Download basic clinical medicine of pinnipeds

PROCEEDINGS OF THE
NORTH AMERICAN VETERINARY CONFERENCE
VOLUME 20
JANUARY 7-11, 2006
ORLANDO, FLORIDA
SMALL ANIMAL EDITION
Reprinted in the IVIS website (http://www.ivis.org) with the permission of the NAVC.
For more information on future NAVC events, visit the NAVC website at www.tnavc.org
Exotics — Aquatic Medicine
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BASIC CLINICAL MEDICINE OF PINNIPEDS
Scott A. Gearhart, DVM
Sea World Adventure Park – Orlando
Orlando, FL
TAXONOMY
The Order Pinnipedia (Latin for “feather” or “fin
footed”) consists of three distinct families. The Phocidae,
or true seals, are characterized by their lack of external
pinnae, relatively small front flippers, and caterpillar-like
method of locomotion on land. They swim very similarly
to fish, with a lateral “to and fro” motion of their rear
flippers. The Otariidae, or eared seals, have external ear
flaps, have relatively large front flippers, and are able to
rotate their pelvis beneath them, allowing them to walk
on all fours. They swim by using their strong pectoral
flippers in a flying type manner. There is only one
species within the Odobenidae. The walruses have no
external pinnae, but are able to walk on all four limbs.
Another unique feature of the walruses is the long upper
canines or tusks, which are possessed by both sexes.
The pinnipeds are wonderfully adapted to their
amphibious lifestyles. The circulatory system is designed
to conserve body heat during diving, shunting blood
away from the extremities to support the brain and heart.
Thick blubber layers insulate the myoglobin-rich
muscles, which allow for maximum storage and effective
utilization of oxygen, and are extremely tolerant of lactic
acid accumulation.
BASIC HUSBANDRY AND DIET
Most pinnipeds, like other marine mammals, are
regulated by the USDA in accordance with the standards
of the Animal Welfare Act. Basic requirements for pool
size, dry resting area, water quality parameters, and so
forth are all elucidated in detail within this piece of
legislation. Walruses fall under the jurisdiction of the U.S
Fish and Wildlife Service in their enforcement of the
Endangered Species Act.
All pinnipeds should be provided with a high quality
diet of some variety. Fish such as herring, capelin,
mackerel, smelt, and sardines are routinely fed, with
squid provided on occasion. Walruses will also routinely
receive clams in their daily diet. It is also important for
the veterinarian to realize that nutritional content of feed
fishes will vary according to the season in which it is
caught. Therefore, it is recommended that one have the
diet analyzed for fat, protein, moisture, and caloric value
when a new catch is acquired. Vitamin supplementation
is provided in the form of a commercially manufactured
multivitamin (Marine Mammal Multivitamins, Mazuri, St.
Louis, MO) on a per kilogram fed basis. Of particular
importance is the supplementation of thiamin, as this is a
B vitamin which routinely breaks down with time in
frozen fish and other species containing high levels of
thiaminase, such as smelt and herring. The addition of
sodium chloride is necessary in those species kept in
fresh water environments, and is normally supplemented
at a dosage of 2–3 grams per kilogram of diet fed.
CAPTURE AND RESTRAINT
At most oceanaria holding pinnipeds, an emphasis on
behavioral training allows the veterinarian to perform a
number of medical procedures without undue stress on
either the animal or the handlers. Should this not be the
case, perhaps the most important element of the safe
capture and restraint of any potentially dangerous animal
is having an experienced, skilled staff familiar with the
species to be handled.
Nets of various sizes and configurations are routinely
used, depending on which species is to be captured.
Hoop nets, bull poles, and pole nets are examples of
restraint devices used with pinnipeds. A manufactured
device commonly known as a squeeze cage can greatly
improve the chances of a successful procedure. This
allows the animal to be restrained with a minimum of
personnel, allowing the veterinarian reasonable access
to his/her patient. If a squeeze cage is unavailable,
adequate manpower or sedation (especially with
walruses) may be necessary.
Restraint of phocids and small otariids is usually
accomplished by kneeling astride the shoulders and
neck and pinning the animal’s head down. A second
person assists by holding on to the rear flippers. Larger
otariids may require yet another person to pin the front
flippers caudally against the animal’s body. The safest
method for handling adult sea lions and walruses is via
the squeeze cage and/or sedation.
DIAGNOSTIC TECHNIQUES
With some exceptions, many of the diagnostic
procedures utilized in companion animal practice may be
pplied to the pinnipeds. Of perhaps the greatest
diagnostic value to the marine mammal veterinarian is
venipuncture, as blood sampling usually provides a
wealth of information on the animal’s clinical condition.
Interdigital veins are commonly used in most species
of pinnipeds, as they are usually the most accessible
(and farthest away from the teeth!). Samples from these
sites may be obtained by inserting a needle at a very
shallow angle over the dorsal surface of a rear flipper,
roughly parallel to the phalanges of the digits. Dilating
the veins by applying a tourniquet at the tarsal joint and
warm compresses over the site for several minutes
increases the clinician’s chance for a successful draw.
