Keratinopathogenic mould fungi and dermatophytes in healthy and diseased hooves of horses

Treponema spp. spirochetes and keratinopathogenic fungi isolated from keratomas in donkeys

Keratoma is an aberrant keratin mass thought to originate from epidermal horn-producing cells interposed between the stratum medium of the hoof wall and the underlying third phalanx. The cause is unknown, although the presence of keratomas is frequently associated with chronic irritation, focal infection, or trauma. A total of 167 donkeys with keratomas were presented in this study. The diagnosis of a keratoma was based on clinical signs, radiography, and histopathologic examination. Surgical excision was attempted on all donkeys with lameness unless euthanasia was advised. Histopathologic examination, including Giemsa, periodic acid Schiff, and Young's silver special histochemical stains, was performed and showed the presence of fungal hyphae and spirochete bacteria within the degenerate keratin. Polymerase chain reaction (PCR) for treponeme bacteria was performed on 10 keratoma lesions and 9 healthy pieces of hoof (controls). All healthy donkey tissues were negative for the 3 recognized digital dermatitis (DD) treponeme phylogroups, whereas 3 of 10 (30%) donkey keratoma samples were positive for one of the DD treponeme phylogroups. Routine fungal culture and PCR for fungi were performed on 8 keratoma lesions and 8 healthy pieces of hoof (controls). Keratinopathogenic fungi were detected in 1 of 8 (12.5%) keratomas, while only non-keratinopathogenic, environmental fungi were detected in 8 control healthy hoof samples. This is the first time the DD treponemes phylogroup and keratinopathogenic fungi have been detected in keratomas. Further studies are required to assess the significance of this finding.

Rare Generalized Form of Fungal Dermatitis in a Horse: Case Report

Simple Summary

The study describes a rare case of generalized Geotrichum SPP dermatitis in a horse. A saddle horse showed well-circumscribed areas of non-pruritic alopecia and the owner, suspecting allergic skin disease, commenced a three-week course of corticosteroids. Clinical signs progressed and a veterinarian was called. At veterinary examination, the horse was lethargic and pyretic with easily epilated hairs and hind limb swelling. Diagnostic procedures included collection and analyses of blood, hair and skin cytology, and biopsy. Geotrichum candidum was isolated and the horse was successfully treated with an antifungal solution and antioxidants. This study may be useful for owners and veterinarians because it describes in detail clinical signs, diagnostic procedures, and treatment of a rare case of generalized Geotrichum infection.

Abstract

A rare case of Geotrichum spp. dermatitis in a horse is presented. After unrelated, previous surgery and antibiotic treatment, a saddle horse showed well-circumscribed areas of non-pruritic alopecia. Suspecting allergic skin disease, the horse was treated with corticosteroids. The skin lesion spread, and a second veterinarian was consulted. At clinical examination, the horse was lethargic, pyretic and hair was shedding/easily epilated over the head, neck, shoulders, and legs and the hind legs were swollen. Blood analysis revealed mild leucocytosis and hyperglobulinemia. Hair, skin scraping, and skin biopsy ruled out parasites and bacteria; cytology identified yeast-like structures with hyphae or pseudohyphae. Geotrichum candidum was isolated on culture. Treatment consisted of stable disinfection, topical application of an antifungal solution, vitamins C and E supplementation and allowing the horse to graze in sunlight for at least 6 h/day. At 3-weeks follow-up, the horse had gained weight, alopecia was decreased, and all other clinical parameters were normal. Antifungal treatment was continued twice a week for three months. This study suggests Geotrichum candidum may cause skin lesions in horses after long-term use of corticosteroids or antibiotics. To avoid unnecessary and prolonged suffering in cases of dermatitis, veterinarians should be promptly consulted, appropriate diagnostic procedures conducted, so that a definitive diagnosis can be reached, and an appropriate treatment regimen implemented.

New methods for isolation of keratolytic bacteria inducing intractable hoof wall cavity (Gidoh) in a horse; double screening procedures of the horn powder agar-translucency test and horn zymography

To establish a new system to isolate keratolytic bacteria from the hoof wall cavity (Gidoh) of a racehorse, we invented the horn powder agar-translucency (HoPAT) test and horn zymography (HZ). Using routine bacteriological techniques and these methods, we isolated five strains of keratolytic soil bacteria, which were then identified by means of 16S ribosomal RNA (rRNA) gene sequencing analysis. The findings from the study on the horse suggested that Brevibacterium luteolum played the main role in the local fragility of the hoof, eventually forming a Gidoh in coordination with four other strains of keratolytic bacteria. The double screening procedures of the HoPAT test and HZ were useful and easy techniques for isolating the keratolytic bacteria from the horn lesions.

