Isolation, Anatomical Distribution and Antifungal Susceptibility of Dermatophytes Affecting Horses in Kwara State, Nigeria

Isolation, Anatomical Distribution and Antifungal Susceptibility of Dermatophytes Affecting Horses in Kwara State, Nigeria.

Abstract

Dermatophytes are fungi that colonize keratinized tissues of humans and animals.

This study was conducted to isolate dermatophytes from both clinical and asymptomatic cases of dermatophytosis in horses in seven Local Government Areas (LGA) of Kwara State and to determine the susceptibility pattern of the dermatophytes isolated from different anatomical sites on horses to five antifungal agents.

Ninety-one samples of plucked hair or scales and scrapings from the skin of horses were initially examined directly using microscopy prior to culture for isolation and identification usingSabouraud‟s dextrose agar (SDA), with 5% NaCl and potato dextrose agar as media for dermatophyte culture and isolation, respectively.

Identification of each isolate was through observation of colonial morphology and microscopic appearance of lactophenol cotton blue stained fungal specimen obtained from culture.

The assessment of antifungal susceptibility patterns of the dermatophytes isolated was by broth microdilution assay using ketoconazole, fluconazole, amphotericin B, griseofulvin and terbinafine as antifungal agents.

From all the samples obtained (91 samples), 14(15.4%) were dermatophytes out of which one was from an asymptomatic horse. These dermatophytes were identified as members of Trichophyton(T.)and Microsporum(M.)genera.

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Table Of Contents

Cover page  i

Title Page         ii

Declaration     iii

Certification        iv

Dedication    v

Acknowledgements     vi

Abstract    vii

Table of Contents       viii

List of Tables   ix

List of Figures     x

List of Plates   xi

List of Abbreviations and Symbols    xii

CHAPTER 1: INTRODUCTION

• Background of the Research 1
• Statement of the Research Problem 4
• Justification of the Study5
• Aim of Study 6
• Objectives of Study 6
• Research Questions 7

CHAPTER 2: LITERATURE REVIEW

• Fungal Infections———— 8
• Historical Background 10
• Nomenclature 12
• Virulence of Dermatophytes 13
• IsolationTechniques 14
• Cultural Characteristics 15
  • Identifying dermatophytes 15

• Microscopic identification process 15
• Macroscopic/colonial morphology 16
• Microscopic morphology 17

• Etiological Agents of Dermatophytes——– 18
• Growth and Nutritional Requirement———– 21
• Effective Chemicals and Physical Agents——— 21
• Serological Properties/Characteristics———– 22
• Susceptible Host Range and Resistance—— 27
  • Transmission 28
  • Clinical signs and anatomical location of lesions—— 29
• Dermatophytosis in Other Domestic Animals— 30
  • Morbidity in other domestic animals 33
• Distribution of Lesions of Dermatophytes——- 35
  • Histopathological findings      36
  • Clinical diagnosis 37
• Dermatophytosis in Humans 39
• Classes of Antifungal Agents and their Resistance— 43
  • Antifungal agents 43
  • Flouropyrimidines 43
  • Polyenes 45
  • Azoles 47
  • Echinocandins 51
  • Other antifungal agents 53

Current Synopsis of Dermatophyte Species and Congeners: Ecological Classification and Endemicity–54

Case Reports of Animal Dermatophytosis in Nigeria–54

Case Reports of Animal Dermatophytosis in Other Parts of the World–57

Reports of Dermatophytosis in Humans in Nigeria–60

Reports of Dermatophytosis in Africa and Other Parts of the World– 64

Antifungal Susceptibility Testing of Dermatophytes— 65

 

CHAPTER 3: MATERIALS AND METHODS

•   Study Area     69
•   Sampling and Sample Size   69
•   Sample Collection 69

3.4   Direct Microscopic Examination of Samples—— 72

• Laboratory Culture of Dermatophytes—- 72
• Identification of Isolates 72
• Slide Culture Preparation 73
• Antifungal Drug Dilution 74
• In-vitro SusceptibityTesting 74
• Preparation of Innoculum 74
•  Antifungal Susceptibility Test Procedure  75

3.12     Data Presentation and Analysis    75

CHAPTER 4: RESULTS

• Occurrence of Dermatophytes in Horses with Skin Lesions-76
• Colonial Morphology and Microscopic Appearance of Trichophyton tonsurans, Trichophytonverrucosum, Trichophytonsoudanense,
• Microsporumgypseum, Microsporumpersicolor, Microsporumequinum and Microsporumfulvum 82
• Minimum Inhibitory Concentrations of ketoconazole, Amphotericin B, Terbinafine, Griseofulvin and Fluconazole against DermatophytesIsolated from horses in Seven Local Government Areas of Kwara State 89

CHAPTER 5: DISCUSSION

CHAPTER 6: SUMMARY, CONCLUSIONS AND RECOMMENDATIONS

• Summary — 98
• Conclusions—- 99
• Recommendations 100

REFERENCES   101

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Introduction

Background Of Study

Dermatophytes are a group of keratinophilic fungi that cause dermatophytosis which is a highly contagious fungal infection of the skin that affects horses and other animals of all ages and breeds.

Dermatophytes produce proteolytic enzymes, keratinases, which are able to hydrolyze keratin the main protein constituent of hair, nails and skin, the infection can be mild to severe, depending on the host immune response (Akcaglar et al., 2011).

The keratin, collagen and elastin constitute 25% of the mass of mammals. The enzyme required to hydrolyze these macromolecules is found in infected tissues and is therefore considered essential to the virulence of dermatophytes (Simpanya, 2000).

Colonization by a dermatophyte, and its ability to cause an infection in the host, depends on several factors, among which are the escape mechanisms of the host resistance.

Including dry skin, a slightly acidic pH, the continuous regeneration of the skin, the fungicidal effect of fatty acids, the state of the keratinized layer and other factors, such as competition with the normal skin microbiota (Cabanes, 2000).

Establishment of an infection is initiated by the inoculation of arthrospores deposited on the skin, favored by a pre-existing skin lesion or abrasion and the microorganism‟s remarkable enzymatic ability to degrade keratin (Simpanya, 2000; Abdel-Rahman, 2001; Macêdo et al., 2005).

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References

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