cat food ad lib supplemented daily
with horsemeat-based canned dog
food, banana, potato and apple.
Sprinkle fruit and potato with calcium
carbonate.
■ Suggested Diet #2: Dry commercial
dog food ad lib supplemented with
horsemeat-based canned dog food,
fruit and vegetables. Sprinkle fruit and
vegetables with calcium carbonate.
Commercial dry hedgehog diet is
being used in place of dry dog/cat
food. No feeding trials have been
performed, but hedgehog diets are
generally lower in fat than dog and cat
foods, which may help control weight.
Sexing
Being a marsupial, the female opossum
has a pouch and marsupial pelvic
bones. The male has a forked glans
penis that is posterior to the scrotum.
Castration is performed as in the sugar
glider (see Lightfoot T: Sugar glider
orchiectomy. Exotic DVM 1[4]:11,
1999), and excess scrotal tissue may
need to be ablated.
Reproduction
Behavioral signs of estrus in the female
may include excessive salivating and
rubbing on objects. The male makes a
peculiar clicking sound when he
detects a female in estrus. Pet females
may urinate more frequently and may
emit a musty odor, whereas a healthy
non-estrus female has little to no body
odor. There are two distinct breeding
periods: one is a short period of high
breeding activity covering 6-7 weeks in
the early spring. The second is a longer,
less intense period beginning 2-4 weeks
later that lasts for 2 months into early
summer. Although the female is
smaller, she can kill a male if she is not
40
EXOTIC ANIMAL CARE
First Visit/Annual
Examination
◗Physical examination (ears should
not have crusty margins; this may be
due to either mange or “crusty ear,”
a bacterial dermatitis)
◗Diet and husbandry review
◗Dental, oral examination
◗Fecal (normal feces should resemble
cat feces; perform stool flotation,
smear, sedimentation for parasites,
protozoa with worming as indicated)
◗CBC/chemistry panel
◗Radiographs to check bone density,
cardiac size
◗Additional tests: cultures (pouch, any
exudates, discharges), biopsy
(masses, crusty lesions), skin
scrapings/ectoparasite examination,
ECG, echocardiography
Common Clinical Conditions
◗“Crusty ear” (ear mange often with
secondary bacterial infection)
◗Cardiomyopathy (includes streptococ-
cal endocarditis, dilative and
hypertrophic cardiomyopathies,
heartworms - Dirofilaria)
◗Metabolic bone disease
◗ Septicemia (particularly in rescued
“pouch” babies)
◗Necrotizing fasciitis (streptococcal
infections)
◗ Bronchopneumonia (Bordetella
bronchiseptica, Pasteurella
multocida)
◗Endoparasites (intestinal, respiratory
tract nematodes)
◗Ectoparasites (fleas, ticks, mites)
◗Obesity
◗Malnutrition
◗Urogenital tract infections, chronic
nephritis
EXOTIC VOLUME 6.6
DVM
To prevent obesity, dry food may need to be
limited and fed as meals rather than ad lib.
Scrotal sac in the male.

in estrus and not interested in breeding.
Copulation lasts 20-40 minutes with
the animals lying on their sides. After
mating, they each go their separate
ways and remain solitary. Females may
have a second litter in the same season.
After emerging from the pouch,
youngsters will be carried on the back
of the female until they are indepen-
dent.
Restraint
Most opossums will urinate/defecate
when initially picked up. Successful
control can be maintained by using a
cat restraint bag or wrapping the
opossum as a “burrito” in a towel.
Blood Collection
The lateral tail vein may be accessed
for blood collection in younger animals
without scarred tails. There are also
ventral veins on either side of the
coccygeal artery. An 18- to 20-gauge
needle without a syringe should be
inserted blindly into the ventral aspect
of the tail and the blood allowed to
flow. Pressure must be applied for
several minutes to prevent hematoma
formation. The cephalic and a tibial
(saphenous) veins can also be accessed,
and pouch veins can be used in the
female.
Zoonotic Potential and Health
Concerns
Virginia opossums may be carriers of
Leptospira spp., Francisella tularensis
(tularemia), Erysipelothrix rhusiopathiae,
Trypanosoma cruzi (Chagas’ disease),
Sarcoptes scabiei, Trichophyton spp.,
Mycobacterium spp., ticks carrying
Borrelia spp. or Rickettsia spp. (Rocky
Mountain spotted fever, typhus),
pseudorabies, Western equine
encephalitis, rabies (rare, fairly resis-
tant) and Sarcocystis sp. Sarcocystis
neurona is major pathogen to horses
(equine protozoal myeloencephalitis)
and hoofed stock, and the Virginia
opossum is the definitive host. Horses
become infected by ingesting feed or
water contaminated with feces from the
opossum. Salmonella spp. have been
recovered from clinically normal
animals.
