CERTAIN ASPECTS OF THE VETERINARY CARE OF CHELONIA
STEPHEN
DIVERS B.Sc.(Hons.), M.I.Biol., C.Biol., B.Vet.Med., M.R.C.V.S.
B.C.G.
Veterinary Liasion Officer
Elands
Veterinary Clinic, Station Road, Dunton Green
Sevenoaks,
Kent TN 13 2XA.
Tel:
01732 452333 Fax:
01732 741614
Presented
to the British Chelonia Group Symposium, 27 April 1996
The Structure
and Diseases of the Chelonian Shell
Turtles,
tortoises and terrapins are unique amongst reptiles in being amongst the oldest
living relics of the class Reptilia and
possessing a bony shell. This shell
is undoubtedly the most obvious physical characteristic of this order comprising
of 244 species in 2 suborders, Pleurodira
and Cryptodira.
Structure of
the Shell
The
shell is composed of an upper domed part called the carapace and a lower flatter
plastron. The two parts are joined
by bridges on either side with openings at the front and back for the head and
limbs. The shell is an extension of
the skin and merges with the skin that covers the limbs and head.
The outer layer of shell is made up of horny shields or scutes arranged
in a specific order and the colour of the shell varies widely from species to
species.
The
shell is developed from a standard skin structure with a dermal and epidermal
components, however the lower layer or dermis has become ossified (bony) and the
epidermis has been modified into a horny keratinised outer covering.
The shell starts to develop within the incubating egg but this process is
incomplete by the time of hatching. Continued
shell growth and development is dependent upon an adequate intake of calcium and
exposure to ultraviolet light for endogenous vitamin D3 production.
The shell grows by producing deeper larger scutes which are visible under
the smaller older scutes, such that a rim of growth is obvious.
In most cases, the old scutes are retained giving rise to a number of
rings, however these scutes may be shed (as in Red-eared Terrapins) making
ageing from counting the rings very imprecise.
The ribs and spinal column are fused to the carapace.
This gives the chelonia the unique attribute of having their pectoral
(shoulder) and pelvic (hip) girdles within their rib cage!
Diseases of
the Shell
Considering
the large nature of the shell and its primary function as an integument (skin)
structure the shell can be diseased by a number of different organisms and for a
number of different reasons. Bacterial,
fungal, viral and parasitic infections have been documented, while of the
non-infectious problems, metabolic bone disease, thermal and chemical burns,
trauma and systemic disease are most often encountered.
The majority of these diseases are caused or exacerbated by poor
husbandry (environment and nutrition) and although potentially serious and even
life-threatening, prompt veterinary attention carries a good prognosis in the
majority of cases.
Primary
infectious diseases are those affecting the integument with, at least initially,
no internal or systemic involvement. Bacteria] shell
disease is quite common and frequently gram-negative bacteria are cultured
and isolated. Aquatic species tend
to be affected by poor filtration and unhygienic water conditions.
Septicaemic cutaneous ulcerative disease (S.C.U.D.) is a severe bacterial
shell infection often caused by Citrobacter
spp. bacteria which is seen commonly in aquatic, soft shell turtles (Trionyx
spp., Apalone spp.). The terrestrial species appear more prone to
shell damage from blunt trauma or thermal injury, which can become secondarily
infected.
Fungal
diseases are
less common and often seen where skin cases are inappropriately diagnosed and
treated with broad-spectrum antibiotics by owners. In these instances the use of broad-spectrum antibiotics has
killed all the bacteria present, including the normal bacterial flora of the
shell, enabling a secondary fungal infection to take place.
Primary fungal infections are more commonly diagnosed in the aquatic
species: wound debridement (exposure and cleaning), fungal culture, and
application of specific anti-fungal preparations are often successful.
Viral
diseases represent
a relatively rare diagnosis in reptile practice but this is probably a
reflection of the difficulty in isolating and identifying viruses and the fact
that viral lesions can quickly become contaminated with a secondary bacteria or
fungus. Primary viral skin diseases
have been identified in turtles (e.g. grey patch disease of green sea turtles)
but the lesions are usually restricted to the skin and not the shell.
Viral bodies are extremely small and beyond normal light microscopy.
Ectoparasitic
diseases are less commonly seen in chelonia than
they are in snakes and lizards, but ticks are still seen with frequency
especially in wild caught specimens. However,
in most cases these ectoparasites feed on the softer skin tissue adjacent to the
shell.
