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INTRODUCTION

The cool wet spring appears to have caused havoc with the captive tortoise population in the UK, so I thought that an article on tortoise respiratory disease would be a good idea.

THE RESPIRATORY SYSTEM

The respiratory system of tortoises may at first glance appear a little strange; after all, everything is encased within that large bony shell and these animals have to move their limbs to breathe. But take a step back and consider the similarities between tortoises and mammals:

Now this is where things change a little between mammals and tortoises. In mammals the bronchus then sub-divides until it terminates in microscopic air sacs called alveoli, and it is across the walls of these alveoli that oxygen and carbon dioxide are exchanged. However, tortoises lack this sophistication; instead, the bronchi terminate in a honeycomb-like lung. The overall effect of the lack of subdivision and the lack of tiny alveoli in the tortoise lung means it is not as efficient as that of mammals. That does not really matter because the respiratory demands of a tortoise are about 7 times less than those of a mammal. Air that is breathed out from the lungs follows a similar but reversed path from the lungs to the outside.

The other major difference between mammals and tortoises is how breathing is achieved. Inhalation is achieved by increasing the lung volume, which causes a decrease in lung air pressure, and as a result air is sucked in. During exhalation, the lung volume is decreased causing lung air pressure to increase and so air is forced out of the lung.

How is this achieved?

In mammals, the ribs and muscular diaphragm are responsible.

But this cannot work in a tortoise! The ribs of the tortoise are fused to the inner surface of the shell and cannot move. The tortoise also lacks a muscular diaphragm, having only a thin membrane to separate the lungs from the rest of the body cavity. The lungs themselves are fixed to the upper part of the carapace. In tortoises, the shell represents a fixed volume, but by pulling the limbs in and out the pressure inside the shell (coelomic cavity) can be altered.

It is also important to realise that because tortoises lack a muscular diaphragm, they cannot cough. This has important medical repercussions, as once infection develops the tortoise cannot cough up infected material from within the lungs, and so infection tends to accumulate and make matters worse.

One last important point to bear in mind is that because there is no muscular diaphragm to divide the chest from the abdomen in tortoises (unlike mammals), any disease affecting the abdomen can also affect the lungs. For example:

Normal tortoise

In the normal tortoise at rest, there should only be slight movement of the forelimbs as the animal breathes. When undisturbed, breathing movements may only occur 4-8 times per minute; but be careful, as soon as your tortoise sees you this may increase as part of the normal fright/flight reflex. There should be no discharge from the nose, and the mouth should be closed. When the mouth is opened, the lining (mucous membranes) should be pale pink and there should be no discharge emanating from the opening to the windpipe (glottis) which is located at the base of the tongue.

Abnormal tortoise

Tortoises with respiratory disease may be lethargic, weak and anorexic. They will often have an increased respiratory rate at rest. During respiration the limb movements will usually be more exaggerated, and audible gurgling or hissing noises will frequently be noticeable. There may be a discharge from the nose, and the mucous membranes may be pale grey or, in severe cases, blue. Examination of the mouth may also reveal the presence of discharge bubbling up from the glottis. In very severe cases the tortoise may fully extend the neck and perform open-mouthed breathing as it craves air.

CASE WORK-UP

A thorough clinical examination may reveal the signs stated above and give the veterinary surgeon an indication that respiratory disease might be present. In a quiet consulting room it is also possible to auscultate the lungs using a stethoscope. However, just like human medicine the diagnosis requires X-rays and laboratory investigation.

Radiography

Radiography provides a two-dimensional black/white image of the animal using a beam of X-rays. Bone is most dense and appears white while air is least dense and appears black; various soft tissues are represented by shades of grey. The lungs of a normal tortoise look dark but the presence of any infection (pus) causes the lungs to become more opaque. An increase in visceral volume (fat, eggs etc.) reduces the lungs so although they may be clear, they are smaller than normal. As X-rays are only two-dimensional images, it is important to take at least two different views so that any problems can be pinpointed in the animal. For example, if there is a localised area of infection in only one lung it is essential to:

Lung wash

In many cases a lung wash is vital as it provides material for:

The lung wash is performed in the sedated or anaesthetised tortoise. A sterile catheter is inserted down the trachea and into the lungs. A small volume of sterile water is instilled and then aspirated into a syringe. On most occasions not all the water is recovered, but that does not matter as being sterile it will be absorbed without causing pneumonia. If the X-rays demonstrate a problem with just one lung it is important to ensure the catheter is placed down the correct bronchus. This can easily be achieved by using a curved stylet to direct the catheter into the correct lung.

Blood tests

Blood tests are quite useful; in particular, a haematology assessment enables the clinician to determine whether the tortoise is responding to an infectious disease, and if so, is the disease overwhelming the tortoise? Certain antibiotic and anti-fungal drugs can put an extra strain on the tortoise’s liver or kidneys, and so it is also important in many cases to ensure that these organs are working adequately before starting therapy. This is achieved by blood biochemistry which looks for indications of liver damage and kidney disease.

Other diagnostic procedures

There are a number of other diagnostic procedures that can be used in special circumstances:

RESPIRATORY DISEASES AND THEIR TREATMENT

There are several conditions that cause respiratory compromise and disease; these include:

INFECTIOUS DISEASES

OTHER CONDITIONS

The specific treatment of respiratory disease obviously depends on the cause of the disease and how serious the problem is. In cases of severe compromise (e.g. drowning, severe pneumonia) it is often necessary to place the tortoise in an oxygen-rich atmosphere. There are a large number of medications that can be used to treat respiratory diseases. These medications can be given by the conventional methods, e.g. orally by stomach tube or by injection. However, it has become apparent that in certain situations a more direct method is more effective.

At the Exotic Animal Centre we have been using two other approaches:

Nebulisation

This method involves placing the tortoise in a high oxygen environment. The oxygen also acts as a carrier for an aerosol of active drug, often an antibiotic or anti-fungal medication. As the animal breathes, so the active drug, in the form of minute droplets, is breathed into the lung directly into the area of infection. This method is particularly useful because it permits the use of drugs that would be considered dangerous if administered by injection (e.g. Neomycin aminoglycoside) or not absorbed and hence ineffective in the lungs if dispensed by stomach tube (e.g. Nystatin anti-fungal).

Intrapulmonary injection

This method is particularly useful when dealing with focal, discrete infections involving one lung. Radiographs are used to pinpoint the infection, and then a hole is drilled through the carapace of the anaesthetised tortoise directly above the site of infection. A sterile catheter is inserted into the area, and capped using an injection port to prevent any communication between the lung and outside. The injection port and catheter are tissue bonded to the shell to form an air and water tight seal. Medication can then be injected directly into the site of the infection, which means the concentration of drug at the infection site is much greater than would be achieved by oral or standard injection methods. Alternatively, the same lung drug concentration can be achieved using a smaller intrapulmonary dose than oral or standard injection dose. This is especially important when using potentially toxic drugs.

PREVENTION OF RESPIRATORY DISEASE

The prevention of disease is what we should really all be aiming for and there are four cardinal rules:

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