Hatchling crocodiles are delicate creatures but as juveniles and adults they are comparatively hardy animals which are not often troubled with disease as long as they are kept warm, reasonably clean and well fed. Failure to make adequate provision for these basic needs is responsible for most disease problems in captivity. The notes that follow offer a general overview of health problems and it will be apparent that prevention is usually easier and in every way better than cure.
Pooley, in his excellent pioneering work on Nile crocodile husbandry, found that young animals refused food when air or water temperatures fell below 15.6°C. This is very cold and other species would probably cease feeding at considerably higher temperatures. Coulson and Hernandez (1983) worked mainly with caimans and American alligators. It was their impression that the ideal temperature for maximal appetite and growth may be as high as 32°C. At temperatures below 25°C appetite is greatly reduced and below 20°C it is gone entirely.
Nor is there any point in force feeding cold animals or in feeding them if they can only be kept warm for a short time. If the food is not digested it will putrefy inside the crocodile and cause its death (Burton, 1978). If the food is digested the crocodile may be killed in a less obvious manner.
When a crocodile digests its food the protein is broken down into amino acids which are absorbed into the crocodile's blood plasma to be rebuilt into new proteins for the crocodile's own growth and body maintenance.
In one experiment Coulson & Hernandez force-fed a group of alligators with pieces of fish and then kept them at 15°C. They had difficulty in digesting the fish and absorbing the amino acids. Those that were absorbed were not synthesized but were still 'Loose' in the blood plasma ten days later. The authors point out that with a large and prolonged increase of amino acids in the plasma the osmotic pressure of the 'alligators' body fluids could become toxic. The reduced appetite of wild alligators in autumn may serve to protect them against being 'poisoned' by the products of their own food which they could not process in a cold period.
An experimental group of alligators kept at 20°C did considerably better when force-fed but still not well and it was concluded that the combined time required for digestion and absorption was several times as long at 20°C than at 28°C and that once the amino acids reached the plasma they were not incorporated into protein very rapidly (Coulson & Hernandez, 1983).
It is probably true to say that appetite, digestion, assimilation and growth are all affected adversely at temperatures below that which a particular species and age class of crocodiles prefers. In addition, it has been found that the immune system of reptiles is also affected by temperature (Jacobsen, 1982). If the immune system is depressed by low temperature the animal will be more susceptible to disease from organisms which it could otherwise resist.
Clearly, temperature is one of the most important considerations and with large enclosures which cannot be heated artificially, the precise location, aspect, shading or exposure of the pens should be planned very carefully (Part 1. section 8.1).
Crocodiles in a pool are surrounded by potential disease organisms. With crocodiles over a year old this usually causes no trouble as long as the animals are feeding well and the pool is not allowed to become foul with uneaten food or excreta which allows pathogens to build up to an intolerable level. Hatchlings seem to have less resistance. Obviously crocodiles in a pool which is both dirty and too cold will be at a very high risk. Some of the pathogens and the diseases they cause are mentioned in section 2.5.
In mammals low blood sugar level and hunger seem to go together. In crocodiles the relationship is not so simple. It has been found that appetite is at its lowest when blood sugar levels are also at their lowest (Coulson & Hernandez, 1983). A practical consequence of this is that crocodiles which have used up their sugar reserves because of starvation or severe stress (see 2.4) may have no appetite so that it is difficult to feed them back to health.
An acute condition known as hypoglycaemic shock (shock from low blood sugar levels) has been reported in animals subjected to cold or stress (Pooley, 1971; Burton, Cardeilhac, 1981). Visible symptoms include: snout pointing upward (star gazing) dilated pupils (wide eyed) - a first sign. tremors loss of the righting reflex (balance)
The treatment suggested by Cardeilhac (1981) is oral glucose at 3 g/kg body weight or a teaspoon of table sugar in a ounce of water for each 5 pounds of body weight. This is about 2 g in 12 ml of water for each kilogramme. It should be given by tube through the mouth.
Gout has been reported as a problem in American alligators, especially when they are being fed for maximum growth. In its early stages, at least, it can be cured simply by withholding food for a week to ten days (Joanen & McNease, 1977, 1981).
Gout in reptiles is believed to be a result of overfeeding so that excess amino acids in the blood are converted into excretory products which accumulate in the kidney tubules, joints or on the surface of internal organs (visceral gout). The first symptom is usually paralysis of the hind legs so that the animal appears to drag them. In advanced cases there is further paralysis and the crocodile may die.
