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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
A practical and comprehensive reference for equine dermatology cases The newly revised Second Edition of Practical Equine Dermatology delivers a thorough exploration of common dermatological conditions affecting horses whilst also drawing attention to rarer conditions. The book offers detailed advice on treatments and products currently available on the veterinary market in a problem-oriented layout that provides a practical approach to quick and efficient diagnosis. Clinical presentations, diagnostic features, and disorder management for each described condition are presented in an easy-to-digest bullet-point format supported by concise references and recommendations for further reading. An ideal quick reference for veterinary practitioners on the key points of equine skin conditions, this new edition also includes: * A thorough introduction to the diagnostic approach, including taking an accurate history, the clinical examination, and diagnostic tests. * Comprehensive exploration of pruritus, including contagious conditions, such as ectoparasites and helminth infestation, and non-contagious conditions, such as insect attack and atopic dermatitis. * Practical discussion of crusting and scaling, including primary seborrhoea and infectious causes, such as superficial fungal infections and environmental factors. * In-depth examination of ulcers and erosions, nodules and swellings, coat problems, and pigmentary disorders. Perfect for any practising veterinarian seeing equine cases in first opinion practice, Practical Equine Dermatology will also be of use to veterinary students with an interest in equine veterinary medicine.
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Table of Contents
Cover
Title Page
Copyright Page
Preface to the second edition
Acknowledgements
Disclaimer
1 The diagnostic approach
TAKING THE HISTORY
CLINICAL EXAMINATION
DIAGNOSTIC TESTS
REFERENCES AND FURTHER READING
2 Pruritus
CONTAGIOUS CONDITIONS
ECTOPARASITIC INFESTATIONS
Free‐living mite infestations
HELMINTH INFESTATIONS
MICROBIAL INFECTIONS
NON‐CONTAGIOUS CONDITIONS
Hypersensitivity disorders
Immune‐mediated disease
Neoplasia
Neurogenic pruritus
REFERENCES AND FURTHER READING
3 Crusting and Scaling
IDIOPATHIC SEBORRHOEIC CONDITIONS
SECONDARY, ACQUIRED KERATINISATION AND CRUSTING DISORDERS
INFECTIOUS CAUSES
IMMUNE‐MEDIATED CAUSES
ENVIRONMENTAL CAUSES
UNCERTAIN AETIOLOGY
REFERENCES AND FURTHER READING
4 Ulcers and Erosions
CONTAGIOUS CAUSES
IMMUNE‐MEDIATED CAUSES
CONGENITAL AND HEREDITARY CAUSES
ENVIRONMENTAL CAUSES
NEOPLASTIC CAUSES
MISCELLANEOUS DERMATOSES
REFERENCES AND FURTHER READING
5 Papules, Nodules, and Masses
PHYSICAL CONDITIONS
CYSTS
VIRAL CONDITIONS
BACTERIAL INFECTIONS
FUNGAL INFECTIONS
PARASITIC CONDITIONS
IMMUNE‐MEDIATED CONDITIONS
NEOPLASIA
MISCELLANEOUS CAUSES
REFERENCES AND FURTHER READING
6 Coat Problems
ALOPECIA
OTHER ABNORMALITIES
REFERENCES AND FURTHER READING
7 Pigmentary Disorders
GENETICS OF SKIN AND COAT COLOUR
HYPOPIGMENTATION DISORDERS
HYPERPIGMENTATION
REFERENCES AND FURTHER READING
8 Therapy in Equine Dermatology
AVAILABILITY OF VETERINARY MEDICINES FOR EQUINE PATIENTS
REFERENCES AND FURTHER READING
Index
End User License Agreement
List of Tables
Chapter 2
Table 2.1 Microbial infections that may feature pruritus
Chapter 3
Table 3.1 Diseases to be considered as underlying causes of greasy heel syn...
Chapter 4
Table 4.1 Cutaneous manifestations of adverse drug reactions
Chapter 6
Table 6.1 Interpretation of plasma ACTH concentrations (Equine Endocrinology...
List of Illustrations
Chapter 1
Figure 1.1 Taking the history. Components and the sequence of the history ta...
Figure 1.2 Clinical examination and diagnostic procedures. A thorough genera...
