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Most species of mites are very small, less than 1 millimetre in length. They can only be identified accurately with a high-powered microscope, and usually by trained professional specialists.
Chorioptic mange is widespread in Australian cattle, but it is not common, and serious infestations are rare. The available information about this pest in Australian cattle is very limited. Transmission of the mite appears to be limited to direct contact between host animals, so this mite does not disperse easily in Australia, where animals are not confined together in close contact. The causative agent, Chorioptes bovis, also occurs in Europe, Asia, North and South America, Russia, and the Middle East. The same species of mite occurs on cattle, goats, horses, sheep, and camels.
Chorioptes bovis is a very small mite, less than half a millimetre in length. The male is smaller than the female and quite different in appearance. The third pair of legs in the male are greatly enlarged and the fourth pair are reduced to small stumps. Both females and males have very long bristles on the third pair of legs. The mite completes its life cycle in about two weeks, but cannot survive off the host for more than a few days.
Chorioptic mange is sometimes referred to as leg itch or barn itch. Diagnosis is confirmed by the presence of Chorioptes bovis in skin scrapings. Infestation in cattle usually starts at the base of the tail, and spreads to the udder and thighs.
Common sites of infestation are the escutcheon, the base of the tail, and especially around the hind feet. The mite does not dig tunnels in skin, but feeds on the surface layer of tissue, where its chewing mouthparts cause considerable irritation to its host.
Light infestations may not cause visible symptoms and may remain undetected. In heavy infestations, cattle respond by rubbing against objects to relieve itching, which can cause considerable skin damage and scab formation. Heavily affected areas become wrinkled and form crusty scabs. Rubbing and irritation can cause reductions in weight gain and milk production.
Ivermectin and related compounds have been successfully used to treat chorioptic mange when applied topically, but multiple treatments are needed and results have been inconsistent. The use of other drugs (acaricides) is limited by the need for withholding periods in dairy cattle.
Mites in the genus Demodex occur in the skin of most species of mammals, including humans. The mites are tiny, less than half a millimetre in length, and occur in hair follicles and the associated secretory glands, where they can occur in large numbers. They have a very elongate worm-like body, with four pairs of very short legs at the anterior end. Each leg ends in two tiny claws. The life cycle of the mite is completed in about a month, and is spent entirely in the skin of its host. Transmission of mites is by direct contact between different host individuals, and the mites quickly die of desiccation away from a host.
Each species of host appears to harbour a different species of mite. The species that occurs on cattle is Demodex bovis. It is common and widespread in Australian cattle, and is considered to be a normal inhabitant of the skin of healthy hosts. Mites are usually found on the neck, shoulders and dewlap of their host. Clinical symptoms in the host are usually mild and often go undetected and untreated. However, heavy infestations of mites can cause the formation of small white nodules in the skin, which can vary from very obscure to 1 centimetre in diameter. These nodules are actually swollen hair follicles packed with large numbers of mites and secondary bacterial infections. They do not appear to cause major distress to the host, and may persist for several years. Mites may spread and cause more extensive infestations in hosts that are stressed by extreme weather or nutritional deficiencies. The importance of the skin nodules becomes apparent during the tanning process, where they can cause visible defects in the leather. Even a moderate infestation can cause major degradation in the quality and commercial value of the hide, and serious economic losses in the leather industry.
Diagnosis of the disease is by microscopic detection of the mites in skin scrapings or in nodules excised from the skin. Most infestations are mild and asymptomatic, and control is usually not attempted.
Raillietia auris has been found infesting the ear canal and inner ear of cattle in widely-scattered areas of Australia and in many other countries. It causes a condition known as otitis media. Light infestations may go undetected, but in severe cases pathology includes localised swelling, pus formation, inflammation, and ulceration. Symptoms can include head shaking, ear rubbing, lack of coordination, facial paralysis, and hearing loss. Mites occur in the ear canal and on the eardrum, and are visible by careful examination of the ear canal. They can be collected from the ear canal by swabbing or flushing with warm water. Adult female mites are mobile, cream-coloured, about 1 mm in length. All developmental stages can be found in a single infestation. Development of the mite from egg to adult is completed in 2–5 days and the adult mite can live for about 30 days.
Raillietia auris is sometimes considered to be a harmless species that feeds on ear wax and other non-living material, but its presence can cause blockage of the ear canal. The mite attaches itself using sharp claws on its legs. These claws, and the piercing mouthparts of the mite, appear to damage the surface of the ear canal. The resulting injuries provide sites for multiplication of bacteria that cause otitis (ear infections).
The occurrence of mites deep inside the ear canal makes chemical control difficult, and experimental treatments have given inconsistent results. Subcutaneous injection and pour-on treatments are not effective in controlling this species. Flumethrin is effective if applied directly into the ear canal using a syringe, but standardised methods of treatment have not yet been developed.
