A mangy story

23 January 2007

Summary Demodectic mange, or follicular mange as it is also known, can cause damage to hides that is sometimes not visible from either the grain or flesh side. Because the damage is hidden it does not become apparent until the leather is split. Consequently, it is often a cause of complaint between wet-blue supplier and dresser because it is often missed at wet-blue sort. The Demodex mite Demodex mites are long thin parasites that live in the hair follicles and sebaceous glands of animals. They can affect all animals; cattle, goats, dogs and even humans. However, each species of animal has its own species of Demodex as they are host-specific. They cause most problems in domestic dogs but, from the tanners' point of view, it is cattle that are most commonly affected. The mites are approximately 0.25mm long and have four pairs of short, stubby legs. They live by sucking out the contents of the cells in the follicles. Their life cycle takes around twenty days to complete. The eggs are laid inside the hair follicles and the nymphs that hatch pass through two larval stages before they reach adulthood. Unusually, virtually all animals have some of these mites on their skins in small numbers and it is believed that infestation is passed on from the mother to the young animals at birth. Under normal circumstances they do not cause any problems because the animal's immune system keeps them at bay. Usually infestation only takes hold and causes mange problems if the animal's immunity is reduced for some reason, eg if it has recently suffered some other illness. Hide Damage There are two forms of Demodectic mange; one form causes hair loss, inflammation and thickening of the skin and is therefore fairly obvious. The other is much more difficult to detect because it causes cysts to form inside the skin at the junction of the grain and corium. The cysts can be up to 1 cm in diameter. They contain a cheese-like substance, which if examined under a microscope can be found to contain hundreds of mites at various stages of development. In mild infestations nothing more than a slight pinhole effect can be seen on the grain side of the leather. However, if the cysts are sufficiently large, they can be felt as little pea-like nodules in the raw hide. By the time the hide has been processed into leather, the cysts have collapsed and they appear as small depressions in the grain. But invariably they go undetected until the leather is split. Often the splitting blade passes right through the middle of the cysts revealing their presence on the split surface rendering the leather useless. In cattle the cysts often form initially on the face, neck and shoulders but can affect all areas in severe cases. In heavy infestations the cysts can sometimes merge together to form much larger holes. There are systemic treatments that will kill the Demodex mites in the follicles but experience has found that invariably an outbreak of mange will spontaneously clear up after a few weeks. Therefore, the disease is often left to run its course, unless secondary bacterial infections occur. However, the hide can still be scarred even after the outbreak has passed.

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