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PARASITES
SKIN DISEASES
whose 93 years were eminently worthwhile British Library Cataloguing in Publication DataA catalogue record for this book is available from the British Library Published in Great Britain in 1995 byJ. A. Allen & Company Limited No part of this book may be reproduced or transmitted in any way or by any means, elec-tronic, or mechanical, including photocopy, recording, or any information storage andretrieval system, without permission in writing from the publishers. All rights reserved.
Production editor: Bill IresonIllustrator: Maggie RaynorCover designer: Nancy LawrencePrinted in Hong Kong Contents
Host Specificity 5 - Quantity of Parasite 6 - Endoparasites in Disease 6 Specific Effects of Endoparasites 7 - Signs of Infestation 13 Management of Infestation 14 - Climatic Conditions 14 - Mixed Infection 16 - Reproduction and Lactation 16 - Productivity 16 Roundworms (Nematodes) 18 - Large Redworm (Strongylus) 20 - Small Redworm (including Cyathostomum) 25 - Threadworm (Strongyloides) 28 - Lungworm (Dictyocaulus) 32 - Horse Roundworm (Parascaris) 34 - Hairworm (Trichostrongylus) 38 - Pinworm (Oxyuris) 41 - Neck Threadworm (Onchocerca) 44 - Abdominal Worm (Setaria) 47 - Eyeworm (Thelazia) 49 - Stomach Worms (Habronema and Draschia) 52 - Gullet Worm (Gongylonema) 54 - Cestodes 56 - Tapeworms 56 - Other Tapeworms 60 — Trematodes 60 — Liver Fluke 60 — Protozoan Infections64 — Other Protozoan Infections 65 Cyathostomes 67 — Limiting Pasture Contamination 70 — Low-level Exposure 71 — Pasture Hygiene 71 — Removing Faeces 72 — Harrowing and Topping 73 — Resting 73 — Mixed Grazing 73 — Dosing Reminders 74 — Vital Points 76 — Stable Hygiene 77 — Control Routines 77 — Practical Aspects of Worming 77 — Worming Procedures 78 — Specific Drugs 79 — Worming Calendar 84 — Insecticides 85 — Antifungals 86 Diagnosis 88 — Faecal Examination 89 — Materials 90 — Procedure 90 —Alternative Procedure 91 Anatomy and Purpose 92 — Skin Musculature 93 — Skin Glands 94 —Sebum 94 — Sweat 94 — Hair 95 — Functions of Skin 96 — Diagnosis of Skin Disease 96 — Laboratory Investigation 97 Skin Repair 99 — Infected Wound Repair 100 — Other Complications 101— Treatment of Wounds 102 — Proud Flesh 106 — Burns 107 Fly Worry 110 — Midges (Culicoides) 113 — Stable Fly (Stomoxys) 117 —House Fly (Musca) 118 — Horse Fly (Tabanus) 118 — Tsetse Fly(Glossina) 119 — Hippoboscids (Hippobosca) 119 — Mosquitoes 119 — Blowfly, Screw-worm 120 –. Wasps and Bees 121 – Botfly 121 – Warble Fly 125 – Lice 127 – Fleas 131 – Mites 131 – Ticks 136 Rain Scald 141 – Greasy Heel or Mud Fever 142 – Folliculitis 144 Abscess and Deeper Infection 145 – Cellulitis 146 – Ulcerative Lymphangitis 146 – Acne 147 – Bacterial Granuloma 147 – Skin Tuberculosis 148 – Glanders 148 – Ringworm 148 – Other Fungal Management of Allergies 154 – Urticaria/Angioedema 158 – Food Allergies 160 – Contact Dermatitis 161 – Other Causes 162 – Poisons 163 Tumours of Skin 167 – Amyloidosis 177 – Anhidrosis 178 – Collagenolytic Granuloma 178 – Ear Diseases 179 – Fistulous Withers 180 – Filling in the Legs 180 – Haematomas 181 – Helminth Diseases 182 – Hereditary Diseases and Pigment Disorders 182 – Hormonal Diseases 185 – Hypothyroidism 186 – Immune Diseases 186 – Keratinization Disorders 189 – Lymphangitis 189 – Nodular Panniculitis 190 – Unilateral Papular Dermatosis 190 – Poll Evil 191 – Protozoan Skin Diseases 191 – Saddle Sores and Girth Galls 191 – Viral Diseases 192 I would like to express my gratitude to Professor Brian J. Sheahan, MA,MVB, MS, PhD, MRCVS, MRCPath, of the Department of VeterinaryPathology, University College Dublin, for the photograhic material he has so generously provided and for his help in reading the manuscript.