Figure 1.3 Example of an examination form for recording distribution and nat...
Figure 1.4 (a) A coarse‐toothed brush (e.g. 90 mm Denman scalp brush) facili...
Figure 1.5 Surface adhesive tape sampling.
Figure 1.6 Fine needle aspiration of a nodular lesion.
Figure 1.7 The punch biopsy procedure enables rapid sampling and is suitable...
Chapter 2
Figure 2.1 Visual analogue scale for owner assessment of pruritus in their h...
Figure 2.2 (a) Alopecia of ventral neck and poor hair coat in a pony with pe...
Figure 2.3 Alopecia and excoriation of tail base due to infestation with suc...
Figure 2.4 Haemorrhagic crusts and exudation affecting the pastern region of...
Figure 2.5 Adult female
Chorioptes bovis
in liquid paraffin (x125).
Figure 2.6 Pony showing extensive alopecia affecting head, neck, trunk, and ...
Figure 2.7 Patchy alopecia of face due to trombiculidiasis.
Figure 2.8 Larva of
Neotrombicula autumnalis
from a skin scraping.
Figure 2.9 Patchy alopecia affecting ventral neck and trunk in a horse house...
Figure 2.10 Multiple wheals and swellings on the lateral neck and trunk of a...
Figure 2.11 Hair loss, crusting, and excoriation affecting the tail and rump...
Figure 2.12
Culicoides
hypersensitivity: alopecia of the mane and crest regi...
Figure 2.13 Ventral midline alopecia with excoriations, crusted papules, and...
Figure 2.14 Intense pruritus in a horse with atopic dermatitis, intradermal ...
Figure 2.15 Urticaria in an atopic horse: multiple raised papules, plaques, ...
Figure 2.16 Intradermal tests in an atopic horse.
Figure 2.17 Alopecia, erythema, scaling, and hyperpigmentation on the lumbar...
Chapter 3
Figure 3.1 Tail seborrhoea in a young thoroughbred colt. Large flakes of des...
Figure 3.2 Mallenders. Horizontal linear crusting and scaling on palmar aspe...
Figure 3.3
Trichophyton
infection. Multiple annular lesions of scaling, crus...
Figure 3.4 Crusted lesions with hair tufts in a case of
Trichophyton equinum
Figure 3.5 Dermatophilosis. Erythema, crusting, and alopecia in the white‐ha...
Figure 3.6 Thick scab with attached hair from a lesion of dermatophilosis. N...
Figure 3.7 Dermatophilosis. Raised crusts and matting of hair, patchy alopec...
Figure 3.8 Dermatophilosis. Giemsa‐stained smear from an emulsified scab. No...
Figure 3.9 Staphylococcal folliculitis and furunculosis.
Figure 3.10 Bacterial folliculitis of pastern and metatarsal regions. Staphy...
Figure 3.11 Mucocutaneous pyoderma affecting the lips and perioral area. Sou...
Figure 3.12 Generalised crusting and coalescing annular alopecia in a stalli...
Figure 3.13 Crusting and matted tufts of hair in a young pony with widesprea...
Figure 3.14 Crusting and haemorrhagic erosion and ulceration affecting the c...
Figure 3.15 Cutaneous lupus erythematosus. Asymmetric patchy depigmentation ...
Figure 3.16 Leucocytoclastic vasculitis. Tightly adherent crusts overlying h...
Figure 3.17 Irritant contact dermatitis caused by leaning against a fence co...
Figure 3.18 Contact dermatitis. Circumscribed patch of scaling, alopecia, an...
Figure 3.19 Generalised patchy alopecia and scaling in a 9‐year‐old hunter w...
Figure 3.20 Cutaneous lesions of scaling and alopecia in generalised granulo...
Figure 3.21 Localised sarcoidosis. Alopecia, scaling, lichenification, and t...
Figure 3.22 Multisystemic eosinophilic epitheliotropic disease (MEED): exfol...
Figure 3.23 Alopecia, scaling, and areas of ulceration affecting the forelim...
Figure 3.24 Linear keratosis. Line of crusted papules affecting medial aspec...
Figure 3.25 Coronary band dystrophy in a Belgian warmblood.
