Dermatophytosis is a highly infectious mycotic disease of great economic, and public health consequences. It is estimated that 20 % of world population is affected with dermatophytosis. The disease is cosmopolitan in distribution, and has been frequently reported in humans as well as in many species of animals including cats and dogs. Dermatophytosis is an occupational mycozoonosis of pet owners, dog handlers, kennel attendants, dog trainers, dog catchers, veterinarians, and persons working in animal shelters. Among several species of dermatophytes, Microsporum canis is the principal cause of ringworm in cats, and dogs; and is recognized as an emerging pathogen of global significance. Transmission of infection can occur by direct contact with diseased animal and man, indirect contact with contaminated fomites or contact with soil. The disease is more severe and common in kittens and puppies. Direct microscopical demonstration of dermatophytes in skin /nail lesions by potassium hydroxide technique, and its isolation in pure growth on Sabouraud medium/DTM still considered the mainstay of diagnosis. A number of topical agents (miconazole, clotrimazole, terbinafine, luliconazole), and systemic drugs such (griseofulvin, ketoconazole, fluconazole, itraconazole) have been tried for the management of disease. The identification of asymptomatic carrier in kennels and catteries by culture of brushing, and use of Wood’s lamp in screening of pet colonies where M. canis is the only concern, is recommended. The role of T. bullosum, a newly emerged zoophilic dermatophyte in the etiology of canine and feline ringworm should be investigated. It is emphasized that Narayan stain, which is cheap, easy to prepare and stable at room temperature, should be widely employed in microbiology and public health laboratories for the morphological studies of dermatophyes, which are implicated in the etiology of human and animal ringworm.
Fungi have emerged as a significant cause of morbidity and mortality in humans and animals throughout the world (Pal, 2007). Recently, there has been an increase in the incidence of fungal infections in developing countries. This may be due frequent and prolonged use of antibacterial antibiotics, corticosteroids, immunosuppressive drugs, neoplastic agents, HIV/AIDS, leukemia, lymphoma, neutropenia, tuberculosis, diabetes mellitus, organ transplantation besides environmental condition (Pal, 2007; Jain et al., 2014). Dermatophytosis (ringworm, tinea) is the most commonly encountered superficial and highly contagious mycosis of humans and animals (Van Cutsem and Rochette, 1991; Pal and Dave, 2005; Pal, 2007; Pal and Dave, 2013; Dave et al., 2014). Disease is reported from many countries of world including India ( Ainsworth and Austwick,1973; Baxter and Rush-Munro, 1980; Pal, 1981; Wright,1989; Bond,2010; Pal and Dave,2013; Dave et al.,2014; Jain et al.,2014); and occurs in sporadic as well as in epidemic form (Pal,1981; Pal and Thapa,1993; Pal and Lee,2000; Pal and Dave, 2005).Dermatophytosis is more prevalent in tropical and subtropical regions where the temperature and relative humidity are high ( Pal, 2007; Jain et al., 2014). The public health implications of animal dermatophytes are well established by many investigators (Pal and Lee, 2000; Pal and Dave, 2005; Dave et al., 2014). In Africa, dermatophytosis is a common skin disease affecting more than 30 % of children in primary schools (Pal, 2011).The global incidence of dermatophytosis is estimated 20 % (Pal, 2007). David Gruby (1840) is credited to record for the first time the ringworm of scalp in children due to Microsporum audouini (Pal, 2007). However, the first record of ringworm in dogs due to Microsporum canis was established by Bodin and Almy in 1897 (Pal, 2007). In cats and dogs, M. canis is the most common cause of dermatophytosis (Wright, 1989). Healthy cats and dogs may remain asymptomatic carriers of M. canis , and hence pose a great risk to humans, particularly those who remain in contact with pet animals (Pal,2007).It is pertinent to mention that about 30 % of dogs and cats in USA are infected with M. canis, a frequent cause of tinea capitis in children (Pal,2011). It is reported that about 80 % of human ringworm in rural areas, and 10 % in urban settings are of animal origin (Pal, 2011).The present communication focuses on the growing significance of dermatophytic fungi, especially M. canis in the etiology of canine and feline ringworm.