Virginia opossums are often heavily
parasitized. Other documented para-
sites include: Besnoitia jellisoni,
Physaloptera, Mesocestoides spp., flukes,
nematodes in the gastrointestinal tract
and lungs, trichomonads and other
protozoa.
Injection Sites
◗
Intramuscular: thighs, arm muscle
mass
◗
Subcutaneous: Intrascapular, flank
area
◗
Intravenous injections can be given in
pouch veins or the lateral tail vein.
◗
Intraosseous catheters can be placed
in the femur as in other mammals.
What Every Owner Should
Know About Virginia
Opossums
◗Prompt veterinary care should be
sought for an initial evaluation of an
opossum.
◗Many infants need special care
after rescuing as they may be
injured or ill after nursing on a dead
mother.
◗To raise an abandoned animal with
the intention of releasing it, several
opossums should be raised
together and none should be
handled.
◗Feces should be handled cautiously.
◗Food should be restricted and
exercise encouraged to prevent
obesity.
◗Fresh food and water should be
available at all times.
◗ The cage must be kept clean and
dry to prevent foot problems.
A tourniquet is used to access the tail vein. The tail is positioned for blood collection.
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DVM 41
Illustrated is an effective method for restraining
a Virginia opossum.

EXOTIC VOLUME 6.6
DVM
42
Drug Route Dosage Comments
Alfaxalone-alfadolone
acetate
IV 0.1-0.2 ml/kg Immobilization sedation
IM 0.25-0.5 ml/kg
IV 15 mg/kg
Aspirin PO 18 mg/kg q72-96h Cardiac disease
Atropine IM, IV, SC 0.02-0.04 mg/kg Control salivation during sedation
Butorphanol IM, SC, PO 0.1-0.5 mg/kg q6-8h PRN Analgesic
Cisapride PO, IM 0.25 mg/kg q8-24h GI motility enhancer
Dexamethasone IV, IM, SC 0.2 mg/kg q12-24h Antiinflammatory
Dexamethasone IV, IM, SC 0.5-2.0 mg/kg Shock
Diazepam IM, PO, IV 0.5-2.0 mg/kg Calming, Higher dosages IV for seizures
Digoxin PO 0.0011-0.0012 mg/kg q24h Cardiac disease, Monitor like cat
Enalapril PO 0.22-0.44 mg/kg q24h Cardiac disease, Monitor like cat
Enrofloxacin PO, IM, SC 2.5-5 mg/kg q12-24h Antibiotic, May cause tissue necrosis SC, IM
Flunixin meglumine SC, IM 0.1-1 mg/kg q12-24 h NSAID, Short term use only
Furosemide SC, IM 1-4 mg/kg q 6-8 h Diuretic
Furosemide PO 1-5 mg/kg q12h Diuretic
Gentamicin SC, IM, IV 1.5-2.5 mg/kg q12h Antibiotic, Fluid support necessary
Glycopyrrolate IM, IV, SC 0.01-0.02 mg/kg Control salivation during sedation
Griseofulvin PO 20 mg/kg q24h x 30-60 d Antidermatophyte, Trichophyton spp.
Ketamine IM 30-50 mg/kg Immobilization
Ketamine +
medetomidine
IM 2-3 mg/kg ket
+ 0.05-0.1 mg/kg med
Immobilization, Reverse meditomidine with atipamezole
0.05-0.4 mg/kg IV
L-carnitine PO 100 mg/kg q12h Cardiac disease
Levamisole PO 10 mg/kg Anthelmintic
SC 6 mg/kg, repeat every 3-4 weeks Antiparasitic
PO, SC 3 mg/kg every 3-4 weeks Immune stimulation, Adjunctive therapy
Meloxicam PO, SC 0.2 mg/kg q24h NSAID, Analgesic
Metoclopramide IV, IM, SC, PO 0.05-0.1 mg/kg q6-12h PRN GI motility enhancer
Piperazine PO 100 mg/kg Anthelmintic
Prednisolone IM, SC, PO 0.1-0.2 mg/kg q24h Corticosteroid
Propranolol PO 0.55-1.10 mg/kg q12-24h Cardiac disease, Monitor like cat
Sulfadimethoxine PO 5-10 mg/kg q12-24h Antibiotic, Make sure well hydrated
Trimethoprim/sulfa IM, PO 10-20 mg/kg q12-24h Antibiotic, Make sure well hydrated, SC may cause necrosis
Vitamin B complex IM 0.01-0.02 ml/kg Vitamin, Be careful of “sting,” Administer under anesthetic or dilute
Vitamin E PO 25 mg/animal/day Vitamin
Vitamin K SC 2 mg/kg q24-72h Adjunctive therapy for cardiac, liver disease
Yohimbine IV 0.2 mg/kg Reverse xylazine
Table 1. Medication and Anesthetic Dosages
Virginia opossums have carnivore/ omnivore gastrointestinal tracts and follow carnivore guidelines for antibiotic choice.