Primary
non-infectious diseases are more common in the solitary pet reptile.Thermal
burns may be acute due to extreme damage such as those induced by overhead
ceramic heaters. Alternatively, the
tortoise may find itself in a garden bonfire, having previously sought sanctuary
within a pile of garden refuge. Garage and house fires, although sporadic and
thankfully rare occurrences, have resulted in serious burns to the housed or
hibernating chelonians. Thermal
injury can be much more insidious in nature and the use of under floor heat mats
can certainly cause chronic damage to the plastron.
In these cases particularly, the thermal injury does not become apparent
until secondary bacterial infection becomes obvious.
Trauma is
often seen in garden tortoises following an attack by a dog or fox, while
hibernating species may succumb to the effects of rats if the hibernating
quarters are not rodent-proof. Accidental
damage caused by the careless use of mallets, sledgehammers, and lawnmowers can
often lead to severe damage to the carapace with shell fractures and
displacement of the fragments into the chelonian body.
Damage to the rim of the shell can often be treated conservatively by
adopting a standard veterinary approach to wound management.
Deep, central wounds to the carapace and plastron can be primarily
repaired with the use of fibreglass patches and epoxy resin, although it must be
stressed
that such repairs should only be
carried out on fresh, uninfected wounds. The
shell is living tissue, and such damage may cause profuse bleeding, resulting in
life-threatening anaemia and the need to perform blood transfusions in extreme
cases. The sensitive nature of the
bony shell also makes anaesthesia and analgesia essential before any surgical
shell repair is undertaken. Infected
wounds must be thoroughly debrided and cleaned under anaesthesia and the use of
wet dressings is usually employed. Primary
repair is unlikely to be recommended but may be possible if all infection is
removed and the infectious disease controlled.
Chemical
burns are a rarity but the author has seen a case of a chemical shell burn due
to contact with industrial hydrochloric acid.
Obviously, such materials have no place in proximity to any animal.
Systemic
diseases can affect many organs including the shell. Metabolic bone disease is a term used to describe a group of
diseases affecting the bones of the skeleton and shell dermis.
An absolute lack of calcium, a diet with a calcium:phosphorus ratio of
less than 1:1, a lack of vitamin D 3
(usually by deprivation of ultraviolet
light) or a high protein diet can produce this problem.
The initial sign is often a softening or pyramiding of the shell but as
the disease progresses so the pull of the thoracic and pelvic muscles cause the
carapace to sink giving the shell a saddle-like appearance.
Radiographs and blood calcium and phosphorus evaluations provide the
diagnosis and although treatment will arrest the condition and improve the
strength of the bones the distortion to the shell is permanent.
Any
disease which affects the metabolism of the chelonian will affect the shell.
Stunting of growth due to undernutrition is demonstrated by a lack of
growth lines, although more frequently extensive growth lines indicate the
commoner problem of overfeeding. Septicaemia
is life threatening and may cause haemorrhages under the scutes giving a diffuse
speckled red pattern to the shell. Young
growing animals are particularly affected by nutritional imbalance.
Shell Health
Many
owners prefer to clean their tortoise's shell and apply oil to add a decorative
shine to the carapace. Keeping the
shell clean is important and will help prevent shell infections.
However, the use of topical oils, although not detrimental, have no real
beneficial effect on the health of the shell.
Good husbandry and sound nutrition are what are important for a healthy
shell.
Measuring
the length of the horizontal carapace can give an indication of the health
status of a chelonian when compared to the animal's weight.
This technique is known as the Jackson Ratio and was first described by
Jackson in 1980. These
weight-length graphs have been produced for a variety of species, in particular
the Mediterranean tortoises (Testudo
graeca and Testudo hermanni) and the red-eared terrapin (Trachemys scripta
elegans). In summary the shell is an indicator of the well-being of
any chelonian and so should be inspected with regularity.
THE TORTOISE
CAESAREAN
Reproductive
problems in tortoises represent a challenge to the veterinary surgeon, not least
because in order to gain access to the reproductive tract (ovaries, oviducts and
shell glands) one must first negotiate the shell.
Its surgical uniqueness is somewhat more problematical and of immense
interest to the reptile surgeon. In
most cases, reptile (particularly lizard and snake) outer surfaces can be
incised with a sharp scalpel blade providing access to the deeper tissues and
organs. However, with a tortoise
some form of high powered surgical saw is needed!
Reproductive
Problems
Surgical
access to the coelomic cavity of the tortoise (similar to the abdominal cavity
of mammals) is often employed to remove abnormal eggs from the oviducts/shell
glands. Affected animals often
present in a state of hyperactivity (nest searching) or if left unaided, become
lethargic and anorexic. A radiograph or X-ray will confirm the presence of eggs.