Figure 3.26 Exudative pastern dermatitis – ‘greasy heels’.
Figure 3.27 Focal crusting regions in a case of chronic pastern dermatitis –...
Chapter 4
Figure 4.1 Cutaneous habronemiasis (summer sores): ulcerated nodular lesions...
Figure 4.2 Coital exanthema showing epidermal vesicles and ulcers with marke...
Figure 4.3 Vulval lesions of EHV‐3 infection.
Figure 4.4 Urticarial wheals and plaques after application of car shampoo....
Figure 4.5 Maculopapular and urticarial eruptions after administration of tr...
Figure 4.6 Papulocrustous rash with focal hair loss, which appeared within 4...
Figure 4.7 Warmblood fragile foal syndrome: extensive ulceration on the fore...
Figures 4.8 Girth gall: erythema, alopecia, and skin thickening associated w...
Figure 4.9 Area of alopecic scarring surrounded by non‐pigmented hair (leuco...
Figure 4.10 Thrush: loss of frog horn, ulceration, and fissuring with black ...
Figure 4.11 Acute sunburn: erythema, ulceration, and crusting on the muzzle ...
Figure 4.12 Sunburnt external naris showing erythema, scaling, and alopecia....
Figure 4.13 Erosion, crusting, and fissuring of the muzzle caused by sunburn...
Figure 4.14 Photosensitisation: alopecia, ulceration, haemorrhagic exudation...
Chapter 5
Figure 5.1 Injection abscess.
Figure 5.2 Haematoma.
Figure 5.3 Capped hock.
Figure 5.4 Umbilical hernia.
Figure 5.5 Heterotopic polyodontia (periauricular cyst) with seepage of muco...
Figure 5.6 Viral papillomata affecting the periocular region of a Thoroughbr...
Figure 5.7 Papillomata affecting the muzzle in a 2‐year‐old.
Figure 5.8 Aural plaques. Depigmented hyperkeratotic plaques on the concave ...
Figure 5.9 Genital papillomata. Hyperkeratotic proliferative papules diffuse...
Figure 5.10 Molluscum contagiosum. Multiple small papules with central white...
Figure 5.11 Strangles. Enlarged retropharyngeal lymph node on the point of r...
Figure 5.12 Nodular lesions of botryomycosis (
Staphylococcus aureus
), 1–2 cm...
Figure 5.13 Fungal mycetoma affecting the tail; caused by soil‐living organi...
Figure 5.14 Demodicosis and folliculitis associated with alopecia, erythema,...
Figure 5.15 Urticaria. Multiple raised papules, plaques, and annular lesions...
Figure 5.16 Angio‐oedema. Diffuse swelling of the head of a horse after inje...
Figure 5.17 Linear urticarial wheals in a cruciform shape on the shoulder of...
Figure 5.18 Cutaneous amyloidosis. Raised, firm plaque affecting the mucocut...
Figure 5.19 Occult (flat) sarcoids. Two annular areas of alopecia with mild ...
Figure 5.20 Verrucose sarcoid. Plaque of thickened skin with surface hyperke...
Figure 5.21 Nodular sarcoids affecting the periocular region.
Figure 5.22 Fibroblastic sarcoid.
Figure 5.23 Malevolent/malignant sarcoid.
Figure 5.24 Squamous cell carcinoma. Ulcerated mass on the non‐pigmented low...
Figure 5.25 Penile squamous cell carcinoma. Nodules, together with multiple ...
Figure 5.26 Multiple melanocytic tumours around the anus, vulva, and ventral...
Figure 5.27 Amelanotic melanomas affecting the perineum and ventral tail bas...
Figure 5.28 Mastocytoma. Multilobular mass with surface ulceration on the do...
Figure 5.29 Lymphohistiocytic T‐cell cutaneous lymphoma. Multiple nodules, p...
Figure 5.30 Multiple urticarial papules and wheals after multiple mosquito b...
Figure 5.31 Papular lesions of eosinophilic granuloma.
Figure 5.32 Congenital epidermal hamartoma in a Friesian foal.
Figure 5.33 Early lesions of chronic progressive lymphoedema. Diffuse swelli...
