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SUMMARY
Mange is a form of ectoparasitic dermatitis characterised by encrustation, alopecia, and pruritus of the skin, initiated by and maintained by a number of mite species. Mites and ticks are a subclass of the Arachnida divided into two superorders, the Parasitiformes (Mesostigmata) and the Acariformes. The Acariformes contains three orders: the Astigmata (Acaridida, not possessing stigmata), the Prostigmata (Actinedida, possessing stigmata behind the gnathosoma) and the Oribatida (Cryptostigmata). All the major mange mite species are contained within the orders Astigmata and Prostigmata. The diagnosis of mange in domestic animals is based on clinical manifestations and the demonstration of mites or their developmental stages in skin scrapings.
Identification of the agent: Mange can be the result of infestation by the astigmatid mites, e.g. Chorioptes, Knemidokoptes, Notoedres, Otodectes, Psoroptes, or Sarcoptes or the prostigmatid mites, e.g. Cheyletiella, Demodex or Psorobia. All mange mites are classified by structure. Specialised illustrated keys should be consulted in order to identify the causative organism.
Requirements for vaccines and diagnostic biologicals: There are no commercial vaccines currently available.
A. INTRODUCTION
Mange is a form of ectoparasitic dermatitis characterised by encrustation, alopecia, and pruritus of the skin, initiated by and maintained by a number of mite species. Mites and ticks make up the Acari, a subclass of the Arachnida. Within this subclass mites are further divided into two superorders: the Parasitiformes and the Acariformes. The Acariformes contains three orders: the Astigmata (acaridida, not possessing stigmata), the Prostigmata (actinedida, possessing stigmata behind the gnathosoma) and the Oribatida (cryptostigmata) (3). All the major mange mite species are contained within the orders Astigmata and Prostigmata. The Astigmata is a well defined group of slow-moving, weakly sclerotised mites, including the families of medical or veterinary importance - Sarcoptidae and Psoroptidae. The Prostigmata is the most heterogeneous of acarine orders with adults ranging in size from 100 µm to 16 mm (21). Included in the Prostigmata are the Trombiculidae (harvest mites), parasitic as larvae but free-living predators in the nymphal and adult stages, and the true mange mite families Psorergatidae (Psorobia [Psorergates] sp.), Demodicidae (Demodex sp.) and Cheyletiellidae (Cheyletiella sp.) (3).
B. DIAGNOSTIC TECHNIQUES
The diagnosis of mange in domestic animals is based on clinical manifestations and the demonstration of mites or their developmental stages in skin scrapings (19). Specialised illustrated keys should be consulted in order to identify the causative organism.
| 1. | Identification of the agent
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| | Mange can be the result of infestation by the astigmatid mites, e.g. Chorioptes, Knemidokoptes, Notoedres, Otodectes, Psoroptes and Sarcoptes or the prostigmatid mites, e.g. Cheyletiella, Demodex and Psorobia.
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| A) | The Astigmata
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| | The Astigmata are small thin-skinned mites, generally lacking obvious shields. The bases of the coxae are sunken into the body and referred to as epimeres when outside the body and apodemes when inside the body. The empodium is claw-like and the pedicel is stalked or sessile. True claws are absent. Fertilised eggs are extruded through an antero-ventral slit, the oviporus or genital opening. Most species of medical or veterinary importance are in the division Psoroptidia, comprising the Psoroptoidea (Sarcoptidae and Psoroptidae), the Analgoidea (Knemidokoptidae, Cytoditidae and Laminosoptidae) and the Pyroglyphoidea (Pyroglyphidae). The division Acaridae contains the stored product mites, which can cause transitory mange and can be an important source of allergens.
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| | i) | Sarcoptidae
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| | | Sarcoptid (sarcoptiform) mites are obligate parasites, burrowing into the skin of mammals. They are globose mites with the ventral surface flattened and the cuticle finely striated. The chelicerae are adapted for cutting and paring.