Sarcoptic mange is caused by the parasitic mite Sarcoptes scabiei. This species includes several varieties that differ slightly in morphology and in their ability to infect different species of hosts. When this mite attacks humans it causes the disease known as scabies. Mites do not easily transfer from one species of host to another, and sarcoptic mange or scabies does not transfer from cattle to humans. The mites roughly circular, less than half a millimetre in diameter, and have very short legs.
Cattle are usually infected by direct contact. Mites can also be spread through straw bedding and other objects that come into contact with infected animals. The entire life cycle of the scabies mite occurs on one host, and is completed in 14 to 21 days. Female mites chew through the skin of the host to form tunnels where they lay their eggs. A female lays three or four eggs each day, and can produce 40 to 50 eggs during her lifetime. Eggs hatch in four or five days, and the complete life cycle is spent within the tunnel in the skin. The mites do not suck blood, but feed on skin tissue and the surrounding fluids. Different individuals and different breeds of cattle vary in their susceptibility to this pest.
Mange produced by the scabies mite can be severe, and the burrowing activity of the mite causes intense itching. Affected animals rub against posts, trees, and other objects to relieve the irritation. This rubbing can result in localised or widespread hair loss, with bleeding and exudate production. The exudate hardens to form a crust, which produces hardened scabs and thickened skin, especially on the inner surface of the thighs, the underside of the neck the brisket, and around the base of the tail. Cattle affected by sarcoptic mange do not gain weight as rapidly as do uninfected cattle, and very severe cases can be fatal. Sarcoptic mange has not been reported on cattle in Australia, despite its occurrence on humans, dogs, foxes and various wildlife species, notably wombats. The cattle-adapted strain of Sarcoptes scabiei must be considered as a threat to the Australian cattle industry. Diagnosis is by detection of mites in skin scrapings, followed by microscopic identification. Mites are effectively controlled by washes, dips, or topical applications.
Mites in the genus Psoroptes are skin parasites of many species of livestock, including cattle, sheep, horses, goats and rabbits. They also occur in some wildlife species such as bighorn sheep, deer, antelope, and buffalo. The mites are small, less than 1 millimetre in length. The whole life cycle is spent on the host. They complete a generation in about 14 days, and adults live for about 50 days. Transmission from one host to another is usually by direct contact, but mites can survive away from a host for several weeks and can be picked up by a host from the environment. They are not transmitted by animal vectors. Diagnosis is by the detection of mites in skin scrapings.
These mites do not burrow, but abrade the skin of their host with their chewing mouthparts, to feed on blood, serum, skin cells, and skin surface lipids. They cause a very severe form of mange that involves major loss of hair or wool and the formation of extensive scabbing. Symptoms are complicated by an allergic reaction in the host, with thickening and scaling of the skin. The resulting injuries are often attacked by flies and secondary infections. The mange causes itching, and infected animals rub themselves against objects, causing further injury. Effects on the host include weight loss, reduced milk production, and general weakness that increases the host’s susceptibility to other illnesses. Damage to the skin also causes significant reduction in leather quality.
Different species of Psoroptes are morphologically very similar, and accurate identification depends on careful microscopic examination. There is variation within species, both in morphology and the ability to infect hosts. As a result, different studies of these mites have produced contradictory results, with varying degrees of success in transferring mites from one species of host to another.Psoroptes ovis is a very damaging parasite of sheep and cattle. It was present on sheep in Australia in the 19th Century, but was successfully eradicated by 1896 and has not been seen since. It is present on sheep and cattle in Africa, North America and Europe, and must be seen as serious biosecurity threat to Australia. It has been listed as a notifiable disease by the Australian Government Department of Agriculture and Water Resources.
The larval stage of chigger mites feed on vertebrates, including cattle, using their pointed mouthparts to penetrate the skin. This can result in red welts and itching. The larval stages are less than a half millimetre in length and are difficult to see with the naked eye. Chiggers are most common in summer. The tea-tree itch mite occurs in the southeast coast of South Australia and the grass itch mite occurs in coastal Queensland and north coastal New South Wales.
These two species do not cause conspicuous clinical symptoms, and they do not appear to be significant veterinary pests. The cattle nasal mite has only rarely been collected in Australia but has been found in the nasal sinuses of cattle in Africa, and of bison in North America.
Mange mite (Chorioptes texanus)
The mange mite Chorioptes texanus has not been reported from Australia, but must be considered as a biosecurity threat to Australian livestock industries. Chorioptes texanus is morphologically very similar to Chorioptes bovis. This species of mite has been reported in the ears, tail, perineum and udder of cattle. It appears to occur only in widely scattered cases and is not considered to be a serious pest. Symptoms are not severe, but include a dried crust of serum exudate, loss of hair, and scabby thickened skin.
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