Figure 5.34 Chronic progressive lymphoedema. Multiple fibrotic corrugations ...
Figure 5.35 Canker. Solar aspect of the hoof showing a proliferative lesion ...
Chapter 6
Figure 6.1
a) and b)
Seasonal asynchronous shedding. Patches of alopecia and...
Figure 6.2 Contact irritant dermatitis resulting in diffuse thinning of the ...
Figure 6.3 Anagen effluvium in a young Thoroughbred. Hair loss began within ...
Figure 6.4 Alopecia areata. Facial alopecia and patchy alopecia of the neck ...
Figure 6.5 Alopecia areata. Extensive generalised alopecia.
Figure 6.6 Alopecia areata. Generalised patchy alopecia with marked alopecia...
Figure 6.7 Chronic selenosis with abnormal horn growth affecting the hoof wa...
Figure 6.8 Chronic selenosis. Diffuse loss of hair from the tail (‘rat tail’...
Figure 6.9 Hypertrichosis and pot‐bellied appearance in a Connemara pony wit...
Chapter 7
Figure 7.1 Leucotrichia and focal alopecia on the caudal carpus secondary to...
Figure 7.2 Depigmentation of the hoof subsequent to inflammation of the coro...
Figure 7.3 Leucotrichia on the caudo‐dorsal rump of a pony with a long histo...
Figure 7.4 Vitiligo. Periocular depigmentation (a) and perianal depigmentati...
Figure 7.5 Melanotrichia. Tufts of hyperpigmented hairs at sites of earlier ...
Guide
Cover Page
Title Page
Copyright Page
Preface to the second edition
Acknowledgements
Disclaimer
Table of Contents
Begin Reading
Index
Wiley End User License Agreement
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Practical Equine Dermatology
Second Edition
Janet D. Littlewood
Veterinary Dermatology Referrals
Cambridge, UK
David H. Lloyd
The Royal Veterinary College
Hatfield, UK
J. Mark Craig
Re‐Fur‐All Referrals
Newbury, UK
This second edition first published 2022© 2022 John Wiley & Sons Ltd
Edition HistoryBlackwell Science Ltd. (1e, 2003)
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions.
The right of Janet D. Littlewood, David H. Lloyd, and J. Mark Craig to be identified as the authors of this work has been asserted in accordance with law.
Registered OfficesJohn Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USAJohn Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK
Editorial Office9600 Garsington Road, Oxford, OX4 2DQ, UK
For details of our global editorial offices, customer services, and more information about Wiley products visit us at www.wiley.com.
Wiley also publishes its books in a variety of electronic formats and by print‐on‐demand. Some content that appears in standard print versions of this book may not be available in other formats.
Limit of Liability/Disclaimer of WarrantyThe contents of this work are intended to facilitate diagnosis and treatment by veterinary practitioners of diseases of equine skin. In view of ongoing research, equipment modifications, changes in governmental regulations, and the constant flow of information relating to the use of medicines, equipment, and devices, the reader is urged to review and evaluate the information provided in the package insert or instructions for each medicine, equipment, or device for, among other things, any changes in the instructions or indication of usage and for added warnings and precautions. While the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives, written sales materials or promotional statements for this work. The fact that an organization, website, or product is referred to in this work as a citation and/or potential source of further information does not mean that the publisher and authors endorse the information or services the organization, website, or product may provide or recommendations it may make. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.
Library of Congress Cataloging‐in‐Publication Data Applied for
[PB: ISBN: 9781119765486]
Cover Design: WileyCover Image: © Janet D. Littlewood, Kieran O’Brien
Preface to the second edition
This second edition of Practical Equine Dermatology updates the text of the first edition and provides information on a number of new diseases. Although much of the information has not changed, it has provided the opportunity to increase greatly the number of illustrations whilst focusing the text more closely on diseases of the skin. Thus, diseases of the foot and associated structures have now been incorporated within the other problem‐orientated chapters, and conditions that are primarily orthopaedic have been omitted. In addition, suggested references and further reading are presented at the end of each chapter in order to make them more readily accessible to the reader, rather than as a single block at the end of the book.