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| | | a) | Sarcoptes scabiei
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| | | The mite (Sarcoptes scabiei) is the cause of scabies, sarcoptic mange, in humans and in a wide range of domestic and wild mammals (both carnivorous and herbivorous) throughout the world, generally affecting the sparsely haired parts of the body. The number of species within the genus is still open to debate. Studies of populations of Sarcoptes mites from a wide range of hosts have suggested that there is only one type species (Sarcoptes scabiei) with a number of variants infesting a wide range of mammalian hosts (14). Recent investigations based on molecular analysis of the ITS-2 of the rRNA gene suggest that the genus Sarcoptes is monospecific (37). Humans are easily infested, particularly in crowded or poor living conditions (35).
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| | | Sarcoptes can be identified on the basis of size, shape and morphology. The body outline of adult mites is circular and approximately 250 µm in length, but as ovaries develop in the female, she can increase in size to 300 to 500 µm in length. The cuticle (integument) is striated, bearing a central patch of raised tooth and peg-like structures on the dorsum that decreases in density posterolaterally. Legs are weakly developed and in both sexes the pretarsi of legs I and II bear empodial claws but the ambulacral suckers are on long unjointed pedicels (stalks). The epimeres (apodemes) of the first pair of legs are fused in a 'Y' shape. Legs III and IV in the female (identified by the transverse egg laying slit [oviporus] in the middle of the ventral surface) are short and end in long setae and lack a stalked pedicel. They are located on the ventral surface and are not visible in dorsal view. Males are smaller and distinguished by the presence of a stalked pedicel on legs IV, between which there is an obvious sclerotised genital apparatus. Nymphs are similar to the female, but smaller and without an oviporus. Larvae resemble nymphs, but have only three pairs of legs. A similar mite, Trixacarus caviae, occurs on guinea-pigs, but is smaller and the anus is dorsal. Secondary immune reactions may produce a rash at sites away from the infested area.
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| | | b) | Notoedres spp.
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| | | Notoedres also burrows into the host epidermis and is similar to Sarcoptes, but can be distinguished by the absence of dorsal spines and by the dorsal anus. Over 20 species of Notoedres have been described of which the cat mange mite, Notoedres cati, is of veterinary interest, producing a highly contagious and intensely pruritic mange on cats (and sometimes dogs and rabbits). Infestations usually start on the head of the cat, from where it may spread. Notoedres muris occurs on rats and N. musculi on house mice. Notoedres cati is similar to S. scabiei having unjointed stalked pedicels with terminal suckers on legs I and II in all stages, and on leg IV in the male. Notoedres cati is considerably smaller, the female being 225 µm and the male 150 µm. The anus is located on the dorsal surface and there are no projecting spines, but mid-dorsally the striae are broken into a scale-like pattern and stout setae replace the conical peg-like setae of S. scabiei.
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| | ii) | Analgoidea
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| | | The Analgoidea include 12 species of the mange mites Knemidokoptes (Knemidokoptidae), the air sac mite of poultry (Cytodites nudus: Cytoditidae) and the Laminosoptidae, represented by Laminosoptes cysticola, infesting the subcutaneous cellular tissue of turkeys and chickens.
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| | | a) | Knemidokoptes sp.
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| | | Three species of Knemidokoptes are of veterinary importance: K. mutans infesting the epidermis of the legs of poultry (causing 'scaley leg'), K. gallinae (Neoknemidokoptes gallinae, Mesoknemidokoptes laevis gallinae), the 'depluming mite' infesting the skin of poultry near the base of the feathers, and K. pilae infesting the ceres of cage and aviary birds (causing 'scaly face'). Female Knemidokoptes are 400 µm long, and dorsal scales, if present, are faint and irregular. Knemidokoptes gallinae (Mesoknemidokoptes) do not have any scales (3). Two sclerotised, almost parallel, longtitudinal bands are present on the anterior mid-dorsal surface, connected posteriorly by a less well developed transverse band. In the male, the epimeres (apodemes) of the first pair of legs are joined in a 'Y' shape, and in the female, the epimeres (apodemes) are joined in a 'U' shape. Stalked pulvilli are present on all legs in the male and larvae, but are absent in the nymphal stages and females. The anus is situated terminally. The female is viviparous and there are one larval and two nymphal stages.
