Fungal Infections of the Upper Respiratory Tract

CE Article #2
Fungal Infections of the
Upper Respiratory Tract
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.
N
o retrospective or prospective studies
have compared various surgical
(debulking, laser, cryotherapy) and
medical (topical, intralesional, systemic) treatment options for fungal granulomas in horses.
Isolated case reports, small case series,1,2 and a
limited number of review articles 3 describe
empirical therapies. A multimodal approach is
often successful, but the relative benefits of the
individual treatment components are unknown.
Treatment options depend on the site and
extent of the infection, accessibility to surgical
intervention, the etiologic agent, the known
antifungal susceptibilities, evidence-based study
results from human medicine, and the financial
resources of the owner.
Although results of several small comparative
studies on treating guttural pouch mycosis have
been reported, to date, no
comparative studies have been
conducted to determine the
ideal therapeutic plan to treat
• Take CE tests
mucosal conidiobolomycosis
• See full-text articles
or cryptococcal infections in
CompendiumEquine.com horses. In human medicine,
CompENdium EQuiNE
208
new antifungals with good efficacy and reduced
toxicities have become available within the past
decade. Pharmacokinetic studies on newer
drugs are being conducted in horses, and as
more drugs become available in generic form,
the cost of relatively more efficacious medical
therapy will be dramatically reduced. This article reviews the reported etiologies of, as well as
the diagnostic techniques and the medical and
surgical therapies for, equine respiratory tract
fungal granulomas.
FUNGI
The fungal kingdom comprises yeasts, molds,
fungal rusts, and mushrooms. Fungi are eukaryotic organisms with a definitive cell wall made
up of chitins, glucans, and mannans. Within the
cell wall, the plasma membrane contains ergosterol, a cell membrane sterol that is frequently
targeted by antifungals. Ergosterol regulates the
permeability of the cell membrane and activity
of membrane-bound enzymes. There are more
than 70,000 species of fungi, but only 50
species have been identified as causes of disease
in people or animals. Pathogenic fungi can be
may 2008
Fungal infections of the upper Respiratory Tract CE
divided into three groups: multinucleate septate filamentous fungi, nonseptate filamentous fungi, and yeasts.
Dimorphic fungi can change between forms, depending
on environmental conditions. In soil and decaying matter, the mycelial form usually is present and is composed
of a collection of hyphae. The mycelia produce infective
spores that can inoculate vertebrate tissue.
CLINICAL SIGNS AND GROSS LESIONS
Mycotic granulomas of the upper respiratory tract have
been found in the nasal passages, paranasal sinuses,
nasopharynx, guttural pouch, and trachea of infected
horses. The most common clinical signs of upper respiratory fungal infection include unilateral or bilateral
serosanguineous or mucopurulent nasal discharge as well
209
For nasal and nasopharyngeal lesions, specimens for
cytology, histopathology, and culture can be obtained by
use of an endoscopically guided biopsy instrument. However, these samples tend to be small, superficial, and often
nondiagnostic. In cultures, mucosal contaminants may
overgrow the organism of interest. Larger biopsy samples
from the nasal passages or the nasopharynx can often be
obtained by use of a uterine biopsy instrument, which can
be passed nasally with visual guidance from a flexible
endoscope. Excisional biopsy or surgical debulking may be
performed through a sinus flap or via laryngotomy.
Cytology
Fungal hyphae may be identified in airway fluid or in
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
include coughing, facial deformation, and dyspnea
caused by partial blockage of nasal passages by granulomatous masses. Fungal plaques in the guttural pouch are
often located over the arterial blood supply. Horses with
guttural pouch mycosis often have episodic serosanguineous nasal discharge. This may progress to potentially fatal epistaxis if there is erosion into an artery. The
duration of clinical signs can vary from days to many
months. Differentials for fungal granulomas of the respiratory tract include ethmoidal hematoma, squamous cell
carcinoma, amyloidosis, or exuberant granulation tissue.
DIAGNOSIS
Diagnostic Samples
Lesions in the nasal passages, turbinates, nasopharynx,
guttural pouch, trachea, and bronchioles can usually be
observed directly during endoscopic examination.