If the eggs appear to be normal in both size, shell thickness and
calcification, then all that may be required is the provision of a suitable nest
site such as loose soil/sand mixture in a sunny position within the garden
enclosure. If this fails to work
then 1-2 injections of the hormone oxytocin are usually effective in stimulating
egg laying as long as the blood calcium levels are adequate.
If the eggs are abnormal on the radiograph, that is to say they are too
large or of an abnormal shape to fit through the pelvic opening, or if an egg is
broken then induction of egg laying may actually make matters worse.
In these, quite rare cases, it is necessary to perform surgery.
Anaesthetic
and Surgical Procedure
Before
surgery, it is important to ensure that the animal is stabilised.
The tortoise may be dehydrated, have a severe egg peritonitis if a broken
egg is present or be suffering from another debilitating disease.
Blood samples for haematology and limited biochemistry enable the vet to
assess the animal's ability to undergo surgery.
The use of an intravenous or intraosseous drip which in addition to the
use of modern anaesthetics such as propofol and isoflurane makes modern reptile
anaesthesia a safe procedure in the vast majority of cases.
Once
stable, the tortoise is anaesthetised with an intravenous injection of propofol,
which causes a rapid loss of consciousness. Then, a small tube is inserted into the wind pipe so that
oxygen and the anaesthetic gas, isoflurane, can be administered during the
operation. The tortoise is then
turned upside down and the plastron is thoroughly scrubbed and disinfected.
There are various instruments to cut through bone, but I use an
oscillating sector plastor/bone cutter. The
serrated edge oscillates, it does not rotate, so it will cut through rigid bone
but merely wobbles soft tissue causing less damage.
Using this saw, a bone flap is cut in the plastron (underside of shell)
being careful not to go too deep and risk damaging the two paired veins that lie
just under the plastron. The bone
flap is cut in the preoperative room as this generates dust, but once the flap
has been cut, the tortoise is moved into a sterile theatre before the square of
shell is removed to reveal the body cavity.
When
in theatre, the tortoise is placed on a heat mat and connected to an ECG and
respiratory monitor. A sterile,
transparent drape covers the tortoise and the shell flap is removed and placed
in sterile saline to keep this bone tissue alive and healthy as it will have to
be replaced at the end of the operation. The
coelomic membrane is cut between the two
ventral veins to reveal the body
cavity. It is usually possible to
see the heart beating during the operation.
Once in, it is a relatively simple task to locate the eggs within the
oviducts and remove them via single or multiple salpingotomy (oviduct/shell
gland) incisions. If there are only
1 or 2 retained eggs then they can be removed.
However, if there is a peritonitis infection due to a broken egg, a large
number of retained eggs or the tortoise has a history of reproductive problems,
then a complete ovariohysterectomy removing both ovaries, oviducts and shell
glands is performed - essentially neutering the female and preventing any future
reproductive problems.
Once
the reproductive surgery has been completed the coelomic membrane is sutured
back or stitched in place and the bone flap is replaced in its original
orientation. The shell is cleaned
and dried before 4-6 fibreglass mesh patches and fibreglass resin are used to
effect a rigid and permanent repair to the shell. Post-operatively, the tortoise is maintained on a drip at 28oC
and may be given antibiotics if required. In
uncomplicated cases the tortoise usually starts eating by the next day and is
then able to go home.
Gastro-Intestinal Nematode Parasites Of Mediterranean
Tortoises (Testudo spp.) Mediterranean tortoises consume large
quantities of food during the warm summer months. However, these conditions of plenty also provide a tortoise's
intestinal worms with an ideal environment in which to thrive and reproduce.
During the summer months tortoises may not exhibit any obvious signs of
parasitism. However, during post
hibernation period of late spring or the cooler months of autumn, parasitic
disease and even death can occur because of the effects of intestinal worms.
These problems can be prevented or at least minimised by appropriate veterinary
care.
Keymer
(1978) reported the two main groups of intestinal worms to infect Testudo
tortoises to be Anisakoidea (Angusticaecum
spp.) and Oxyuroidea
(Tachygonetria and Atractis spp.).
This study, based on the postmortem examination of 144 tortoises, reported that
nematode infestations were found in 43.8% of all the tortoises examined.
Holt, Cooper and Needham (1979) examined 70 live tortoises and diagnosed
gastrointestinal worms in 30%. Therefore,
scientific evidence suggests that your tortoises have a 30-40% chance of being
currently infected with worms!
The
life-cycles of many reptile parasites have not yet been conclusively described.