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| | iii) | Psoroptidae
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| | | Members of the family Psoroptidae are oval, nonburrowing mites, parasitic on mammalian skin. The cuticle (integument) is striated, legs III and IV are usually visible from above, the epimeres (apodemes) of leg I are not fused, and there are no vertical setae on the propodosoma. The male has prominent adanal suckers that engage with the copulatory tubercles of the female tritonymph ('pubescent female'). The inverted U-shaped oviporus is prominent on the venter of the ovigerous female, posterior to leg II. Three genera, Psoroptes, Chorioptes and Otodectes are of veterinary importance.
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| | | a) | Psoroptes spp.
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| | | Psoroptes spp. have strongly developed legs bearing, in all stages, funnel-shaped suckers on long three-segmented pedicels. The ovigerous mite is pearly white and 750 µm in length. The male has a pair of opisthosomal lobes and a pair of copulatory suckers. Psoroptes mites cause a debilitating dermatitis involving wool/hair loss and a pruritic scab formation. Five species of Psoroptes are recognised (33): Psoroptes ovis, a body mite causing mange in sheep, cattle and horses, P. equi, a body mite of equids, P. natalensis, a body mite of cattle and horses, P. cuniculi, the ear mite of rabbits, goats, horses and sheep and P. cervinus, an ear mite of bighorn sheep, elk and wapiti. A sixth, unvalidated, species is P. auchinae, an ear mite of New World camelids. Psoroptes natalensis and P. equi can be distinguished morphologically by the length of the fourth outer opisthosomal seta (L4OOS) of the male (33). In P. natalensis the seta is also spatulate, as is the shorter L4OOS of male P. cervinus (22). It is difficult to separate P. ovis and P. cuniculi on morphological grounds. Like the genus Sarcoptes, the number of species in the genus Psoroptes is open to debate (25); P. ovis and P. cuniculi may be variants of the same species (4).
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| | | b) | Chorioptes
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| | | Legs of Chorioptes mites have broad bowl-shaped ambulacra borne on very short unsegmented pedicels, except on legs III of the female, which terminate in two long setae. Ovigerous C. bovis are smaller than Psoroptes, being 400 µm in length. The male C. bovis has pedicels on all four pairs of legs, a pair of squarish to rectangular opisthosomal lobes and a pair of copulatory suckers anteriorly. The opisthosomal lobes bear two spatulate (paddle-like) hairs, together with three normal setae of varying length. The mouthparts are broad and rounded, adapted for chewing. C. bovis, infests cattle, goats, horses, sheep, camelids and rabbits, and C. texanus has been recorded on goats, reindeer and cattle (28, 32). A third species, C. panda, has been recorded infesting the Giant Panda (15). The opisthosomal lobes of C. texanus are more triangular in outline to C. bovis and the pair of spatulate opisthosomal setae are much longer. In goats, horses and camels C. texanus generally inhabits the lower parts of the leg, as does C. bovis on sheep, but in the latter case, the scrotum may also be infested and has been associated with infertility in rams. In cattle chorioptic mange commonly occurs on the base of the tail, the perineum and the back of the udder. The mite feeds at the external surface of the skin causing inflammation, exudation and scab formation. Heavy infestations can cause loss of condition, which can lead to emaciation and damage to hides (35).
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| | | c) | Otodectes
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| | | Male Otodectes are similar to Chorioptes, but the opisthosomal lobes are much less distinct, copulatory suckers are present and the hairs are less spatulate. The epimeres extending from the bases of legs I and II are joined. The male has broad bowl-shaped ambulacra borne on very short unsegmented pedicels on all the legs, but only legs I and II of the female have pedicels and amulacra. Legs III of the female terminate in two long setae and legs IV are reduced (3). Otodectes cynotis occurs in the ears, causing parasitic otitis (and occasionally elsewhere on the body) of domestic dogs, cats, foxes and ferrets together with a number of wild carnivores (34). Otodectes cynotis feeds on the external surface of the skin causing inflammation and exudation. Excessive exudation may lead to wet eczema on adjacent skin surfaces. The tympanic membrane may be perforated and otitis media and nervous signs (e.g. convulsions) can develop.