My thanks also to a number of individuals: Professor Kenneth P. Baker, MA, MSc, Phd, DVD, FRCVS, of the Department of Veterinary ClinicalMedicine, University College Dublin, for his help with that part of the bookon skin diseases; David Byron, of MSD AGVET, for his most generoushelp with material, especially the use of the many photographs included inthe text; Jane Parry, BVetMed, MRCVS, also of MSD AGVET, for refer-ence material she supplied; Jacqueline Meldon, of Pfizer Animal HealthLimited, who also very kindly provided photographic material; andDeborah J. Baker, BVetMed., MRCVS, of Hoechst UK Limited.
To Raymond Hopes, BVMS, MRCVS, of Rossdale and Partners, Newmarket, Suffolk, I am indebted for the use of photographs and slideson skin conditions. For the photographs they supplied, my thanks to: PeterD. Rossdale, MA, PhD, DESM, FRCVS; Colin K. Peace, MA, VetMB,MRCVS; and Alan Wright, BVSc, MRCVS.
For help provided I would also like to thank: Roger R. Dawson, BSc, PhD, Animal Medicines Training Regulatory Authority (AMTRA); RogerCook, National Office of Animal Health (NOAH); and the staff of theWellcome Library, Royal College of Veterinary Surgeons (RCVS).
My special thanks, too, to Maggie Raynor for her excellent artwork; to Bill Ireson for his production editing; to Nancy Lawrence for the coverdesign; and to my publishers for their help and encouragement.
Illustration Acknowledgements
I am grateful to the individuals and organisations listed below for givingtheir permission to reproduce original material. Each subject used is listedby the relevant page number in this book.
Note that many subjects have been enlarged or reduced and are thereforenot to scale. J. A. Allen & Co. Ltd.: p. 31, p. 93.
Raymond Hopes: p. 101 (bottom), p. 135, p. 159 (two), p. 172 (two), p. 181, p. 186, p. 188, p. 190, p. 191.
MSD AGVET: p. 24 (two), p. 26, p. 30, p. 36, p. 40 (top), p. 43 (top), p. 46, p. 51 (two), p. 58 (top and centre), p. 63, p. 114, p. 120 (two), p. 124(three), p. 130 (bottom), p. 134 (top), p. 139 (two).
Colin K. Peace: p. 100 (two).
Pfizer Limited: p. 8, p. 43 (centre and bottom), p. 58 (bottom), p. 71.
Peter D. Rossdale: p. 176.
Brian J. Sheahan: p. 9, p. 40 (bottom), p. 169 (three).
Alan Wright: p. 130 (top), p. 134 (bottom), p. 150 (two), p. 171.
Introduction
Parasites and skin diseases of horses are two subjects about which theaverage horse owner knows little. The difficulty lies in that they are spe-cialist subjects, filled with their own technical terminology and thereforehard to interpret.
However, the clinical importance of these fields is evident in everday horse management. Worms and other parasites have a significant ongoingeffect on growth and production. Skin conditions, be they contagious ornot, are a familiar form of equine disease and a regular reason why horsescannot be ridden.
In attempting to make these subjects understandable to the lay person, therefore, it is necessary in this book to begin at the practical base. Forexample, common names, like `redworm' and lungworm' , are used inconjunction with the generic names, Strongylus and Dictyocaulus. Forcorrectness, however, the generic names will be used in parentheses in section headings, but every effort is made to enable the reader to gain theinformation he or she requires without being overcome by the technicalnomenclature which is vital to the scientist/veterinarian.
Similarly, in discussing the effects of parasite infection, it is not intended to delve into the complexities of equine pathology. Yet it shouldbe understood that pathology means the study of diseases, or, more prop-erly, the study of the changes in body tissues that result from disease.
Thus, a worm is not just an undesirable resident of the digestive system;it may damage the lining to the bowel, it may migrate through other tis-sues, causing damage to remote organs. It may also interfere withdigestion, preventing the absorption of food elements from the bowel;this may lead to weight loss, stunted growth, and improper developmentof the horse's skeleton. Pathology therefore is a vital part of our discourse here; anyone who has an interest in horses and responsibility for theirwelfare will be better for an understanding of pathology, and more able tounderstand the wider practical effects of a given disease.
This book is, then, organised in a way that should make most sense to such a reader. It is not the way in which parasites and skin diseases are dealt with in professional literature, but that need not be of concern. Anyreader who digests the contents of this book and wants more informationmight well be ready to tackle the complexities of specialist professionaltexts. In order to help the reader with the more technical terms, a glossaryis included at the end of the book.