Non-dermatophyte Dermatoses Mimicking Dermatophytoses in Animals

Dermatophytoses in animals are fungal diseases of the skin caused by dermatophyte fungi of the genus Microsporum or Trichophyton. Because the infection is generally follicular, the most common clinical sign is one or many circular areas of alopecia with variable erythema, scaling and crusting, and the primary differential diagnoses are follicular infections, such as bacterial folliculitis and demodicosis. Although dermatophyte folliculitis or ringworm is the most commonly observed lesion of dermatophytoses in animals, other presentations may be observed according to the host species and the dermatophyte involved: dermatophyte folliculitis or ringworm, scaling and crusting in dermatophytosis due to Microsporum persicolor, nodule in case of kerion or mycetoma, matted hairs, seborrheic dermatosis or miliary dermatitis in cats, generalized exfoliative dermatoses in dogs, cats and horses, superficial non-follicular pustules, papules and macules in the Devon Rex cat, pruritic dermatophytoses in dogs, cats and horses, and onychomycosis in dogs, cats and horses. Since manifestations of dermatophytosis are highly variable, particularly in the cat, dermatophytosis should be considered in case of any annular, papular, nodular or pustular dermatoses, alopecic or not, sometimes pruritic, and nodular dermatoses as well.

Advances in Microbiology, Infectious Diseases and Public Health: Fungal Occurrence in the Hair and Skin of Symptomatic Pets in Turin, Italy

Companion animals, often asymptomatic reservoir of fungi, can be important sources of infection in humans, due to the close contact with their owners. The present study was aimed to assess the occurrence of dermatophytes and other fungi isolated from pet dermatological lesions in Turin, Italy. Dermatological specimens were examined for fungal elements by direct microscopy and cultured to detect dermatophytes, other filamentous fungi and yeasts: 247 pets (118 cats, 111 dogs and 18 dwarf rabbits) were positive for fungal detection in culture. Microsporum canis was the most frequent dermatophyte in cats and dogs, whereas Trichophyton mentagrophytes was the most common in rabbits. Among the other fungi, for all examined pets, dematiaceous fungi were the most isolated, followed by Mucorales, penicilli, yeasts and yeast-like fungi, and aspergilli. No gender predisposition was detected for dermatophyte growth; on the contrary, for the other fungi male cats were more susceptible than female. The highest fungal occurrence was recorded in <1-year-old cats for dermatophytes, and in <5-year-old cats and dogs for the other fungi. Autumn was the period associated with a relevant incidence of fungal infection. Finally, fungi were more frequent in non pure-breed cats and in pure-breed dogs. These data underline the importance to timely inform pet owners about the potential health risk of infection caused not only by dermatophytes but also by non-dermatophyte fungi, routinely considered to be contaminants or harmless colonizers, since their role as source of zoonotic infections is not to be excluded.

An outbreak of Arthroderma vanbreuseghemii dermatophytosis at a veterinary school associated with an infected horse

We report a case of an outbreak of inflammatory dermatophytoses caused by Arthroderma vanbreuseghemii (formally Trichophyton mentagrophytes pro parte) that involved an infected horse, the owner and at least 20 students, staff and stablemen at a veterinary school in Bern (Switzerland) that presented highly inflammatory dermatitis of the body and the face. Transmission from human to human was also recorded as one patient was the partner of an infected person. Both the phenotypic characteristics and ITS sequence of the dermatophytes isolated from the horse and patients were identical, consistent with the conclusion that the fungus originated from the horse. Three infected persons had not been in direct contact with the horse. Although direct transmission from human to human cannot be ruled out, fomites were most likely the source of infection for these three patients. Inspection of the literature at the end of the nineteenth and beginning of the twentieth century revealed that this dermatophyte was frequently transmitted from horses to humans in contact with horses (stablemen, coachmen, carters and artillery soldiers). The rarity of the present case report at the present time is likely related to the transformation of civilisation from the nineteenth century to nowadays in Europe with the change of horse husbandry. In addition, the inadequate immune response of the horse and the high number of people in contact with it at the equine clinic may explain the exceptional aspect of this case report.

Fungal diseases of horses

Among diseases of horses caused by fungi (=mycoses), dermatophytosis, cryptococcosis and aspergillosis are of particular concern, due their worldwide diffusion and, for some of them, zoonotic potential. Conversely, other mycoses such as subcutaneous (i.e., pythiosis and mycetoma) or deep mycoses (i.e., blastomycosis and coccidioidomycosis) are rare, and/or limited to restricted geographical areas. Generally, subcutaneous and deep mycoses are chronic and progressive diseases; clinical signs include extensive, painful lesions (not pathognomonic), which resemble to other microbial infections. In all cases, early diagnosis is crucial in order to achieve a favorable prognosis. Knowledge of the epidemiology, clinical signs, and diagnosis of fungal diseases is essential for the establishment of effective therapeutic strategies. This article reviews the clinical manifestations, diagnosis and therapeutic protocols of equine fungal infections as a support to early diagnosis and application of targeted therapeutic and control strategies.