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| | iv) | Free-living astigmatid mites
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| | | Free-living astigmatid ('forage') mites can occur in large numbers in stored food, spilled grain, poultry feed, etc. Their ingestion can lead to gastrointestinal disturbance. Mites may also be the cause of incidental mange of mammals through contact with antigenic material present in infested feed or the environment. Workers handling infested stored food can develop reactions to the mites and suffer from pruritus, dermatitis, rhinitis or asthma (35). The cause of the reaction has not been established but is assumed to be allergic or possibly do to bites. The most obvious characteristic of the more common forage mites (Acaridae) is the possession of many 'hairs', which are much longer than the parasitic forms, and may be simple, branched or spatulate. In some genera (e.g. Glycyphagus) the posterior hairs often become entangled in debris. Acarus siro, probably the commonest of these mites, has shorter hairs.
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| B) | The Prostigmata
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| | Prostigmatid mites are weakly sclerotised and, where there is a respiratory system, the stigmata open on the gnathosoma or anterior part of the propodosoma. The palpi are usually free and highly developed, either as pincer-like clasping or sensory organs. The chelicerae are usually modified for piercing (3, 35). Included in the Prostigmata are the Trombiculidae (harvest or chigger mites), parasitic as larvae, but free-living predators in the nymphal and adult stages, and the true mange mite families Psorergatidae (Psorobia [Psoreregates] sp.), Demodicidae (Demodex sp.) and Cheyletiellidae (Cheyletiella sp.) (3).
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| | i) | Psorobia (Psorergates) spp.
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| | | Two species of Psorobia have been isolated from domestic animals and one species from laboratory animals: the benign 'parasite' P. bos from cattle, the more important P. ovis occurring in Merino sheep and Psorergates simplex (Psoreregates muricola) from laboratory animals (3). Larval Psorobia hatch with reduced legs that become progressively larger at each of three nymphal moults, and by the adult stage the legs are well developed and the mites are motile. Adults of both sexes are very small (200 µm) and can be recognised by the radially arranged legs around a more or less circular body. Each leg has an inward curving spine on each femur. Most mites are found under the host stratum corneum in the superficial layers of the skin of the sides, flanks and thighs, feeding on the exuding fluid. The infested area is dry and scruffy, wool fibres break easily with the remaining wool coming together as ragged tufts. Irritation causes the sheep to rub and kick the affected area and chew its fleece, resulting in 'fleece derangement' and downgrading of the wool clip.
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| | ii) | Cheyletiella spp.
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| | | Cheyletiella (fur mites) are large mites (385 µm) with large curved palpal claws and an obvious 'M' shaped respiratory peritreme or stomata at the bases of the chelicerae. Cheyletiella is an obligate parasite, inhabiting the keratin layer of the epidermis. The mites develop rapidly, giving rise to the term 'walking dandruff'. Three species are of veterinary importance, causing mild, nonsuppurative dermatitis in mammals and transitory dermatitis in humans: C. parasitovorax occurring on cats, the scapular region of rabbits and occasionally humans, C. yasguri causing a highly infectious infestation of puppies (adult dogs as carriers), and C. blakei causing a mild dermatitis in cats. Cheyletiella parasitovorax has an ovate (spade-shaped) sensory organ or seta (solenidion) on the genu of the first leg, whereas that of C. yasguri is apically cleaved (heart-shaped) (3).
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| | iii) | Demodex spp.
