Aiden P Foster PhD DipACVD MRCVS
Chorioptic mange in camelids is associated with Chorioptes bovis. Chorioptic mange is also occasionally seen in cattle and uncommonly in sheep (C. ovis). In horses C. equi can be a major problem particularly in large groups where there may be widespread asymptomatic infestation. These mites are obligate parasites although they have been reported to survive off the host for up to 70 days. They tend to be found on the distal limbs near the hooves, but they can also move on to other areas of the body. They do not burrow into the skin and they feed on epidermal debris.
Clinical signs may include mild to moderate pruritus, which then leads to alopecia and scaling of the feet and tail base with extension to the ventral abdomen, medial limbs, and the ears. Thickening (lichenification) and hyperpigmentation (greying) of the skin may develop with chronic disease.
Chorioptes (and other) mites may be found by collecting superficial skin scrapings with a blunted scalpel blade into liquid paraffin and examining the slide with a cover slip under a low-power microscope lens. Good sites for collecting scrapings for Chorioptes in alpacas are the dorsal interdigital and axilla areas. Ideally animals in the group that appear to be unaffected should be sampled because there may be asymptomatic infestation. This may reflect that some animals like horses may harbour small numbers of mites with no ill effect.
There may be some difficulty finding mites in animals with severe skin problems. This situation may be due, in some camelids, to a hypersensitivity response to the activity of the mites. In some cases of chronic chorioptic mange there may be severe scaling, alopecia and thickening of the skin, which may lead to some confusion with various hyperkeratosis syndromes that have been described particularly in llamas. Such syndromes have been associated apparently with partial or good responses to supplementation with zinc but it would be essential to rule out ectoparasites before trying various feed supplements. Unfortunately there are no simple blood biochemistry tests or histological changes in skin biopsies to provide a definitive diagnosis for camelids with chronic disease. Management of such cases can be a challenge for the veterinary clinician and owner alike.
Sarcoptic mange has been reported in the UK and is usually associated with substantial pruritus and there is a risk of transmission of the mites to humans handling affected animals. Psoroptic mange may also be seen in camelids in the UK and is particularly associated with ear infestation although like sarcoptic and chorioptic mange the signs of skin irritation and secondary disease may be generalised over the whole body.
A number of factors should be considered before starting therapy for ectoparasites, particularly Chorioptic mange. Firstly all products used are not licensed in the UK for camelids. Secondly, ideally a definitive diagnosis based on examination of skin scrapings should be established before embarking on therapy.
· Llama and alpaca hair does not contain lanolin; consequently topical applications of insecticidal/acaricidal products used on other ruminants may not be as effective in camelids. Consequently there may be reliance upon the use of systemic therapies particularly macrocyclic lactones (ivermectin, moxidectin, eprinomectin, and doramectin).
· In order to achieve eradication or a marked reduction in numbers of any form of suspected or confirmed mite infestation owners should weigh and treat all animals within a herd with an accurately measured dose.
· In the case of the surface dwelling Chorioptes mites repeated administration of injectable or topical macrocyclic lactone products might substantially reduce but not eradicate infestation. Consequently eliminating such infestations may also require application of acaricidal sprays such as that reported with fipronil-based products, although cost and large herd size will deter owners from pursuing this approach. In one study of Chorioptes mite infestation there was a good response (but not complete eradication) to the weekly application of four treatments with an eprinomectin-based product (D’Alterio et al 2005a).
Some camelids are treated for ectoparasites with sprays or dips used for the control of flies or mites in sheep. Dipping can be stressful for camelids and there is limited anecdotal information about the efficacy and safety of dip/spray products, so they are not recommended.
· Mite infestations are usually host specific and it is most likely that camelids are infested by close contact with other camelids but they may possibly be infested from other animals and livestock. The risk of transfer of mite infestation between camelids and other species of livestock is unknown. For camelids grazing with cattle and or sheep treatment of all the animals in the group would ensure control of mite infestation.