Scanning electron microscopy and fungal culture of hoof horn from horses suffering from onychomycosis

Horn samples were taken from the hooves of eight horses with clinical signs of equine onychomycosis in at least one hoof capsule. None of the horses had a documented mycological history. The predominant alterations of the horn capsules were sand cracks, white line disease, brittleness (especially around the nail holes), parakeratosis and bruising. The horn samples were stored in sterile tubes for transportation and transferred onto Sabouraud Dextrose Agar and dermatophyte test agar for mycological examination within 6 h. Fungal cultures were incubated for 30 days at room temperature. Fungal identification was based on colonial morphology and microscopic examination of conidia. Horn samples were also stored at -80°C until used for scanning electron microscopy (SEM). The fungal culture revealed that the hoof horn from all eight horses was infected with keratinophilic fungi. The keratinopathogenic fungi Trichophyton spp and Scopulariopsis brevicaulis were also detected in six horses. SEM revealed severe alterations of the horn structure in horn samples infected with keratinopathogenic fungi compared to horn samples from a sound hoof. The most evident changes were deterioration of the tubular structure of the horn wall, disruption of the horny layers, superficial lysis of cornified cells and the presence of fungal elements. Samples without dermatophyte or Scopulariopsis infection, in contrast, were similar to healthy hoof horn.

Generalized hyperkeratosis caused by Scopulariopsis brevicaulis in a Japanese Black calf

A 6-month-old Japanese Black female calf became gradually emaciated over a 40-day period and was humanely killed. At necropsy, hyperkeratotic nodules were seen to have spread over almost the entire body surface. Scopulariopsis brevicaulis was isolated from the skin and identified morphologically and by gene sequence analysis of the D1/D2 domain of large subunit ribosomal RNA. Numerous periodic acid-Schiff-positive, lemon-shaped conidia were detected histologically in the keratinized layer and the hair follicles. The distribution of the fungal elements in the skin corresponded to that of the hyperkeratotic lesions. This is the first report of a disease caused by S. brevicaulis in animals. Previously reported human infections have not included generalized hyperkeratosis.

In vitro effects of fungi isolated from equine hooves on primary human keratinocytes

The effects of two dermatophytes (Microsporum gypseum and Trichophyton mentagrophytes) and four moulds (Scopulariopsis brevicaulis, Alternaria alternata, Geotrichum candidum and Penicillium spp.) on living keratinocyte cultures were examined in vitro using primary human keratinocytes. Rates of apoptosis of infected cells were determined using a colorimetric TUNEL system which detects the characteristic nuclear DNA fragmentation of apoptotic cells. The cytotoxicity of the individual fungi was tested by quantitatively measuring cytosolic enzyme lactate dehydrogenase, released upon cell lysis, in culture supernatants. Additionally, the cell structures within the infected keratinocytes in cultures were examined by scanning electron microscopy. All of the fungi exhibited high cytotoxicity, whereas the development of only the two dermatophytes and the mould Scopulariopsis brevicaulis resulted in distinctly increased apoptosis. Electron microscopy showed that all fungi studied caused similar alterations in the cell structure, with Microsporum gypseum being the most harmful. Increasing loss of cell adhesion as a consequence of a decreasing number of reticulating cell appendices and a reduced cell plasticity were the most evident alterations.

Use of a topical disinfectant as part of a hoof care programme for horses with diseases of the hoof capsule

Twenty-three horses with persistent hoof horn defects were treated topically with a hoof disinfectant as part of a hoof care programme for a year. The active ingredients of the disinfectant were a poloaximer-iodine complex, ethylenediamine dihydriodide, isopropyl alcohol and propylene glycol. Hoof trimmings were taken at the start of the study and every six weeks, and examined by scanning and transmission electron microscopy. At the beginning of the study all the horn samples contained large numbers of bacteria, and samples from eight of the horses also had fungal hyphae intermingled with the bacteria. After the application of the hoof disinfectant and adjustments to their diet, there were rapid improvements in the gross appearance of the feet of all the horses; some of them improved within two to three weeks and by 12 weeks the horn quality of all the horses had greatly improved.

Coronary band dystrophy in two horses

Two mature large-breed horses with coronary band dystrophy and chorioptic mange are described. They both had clinical signs of coronary band scaling and crusting but were not lame. Coronary band dystrophy can be differentiated from similar clinical conditions on the basis of the histological appearance of skin biopsy specimens, and by the exclusion of other possible disease processes. Its aetiology is uncertain, but probably involves a localised defect of keratinisation affecting the specialised epithelium of the coronary band.