Disease is caused by dermatophytes, which are keratin digesting, aerobic, non-motile, non-capsulated, filamentous fungi. Dermatophytes represent 42 species classified in three genera namely, Epidermophyton, Microsporum and Trichophyton (Pal, 2011). They are sensitive to dry, and moist heat, and also susceptible to sodium hypochorite, idophors, formaldehyde, benzalkonium chloride, and glutaraldehyde (CFSPH, 2013). In cats, about 98 % of ringworm infection is caused by Microsporum canis. However, in dogs, M. canis is responsible for over 70 % of cases (Aiello and Mays, 1998).The other dermatophytic fungi isolated from canine and feline include M. gypseum, M. persicolor, T. equinum, T. erinacei, T. mentagrophytes, T. rubrum, T. tonsurans and T. verrucosum (Ainsworth and Austwick,1973; Pal,1981; Pal et al.,1990; Yamada et al.,1991; Bernardo et al., 2005; Brilhante et al.,2006; Sharma et al.,2009; CFSPH,2013).The spores of M. canis in infected building can remain viable for one year (Menelaos ,2006).
The source of infection is always exogenous. The cats and dogs can be infected with zoophilic (animal) dermatophytes, geophilic dermatophytes (soil), and anthropophilic dermatophytes (man). The direct contact with patient and indirect contact with contaminated fomites serve as means of transmission of dermatophytes. The infection can also be acquired from the contaminated soil (Pal, 2007).
Many cats with dermatophytes show few or no lesions. The cats may develop a carrier state in the absence of clinically appearing lesions, and can represent an insidious source of contamination to other animals (Menelaos, 2006). The kittens are most frequently affected, and typical lesions which consist of focal alopecia, scaling, and thin, greyish white crusts, are mostly observed around the ears, and face or extremities (Aiello and Mays, 1998)). These lesions may or may not pruritic. The grooming nature of the cats may eventually spread the infection to the entire body. The large, alopecic, and exudative lesions occur in severe form of ringworm in debilitated cats. In some long haired cats, especially Persians, the firm, subcutaneous nodules known as pseudomycetoma, are seen on the neck and back (CFSPH, 3013).True feline mycetoma due to M. canis, which is a rare clinical manifestation, is reported from Japan by Kanbe and other (2009).Occasionally, the nails may be affected along with the skin and hairs (CFSPH,2013).
The ringworm infection is most commonly encountered in young dogs less than 1- year-old (Menelos, 2006). The lesions in puppies may show alopecia, scales, vesicles, pustules, and crust. Other forms of dermatophytosis include kerion, and pseudomycetomas. In addition, onychomycosis may occur concurrently with ringworm infection (CFSPH, 2013). Older dogs are less susceptible, and if previously exposed to dermatophytes, may have developed immunity (Menelaos, 2006).The generalized ringworm is uncommon in dogs, and is usually accompanied by immunodeficiency (Aiello and Mays, 1998).
The clinical signs are not very characteristic to warrant the diagnosis of dermatophytosis. In immunosuppressed patients, laboratory test include a complete blood count, biochemical profile, and urine analysis. The examination of lesion or infected hair under Wood’s lamp is helpful to make a tentative diagnosis of canine and feline ringworm caused by M. canis. This zoophilc dermatophyte exhibits a bright greenish yellow fluorescence under UV light (Pal and Dave, 2013).The microscopic examination of skin scrapings, broken hairs or nails in potassium hydroxide (KOH) solution reveal the presence of thin , long , branched hyaline hyphae and arthrospores (Pal, 2007).The isolation of dermatophytes is attempted in Sabouraud dextrose medium with chloramphenicol and actidione (Pal, 2007) and also on dermatophyte test medium (DTM) (Taplin et al.,1969).The later medium becomes red due to rise in pH through metabolic activity of dermatophytes (Pal and Dave,2013). As some of the dermatophytes grow slowly, the incubated media should be examined daily for up to four weeks before discarding as negative. The detailed morphology of dermatophytes is studied in Narayan stain (Pal, 2004).This stain contains 0.5 ml of methylene blue (3 % aqueous solution),6.0 ml of dimethyl sulfoxide (DMSO) and 4.0 ml of glycerin. The skin biopsy should be performed in nodular dermatitis or in the event of negative cultural finding. The hyphae and arthrospores are better demonstrated by periodic acid Schiff (PAS) technique (Pal, 2007).Very recently, molecular tools are also applied in the diagnosis of the dermatophyte infections (Brilhante et al.,2006; Kanbe, 2008; Jensen and Arendrup, 2012).The differential diagnosis includes bacterial folliculitis, demodicosis, malasseziosis, scabies, and seborrheic dermatitits (Pal, 2011).