In post mortem examination the deposits of excretory products (urate crystals) may be seen as a white substance in the kidneys and other affected areas (Cardeilhac, 1981; Foggin, 1985).
Gout has not been a problem in Papua New Guinea and is not commonly seen in Zimbabwe.
This is the name given to a group of bone diseases caused by abnormal calcium
metabolism. Several possible causes have been listed by Cardeilhac (1981) but, as he
points out, in captivity the disease is usually caused by a shortage of calcium. Calcium
deficiency is to be expected if crocodiles are fed boneless meat and not given access to
Symptoms include visible abnormalities of the skeleton such as a rubbery snout, loss of teeth or teeth growing out at abnormal angles. Treatment and prevention consist in giving whole animals as food (e.g. fish, rats) and/or supplementing the diet with calcium in the form of steamed bone meal, crushed bone or tricalcium phosphate.
The ideal calcium: phosphorus ration in the diet is 1:5 or 2:1. Viscera and muscle meat without bone have a calcium: phosphorus ratio of about 1:12 (Jacobsen, 1982).
The animal's body fat becomes yellowish and inflamed. Appetite is poor and there is little activity. Linear ulcers may appear in the cloaca filled with a yellowish horny material (Cardeilhac, 1981).
It is well known that excessive feeding of polyunsaturated fatty acid or rancid fish oils leads to exhaustion of vitamin E stores (Burton, 1978). This condition has been reported in alligators which were fed on oily fish such as mackerel. Such a diet is high in unsaturated fatty acids and low in vitamin E. Rancid unsaturated fatty acids are particularly troublesome so that fish must be absolutely fresh.
Cardeilhac (1981) recommends treating sick animals with 100 IU vitamin E per day.
He also recommends supplementing fish diets with 20 IU vitamin E per day or adding liver to the diet.
The writer has not observed this disease in thousands of crocodiles fed on whole, mixed sea fish.
Thiamine (vitamin B1) has occurred in American alligators which were fed on certain brackish water fish known as mullet. The fish may contain large quantities of an enzyme (thiaminase) which destroys thiamine. Cardeilhac (1981) has described the symptoms and treatment as follows:
Uncoordination and drowning
Injection of 44 mg of thiamine per kg body weight.
Diet should contain 5 mg thiamine per animal. One kg of supplement containing 1100 mg per kg should be added to 100 kg of feed.
The nervous system and the glands of the endocrine system act together during a great many bodily functions. Hormones ('chemical messengers') are released into the blood stream where they have their effect upon 'target' organs or tissues which are programmed to respond to them. Whereas the nervous system can send messages with great speed the message does not persist and it can be changed very quickly. Hormones travel slowly in the blood stream but the message can be kept there constantly for hours, days or even months.
In the endocrine system the adrenal glands are concerned with stress which may result from mating, fighting of fear. The adrenals, in all vertebrates, are located near the kidneys. In reptiles one gland lies near the anterior tip of each kidney. Each gland contains two kinds of tissue - the medulla and the cortex.
In mammals it is well known that during short periods of stress the hormone adrenalin is released from the medulla into the blood stream. This stimulates the animal in ways which prepare it for physical effort. The adrenalin soon disappears.
If the stress situation persists then another gland at the base of the brain (the pituitary) releases a hormone which in turn stimulates the cortex of the adrenal gland to release its hormones. Hormones of the adrenal cortex have profound effects which include changes in the blood chemistry. Continued stress causes the adrenal cortex to enlarge and produce more hormones. If the stress is not relieved it can cause serious illness and even death. Experimentally, rats can be killed in this way if they are forced to live in the territories of other rats or in a very crowded situation.
It has been shown (Lance, 1981) that if the relevant pituitary hormone from a pig is injected into an alligator the alligator's blood soon shows a significant rise in adrenal hormone level. Even handling and injecting the alligator with harmless saline caused an increase in adrenal hormone. Burton (1978) refers to a 'maladaptation syndrome, which in its acute form appears in reptiles as hypoglycaemic shock (see 2.3.1) but in its chronic form can be the end result of continual stress. In this state wounds fail to heal and become secondarily infected and parasites build up in the animal to overwhelming proportions. At post mortem, apart from secondary lesions, the animal will have no fat deposits and the tissues, especially the skin, tear easily. There is reason to believe, then, that crocodiles, like mammals, may show a variety of symptoms which are really the indirect result of prolonged stress.
Short periods of violent excercise may cause exhaustion in the very short term. Changes in blood chamistry associated with physical exertion are well documented in human beings but animals being chased may also experience fear.
