CE Article #2 Fungal Infections of the Upper RespiratoryTract Allison J. Stewart, BVSc(Hons), MS, DACVIM Elizabeth G. Welles, DVM, PhD, DACVP Tricia Salazar, MS, DVM Auburn University ABSTRACT: Fungal infection of the upper respiratory tract presents diagnostic challenges and therapeutic dilemmas. Diagnosis of upper respiratory tract granuloma is based on clinical signs, identification of mass lesions during endoscopic examination, and collection of tissue samples by biopsy or by mucosal scraping. Cytologic or histologic examination of lesions may identify characteristic morphologic features of fungal organisms. The etiologic agent can be definitively identified by microbiologic culture, immunohistochemistry, polymerase chain reaction, or serology. o retrospective or prospective studies new antifungals with good efficacy and reduced have compared various surgical toxicities have become available within the past N(debulking, laser, cryotherapy) and decade. Pharmacokinetic studies on newer medical (topical, intralesional , systemic) treat - drugs are being conducted in horses, and as ment options for fungal granulomas in horses. more drugs become available in generic form, Isolated case reports, small case series ,1,2 and a the cost of relatively more efficacious medical limited number of review articles 3 describe therapy will be dramatically reduced. This arti - empirical therapies. A multimodal approach is cle reviews the reported etiologies of , as well as often successful, but the relative benefits of the the diagnostic techniques and the medical and individual treatment components are unknown. surgical therapies for , equine respiratory tract Treatment options depend on the site and fungal granulomas. extent of the infection, accessibility to surgical intervention, the etiologic agent, the known FUNGI antifungal susceptibilities, evidence-based study The fungal kingdom comprises yeasts, molds, results from human medicine , and the financial fungal rusts, and mushrooms. Fungi are eukary - resources of the owner. otic organisms with a definitive cell wall made Although results of several small comparative up of chitins, glucans, and mannans. Within the studies on treating guttural pouch mycosis have cell wall, the plasma membrane contains ergos - been reported , to date, no terol, a cell membrane sterol that is frequently comparative studies have been targeted by antifungals. Ergosterol regulates the conducted to determine the permeability of the cell membrane and activity •Take CE tests ideal therapeutic plan to treat of membrane -bound enzymes. There are more • See full-text articles mucosal conidiobolomycosis than 70,000 species of fungi, but only 50 CompendiumEquine.com or cryptococcal infections in species have been identified as causes of disease horses. In human medicine, in people or animals. Pathogenic fungi can be CompENdium EQuiNE 208 may 2008 Fungal infections of the upper Respiratory Tract CE 209 divided into three groups: multinucleate septate fila - For nasal and nasopharyngeal lesions, specimens for mentous fungi, nonseptate filamentous fungi , and yeasts. cytology, histopathology , and culture can be obtained by Dimorphic fungi can change between forms , depending use of an endoscopically guided biopsy instrument. How - on environmental conditions. In soil and decaying mat - ever, these samples tend to be small, superficial , and often ter, the mycelial form usually is present and is composed nondiagnostic. In cultures, mucosal contaminants may of a collection of hyphae. The mycelia produce infective overgrow the organism of interest. Larger biopsy samples spores that can inoculate vertebrate tissue. from the nasal passages or the nasopharynx can often be obtained by use of a uterine biopsy instrument, which can CLINICAL SIGNS AND GROSS LESIONS be passed nasally with visual guidance from a flexible Mycotic granulomas of the upper respiratory tract have endoscope. Excisional biopsy or surgical debulking may be been found in the nasal passages, paranasal sinuses, performed through a sinus flap or via laryngotomy. nasopharynx, guttural pouch, and trachea of infected horses. The most common clinical signs of upper respira - Cytology tory fungal infection include unilateral or bilateral Fungal hyphae may be identified in airway fluid or in serosanguineous or mucopurulent nasal discharge as well impression smears from masses obtained by biopsy. Fungal diseases of the upper respiratory tract include conidiobolomycosis, cryptococcosis, rhinosporidiosis, coccidioidomycosis, pseudallescheriosis , and aspergillosis. as inspiratory or expiratory noise. Other clinical signs Some fungi have characteristic morphologic features that include coughing, facial deformation, and dyspnea can allow an early presumptive