As before, the aim has been to provide a concise, problem‐orientated text facilitating a well‐organised diagnostic approach together with a basic presentation of equine dermatology in a practical format illustrated with pictures of the principal conditions, particularly those in which visual information is an important part of diagnosis. All of the conditions likely to be encountered in the UK are included, and information on some rarer conditions, such as those that may occur in imported horses, is also provided. However, detailed information on rare and complex diseases is not included as it is anticipated that such conditions will require referral to a specialist in equine dermatology.
Indications for treatment are given within the text. These are generally based on UK practice and on products available within the UK. Where unlicensed preparations are mentioned, readers should understand that these should be used only when licensed products are not available and that efficacy and safety of unlicensed products and ‘off‐label’ use cannot be guaranteed. Issues relating to drug use in horses are considered in the final chapter on Therapy in Equine Dermatology.
This edition has been revised principally by Janet Littlewood and David Lloyd, with assistance by Mark Craig. Sadly, ‘Tommy’ Lovell Thomsett, who was a pioneer of equine dermatology in the UK, has passed away. However, his knowledge and wisdom remain as an important component of the book.
The authors hope that this text will not only provide practical help on the everyday problems of skin disease in equine practice but that it will also stimulate a deeper interest in equine dermatology.
Janet D. Littlewood
David H. Lloyd
J. Mark Craig
March 2021
Acknowledgements
The authors would like to acknowledge colleagues at Rossdales Equine Hospital and Practices for their generosity in contributing images and for support and advice during the preparation and updating of this edition of the book. They relied on the Royal Veterinary College Dermatology Group slide collection and also wish to acknowledge in particular contributions from the late Dr Keith Barnett, Dr Malcolm Brearley, Dr Harriet Brooks, Mr Andrew Browning, Dr Greg Burton, Dr Alistair Cox, Ms. K. Clarke, Dr Emily Floyd, Dr Marcus Head, Dr Sandeep Johnson, Dr Ewan Macauley, Professor Celia Marr, Mrs Jacqueline Mortimer, Dr Kieran O’Brien, Dr Richard Payne, Dr Rob Pilsworth, Dr Oliver Pynn, Dr Stephen Shaw, and Dr Liz Stevens.
Disclaimer
While every care has been taken by the authors and publisher to ensure that the drug uses, dosages and information in this book are accurate, errors may occur and readers should refer to the manufacturer or approved labelling information for additional information.
Readers should also note that this text includes information on drugs that are not licensed for use in horses. Readers should therefore check manufacturers’ product information before using such drugs.
1 The diagnostic approach
A structured approach is essential. Vital information is obtained during the history‐taking process and sufficient time must be allowed for this. Accurate information on husbandry is particularly important. Clinical examination must include systemic and skin components. The process is illustrated with flow diagrams (Figures 1.1 and 1.2).
TAKING THE HISTORY
The approach (Figure 1.1) is similar to that adopted in other species.Points to include are:
Breed, age, sex, origin:
Consider these aspects carefully; in many conditions, these simple data will have an important impact on your diagnostic considerations.
History of skin problems in related animals.
Type of husbandry and use:
Length of time owned.
Use – competitions, general riding, breeding, racing.
Feeding regimen.
Periods spent in stable or at pasture.
Type of stable and bedding – stable hygiene, contamination.
Conditions in paddocks – mature meadow pasture or new grass ley, proximity of water, trees.
Seasonal changes in management.
Routine health care procedures – vaccination, deworming.
Figure 1.1 Taking the history. Components and the sequence of the history taking process. Analysis of the history should enable the clinician to construct an initial list of differential diagnoses that may help to focus the clinical examination along particular diagnostic lines. It may enable the diagnostic process to be abbreviated where a likely diagnosis is indicated, or it may point towards the need for a more detailed approach.
Grooming procedures – sharing of grooming kit, tack, grooms.
Equipment used in contact with horse – boots, bandages, saddle cloths, rugs.
Contact with other horses, other species – opportunities for disease transmission.
History of the current problem.
First signs, progression, response to treatment and management changes.
Seasonal effects.
Previous episodes of disease.
Results of any diagnostic tests.
Current or recent therapy – includes questions about use of over‐the‐counter and non‐veterinary products.