Recently some detailed studies of the blood chemistry of salt water crocodiles were made during rest and after forced exhaustive activity (Seymour, Bennet & Bradford, 1985). The chemical changes in the blood were of the kind to be expected but were remarkable in being so severe. The largest crocodiles tested (180 kg) were the most seriously affected and it took several hours for their blood to return to normal. The researchers concluded that the 'severity of acid-base disturbance in large crocodiles could be related to their susceptibility to post-capture mortality'.
Clearly, circumstances which might produce stress, either chronic or acute, in captive crocodiles should be avoided as far as possible.
Crocodiles suspected of having an infectious disease should be isolated from healthy animals. Water from the sick pen should not be able to drain into other pens.
Organisms which may cause infectious diseases are listed below.
Shotts (1981) reviewed the data then available and concluded that most if not all bacterial diseases of alligators seemed to be secondary infections rather than primary ones. That is to say the bacteria associated with the disease had taken the opportunity to infect alligators which were already vulnerable because of some other health problem. He considered that stress had often lowered the alligators' resistance to bacterial infection.
Many of the bacteria types isolated from sick alligators in America were to be found in apparently healthy animals or in the water. In Zimbabwe, Foggin (1985) also noted that 40% of the bacteria isolated from sick crocodiles also occurred in the absence of any obvious pathology.
A very similar list of bacteria to that compiled by Shotts was obtained by Ippen & Schroder (1977) from diseased captive alligators in Germany (Table 2).
| USA l/
| Germany 2/
|% 4/|| Zimbabwe 3/
|G - Pasturella||Aeromonas||40.5||Salmonella arizona|
|Aeromonas||Salmonella||26.2||Salmonella (other types)|
1/ From Shotts 1981
2/ From Ippen & Schroder (1977) in Shotts
3/ From Foggin 1985
4/ reported prevalence
|Strep. gp. C.|
G + Staphylococcus
In Papua New Guinea a number of crocodiles which lost their appetite, became emaciated and eventually died were sent for laboratory examination but with no positive conclusions being reached. Bacterial studies revealed Aeromonas, Proteus, Edwardsiella, Escheria coli and a range of Salmonella serotypes without disease being directly attributable to any of them.
Antibiotics can be tried where symptoms indicate that bacteria are involved but Foggin points out that when antibiotics are used bacterial culture and antibiogram should be performed in a laboratory to monitor antibiotic resistance. Jacobsen (1981) also warns that the dosages of antibiotics for reptiles should be a fraction of that normally used for mammals. Some antibiotics (e.g. gentamicin, tobramicin) are effective against Gram negatives but are also very toxic. In mammals they may disappear from the blood in 8-12 hours but in reptiles the drug may still be present at high levels after 3-4 days.
Antibiotics have been tried with crocodiles in the following circumstances:
Often a sequel to other infection of the intestine, bacterial enteritis has been treated with oxytetracycline hydrochloride powder1/ mixed with food at 500 mg/kg for three consecutive days (Foggin, 1985).
Jacobsen (1982) mentions that the bacteria Pasteurella multocida and Staphylococcus aureus were cultured from alligators with a respiratory disease involving coughing, sneezing and discharge from the nostrils. Some improvement was obtained with chloramphenicol at 16 mg/kg body weight2/. Crocodiles are best injected in the muscle of the upper part of the hind limb.
Mouth rot or canker
This appears in many reptiles as swelling and redness of the gums which later becomes ulcerated and coated with a cheesy material as the tissue degenerates. The condition may by started by damage to the mouth which is then ivaded by bacteria. Vitamin C deficiency might also be involved.
Burton (1978), writing on reptiles in general, recommends gentle cleaning of the mouth, flushing with hydrogen peroxide, rinsing with saline and painting with sulphadimine or . streptomycin. A broad spectrum antibiotic such as chloramphenicol should be given by injection and vitamin C should be given daily (orally or by injection) for a week.
1/ Terramycin soluble powder (Pfizer) containing 55 mg oxytetracycline hydrochloride
2/ Chloro-25 injectable (CAPS) containing chloramphenicol 250 mg/ml.
If there is no response the antibiotic must be changed according to culture and sensitivity tests.
Foggin (1985) reports that hatchlings and yearlings are prone to this condition in Zimbabwe. At first there is a watery discharge from the eyes which may stick the eyelids together. Later the surface membranes of the eye become inflamed and cheesy. The whole eye-socket may be swollen. Streptococci and Aeromonas have been isolated from affected eyes (see also under viruses). The disease is debilitating and the animal gradually loses condition.