A parasite is a living organism that lives upon or within another livingorganism from whence it ekes its existence. Its affect on the host variesbut may occur directly through invasion of tissues, or through the inges-tion of blood as the redworm does. Mange mites live on surface cells, some even burrowing within the skin. Some parasites live within thebowel, in the lumen (centre of the tract) unattached, obtaining their foodfrom the bowel contents.
Parasites that exist within the animal are called endoparasites. Those that live on the skin are called ectoparasites.
The animal that supports the parasite is referred to as the host. In this book, the host in all cases is the horse and we will at times distinguishbetween the influence parasites have on horses at different stages ofgrowth.
In the main we are dealing with helminth parasites among which are the common worms (divided into nematodes, cestodes and trematodes) ofthe horse's bowel and arthropod parasites (ticks, mites, lice and flies).
Many parasites are what is known as 'host-specific', meaning they confine themselves to a single species. Others are not and can be found indifferent animals. It is evident that a worm which is common to cattle, sheep and horses would therefore have a special significance where eachof these species were grazed on the same piece of land.
Each parasite has a specific location within a host where it is most commonly found – called a predilection site – and which may play a partin the technical naming of the parasite. Needless to say parasitic infesta-tion may cause interference with the horse's body defences and thus pavethe way for secondary infection with bacteria and viruses. A further prob-lem (associated mainly with ectoparasites) is the ability of some parasitesto transmit disease (e.g. encephalitis virus and swamp fever, transmittedby biting flies and mosquitoes; human malaria is a protozoan disease,transmitted by mosquitoes).
Other factors which may influence disease are the age of the host and physical condition, also matters like season, climate, geographic location,and so on. Internal worm burdens have a more insidious effect in cold,wet conditions and external parasites may irritate most in warmer Climatic factors also dictate the manner in which parasites survive out- side the host. Most endoparasites lay eggs which pass onto pasture in thefaeces. These may hatch into larvae which are ingested by the next host.
The capacity of larvae to survive externally is influenced by heat andcold, the quality of the pasture, exposure to sunlight, and so on. Becauseof this life cycle, horses which are stabled are less likely to encounter par-asites than when kept at grass. However, parasitic risk is not completelyeliminated by stabling, and stable hygiene is important in preventing Of course, very few infections are caused by a single parasite. The type and number involved may vary, and there may be external and internalparasites occurring at the same time. This, naturally, will influence theeffect on the host. The most important aspect of all this is the daily influ-ence parasites have on management. What are the risks of your horsebeing affected by diseases which are not altogether evident on the sur- face? How can you recognise a worm infection? What is the life cycle?What is the prevention? What is the treatment? Horses, being animals which are kept for pleasure, not food, suffer because research on their diseases is often deemed uneconomical. Wemust rely therefore to some extent on information from other sources, likeresearch into cattle and sheep diseases. Yet this does not reduce the value of the information as long as it is understood that principles applying toparasitic infection in general may be diluted in certain circumstancesbecause of the nature of the horse. The horse owner is, of course, moreinterested in bone development, or diseases of bone that may ensue fromnutritional problems. He or she is also interested in weight gain, in the full, normal physical development of an athletic animal; of its ability toperform, to stand up to training and to carry weight. But our primaryinterest must be in the soundness of our horses, not weight gain per se.
We simply wish for the animal to reach its natural potential without duehindrance.
Skin diseases are also complex and have a variety of causes besides exter- nal parasites. For example, modern medicine recognises such diverse causes as infection, diet, contact with irritant or allergenic substances, allergies, hereditary and auto-immune disease. Each of these are dealt with in some detail in this book, hopefully thus making it easier for thereader to understand and recognise the different expressions of skin dis-ease. There is a great deal that horse owners themselves can do tominimise the problems related to them.
In a book combining these two subjects, parasites and skin diseases, it isinevitable that there might be some duplication or variation from an idealline. For example, the botfly parasitises the horse's stomach in its larvalstages; the warble fly, when it affects horses, is most significant when adeveloping larva appears under the skin of the back. In this book, both areincluded with other conditions caused by flies, and are therefore treatedas external parasites. The reader should not suffer on that account.
skin graze, as with rope burn, grazed knee inherited absence of pigment in hair, skin and eyes lowered red blood cells and/or haemoglobin condition marked by painless swellings under the skin andmucous membranes body defence, produced by lymphocyte cells causes antibody production (virus, bacterium, etc.) hereditary absence of skin (as epitheliogenesis imperfecta) family that includes arachnids and insects ear lesion, raised and circumscribed, said to be form ofpapillomatosis derived from same animal; autogenous vaccine is producedfrom organisms taken from an affected animal basal cell tumour rare, benign tumour of skinBasidiobolus sample from living tissue for diagnostic purposes tissue injury resulting from heat, cold, chemicals, etc.