Masses in the paranasal sinuses may be observed using
radiography. Computed tomography or magnetic resonance imaging provides detailed imaging of the equine
skull and can determine the extent of lesions and degree
of bony invasion. A sterile rigid arthroscope or flexible
endoscope can be passed through an 8- to 20-mm
trephine that is drilled into the conchofrontal or maxillary sinus to directly view some lesions within the
paranasal sinuses.
may 2008
Some fungi have characteristic morphologic features that
can allow an early presumptive identification (Table 1).
Histopathology
Hyphae of certain fungi may be poorly visualized
using routine hematoxylin–eosin staining. Therefore,
special stains (e.g., periodic acid-Schiff, Gridley’s fungus, Grocott-Gomori methenamine-silver nitrate) can
be useful in staining histopathologic specimens. In
patients with chronic fungal infections, there is often
evidence of extensive fibrosis on histopathology.
Microbiologic Culture
Some fungi have fastidious growth requirements and
may take up to several weeks to grow on culture media or
may be overgrown by contaminant bacteria. Tissue samples submitted for microbiologic culture should be placed
in a prepared culture media and transported at room
temperature. Specific culture media such as Sabouraud’s
dextrose agar (Remel, Lenexa, KS), inhibitory mold agar,
or Mycobiotic (Remel), which contains cycloheximide
and chloramphenicol, are useful.
Molecular Techniques
Serologic tests that use immunodiffusion,4 radioimmunoassays, latex agglutination, complement fixation, or
ELISAs5 are available to detect circulating antigens or
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
Agent
Cytologic Morphology
Serologic Test
Cryptococcus
neoformans
Round, thin-walled, yeast-like fungus (5–10 µm) with Capsular antigen ELISA (antigen)
a large heteropolysaccharide capsule (1–30 µm) that
7
does not take up common cytologic stains.The capsule Latex agglutination (antigen)
is best stained with mucicarmine stain.The organisms
show narrow-based budding and lack endospores.
Conidiobolus
coronatus
Broad, thin-walled, highly septate, irregularly
branched hyphae (5–13 µm)31; often surrounded by
acidophilic-staining, glycoprotein antigen–antibody
complexes known as Splendore-Hoeppli material.
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
immitis
Aspergillus
spp
Immunodiffusion is highly sensitive
and specific. A decreasing titer
correlates with disease resolution in
horses.8,9
Cost and
Laboratory
$16 at UGA
$18 at NMDA
$20 at CSU
$30 at UT
Serologic
testing is
not widely
available.
—
—
Relatively large, round spherules (20–80 µm; up to
200 µm) with a double-contoured cell wall.The
mature spherules are called sporangiospores (2–5 µm).
Agar gel immunodiffusion (antibody)
for IgM and IgG47,52,a
$8 at NMDA
$12 at CSU
$12 at NMDA
$15 at UT
Broad (2–4 µm), septate hyphae with parallel sides
and acute, right-angled branching.
Aspergillus Galactomannan enzyme
immunoassay (sandwich
immunoassay) antigen test; 80.7%
sensitive and 89.2% specific; some
reactivity to Penicillium, Alternaria
and Paecilomyces spp
CF (antibody)47,51,b: may have some
false-positive resultsa
Agar gel immunodiffusion
(antibody): A. fumigatus only
Fungal panel
—
Agar gel immunodiffusion
Platelia Aspergillus
antigen enzyme
immunoassay by
MDL
$15 at UT
$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. JAVMA 1956;160:546-552.
CF = Complement fixation.
CSU = Colorado State University College of Veterinary Medicine and Biomedical Sciences. Phone 970-297-1281; fax 970-297-0320;
www.dlab.colostate.edu.
CU = Cornell University Animal Health Diagnostic Center. Phone 607-253-3900; fax 607-253-3943; diagcenter.vet.cornell.edu.
MDL = MiraVista Diagnostics Laboratory, Indianapolis, IN. Phone 317-856-2681; fax 317-856-3685; www.miravistalabs.com.
NMDA = New Mexico Department of Agriculture Veterinary Diagnostic Services. Phone 505-841-2576; www.nmda.nmsu.edu/animal-andplant-protection/veterinary-diagnostic-services.