· Pharmacokinetic studies of macrocyclic lactones in camelids are limited in number but suggest that compared with other ruminants that absorption is somewhat reduced / slower whatever the route of administration. The clinical impact of the absorption of such products - in terms of skin disease and mite infestation - remains unclear.
· Repeated use of topical products for ectoparasite control may temporarily stain the hair and this may be a concern with show animals.
· When using macrocyclic lactone products for ectoparasite control there will potentially be an effect on endoparasites. Camelids harbour some nematode species that are common to sheep and cattle including Ostertagia and Trichostronglye spp.. In recent years there have been growing concerns about the development of resistance to worming products in sheep and cattle. This has led to the formation of the Sustainable Control of Parasites in Sheep initiative (SCOPS).
· While camelids usually access a communal dung area there will be potential for contamination of pasture – particularly with high stocking densities and limited availability of pasture - with nematode larvae. Ideally before embarking on the use of worming products or when considering treatment for ectoparasites with macrocylic lactones there should be consideration of what parasites are being treated. Consequently faecal egg count (FEC) monitoring is recommended as a means of assessing the treatment requirements and can be used to check for evidence of nematode resistance. Careful use of worming products including consideration of rotation of product types, and pasture rotation, may help to reduce selection for resistance in nematodes when dealing with camelid herds and particularly where there is shared grazing with other ruminants.
· The SCOPS initiative aims to reduce the commonplace employment of particularly regular and repeated worming programs, which have been associated with the development of substantial resistance problems. In camelids, for example, treating them twice yearly in spring and autumn, when moving out or into housing, may eventually lead to problems with resistance and incomplete control of ectoparasite and endoparasites – particularly when using macrocyclic lactone type products.
· For more information on SCOPS and the control of endo- and ectoparasites (in sheep) see http://www.nationalsheep.org.uk/health/scops.htm and http://www.defra.gov.uk/animalh/diseases/control/parasite_control.htm
· In camelids macrocyclic lactone products based on ivermectin, moxidectin, eprinomectin, and doramectin have been reported to have variable to good effects on mite infestation with Psoroptes and Sarcoptes mites and in sucking lice. Since in most infestations the life cycle of the parasite lasts approximately three weeks it is usually necessary to provide treatment for two life cycles and that will last for up to six weeks to establish good control or eradication. Even so, there have also been suggestions of using higher than label doses of ivermectin-based products for ectoparasites (particularly Chorioptes) in alpacas and llamas, such as 400 micrograms/kg subcutaneously on a weekly basis, because of perceived ineffectiveness of standard dosages used in other ruminants.
Anecdotal reports of various treatment regimes for the control of ectoparasites clearly demonstrate that there is a need for controlled clinical trial work to clarify the dosing regimen for macrocyclic lactones and other products for camelids, including alpacas and llamas, with various types of mite (or lice) infestation. Furthermore any treatment regime for ecto- or endoparasites should be based ideally on a definitive diagnosis of the parasites involved using, as appropriate, examination of skin scrapes and faecal egg counts. This information should form part of a herd health plan to control parasite exposure that may otherwise lead to substantial cutaneous and gastrointestinal diseases.
D’ALTERIO, G.L., JACKSON, A.P., KNOWLES, T.G., FOSTER, A.P. (2005a) Comparative study of the efficacy of eprinomectin versus ivermectin, and field efficacy of eprinomectin only, for the treatment of Chorioptes mange in alpacas. Veterinary Parasitology 130, 267-275.
D’ ALTERIO, G.L, CALLAGHAN, C., JUST, C., MANNER-SMITH, A., FOSTER, A.P., KNOWLES, T.G. (2005b) Prevalence of Chorioptes sp. mite infestation in alpaca (Lama pacos) in the south-west of England: implications for skin health. Small Ruminant Research 57, 221-228.
D’ALTERIO, G.L., KNOWLES, T.G., EKNAES, E.I., LOEVLAND, I.E., FOSTER, A.P. (2006) Postal survey of the population of South American camelids in the United Kingdom in 2000-01. Veterinary Record 158, 86-90.
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