fluid-filled sac often between bone and tendon/muscle (falsebursa – forms on the knee, etc., as a result of injury; spinousbursitis – fistulous withers) circumscripta localised nodule of calcium local thickening of skin due to friction, etc.
fungal organism that may be associated with disease inflammatory reaction spreading beneath the skin chemotherapy treatment by chemical substances or drugs coital exanthema viral venereal diseasecolic structural protein of white fibres of skin, etc.
surgery by freezing, either with dry ice (liquid nitrogen) orcarbon dioxide decubital ulcer skin ulcer due to lying downdepigmentation loss of colour from skindermatology bacterial cause of rain scald and greasy heel organism that causes fungal infection of skin skin area between epidermis and fat layers clot in blood, blocking artery (usually part of thrombus) subcutaneous nodules containing eosinophils immune complex disease with annular lesions open skin tract, possibly from deep infection fomes (fomites) inanimate object capable of spreading infectionfurunculosis death of body tissue with invasion by saprophytic bacteria (drygangrene occurs with arterial damage at peripheral sites, suchas the ear; gas gangrene infection caused by anerobicorganisms; moist gangrene caused by loss of blood supply,as in torsion) disease caused by Habronema species (also called summer sores, bursatii, swamp cancer, kunkers, esponja and granulardermatitis) subcutaneous swelling consisting of blood fungal infection with primary focus in lungs (also cause ofepizootic lymphangitis, pseudoglanders or African farcy) a benign disease caused by a poxvirus.
excessive sweating, often seen after prostaglandin injection therapy designed to aid or stimulate immunity disease caused by microorganisms or internal parasites local tissue loss on ears, etc., a symptom of ergot poisoning leiomyosarcoma malignant tumour of smooth musclelesion spread of disease from one organ to another larval stage of worms like Onchocerca and Setaria fluid accumulation under skin or in body cavity inflammatory condition of subcutaneous fat condition of skin due to sunlight exposure predilection site situation parasite lives in/on bodyproboscis single-cell family of organisms (includes Coccidia) animal that acts as source of infection for others, usually withoutshowing signs of disease enlargement of spermatic cord after castration increase of sebum production with scaling and crusts open to disease, or organism susceptible to drug cavity, as in paranasal sinus, or open discharging tract malignant tumour of skin/mucous membrane junction a bacterial disease marked by abscess formation stratum corneum outer layer of the skinsubcutis skin disease due to fly bites (also called Queensland itch,dhobie itch, Kasen, summer eczema) late, inherited trait appearing after birth bacterial disease caused by Clostridium tetani clot within vessel, may include worm larvae serum level measured against specific entity, like a virus application of drug, etc., to local skin area trypanosomiasis protozoan disease caused by Trypanosoma speciestumefaction a mass or swelling, synonymous with neoplasm thermal injury burn (including firing marks, cryosurgery)ulcer a lesion that penetrates the skin (or other tissues) lymphangitis bacterial infection of lymphatics in lower limbs papules that appear on one side only of horse, cause unknown benzimidazole drugs 67, 75, Chrysomya 112, 121 Anoplocephala magna 56-8 Boophilus 136 Dictyocaulus arnfieldi 5, 32, erythroderma 107 Culicoides 113-17, 156, 159 dosing 74, 78 Draschia megastoma 52, 54, Fasciola 6, 60-4, 68, 69 cyathostomes 25, 67, 68, 70, Echidnophaga 131 haemorrhoidalis 122, 123 horse roundworm 8, 34-8 Habronema muscae 52, 118 Ixodes holocyclus 138, haemangioendothelioma 168 Ixodes ricinus 137, Haemaphysalis longicornis keratinization disorders 189 Merchants List Category) Sarcoptes 131, 133 Onchocerca cervicalis 44-7, poisons 163 76, 77, 80, 81, 82, 83, 84, Psoroptes equi 133 Oxyuris equi (pinworm) 18, puncture wounds 99 Rhodococcus equi 145, 146, stable hygiene 72, 77 Streptococcus equi 144, 145, Taenia multiceps 60 Thelazia 20, 49-52, 68, 118 urticaria 158 Strongyloides 20, 69, 76, 80, thiabendazole 75, 83 Strongylus edentatus 20, 22, trematodes 60

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