In small to medium phocids, blood may also be obtained
from a vein running medially along the plantar surface of
the tarsus.
In walruses and seals, there is a large intravertebral
epidural sinus, the preferred site for obtaining large
volumes of blood. To access this site, one introduces a
3.5- to 5-inch spinal needle into lumbar intervertebral
space caudal to L3.
The caudal gluteal vein is an excellent vessel to use
in sea lions. As a rule of thumb, it is found by palpating
the greater trochanters of the femurs, then inserting the
needle at one third of the distance between these and
the base of the tail, approximately one half to two inches
off the midline (usually about perpendicular to the lateralmost edge of the vertebra).
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The North American Veterinary Conference — 2006
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Other valuable information may be gathered from
such noninvasive techniques as the routine collection of
fecal and urine samples as in companion animals. These
samples are usually submitted for culture and cytology.
Diagnostic modalities such as radiographs, ultrasound,
and endoscopy have also often proven useful in these
species. Thermography is an extremely effective tool to
diagnose arthritides, nonspecific bite wounds, or other
lesions not always readily evident, especially at a
distance from the animal.
SEDATION/ANESTHESIA
Unless the animal is trained for husbandry type
behaviors, it is often necessary to anesthetize pinnipeds.
Diagnostic procedures that require a compliant patient,
such as radiographs, ultrasound, endoscopy, or any
other potentially painful invasive techniques require the
administration of anesthetic agents. The injectable
compounds midazolam, medetomidine, ketamine, and
others are very frequently used for sedation or as
induction agents (an excellent reference for various
anesthetic regimens is the CRC Handbook of Marine
Mammal Medicine, second edition, although a few
dosages for sedatives are listed at the end of this
manuscript). These drugs are almost entirely used in
combination with each other, and nearly always given
intramuscularly. Intramuscular injections are normally
given in the dorsal pelvic or muscles of the rear limb,
although epaxials and shoulder muscles have also been
used. On larger animals, it may be necessary to use
needles two inches long or more to ensure proper
placement of drug.
Should the animal require general anesthesia, an
important anatomic feature of the otariids should be
noted. The trachea of a sea lion is relatively short, with
the bifurcation located near the thoracic inlet. Thus,
when intubating these animals, one should ensure that
the endotracheal tube is not advanced too far past the
glottis and down into one mainstem bronchus, thereby
aerating only a single lung. This is not as critical in the
odobenids or phocids.
It is also extremely important to emphasize that that
these animals be very closely monitored while under
anesthesia as they will often become hypoxic or even
apneic as part of their natural diving reflex. One must be
sure to provide adequate assisted ventilation to ensure
proper oxygenation of the patient during any anesthetic
procedure, therefore the use of such techniques as
pulse oximetry, capnography, blood pressure monitoring,
and electrocardiography is encouraged.
COMMON NONINFECTIOUS DISEASES
Traumatic injuries are one of the more common
problems seen in pinnipeds. Intraspecies aggression,
particularly between males during mating season, is a
fairly regular occurrence, and can result in significant
lacerations in the form of bite wounds. Treatment with
appropriate antibiotics and topical cleansing and flushing
with antiseptic solutions (if practical) usually resolves
these types of issues, although abscessation has
occurred on occasion. These cases may require more
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aggressive intervention and often involve anesthesia to
remedy the problem.
Fractured teeth are also commonly seen, and are
extracted should they become sites of recurrent
inflammation or abscessation. Similarly, walruses will
often rub and cause wear on the enamel layer on their
tusks, predisposing them to a bacterial infection which
ascends through the pulp cavity into the skull. Swelling
on the side of the face over the affected tusk may be the
first indication to the clinician that a problem exists.
Without medical intervention, this type of infection may
escalate into a severe osteomyelitis (they do not have
sinuses at the bases of the tusks), which can
permanently disfigure the animal, and sometimes can
result in a chronic draining fistulous tract that may be
extremely difficult to cure. For that reason, tusk removal
is the best treatment option, once the walrus has begun
to show signs of a tusk infection.
Foreign body ingestion is another common problem
encountered in pinniped medicine. Walruses are
notorious for their destructive nature and propensity for
consuming all kinds of inappropriate items. Younger
pinnipeds should also be closely watched and attention
paid to the construction of their holding areas so as to
lessen the chance of or prevent any accidental foreign
body ingestion. Foreign body ingestion should always be
included on the list of differentials for any of those
animals who are lethargic or inappetent. Administration
of emetics is sometimes helpful, although surgical
intervention often is necessary, particularly in walruses.
Prognosis is often guarded at best in these cases, thus
prevention is crucial.
Nearly all aged pinnipeds under human care develop
lenticular opacities that progress to cataracts. Several
different etiologies such as diet, genetics, or ultraviolet
radiation exposure have been suggested, and research
is currently being conducted to help delineate a more
definitive cause. Successful manual removal of the lens
via surgery has been performed in several species.