Most infections in healthy animals heal spontaneously within one to a few months. The primary objective of treatment in dermatophytosis of pet animals are to hasten the speed of recovery ,prevent the spread of infection, and reduce the risk of transmission to humans and other animals (CFSPH, 2013). The treatment for ringworm infection can be frustrating due to its relapse, and expensive because of high costs of antifungal drugs. Both topical and systemic therapy is recommended in small animal clinical practice. Local lesion may be treated with topical application of miconazole (2%), clorimazole (1%), terbinafine (1%), and luliconazole (1%) cream. The drug is applied as a thin layer twice a day on the lesions for 15 to 21 days. In chronic, severe, generalized cases, and also in long haired cats, systemic therapy is indicated. A number of drugs such as griseofulvin (25-100 mg/ kg body weight) in dog, and (25-50 mg /kg body weight) in cat in divided doses with fatty meal, ketoconazole (10 mg / kg body weight), and itraconazole (5 mg/kg body weight) are given daily. The cats may develop bone marrow depression; especially the neutopenia at higher doses of griseofulvin. This drug is highly contraindicated in pregnancy. Moreover, gastrointestinal upset is a common sequela of griseofulvin administration (Aiello and Mays, 1998).Treatment for ringworm should be continued for 2 -4 weeks past clinical cure (Aiello and Mays, 1998). It is advised that mycological monitoring of therapy is imperative to see the efficacy and response of drugs.
Prevention and Control
The complete eradication of dermatophytes from the environment of catteries, kennels, and animal shelters seems impracticable. However, proper cleaning and disinfection of premises, decontamination of fomites, isolation of sick animal, quarantine of newly purchased pet and its fungal culture for the presence of dermatophyte, treatment of affected pets will certainly minimize the prevalence and incidence of dermatophytosis in cats and dogs. As animal dermatophytes are highly communicable to human beings, persons keeping the pets should be imparted health education about the source of infection, mode of transmission and personal hygiene (Pal, 2007; Pal and Dave, 2013). It is emphasized to detect the infection of dermatophytes in asymptomatic carrier animals by employing standard mycological technique.
Dermatophytosis, a global, superficial, infectious mycotic disease of humans and animals, is caused by many species of dermatophytes. The disease is reported from developed and under developing nations of the world. In cats and dogs, M. canis is the most common cause of ringworm. Clinically affected and asymptomatic pets are an important source of ringworm in humans particularly in children. About 30 % of animal ringworm cases can lead to human involvement. Chronic or aggressive steroid therapy has been associated with protected disease. The infection can be more persistent or widespread in young or sick animals. Since zoophilic dermatophytes have public health implications, proper care must be observed when dealing with the sick animals. It is advised that immonocompromised patients should not handle the pet animals. As M. canishas emerged as a global pathogen, its role in various dermatological disorders of humans and animals should be further investigated. More studies are needed to develop a potent, safe, and low cost immunotherapeutic agent to protect canines and felines from ringworm, which is an important fungal zoonosis of global significance.
We are highly indebted to Prof. Dr. R. K. Narayan for critically reviewing our manuscript. Thanks are also due to Anubha Priyabandhu for sending some of the relevant literature on the subject.