Almost all mammals, both wild and domestic, are host to various internal and external parasites. Many of these parasites are harmless, but some may be detrimental to the animal's health. When Europeans first brought out their sheep and cattle, pigs and goats, camels, donkeys, deer, dogs, cats, foxes, rabbits - the full list is formidable - they also unwittingly brought a whole new spectrum of parasites and insect pests. The native marsupials undoubtedly carried parasites of various kinds long before Europeans arrived, but they had much less resistance to the new imports. The diseases that affect the wombat most severely are all caused by parasites originally carried by introduced domestic animals.
Several kinds of external parasites have been found on wombats, including fleas, lice, mites and ticks. It is a mite that gives rise to the wombat's most serious disease: the condition known as sarcoptic mange.
The mange mite, Sarcoptes scabei, burrows into the skin where it lays its eggs and causes intense irritation. The wombat scratches and rubs to relieve the irritation, and hair loss results, followed by crusting and scabbing of the skin, especially on the head and ears. In severe cases the eyes may be virtually closed by the lesions, and the animal loses most or all of its hair, the bald skin becoming wrinkled and thickened (see Plate 22). The wombat's vision and ability to eat are severely affected, and it becomes weak and emaciated and eventually dies. Mange is prevalent in both bare-nosed and southern hairy-nosed wombats but it has not been found in the northerns.
Whether the sarcoptes mite came to this country with the dingo about 4000 years ago, or with domestic dogs and foxes in the last 200 years is not known - probably both, as it infects wolves (the dingo is an Asiatic wolf) as well as dogs and foxes.
A wombat contracts mange either by contact with an infected wombat, or by being exposed to a large quantity of mites in a burrow. Casual burrow-sharing is not thought to be the means by which mites are transferred from one animal to another. Mites can only live for a maximum of three weeks off a host, so burrows are unlikely to harbour them in large numbers unless an infected wombat has recently died in the burrow.
Skerratt's work showed that whether wombats will develop clinical signs of mange or not depends on the number of mites they are infected with, and that perfectly healthy wombats will contract the disease if they are exposed to a large number of mites. He also showed that mange can be treated effectively. He found that when infected animals were treated with three injections of Ivermectin, 300 micrograms/kg, 10 days apart, all signs of the mange disappeared. However, the mites were not entirely eliminated until the wombats received a second regime of treatment. (Further information about the treatment of mange is given in Appendix 2.)
Other mites commonly found on wombats are the earmite Raillieta australis and the skin mite Acaroptes vombatus. Skerratt, in a study of parasites and diseases of the bare-nosed wombat, found that these mites, and the common wombat tick, Aponomma auruginans, were not found on wombats suffering from sarcoptic mange but were common on those without mange.
Although wombats living near the eastern coast of Australia appear to have developed immunity to the paralysis tick, Ixodes holocyclus, which infests that area, they are plagued by the common wombat tick and several other species of ticks. A severe tick burden, which can cause anaemia, can weaken a wombat to the point of killing it. Even the wombat's vigorous scratching often will not dislodge an embedded tick. A female wombat has an added discomfort, as these bloodsucking parasites often establish themselves on the outer rim of her pouch, and occasionally even inside it, being attracted by its warm, moist skin, and she is virtually helpless to remove them.
As well as ticks there are many other external parasites that also visit their host, feed and then leave. Mosquitoes, sand flies, march flies, louse flies and other bloodsucking insects all harass the wombat, both inside and outside the burrow, although it escapes some of their depredations by being mainly nocturnal. Blowflies of both native and introduced species attack any animal with an open wound in order to lay their eggs, which hatch into maggots and feed on the raw flesh. The wombat's habit of coating its wounds with a 'plaster' of soil gives it some protection against these pests, but it is still vulnerable to fly strike.
Like the majority of animals, the wombat is host to several internal parasites such as worms of various kinds. Most of these, if present in small numbers, apparently do the animal little or no harm. Thick white roundworms are common in the colon of the wombat, and smaller roundworms have been found in the walls of the small intestine and in various organs, such as the lungs. Several harmless species of tapeworms are occasionally present in the intestines, but the wombat is not a host for hydatid cysts.
Wombats grazing in areas where sheep have also grazed are susceptible to a more serious internal parasite. Liver fluke is a relatively common parasite in sheep, and wombats with severely affected livers have been found.
Pasture contaminated by domestic stock is also responsible for the disease called leptospirosis, but in this case cattle are the principal hosts. Sheep, goats, pigs, dogs and rats also carry this infectious bacterial disease, which may be transmitted to man through the excretions of infected animals. In wombats, which probably acquire leptospiral infections when grazing on swampy pastures, the disease causes serious kidney damage.
The cysts of other disease-causing parasites such as coccidia have been found in young wild wombats; a major cause of death in hand-reared and captive wombats is toxoplasmosis, in which the animals become infected by accidentally ingesting the microscopic toxoplasma oocysts. These cysts are often passed in the faeces of cats, particularly kittens. The disease develops suddenly and severely, the animals showing almost no symptoms before collapsing and dying. Toxoplasmosis is undoubtedly carried by feral cats as well as domestic ones, so wild wombats also are at risk of acquiring it.
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