Other ophthalmologic conditions such as keratitis and
conjunctivitis do occur with some regularity, usually as a
result of improper water quality, and are routinely treated
with topical ophthalmic solutions as in other species.
Heartworm, or Dirofilaria immitis, has been known to
infect pinnipeds. All animals held in endemic areas
should be started on a preventative as soon as the
animals are tested negative and taking solid food.
Ivermectin at 0.2 mg/kg PO is given on a monthly basis
at Sea World. The longer-acting avermectins have not
been extensively studied for their use as yet.
Neoplasias are perhaps the most frequently identified
diseases in animals at Sea World parks other than
ophthalmic conditions. This is most likely the result of
their extended life spans while under human care.
Urogenital carcinomas are very commonly diagnosed
neoplasias, and are theorized to be caused by a
gammaherpesvirus. Other types of tumors seen are
adenocarcinomas, fibrosarcomas, lymphosarcomas, and
malignant melanomas, to name a few. Complete surgical
excision is often attempted, but has been only marginally
successful in most cases.
Exotics — Aquatic Medicine
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integument and are of minor significance. Serologic
Hyponatremia has been observed in some pinnipeds
ELISA tests are available for identification of exposure to
held in freshwater habitats not sufficiently supplemented
these agents. Other viruses such as seal pox may be
with sodium chloride, but it can also affect any animals
highly contagious to susceptible animals, but primarily
that drink excessive amounts of fresh water. In the
causes a self-limiting, dermatologic disease.
author’s experience, young California sea lions who
The most important bacterial disease common to both
spend a lot of time drinking from puddles of rainwater
stranded pinnipeds and those in marine parks may be
that collect in their exhibits may show signs including
leptospirosis. It is more widely seen in California sea
dullness, lethargy, inappetence, or even suffer from
lions, but has been reported in harbor seals as well.
seizures as a result. Sodium levels may drop below
Typically, the classic signs of polydipsia, abnormal
130 mg/dl, and must be treated aggressively with fluids
urination, and abortion have been seen. These infections
containing sodium chloride. Prognosis is fair to good with
are normally treated with penicillins and tetracyclines.
prompt intervention, and it is imperative that those
Gastrointestinal diseases caused by a variety of
personnel working closely with these animals quickly
gram-negative or clostridial organisms are routinely
recognize and report any pup that may be exhibiting this
observed and are treated with appropriate antibiotics as
behavior.
dictated by culture and sensitivity. Likewise, respiratory
diseases from gram-negative bacteria such as
COMMON INFECTIOUS DISEASES
Pseudomonas occur occasionally and antibiotics are
Viral diseases are often seen in pinnipeds. Recently,
similarly administered.
West Nile Virus has been recognized as an emerging
Fungal dermatitides occur in walruses, usually as a
pathogen of importance, particularly in phocids. Some
result of the animal spending a good deal of time lying in
marine mammal parks now vaccinate their seal
their own eliminations, particularly when sleeping.
collections against this deadly illness. Morbilliviruses
Aspergillus and other fungi have been implicated as
such as phocine distemper virus (PDV) have also been
significant etiologic agents of some pneumonias in
particularly virulent agents, responsible for several
pinnipeds. Pulmonary infections frequently have been
epizootics and mass mortality in wild seals.
attributed to the aerosolization of these organisms during
Some herpesviruses have been described in most
high-pressure washing around animal habitats, and thus
species of pinnipeds and can result in serious pathologic
it is recommended that this type of cleaning practice be
discouraged.
conditions such as the urogenital carcinomas described
above. More frequently, however, they are limited to the
FORMULARY OF COMMONLY USED MEDICATIONS IN PINNIPEDS
Antibiotics
Amikacin
Amoxicillin
Amoxicillin/Clavulanic acid
Cefuroxime axetil
Ceftriaxone
Ciprofloxacin
Clindamycin
Enrofloxacin
Metronidazole
Penicillin
benzathine/procaine
Tetracycline
Trimethoprim/
Sulfadiazine
Antifungals
Itraconazole
Nystatin
Sedatives
Diazepam
Midazolam
Meperidine
Dosage (mg/kg)
7
22
22
22
22
7.5
8-11
2.5-5
10
4545–9090 (IU/kg)
Route
IM
PO, IM
PO, IM
PO
IM
PO
PO
PO
PO
IM
Frequency
BID
BID
BID
BID-TID
SID
BID-TID
BID
BID
TID
SID
22 (sea lions)
44 (walruses)
10–12 (walruses)
22–30 (sea lions)
PO
BID-TID
PO
SID
0.5–1.0 (seals,
sea lions)
1.5–2.0 (walruses)
600,000 (IU/kg)
PO
BID
PO
SID
TID
0.2
0.15
0.03–0.1
1-2
PO
IM
IM
IM
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