Evidence of transmission – lesions in other horses, other species, humans.
General health – concurrent or previous conditions.
Figure 1.2 Clinical examination and diagnostic procedures. A thorough general and dermatological examination should be carried out unless the history points clearly towards a diagnosis. Examination coupled with history enable a list of differential diagnoses to be drawn up, formulation of a diagnostic plan and the selection of appropriate tests and sites to be sampled, and/or therapeutic trials.
CLINICAL EXAMINATION
A full clinical examination to assess both the general health status and the skin is necessary in most cases. Ensure that the animal is adequately restrained and that you have sufficient light. Work systematically down each body region, beginning at the head and ending at the tail and perineal region. Be sure to include all aspects of the feet including the coronary band and the frog. The skin may need to be cleaned to observe some lesions. In some instances, sedation may be necessary.
A record of the distribution and severity of primary and secondary lesions should be kept. Forms including a horse outline make this much easier (Figure 1.3).
It may be helpful to visit and examine the paddocks and exercise areas used.
Figure 1.3 Example of an examination form for recording distribution and nature of lesions in equine dermatology cases.
DIAGNOSTIC TESTS
The history and clinical examination should enable you to formulate a list of differential diagnoses. It may help to create a problem list, identifying the relevant historical features and predominant clinical signs, categorising them as contagious or non‐contagious, and allocating the disease within the following groups, which form the basis for the problem‐orientated approach in this book:
Pruritic
Crusting and scaling
Ulcerative and erosive
Nodular or swollen
Alopecia/hair coat changes
Pigmentary disorders
A diagnostic plan can then be constructed, diagnostic procedures selected, and samples collected. Sample collection may include the following techniques.
Hair plucks
Useful to determine whether the lesions of alopecia or hypotrichosis are due to self‐inflicted damage (fractured hair shafts, split ends) indicating that the condition is pruritic, or due to abnormal hair growth (absence of anagen roots, abnormal catagen roots), and to examine for dermatophytes and for parasite eggs.
Choose fresh, unmedicated lesions.
For suspected dermatophytosis, where cultures are required, first lightly clean the areas to be sampled with 70% alcohol (to reduce contaminant organisms).
Tissue or epilation forceps can be used to grasp gently and pull out hairs from the periphery of the lesion.
Samples for microscopy can be placed on adhesive tape wrapped around a microscope slide and mounted in a drop of liquid paraffin just prior to examination.
Samples for fungal culture submission should be held in paper or sterile, non‐airtight containers to prevent a humid environment that might support the growth of saprophytic organisms.
Crusts
Useful for cytological examination looking for bacterial organisms (particularly Dermatophilus) and for submission for fungal and bacterial culture.
Choose a fresh, unmedicated lesion.
Impression smears of the underside of freshly removed crusts, stained with a rapid Romanowsky‐type stain (e.g. Diff‐Quik, Hemacolor, Rapi‐Diff, Speedy‐Diff) or Gram’s stain, can provide a quick method of diagnosis for dermatophilosis.
Crusts can be collected and held in paper envelopes or sterile containers for transport to the laboratory.
Dried crusts can be emulsified in a drop of sterile saline on a slide, warmed to allow rehydration of material, prior to air‐drying and fixing (heat fixation for Gram’s stain, methanol/ethanol fixation for rapid‐differentiating Romanowsky‐type stains) for cytological examination and identification of bacterial and fungal organisms.
Coat brushings
These allow for examination for surface‐living external parasites and dermatophytes where the lesions are diffuse or extensive. Scrapings are better for deeper resident mite infestations.
Use a sterile scalp brush or new toothbrush to brush firmly over the lesions (Mackenzie brush technique;
Figures 1.4
a and b). Place the brush in a paper envelope to protect it prior to submission for dermatophyte culture.
A scalp brush or wooden tongue depressor can be used to collect debris directly into a sterile Petri dish for external parasites. Material should be examined promptly as chorioptic mange mites are highly motile and easily lost from sample containers.
Figure 1.4 (a) A coarse‐toothed brush (e.g. 90 mm Denman scalp brush) facilitates sampling of large areas of skin and coat. The collected hair can be removed and examined, or the teeth may be embedded in a fungal culture medium as illustrated. (b) Here Microsporum canis has been isolated using this technique.