UGA = The University of Georgia College of Veterinary Medicine. Phone 706-542-5568; fax 706-542-5233; www.vet.uga.edu/dlab/index.php.
UT = University of Tennessee College of Veterinary Medicine. Phone 856-974-5639; fax 865-946-1788; www.vet.utk.edu/diagnostic/
bacteriology.
CompENdium EQuiNE
may 2008
Fungal infections of the upper Respiratory Tract CE
antibodies against several fungal organisms (Table 1).
These tests have been used to assist in the diagnosis of
equine fungal infections caused by Cryptococcus spp,6,7
Conidiobolus coronatus,3,8,9 and Aspergillus spp.10 Because
of cross-reactivity between some related fungal species,
care must be taken in interpreting test results. Many
healthy horses have antibodies against Aspergillus spp as
a result of environmental exposure. The development of
a commercial ELISA with less reactivity is promising.5,11
Serologic testing is especially useful if biopsy samples
are difficult to obtain.
Immunohistochemistry, fluorescent in situ hybridization, and DNA probes can also be used to positively
diagnose fungal organisms in histopathologic sections.
ANTIFUNGAL THERAPEUTICS
During the past decade, there has been significant
progress in the development of new antifungals in human
medicine and in the subsequent empirical use and determination of pharmacokinetic profiles in horses. Although
systemic therapy is expensive, it has resulted in an
increased incidence of successful treatment of fungal diseases in horses. As various antifungals become available in
generic form, the cost of antifungal therapy for horses will
become more affordable. New antifungals differ in their
mode of activity, toxicity, and propensity to interact with
other drugs. Therefore, antifungal therapy must be tailored to the etiologic agent, site and extensiveness of
infection, adjunctive therapies, and financial resources.
In Vitro Sensitivity Testing
For many years, clinically relevant antifungal susceptibility testing was nonexistent. Consequently, antifungal
therapy in human medicine was largely empirical and
based on evidence-based medicine rather than guided
by susceptibility data. Selection of antifungal therapy for
horses was based on recommendations from human literature, although it was limited by high expense and
lack of pharmacokinetic information specific to horses.
Currently, the National Committee for Clinical Laboratory Standards (NCCLS) has a published, approved reference method for susceptibility testing for yeasts
(M27-A).12 This method is useful for interpreting susceptibility data for azole antifungals and flucytosine in
human medicine, but interpretation of results for
amphotericin B has been problematic. 12 To date, no
interpretive breakpoints exist for any antifungal agent
against Cryptococcus neoformans or for azoles against any
of the molds. The NCCLS has published a proposed
may 2008
211
reference method for molds (M38-P), but clinical applicability is in its infancy.12 It is likely that in vitro susceptibility testing for yeasts and molds will evolve to allow
more selective use of antifungals, but to date, clinicians
should not rely solely on results of these methods to
guide therapy.12
Amphotericin B
Amphotericin B is a polyene antibiotic that combines
with ergosterol in the fungal cell membrane and causes
an increase in cell permeability. Intravenous amphotericin B is one of the most efficacious antifungal therapies but can cause nephrotoxicity and phlebitis. Other
possible adverse effects include anorexia, anemia, cardiac
arrhythmias, hepatic and renal dysfunction, and hypersensitivity reactions.13 Reported doses range from 0.3 to
0.9 mg/kg (diluted in saline) IV administered over 1
hour for approximately 30 days. Topical amphotericin B
can also be used.14,15
Azoles
Benzimidazole derivatives in the azole class (e.g.,
clotrimazole, econazole, miconazole, enilconazole, ketoconazole, isoconazole, itraconazole, fluconazole,
voriconazole) kill fungi by inhibition of ergosterol
biosynthesis in the fungal cell membrane. Ketoconazole
is absorbed poorly in the nonacidified form16 but can be
acidified for better absorption (30 mg/kg via nasogastric
tube q12h mixed with 0.2 normal hydrochloric acid).17
Itraconazole (Sporanox; Janssen-Ortho, Toronto
Ontario, Canada) solution is absorbed well orally
(bioavailability: 60%). A dose of 5 mg/kg PO q24h
maintains concentrations above minimum inhibitory
concentration for susceptible yeasts and Aspergillus spp,
with no detectable adverse effects.18 Itraconazole (Sporanox) suspension is very expensive, and because of the
large volume required, administration by nasogastric
tube is recommended. The use of compounded itraconazole is not recommended. Itraconazole is very unstable
(requires a low pH) and, owing to its lipophilic nature, is
difficult to formulate in aqueous solution.