Treatment has included chloramphenicol/gentian violet aerosol spray 3/ preferably applied daily.
Disinfectants can be tried to prevent the spread of diseases in the sick pen. Limited experience in Zimbabwe indicates that chlorine in the water at 2-4 parts per million does no harm to crocodiles. Potassium permanganate at 10 parts per million could also be tried.
Mycotic or fungal diseases occur in all kinds of animals throughout the world. A number of fungal types have been isolated from crocodiles but, as with bacteria, they often seem to be secondary invaders. Diagnosis is difficult because similar signs can be produced by quite different agents.
Pneumonias and dermatitis appear to be the most common signs that appear with fungal infections. Candida albicans has been identified as the agent responsible for pneumonia in certain crocodiles and Aspergillus fumigatus and A. ustus have been cultured from pneumonic lesions in young captive American alligators (Jacobsen, 1982).
Many fungi, such as Candida are to be found in healthy animals, including man, where they live with bacteria. It may happen that the fungi multiply and become a problem if the bacteria are killed by antibi otics used to treat another illness. A whole range of antifungal creams and powders are available for human infections. A few antibiotics have both antibacterial and antifungal effects but, as a rule, antibiotics should not be used indiscriminately as this can lead to further problems.
Too much fat in the diet and the pools has been associated with external skin fungus (Pooley, 1971) and low temperature is said to be an important factor in mycotic infections (Jacobsen, 1981).
Foggin (1985) reports that fungal dermatitis is a common condition in Zimbabwe farms. The skin of the back has a fine white coating which may form thicker patches in the mouth. The fungus has not been identified but the infection usually disappears without treatment. Potassium permanganate as a disinfectant in the water could be helpful. Copper sulphate ("bluestone") could be added to the water used for scrubbing cement pools before re-filling with clean water.
Until recently the only report of a virus-associated disease in crocodiles was a pox virus infection in three caimans (Jacobsen et al., 1979). The animals had greyishwhite circular skin lesions scattered over the body surface and particularly on the jaws, eyelids and ear drums. Foggin (1985) reports that over four hundred hatchlings died from this disease on Zimbabwe farms in 1982. In this instance the infection appeared as brown patches on the pale belly skin which were either raised or in the form of shallow ulcers. Brown plaques usually appeared in the mouth.
3/ Pedichlor aerosol (CAPS) containing 5% chloramphenicol with gentian violet.
As the disease advanced there was shirnkage of the skin covering the head and neck and this caused deformity of the jaws and the raised part of the ear. In 1984, the disease reappeared on the same farm but was considerably less severe and caused fewer deaths.
More recently a virus has been found in association with pathological conditions of the liver and intestine of captive Nile crocodiles in Zimbabwe. It is uncertain whether two different viruses are involved or the same virus affects both organ systems (Foggin, 1985). The symptoms and gross pathological findings were non-specific. In common with most diseases, infection is most frequently seen in small, weak hatchlings.
Finally, Foggin (1985) reports the presence of pox virus in the skin of the eyelids of some crocodiles with ophthalmia but it is not known if the virus is a primary cause of the problem.
A number of parasites have been identified in captive crocodiles but only a few have been associated with disease.
Single-celled parasites (Protozoa)
Intestinal protozoans of a group called Coccidia cause diseases in many animals including domestic rabbits and poultry. The parasite lives inside the cells of its host and commonly it is the lining of the gut which is affected. Foggin (1985) has found coccidiosis to be a major disease of crocodiles in Zimbabwean farms though, again, it is the small wealkings (runts) which most often fall sick.
Jacobsen (1982) notes that most free-ranging reptiles are parasitised by Coccidia
without any sign of illness but after stress young animals, especially, may fall ill.
Diarrhoea, often with blood, is a usual symptom. Positive diagnosis will probably require
post mortem microscopic examination of the gut and other parts, notably the gall bladder
and bile duct.
Coccidiosis may be treated with sulphachloropyrazine 4/ in the food at 1.5 g/kg for three consecutive feeds or dosed as a 3% solution at 5 ml/kg body weight by stomach tube daily for three days (Foggin, 1985).
In American alligators and in Nile crocodiles in Zimbabwe the nematode (roundworm) worm Dujardinascaris can be troublesome. The worm lives in the stomach and can cause ulcerative lesions. Roundworms are commonly found in apparently healthy crocodiles where presumably they can be tolerated provided the parasite load is not too great. In Papua New Guinea at least three farmers have used proprietary dog-worming powder dusted on the crocodiles' food as recommended for dogs. Dead nematodes were seen in the pools next morning and the crocodiles were not apparently harmed.