Dosages are anecdotal as reported in the literature.
EXOTIC ANIMAL CARE
Table 2. Electrocardiogram Measurements11
Lead Heart
Rate
B/M
P-R
Sec
QRS
Sec
QR
MV
Q-T
Sec
T MV T Sec P MV R-R
I200 0.08 0.02 0.6 0.14 0.1 0.06 0.01 0.32
II 200 0.08 0.03 1.7 0.14 0.1 0.08 0.01 0.32
III 200 0.08 0.30 1.0 0.14 < 0.05 0.06 < 0.01 0.32

Parameter A
*
B
*
RBC (10
6
/mm
3
)3.3-5.9 3.4-6.5
PVC (%) 28-47 33-51
Hgb (g%; g/dl) 8.3-16.2 11.7-17.9
MCV (µm
3
)64.7-102.9 73-113
MCH (pµg) 22.5-35.9 24.4-39.5
MCHC (g/dl) 28-43 32.7-40.0
WBC (10
3
/mm
3
)14.0-22.9 3.9-12.6
Neut (%) 12-67 11-48
Lymph (%) 13.0-67.5 26-82
Mono (%) 0-2 0-8
Baso (%) 0-2 0-3
Eosin (%) 2-15 6-17
Total protein (g/dl) 5.6-8.0 3.8-7.2
Albumin (g/dl) 0.2-0.9 0.3-4.9
Globulin (g%) 3.7-7.1 —
BUN (mg/dl) 23-60 23-38
Creatinine (mg/dl) —0.4-7.3
Glucose (mg/dl) 99-145 64-130
Uric acid (mg%) 0.9-2.2 —
Total bilirubin (mg/dl) 0.3-0.8 0.1-0.8
Cholesterol (mEq/L) 80-151 85-203
Calcium (mg/dl) 9.6-11.2 9.7
Phosphorus (mg/dl) 4.6-8.2 2.1-7.7
Alk phos (IU/L) —137
SGOT (AST) (Ku)(IU/L) 250 339
ALT (IU/L) —
68
Na (mEq/L) 143-155 101-129
K (mEq/L) 4.1-6.1 3.1-5.1
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DVM 43
Table 3. Hematologic and
Biochemistry References Ranges
*A. Wallach & Boever
11
B. Ness
6
Scout radiographs of a healthy 6-month-old female Virginia opossum.
Shown is a severe case of osteodystrophy in a Virginia opossum.
References and Further
Reading
1. Andrews FM, Bernard WV, Furr MO,
et al: Diagnosing equine protozoal
myeloencephalitis. Vet Exchange,
Supplmt to Comp on CE Prac Vet
22(7A):1-16, 2000.
2. Finnie EP, Bergin TJ, Hume ID, et al:
Monotremes and marsupials
(Monotremata and Marsupialia). In
Fowler ME (ed): Zoo and Wild Animal
Medicine 2nd ed. Philadelphia, WB
Saunders Co, 1986, pp 557-593.
3. Fowler ME: Metabolic bone disease.
In Fowler ME (ed): Zoo and Wild
Animal Medicine 2nd ed. Philadelphia,
WB Saunders Co, 1986, pp 70-90.
4. Johnson-Delaney CA: Skunks and
opossums. Proc Exotic Small
Mammal Med and Mgt, AAV Conf,
2000, pp 67-71.
5. Johnson-Delaney CA: Therapeutics of
companion exotic marsupials. Vet
Clin No Am Exot Anim Prac
3(1):173-181, 2000
6. Ness RD: Clinical pathology and
sample collection of exotic small
mammals. Vet Clin No Am Exot Anim
Prac 2(3):591-620, 1999.
7. Potkay S. Diseases of the opossum
(Didelphis marsupialis): A review.
Lab Anim Sci 20:502-511, 1970.
8. Prater MR, Duncan RB, Gaydos J:
Characterization of metastatic
intestinal adenocarcinoma with
differentiation into multiple
morphologic cell types in a Virginia
opossum. Vet Pathol 36(5):463-
468, 1999.
9. Spelman LH: Vermin control. In
Fowler ME, Miller RE (eds): Zoo and
Wild Animal Medicine Current
Therapy 4. Philadelphia, WB
Saunders Co, 1999, pp 114-120.
10. Technical Information, Reference
Directory, AALAS, 2000/2001,
Memphis, 2000.
11. Wallach JD, Boever WJ: Marsupialia
and monotremes. In Diseases of
Exotic Animals: Medical and
Surgical Management. Philadelphia,
WB Saunders Co, 1983, pp 574-
611.
12. Williams CSF: Opossum. Practical
Guide to Laboratory Animals. St.
Louis, CV Mosby Co, 1976, pp
142-147.