Oral fluconazole at a loading dose of 14 mg/kg, followed by 5 mg/kg q24h, yields concentrations in
plasma, cerebrospinal fluid, synovial fluid, aqueous
humor, and urine above the minimum inhibitory concentration reported for several equine fungal pathogens.19 However, fluconazole reportedly has minimal
activity against filamentous fungi (Aspergillus and Fusarium spp). Low-dose oral fluconazole (1 mg/kg PO
CompENdium EQuiNE
212
CE Fungal infections of the upper Respiratory Tract
Figure 1. Surgical debulking of a mass via a conchofrontal sinus bone flap in a standing horse.
Local subcutaneous infiltration with lidocaine.
Access to the frontal sinus through a
conchofrontal sinus bone flap.
q24h) for at least 10 to 15 days has been anecdotally
successful in treating fungal keratitis. Compounded fluconazole formulations are very stable.
Voriconazole, a new broad-spectrum triazole antifungal,
is preferred for initial treatment of invasive aspergillosis,
candidiasis, and cryptococcosis in human patients who
cannot tolerate or have infections that are refractory to
other therapeutic agents.20,21 A recently published pharmacokinetic study of voriconazole in horses showed excellent
oral bioavailability and a long half-life.22 The authors proposed a dose of 4 mg/kg PO q24h to achieve plasma concentrations greater than 1 µg/mL but recommended that
because of potential accumulation, multiple-dosing studies
should be conducted before clinical use in horses. 22
Voriconazole is presently very expensive but is likely to
achieve therapeutic concentrations in the brain, retina, and
lungs.20 Topical miconazole and enilconazole have successfully been used to treat guttural pouch mycosis. 23–26
Miconazole is suitable only for topical administration
because it is toxic when given intravenously.
Systemic Iodide Therapy
Iodides have very little, if any, in vitro antibiotic effect,
but they seem to have a beneficial effect on the granulomatous inflammatory process. 27 Although the exact
mode of action is unknown, in several successfully
treated cases, iodides were used as primary or adjunctive
therapy for fungal granulomas.9,28 However, overall, the
efficacy of iodides is considered limited at best. The
treatment is inexpensive, but toxicity and resistance can
CompENdium EQuiNE
Significant hemorrhage resulting from
surgery to the conchofrontal sinus.
occur. Iodide toxicity is characterized by excessive
lacrimation, a nonproductive cough, increased respiratory secretions, and dermatitis.9 The recommended dose
of 20% sodium iodide is 20 to 40 mg/kg/day IV for 7 to
10 days.9,15,29 Orally administered iodide is available in
two forms:
•
Inorganic potassium iodide (10 to 40 mg/kg/day) is
available only in a chemical grade and is unstable in
the presence of light, heat, and excessive humidity.15,29
•
Organic ethylenediamine dihydroiodide (EDDI) is
commercially available (0.86 to 1.72 mg/kg of EDDI
is equivalent to 20 to 40 mg/kg/day of the 4.57%
dextrose powdered form).29
Because of the risk for developmental congenital
hypothyroidism in foals, administration of iodides
should be avoided in pregnant mares.