identification (Table 1). caused by partial blockage of nasal passages by granulo - matous masses. Fungal plaques in the guttural pouch are Histopathology often located over the arterial blood supply. Horses with Hyphae of certain fungi may be poorly visualized guttural pouch mycosis often have episodic serosan - using routine hematoxylin –eosin staining. Therefore , guineous nasal discharge. This may progress to poten - special stains (e.g., periodic acid-Schiff, Gridley’s fun - tially fatal epistaxis if there is erosion into an artery. The gus , Grocott-Gomori methenamine-silver nitrate ) can duration of clinical signs can vary from days to many be useful in staining histopathologic specimens. In months. Differentials for fungal granulomas of the respi - patients with chronic fungal infections, there is often ratory tract include ethmoidal hematoma, squamous cell evidence of extensive fibrosis on histopathology. carcinoma, amyloidosis, or exuberant granulation tissue. Microbiologic Culture DIAGNOSIS Some fungi have fastidious growth requirements and Diagnostic Samples may take up to several weeks to grow on culture media or Lesions in the nasal passages, turbinates, nasopharynx, may be overgrown by contaminant bacteria. Tissue sam - guttural pouch, trachea, and bronchioles can usually be ples submitted for microbiologic culture should be placed observed directly during endoscopic examination. in a prepared culture media and transported at room Masses in the paranasal sinuses may be observed using temperature. Specific culture media such as Sabouraud’s radiography. Computed tomography or magnetic reso - dextrose agar (Remel, Lenexa, KS), inhibitory mold agar, nance imaging provides detailed imaging of the equine or Mycobiotic (Remel), which contains cycloheximide skull and can determine the extent of lesions and degree and chloramphenicol, are useful. of bony invasion. A sterile rigid arthroscope or flexible endoscope can be passed through an 8- to 20- mm Molecular Techniques trephine that is drilled into the conchofrontal or maxil - Serologic tests that use immunodiffusion, 4 radioim - lary sinus to directly view some lesions within the munoassays, latex agglutination, complement fixation , or paranasal sinuses. ELISAs 5 are available to detect circulating antigens or may 2008 CompENdium EQuiNE 210 CE Fungal infections of the upper Respiratory Tract Table 1. Characteristic Morphologic Features of, and Availability of SerologicTests for, Fungal Organisms Reported to Cause Fungal Granulomas in the Equine Upper RespiratoryTract Cost and Agent Cytologic Morphology SerologicTest Laboratory Cryptococcus Round, thin-walled, yeast-like fungus (5–10 µm) with Capsular antigen ELISA (antigen) $16 at UGA neoformans a large heteropolysaccharide capsule (1–30 µm) that 7 $18 at NMDA does not take up common cytologic stains. The capsule Latex agglutination (antigen) $20 at CSU is best stained with mucicarmine stain. The organisms show narrow-based budding and lack endospores. $30 at UT Conidiobolus Broad, thin-walled, highly septate, irregularly Immunodiffusion is highly sensitive Serologic coronatus branched hyphae (5–13 µm) 31 ; often surrounded by and specific. A decreasing titer testing is acidophilic-staining, glycoprotein antigen –antibody correlates with disease resolution in not widely complexes known as Splendore-Hoeppli material . horses. 8,9 available. Pseudallescheria Hyaline, nonpigmented, septate, randomly branched —— boydii hyphae (2–5 µm) with regular hyphal contours. The asexual form has nonbranching conidiophores with terminal conidia. The sexual form in culture has a cleistothecium (large, round body) and ascospores. 28 Coccidioides Relatively large, round spherules (20–80 µm; up to Agar gel immunodiffusion (antibody) $8 at NMDA 47,52, a immitis 200 µm) with a double-contoured cell wall. The for IgM and IgG $12 at CSU mature spherules are called sporangiospores (2–5 µm). CF (antibody) 47,51, b: may have some $12 at NMDA a false-positive results $15 at UT Aspergillus Broad (2–4 µm), septate hyphae with parallel sides Aspergillus Galactomannan enzyme Platelia Aspergillus spp and acute, right-angled branching. immunoassay (sandwich antigen enzyme immunoassay) antigen test; 80.7% immunoassay by sensitive and 89.2% specific; some MDL reactivity to Penicillium , Alternaria and Paecilomyces spp Agar gel immunodiffusion $15 at UT (antibody): A. fumigatus only Fungal panel — Agar gel immunodiffusion $28 at MDL (Aspergillus , Blastomyces , Coccidioides , and Histoplasma spp) $40 at CSU $55 at CU aHiggins JC, Leith GS, Voss ED, et al. Seroprevalence of antibodies against Coccidioides immitis in healthy horses. JAVMA 2005;226:1888-1892. bSmith CE, Saito MT, Simons SA. Pattern of 39,500 serologic tests in coccidioidomycosis.