Skin scrapings
Skin scrapings can be performed for detection of external parasitic diseases such as chorioptic mange, larval stages of harvest mites, demodicosis (rare), or for dermatophyte culture and cytology.
If necessary, remove hair over areas to be sampled by careful clipping.
Use a wooden tongue depressor for superficial sampling or a large, curved scalpel blade if deeper samples are required, with the sharp edge blunted to reduce the risk of injuring the horse or operator.
Moisten the sample site or the collection tool with liquid paraffin (more useful for examination for mites), water or normal saline (for dermatophytes).
Gently scrape crusts, scales, and associated hair so that the material accumulates on the blade or tongue depressor. Transfer onto a microscope slide with more liquid paraffin, or with potassium hydroxide solution if collected in aqueous medium, which allows clearing of debris and easier identification of pathogens.
Deeper scrapings are needed for suspected demodicosis, deep enough to cause capillary ooze.
Sample several sites, collect plenty of material, and divide amongst several slides to make thin suspensions, which are quicker and easier to examine efficiently.
Surface adhesive tape samples
An alternative method for obtaining surface material, including Oxyuris equi eggs, surface‐living ectoparasites, hair fragments, exfoliated cellular material, and surface microorganisms for direct microscopical examination or after staining; it is less traumatic and avoids the risk of injury associated with skin scrapes. This technique is particularly useful for identification of chorioptic mange mites which are highly motile, but also allows detection of other pathogens including dermatophytes and yeasts.
A piece of clear adhesive tape (e.g. 3M Scotch Crystal, Sellotape Clear) is applied to the lesional area 3–4 times (
Figure 1.5
).
Tape is applied (sticky side down) to a microscope slide over a drop of liquid paraffin for direct examination or over a drop of blue dye from a rapid Romanowsky‐type stain kit.
Excessive mounting medium or stain is removed by wiping with soft paper towel prior to microscopical examination.
Figure 1.5 Surface adhesive tape sampling.
Direct smears
From fresh, exudative, crusted, excoriated, or pustular lesions, a direct impression smear can be made for cytological examination and for microorganisms.
Press a glass slide against the concave undersurface of a removed exudative crust, or against the surface of a freshly exposed lesion.
For an intact pustule, gently break the overlying skin with a 25 g needle and press a clean glass slide to the ruptured lesion, or purulent material may be collected in the needle bevel and then transferred to the glass slide.
For lesions at sites where it is difficult to apply a slide directly, material can be collected with a dry swab and then rolled onto a glass slide.
Air‐dry the slide and store in a slide box prior to heatfixing (for Gram staining) or immersion in methanol (for Romanowsky‐type staining).
Wet crust preparations
For older, crusted lesions this technique enables microscopical examination of dried exudate.
Representative sample of crust is placed on a glass slide with a few drops of normal saline.
Material is finely chopped and macerated with a scalpel blade.
Slide is left in a warm place for 20–30 min to allow rehydration of cellular material.
Any large clumps of debris are gently removed prior to thorough drying and heat fixing of the remaining suspension prior to staining with a rapid Romanowsky‐type stain kit.
Swabs
May be useful for bacteriology and fungal culture and collecting material for cytological examination.
If the sample is to be processed within 30 min of collection, a dry, sterile swab can be used for bacterial and fungal culture, and smears. Otherwise, place swabs into suitable transport media (e.g. Amies charcoal medium, or Copan ESwabs).
Samples collected from the skin surface may not be representative of the causative agent, so collect pus from an intact pustule or the underside of a freshly removed scab, or submit biopsy material for culture. Useful cultures may sometimes be obtained from a dry crust by rehydrating with sterile normal saline prior to processing.
Needle aspirates
This technique is used for sampling nodules, masses, and enlarged superficial lymph nodes.
A 20–22 g needle can be used, with or without a 5 ml syringe. The area to be aspirated should be carefully cleaned and disinfected.
The needle is inserted into the nodule (
Figure 1.6
), mass, or lymph node and used to probe the tissue in several places, initially without aspirating, and subsequently whilst gently aspirating.