The life cycle of the oxyurid roundworms is direct without intermediate
hosts, while the life cycle of most members of the Anisakoidea roundworms is
indirect. However as far as I am
aware no intermediate host for the tortoise Angusticaecum
has been identified and therefore this parasite probably has a direct life
cycle as well. The direct life
cycle of these two important worms results in the adult worms within the
intestines producing thousands of eggs which are deposited in the garden (or
vivarium). These eggs hatch into
larvae which, after a short period of time, become infective and are ingested
with food as the tortoise feeds. During
the autumn the eggs may remain dormant on the ground and only develop into
infective stages during the following spring.
The practical outcome of these biological features in the captive
situation of confined space is a high density of infective material leading to a
high worm burden in the tortoise.
Intestinal
Worms and Disease
It
is probably true to say that most tortoises with worms do not show obvious
clinical signs. However, these
parasites compete with the tortoise for the food material within the intestines,
and food that an intestinal worm uses is at the expense of the efficiency of the
host (tortoise). Therefore they are
detrimental being responsible for reduced growth and breeding performance.
If a female tortoise has a moderate worm burden and lays 5 eggs a year,
it may be possible to improve her breeding output to 6 eggs a year if the worm
burden was eliminated or reduced. Similar
improvements in growth rate may also be attained in juvenile specimens that have
their worm burden reduced. These
subtle improvements may not seem important, but one extra hatchling would
probably cover the costs of health checks and worming for both the adults in the
year to come!
Worm
burdens become more of a problem during periods of reproduction and stress,
especially during early spring and autumn. Clinical signs of worms include
diarrhoea, regurgitation, anorexia, poor weight gain/weight loss, breeding
failure, adult worms passed in faeces, and even death can occur.
There
is also a potential problem of abnormal host-parasite relationships. Testudo
tortoises and the roundworm Angusticaecum have evolved together over thousands
of years, and consequently in the wild, worm and tortoise live in a steady
state. An efficient parasite does
not kill its host. In the
confinement of the vivarium or small garden parasite numbers can increase to
abnormally high levels, capable of causing disease in the natural host.
However, if an unnatural host such as a box tortoise or leopard tortoise
becomes infected it is possible that, because the host has never been exposed to
a particular parasite before and therefore has no inherent defence against it,
small numbers of parasites could cause severe disease and even death.
This is the reason why Entamoeba
invadens, a normal gut protozoon of aquatic chelonia (natural host) can
cause a fatal amoebic dysentery in snakes (unnatural host).
It is obvious that different species of reptiles/ amphibians should not
be mixed in captivity. Sometimes
parasites cause disease when they take the wrong route in the host and arrive in
a different organ.
Diagnosis and
treatment
The
chances are that existing tortoise populations will be infected with worms.
A veterinary surgeon will often make a diagnosis of parasitism based upon
the examination of a fresh faecal sample. Depending
upon the type of parasite your veterinary surgeon will choose the most
appropriate drug. I have found
oxfendazole to be most effective against nematodes but other benzimidazole
anthelmintics can be used, albeit repeatedly.
Never attempt DIY diagnosis and treatment as effective treatment
necessitates proper egg identification, and certain, commonly used,
antheimintics (ivomeclin) can have fatal consequences if used in chelonia.
In general worming is recommended during the spring (March/April/May) and
again in late summer (August, September).
Surely
our reptilian pets deserve the same level of care as our domestic dogs and cats.
A routine health examination, faecal check and worming protocol will go a
long way to improve tortoise health and should therefore form the basis of your
chelonian health programme. Many
owners are now having all new tortoises blood screened so that their, normal'
blood results can be filed and used to assess a 'sick' blood result when the
tortoise falls ill.
Finally,
reptile health insurance is currently available through Exotic Direct on
0171
6806009/6806016.
References
and further reading
Beynon
P.H, Lawton M.P.C. and Cooper J.E. (1992). Manual of Reptiles. BSAVA,
Cheltenham.
Frye,
F.L. (1991). Biomedical and
Surgical Aspects of Captive Reptile Husbandry. Second edition. Krieger, Malabar.
Holt,
P.E., Cooper, J.E. and Needham, J.R. (1979).
Disease of tortoises: a review of seventy cases.
Journal of Small Animal Practice
20: 269286.
Jackson,
O.F. (1980). Weight and measurement
data on tortoises (Testudo graeca and
T hermanni) and their relationship to health. Journal of Small Animal Practice
21, 409.
Keymer,
I.F. (1978). Disease of chelonians:
(1) Necropsy survey of tortoises. Veterinary
Record 103: 548-552.
Mader,
D. (1 996). Reptile Medicine and
Surgery. WB Saunders, Philadelphia.