Onychomycosis among rural farmers in a southwestern part of Nigeria

Background and Objectives: Onychomycosis, a fungal infection of nails occurs worldwide with dermatophytes as the most common causal agents, although yeasts and moulds are also involved. The diagnosis usually involves direct microscopy and culture to prove actual existence of onychomycosis. This present study aims to provide knowledge of the epidemiology and mycological characteristics of onychomycosis involving toenails among rural farmers in a southwestern part of Nigeria. Methods: Direct microscopic examination using 20% potassium hydroxide (KOH) and mycological culture of 631 sub-ungual scrapings and toenail clippings from farmers suspected to have onychomycosis were prepared to identify the causative agents. Results: Trichophyton rubrum occurred as the predominant species of the total dermatophytes isolated (63.8%). The highest prevalence of individual etiologic agent was Trichophyton rubrum (16.9%), followed by Candida albicans (14.6%). One hundred and six non-dermatophyte moulds, of which Aspergillus niger and Fusarium moniliforme were the most frequent species (13.4% and 7.3% respectively) were also recovered from the specimens. Distal and lateral sub-ungual onychomycosis (DLSO) was the most prevalent clinical form occurring in 166 (63.6%) of the positive cultures followed by white superficial onychomycosis (WSO) in 51 (19.5%). Conclusion: The study revealed that dermatophytes and Candida species are involved in the pathogenesis of toenail infections among rural farmers in southwestern Nigeria. The occurrence of non-dermatophytic moulds should also not be ignored. Egyptian Dermatology Online Journal Vol. 7 No 1:4, June 2011 Page 2 of 9 http://www.edoj.org.eg Introduction Onychomycosis is a general term used for any fungal infection of the nail plate. This contrasts with the term tinea unguium which is specifically used for infection of the nails caused by dermatophytes. Zaias [1] divided onychomycosis into four clinical types; distal sub-ungual onychomycosis, which is the most common type of onychomycosis caused by dermatophytes, Candida species and miscellaneous mould and yeasts; proximal sub-ungual onychomycosis caused exclusively by dermatophytes and is the least common; white superficial onychomycosis; and candidal onychomycosis caused mainly by Candida albicans and non-albican species such as C. parapilosis, C krusei and C. gullermondii [2]. Onychomycosis accounts for 50% of all nail disorders [3,4] with those affecting the toenails being 25 times more than that of the fingernails [5].They are mainly caused by dermatophytes. The dermatophytes commonly associated with onychomycosis include Trichophyton rubrum and T. mentagrophytes with the former occurring in up to 90% of cases [6,7]. Onychomycosis are caused, to a lesser extent, by moulds and yeasts. The moulds most frequently isolated from diseased nails are Aspergillus spp., Fusarium spp, Scopulariopsis brevicaulis, Scytalidium dimidiatum, S. hyalinum, Onychocola canadensis [8,9,10,11,12,13]. Reports in the literature revealed geographical differences in the epidemiology of onychomycosis. The clinical patterns of onychomycosis are changing because of the involvement of non-dermatophytic moulds. In Nigeria, most of the research work done on the superficial mycoses has been on the skin. There is paucity in the literature on reports on onychomycosis in Nigeria. The reports of Gugnani et al., [14] and Greer [15] were the only reports in the literature known to the authors in Nigeria. Therefore this study was undertaken to investigate the prevalence of onychomycosis among rural farmers, who, through the authors interaction were observed to have conspicuous black pigmentation of toenails accompanied, in some cases, by painful inflammation and decay of underlying tissues, resulting in fall-off of the nails. This to the authors' knowledge is the first report in southwestern Nigeria documenting fungi from toenails of farmers suspected to have onychomycosis. Materials And Methods Specimen collection: The study was carried out in three villages located in Akinyele Local Government in lbadan, southwestern Nigeria between May 2002 and March 2006. Farmers, all of who were males between the ages of 25-67 years with discoloured toenails and sometimes with painful inflammation and decayed underlying tissues were included in this study. A total of 631 sub-ungual scrapings and toenail clippings were collected in separate universal plastic bottles (Sayag, France) after cleaning the affected areas with 95% ethanol and transported to the laboratory immediately after collection. Microscopy, culture and strain identification: Direct microscopic examination was carried out on the specimens by dissolving a portion of each sample in 20% potassium hydroxide (KOH) for 60 minutes to be examined under low and high power microscope for the presence of fungal elements such as hyphae, pseudo-hyphae, budding cells, spores or blastoconidia. Culture of all specimens irrespective of direct microscopy results was carried out on Dermasel agar (Oxoid), Sabouraud Dextrose Agar containing cycloheximide (Oxoid) and Dermatophyte Test medium (DTM) [16]. The culture media were incubated at room temperature (28+ 20C) and examined daily for two weeks. The change of colour from yellow to red on DTM indicated the growth of a dermatophyte. Egyptian Dermatology Online Journal Vol. 7 No 1:4, June 2011 Page 3 of 9 http://www.edoj.org.eg Macroscopic and microscopic examinations of fungal colonies were carried out as follows. Wet mounts of moulds was carried out with Lactophenol cotton blue. The moulds were identified further according to the taxonomic schemes of Klich and Pitt [17] for Aspergillus spp, Nelson et al. [18] for Fusarium spp. All Candida albicans isolates were examined for germ-tube production in human serum and for chlamydospores formation in corn-meal agar Tween 80. Other yeasts species other than C. albicans were identified using their sugar fermentation and assimilation profiles. The morphology of the dermatophytes and other moulds as described by AlDoory [16] were employed for their identification.