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| | | Demodex are easily recognised by their annulate, vermiform ('worm-like') shape, but may be overlooked on account of their small size 100-400 µm. Demodex inhabit the hair follicles and the sebaceous and meibomian glands of the skin of a number of wild and domesticated mammals, including humans. Male Demodex live at or near the skin surface and females in the follicles. Different species occur on different hosts, and more than one species may occur on the same host, e.g. D. folliculorum and D. brevis on humans (12). Demodectic mange is of great importance in dogs (especially short-haired breeds), goats and pigs, and of lesser importance in cattle, horses, sheep and cats. There is usually no irritation or pathological conditions, but in some individuals the number and spread of mites on the hosts increases to form clinical demodecosis. On cattle this occurs as flat nodules in the skin with a massive enlargement of the sebaceous glands that contain vast numbers of Demodex mites. In dogs infestations may become generalised as a squamous form, with associated hair loss and thickening of the skin. Pustular demodecosis is a more severe form in dogs and is complicated by secondary bacterial infection. Diagnosis of demodecosis is dependant on the recovery of mites from deep skin scrapings. Mites can easily be identified as Demodex, but specialised keys are required for specific identification (23).
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| 2. | Diagnosis of scabies or mange
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| | A firm diagnosis of scabies or mange must be based on the recovery and identification of the mite from the affected hosts. Visual examination of a suspect mange lesion may reveal the larger mites (e.g. Psoroptes), but in most cases it is necessary to take skin scrapings from the edge of visible lesions. Specialised illustrated keys should be consulted in order to identify the causative organism (3).
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| | An indication of the presence of Psoroptes mites is the reaction of the host to scratching or rubbing of the affected skin by the operator, where it responds by a nibbling mouth reflex and/or scratching itself. Forced exercise followed by close penning will increase body heat and the associated percutaneous absorption of mite antigens/irritants inducing the presentation of clinical signs. Skin scrapings are taken from the affected area. In diagnosing sarcoptic scabies it must be borne in mind that the distribution of rash on the body bears no relation to the distribution of mites. Wool or hair should be clipped (and stored for the differential diagnosis of other ectoparasites or mycoses). The area selected for scraping should be the moist part or the edge of the lesion. If sarcoptic mange is suspected the scraping should be taken from the hairless area or where pruritus or pimples are seen. In psoroptic mange of sheep (sheep scab) the area selected is the edge of the progressing lesion, but scrapings can be taken from any part of the lesion for Psoroptes infestations of rabbits or cattle. In general for mites living on the skin surface (i.e. Psoroptes or Chorioptes) scrapings should be taken with the scalpel blade held at an acute angle, shaving rather than scraping off the outer epidermis. Demodex, Psorobia or Sarcoptes are found burrowing into the skin and the scalpel blade should be held at right angles and the skin scraped until it oozes blood. A drop of glycerine or liquid paraffin put on the skin or scalpel blade before the skin is scraped will aid in the collection of mites (29). In pustular demodectic mange, mites are usually abundant and can be demonstrated on examination of the cheesy contents of an expressed or incised pustule. In the case of squamous lesions, a deep scraping may be necessary. In cases of ear mange (canker) in cats, dogs or rabbits the scabby material within the external ear may be detached with blunt-ended forceps. A vacuum cleaner technique for collecting mange mites has been found to be useful and more sensitive than skin scraping (21). These authors found Cheyletiella, Sarcoptes, Psoroptes, Otodectes, Demodex and forage mites from infested dogs, sheep or swine, using 10% KOH treatment of the vacuum collected material before microscopic examination. Occasionally a diagnosis of mange can be made when mites are found in faecal samples, from pruritic dogs for example.
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| | In suspect cases of otoacariasis (Otodectes or Psoroptes) in the ears of cats, dogs, rabbits, sheep and goats, live mites can be observed through auroscopic examination of the external ear canal (EAC), but this technique may be difficult if applied to larger animals or large numbers of animals. In this situation it may be necessary to swab the external ear canal. Suitable sized swabs are inserted into the EAC until resistance is met, then gently twisted and removed. Care must be taken that the swabs enter the EAC and not the blind pouches of the tragus. Care should also be taken with young animals.
