{"id":23183,"date":"2021-04-09T13:13:50","date_gmt":"2021-04-09T13:13:50","guid":{"rendered":"https:\/\/todaysveterinarypractice.com\/?p=23183"},"modified":"2022-03-30T20:29:10","modified_gmt":"2022-03-30T20:29:10","slug":"approaches-to-opportunistic-fungal-infections-in-small-animals","status":"publish","type":"post","link":"https:\/\/navc.sitepreview.app\/todaysveterinarypractice.com\/internal-medicine\/approaches-to-opportunistic-fungal-infections-in-small-animals\/","title":{"rendered":"Approaches to Opportunistic Fungal Infections in Small Animals"},"content":{"rendered":"

Opportunistic fungal infections are of increasing importance in veterinary medicine, especially for patients receiving immunosuppressant therapy or those that are otherwise immunocompromised.1-3<\/sup> Opportunists are ubiquitous in the environment and are transmitted by either spore inhalation or percutaneous inoculation. Infections can be localized, causing superficial cutaneous nonhealing wounds that are refractory to antibiotic therapy, or they can cause life-threatening systemic illness.1,2<\/sup> Patients often have superficial ulcers\/erosions or nodules that may have an associated draining tract on the feet, ears, and\/or nose.1-5<\/sup>\u00a0<\/span><\/span><\/p>\n

In human medicine, opportunistic fungal infections have been reported for up to 0.7% of organ transplant patients and 20% of patients receiving immunosuppressant cyclosporine<\/a>.6<\/sup> In veterinary medicine, the reported prevalence among dogs receiving immunosuppressant therapy is 13%; opportunistic fungal infections are significantly more likely to develop in dogs receiving immunosuppressant cyclosporine (20% prevalence).3<\/sup> Predisposition to opportunistic fungal infections can also be found in dogs and cats with naturally occurring causes of immunosuppression, such as diabetes mellitus<\/a>, retrovirus infection (e.g., feline leukemia virus, feline immunodeficiency virus), cobalamin deficiency<\/a>, and familial multifactorial immunodeficiency in German shepherd dogs.2<\/sup> The opportunistic fungal infections seen in veterinary medicine are categorized as phaeohyphomycosis, hyalohyphomycosis, and eumycotic mycetomas (<\/span>TABLE 1<\/span><\/strong>).\u00a0<\/span><\/span><\/p>\n

\"PascuttiWalton_TVPMayJune21_FungalInfections_Table1\"<\/a><\/p>\n

Phaeohyphomycosis<\/b> (<\/span>FIGURE 1<\/span><\/strong>) is a rare infection caused by ubiquitous, pigmented saprophytic fungi of a number of genera, including but not limited to Alternaria<\/i>, Bipolaris<\/i>, Cladophialophora<\/i>, Curvularia<\/i>, <\/i>and Exophiala<\/i> (<\/span>TABLE<\/strong> 1<\/strong><\/span>).1,2<\/sup> Pigment, seen within tissue and in culture, is derived from melanin in the cell wall of hyphal elements and conveys virulence.1,2,7<\/sup> Clinical infection is rare; both yeast (unicellular) and hyphal (multicellular) forms exist in tissue.1,2<\/sup> Phaeohyphomycosis is most commonly seen as locally invasive subcutaneous lesions, especially on areas exposed to soil (i.e., nose, ears, digits). Among immunocompetent animals, it is more likely to cause cutaneous lesions in cats than dogs. Phaeoid fungi rarely cause central nervous system (CNS) or disseminated systemic disease.1,2<\/sup><\/span><\/p>\n

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Figure 1. Phaeohyphomycosis, seen in a 3-year-old spayed female boxer dog with nonhealing cutaneous skin lesions on her ventral abdomen and inguinal region; diagnosed by cytology and culture.<\/p><\/div>\n

Hyalohyphomycosis<\/b> (<\/span>FIGURE 2<\/span><\/strong>) <\/b>is caused by ubiquitous, nonpigmented saprophytic fungi that are transparent, or hyaline, in tissues. This heterogenous group of fungi includes Fusarium<\/i>, Penicillium<\/i>, Paecilomyces<\/i>, and Acremonium <\/i>species <\/i>(<\/span>TABLE 1<\/span><\/strong>). Hyalohyphomycosis most commonly affects young, large breed dogs.1,2<\/sup> In cats, hyaline fungi are the most common cause of nodular fungal granulomatous skin lesions.8,9<\/sup> Disease is hyphal in origin, occurring as either local cutaneous\/osseous infection or disseminated disease involving one or multiple organs.1<\/sup> In immunosuppressed animals, disseminated illness is associated with a guarded to poor prognosis.1,2<\/sup> In immunocompetent animals, disease is usually confined to the skin and may respond to medical therapy alone.<\/span><\/p>\n

\"FigureFigure 2A. Hyalohyphomycosis in a 2-year-old neutered male French bulldog seen for meningoencephalitis of unknown etiology. Hyalohyphomycosis diagnosed by cytology; Sporotrichum species diagnosed by culture. Immunosuppressive therapies at the time of diagnosis included cytosar, prednisone, and cyclosporine. (A) Skin lesions on the forearm and between the toes noted during physical examination.<\/span><\/a><\/div>
\"2B.2B. Interdigital skin lesion caused by hyalohyphomycosis fungal infection.<\/span><\/a><\/div>
\"2C.2C. Hyalohyphomycosis fungal spore (arrow) observed on cytology slide of a cutaneous skin lesion.<\/span><\/a><\/div>
\"2D.2D. Hyalohyphomycosis fungal hypha (arrow) observed on cytology slide of a cutaneous skin lesion. The fungal hypha is nonpigmented and branches at an acute angle.<\/span><\/a><\/div>
<\/div><\/div><\/span><\/p>\n

Eumycotic mycetomas<\/b> are tumor-like subcutaneous swellings that form within tissue. Infection is characterized by chronic pyogranulomatous inflammation with aggregates of fungal hyphae that form \u201cgrains,\u201d or aggregations of fungal organisms, within the draining tracts of the lesions.1,2<\/sup> These grains enable differentiation of pigmented and nonpigmented fungi within the tissue. Mycetomas are further classified as pigmented (black grain mycetoma) or nonpigmented (white grain mycetomas); color depends on the organism causing the lesion.1,2<\/sup>\u00a0<\/span><\/span><\/p>\n