For the treatment of crocodiles with Dujardinascariasis, Foggin (1985) recommends fenbendazole -5/ mixed in feed at 200 mg/kg for two consecutive feeds.
Lungworms (Pentasomida) are common parasites of wild alligators in Florida and can injure their hosts by burrowing through the lung walls. Like Dujardinascaris they probably have a larval stage in fish and so crocodiles become infected through their food. it has been suggested that freezing fish, would probably serve to interrupt this transmission (Telford & Campbell, 1981).
Worms have occasionally been found in the lungs and body cavity of crocodiles in Papua New Guinea but they are not known to have been a significant factor in the health of captive stock.
4/ ESB3 water soluble powder (Ciba-Geigy) containing 30% sulphachlorpyrazine
5/ Panacur (Hoechst) containing 10% fenbendazole
A very common parasite of the New Guinea freshwater crocodiles is a nematode which burrows in the belly skin and leaves zig-zag trails visible on the surface. They do not appear to affect the health of the crocodile but the marks lower the value of the skin so they are of economic importance. The worm is 2-7 cm long and thread-like.
Specimens of the worm collected from New Guinea freshwater crocodiles were described as a new genus and species by Ashford & Muller (1978) under the name of Paratrichosoma crocodilus. This worm also occurs in C. porosus in Papua New Guinea but less frequently. It has been noted that the worm is rare or absent in crocodiles from saline waters but it seems to be much less common in C. porosus even from fresh waters remote from the sea. The disparity appears to persist when both species are kept together in captivity. In one farm on the Sepik River it occurred in 58% of a batch of 191 freshwater crocodiles and 12% of a batch of 81 C. porosus. All these young crocodiles had been caught more than 200 km from the nearest tidal or brackish water.
Similar worm tracks have been recorded in the belly skins of C. intermedius, C. niloticus, C. johnsoni and C. moreletii (King and Brazaitis, 1971). They are well known in the leather trade and one experienced tanner claims that burrow marks on crocodile skins from South America are distinct in appearance. No control measures have been reported.
Observers in different parts of the world have noted that in any batch of hatchlings some individuals may be vigorous and make rapid growth while others, for no obvious reason, remain small and weak even though they receive identical treatment. This is familiar to crocodile farmers in Papua New Guinea, Zimbabwe and South Africa. Writing in 1971 Pooley pointed out that from one clutch of eggs a few individuals 'may be classed as runts, hardly growing at all'.
Today, despite recent findings about the influences of incubation temperature and the special requirements of newlyhatched crocodiles, the occurrence of runts has not been satisfactorily explained. It is not known whether the syndrome is a result of a specific disease or whether it results from a combination of hereditary/congenital, environmental, nutritional and infectious conditions. In Zimbabwe up to 30% of hatchlings may be affected (Foggin, 1985). Runts can be identified a few weeks after hatching.
Upon examining runts Foggin found some changes in blood and biochemical values but they
were not considered diagnostic. Post mortem findings were non-specific. Apart from poor
body condition the belly was usually slightly distended with fluid and the intestines and
liver were atrophied. The liver was usually grey and there was no stored fat to be seen in
The presence of runts in a hatchling enclosure is important not only because of their low value but because it is in the runts that disease organisms are most likely to build up to dangerous levels. It seems sensible therefore to regard runts as a potential source of disease which could spread to healthier crocodiles.
In the course of size segregation the runts will automatically be brought together. Of course they should be given special treatment such as the best possible diet, warmth and particular attention to hygiene. But as a precaution the feeding and cleaning utensils for the runts should not be used for the other pens. From a management point of view runts are one step from the hospital pen. It would be unreasonable to put them with obviously diseased animals prematurely. But it seems unwise to wait until they fall sick before isolating them from healthier stock.
Deformities at hatching (such as no tail) are likely to be caused by incorrect incubation temperature. Stump-tailed crocodiles can grow well in captivity although of course their swimming is affected.
Blindness, almost always in one eye, has been observed in young captive crocodiles, in New Guinea and appears to be due to a condition resembling cataract.It does not appear to be infectious and affected crocodiles can still do well in captivity.
Wounds resulting from fighting can be severe. Occasionally crocodiles in village pens of Papua New Guinea survived the loss of part of the lower or even upper jaws. To reduce the risk of infection skin wounds can be cleaned with hydrogen peroxide and painted with iodine as an antiseptic. Compounds of phenol or coal tar derivatives should never be used as antiseptics or disinfectants for reptiles (Murphy, 1975.).