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| | Skin scrapings or ear swabs should be immediately transferred into small tubes that can be securely stoppered or lidded plastic bottles. Submission in sealed envelopes is not recommended as they may dry out or be lost. Live Chorioptes, Otodectes, Psoroptes and Sarcoptes can easily be seen during direct examination of the original skin scraping or ear swab under a dissecting microscope ((40) with overhead lighting. Mites will be active after incubation of the sample at 37(C for 30 minutes and can easily be transferred to microscope slides using a mounted needle.
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| | Mites can be mounted directly in either Berlese's fluid (gum chloral), Vitzhumis fluid, Hoyer's medium or Heinze's modified PVA medium (13). Put a drop of medium on the centre of the slide and transfer the specimen into it by means of a fine brush or mounted needle, and remove air bubbles with a needle. Put the cover-slip on its edge to the side of the medium and let it down slowly using a needle and then press slightly with the needle. If there is too much medium the pressure will force some of it out. If there is too little medium, add small drops, one at a time, letting it flow under the cover-slip. After mounting, allow the slides to dry at room temperature for 5-7 days before ringing with nail-polish or another nonsoluble sealant. The drying time can be decreased by placing the slides in an oven (40-45°C) for at least 2 days.
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| | To locate dead mites and live mites of smaller mite species (e.g. Demodex) the scraping will have to be processed in hot potassium hydroxide. Large amounts of material (up to 5.0 g) can be placed in a glass boiling tube and covered with 10% potassium hydroxide. The tube is then placed in a beaker of water, which is gradually brought to the boil for 5-10 minutes. A safer and as effective method is to heat to 37°C for a longer period. The digest is allowed to cool and then centrifuged at 600 g (2000 rpm) for 10 minutes. Prolonged boiling should be avoided as the mites may eventually disintegrate. Faster centrifugation may be required for smaller species. The supernatant is quickly decanted and the deposit examined microscopically. It has been suggested that a flotation procedure on the deposit after decanting the supernatant can greatly enhance mite recovery. Alternatively small numbers of specimens can be placed in lactic acid on a glass cavity (indented) slide. The slide is then passed constantly over a Bunsen or spirit lamp flame. Care must be taken that the slide does not get too hot, as escaping body gases in the mite may cause the mites to 'jump'. If smoke appears on the surface of the fluid the process is too hot. These methods are necessary to clear out the opaque body contents in order to prepare the mites for microscopic examination. It is advisable to carry out both these methods in a cabinet with an extractor fan due to the caustic fumes released. Staining using lignin pink or chlorazol black can help highlight structures or identify mites embedded in host tissue (3).
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| | Potential zoonotic problems may occur when handling infested animals or diagnostic material containing Cheyletiella, Sarcoptes, Notoedres or Trixacarus. Faeces or cuticular debris from any mite species may be a hazard to those prone to house dust mite (Dermatophagoides pteronyssinus) allergy.
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| 3. | Serological tests
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| | An enzyme linked immunosorbent assay (ELISA) for the serological diagnosis of sarcoptic mange in dogs and pigs is used in Sweden (1, 2, 8, 9), and is currently used in the porcine scabies eradication campaigns in Sweden (18) and Switzerland (20). An ELISA kit for the serodiagnosis of sarcoptic mange in pigs and dogs (Sarcoptes-ELISA 2001( PIG; DOG) is now commercially available. ELISA techniques have been developed to monitor Psoroptes infestations of sheep, cattle and nondomesticated animals (10, 11, 16, 17, 22, 24, 36), but none is currently commercially available.
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| | However, ELISAs are in routine use by researchers for detection of specific antibodies to S. scabiei (1, 2).
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C. REQUIREMENTS FOR VACCINES AND DIAGNOSTIC BIOLOGICALS
There are no commercial vaccines currently available to protect animals against mange mites. Mange vaccines would a) reduce the need for chemical acaricides, b) reduce environmental pollution, c) have minimal meat/milk/wool residues and d) reduce the risk of resistance. The potential for the immunological control of Psoroptes ovis has been investigated for sheep (5-7, 26, 30, 31) and cattle (27). All these studies demonstrated that soluble fractions of P. ovis, under experimental conditions, significantly reduce the pathology of sheep scab and inhibited P. ovis population increase.
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