Surgical Therapy
Surgical debulking, endoscopic laser surgery, and
cryotherapy can be used as primary treatments or as premedical therapy in treating fungal granulomas. Surgical
debulking can be performed through a conchofrontal or
nasomaxillary sinus flap or through a laryngotomy incision. Surgery via a sinus flap can be performed with the
use of either sedation and local anesthesia in standing
patients (Figure 1) or general anesthesia in patients in
lateral recumbency (Figure 2). As with all sinonasal surgeries, there is a significant risk for hemorrhage, and the
need for blood transfusion is not uncommon. If marked
may 2008
Fungal infections of the upper Respiratory Tract CE
213
Figure 2. Surgical debulking via a conchofrontal sinus
Figure 3. Endoscopic image of mycotic granulomas
flap in a horse under general anesthesia and in lateral
recumbency.
caused by C. coronatus in the nasal passages of a horse.
hemorrhage is anticipated, a blood transfusion should be
prepared for preoperatively. If marked hemorrhage
occurs, temporary bilateral carotid artery occlusion can
be used (up to 16 minutes) to reduce intraoperative
hemorrhage.30 Direct pressure provided by gauze packing is often required for 48 to 72 hours after surgery.
Surgery is often combined with local injection of
amphotericin B or adjunctive medical therapy. Treatment has been unsuccessful in many horses that were
treated for many months by medical and surgical means,
thereby necessitating placement of a permanent tracheostomy as a salvage procedure to prolong life for
breeding or for pasture soundness.
passages, the trachea, or the soft palate can be observed
endoscopically (Figure 3). The histologic appearance of
conidiobolomycosis is similar to those of pythiosis and
basidiobolomycosis. Basidiobolus spp and P. insidiosum
tend to infect subcutaneous tissue of the limbs and
trunk, whereas C. coronatus generally infects the mucous
membranes of the upper respiratory tract. Although
nasal pythiosis has occasionally been reported, P. insidiosum is not a true fungus but rather is classified among
the Oomycetes and is discussed elsewhere.32 Hyphae of
C. coronatus are thin-walled, highly septate, and irregularly branched (5 to 13 µm). The lesions typically have
large numbers of eosinophils and fewer macrophages,
neutrophils, plasma cells, and lymphocytes that surround
hyphae (Figure 4). The definitive diagnosis is based on
microbiologic culture, immunodiffusion, or polymerase
chain reaction. 3 Detection of serum antibodies by
immunodiffusion is considered highly sensitive and specific9 and can be used to monitor response to treatment.
A nested polymerase chain reaction pythiosis assay has
also been used to identify C. coronatus.33
Conidiobolomycosis lesions can be treated with surgical excision, cryotherapy, or long-term administration of
iodides or antifungals. 3 Pharyngeal masses can be
approached via laryngotomy and visualized with a flexible endoscope. Surgical debulking followed by intralesional injection of amphotericin B (20 mg) via an 8-inch
spinal needle through the surgical incision, followed by
10 days of a topical mixture of amphotericin B (20 mg),
potassium penicillin (100,000 IU), and dimethyl sulfoxide (30 ml), was successfully used to treat pharyngeal
ETIOLOGIC AGENTS
Phycomycosis Disease Complex
Organisms within the phycomycosis (subcutaneous
mass due to fungus or bacteria) disease complex 31
include C. coronatus, Basidiobolus spp, and Pythium
insidiosum, which are in the class Zygomycetes and
order Entomophthorales. Fungi within this order are
opportunistic. They infect immunocompetent animals
and tend to form nondisseminating subcutaneous
masses. In contrast, other members of Zygomycetes
(Rhizopus, Mucor, and Absidia spp) often disseminate to
cause systemic disease.
Conidiobolomycosis
C. coronatus is a saprophytic fungus that causes granulomatous lesions of the upper respiratory tract in horses.
Single to multiple granulomatous lesions in the nasal
may 2008
CompENdium EQuiNE
214
CE Fungal infections of the upper Respiratory Tract
Figure 4. Conidiobolomycosis lesions characteristically
contain large numbers of eosinophils and fewer numbers of
macrophages, neutrophils, plasma cells, and lymphocytes.
C. coronatus has broad, thin-walled hyphae (white arrows).The hyphae
are surrounded by acidophilic-stained glycoprotein antigen–antibody
complexes (black arrows), which are known as Splendore-Hoeppli
material. (Hematoxylin–eosin stain; bar = 40 μm; courtesy of Jennifer
Taintor and Joe Newton, Auburn university)
infection with C. coronatus in one horse.14 There are
several other reports of successful treatment of nasopharyngeal infection with C. coronatus using topical or
intralesional amphotericin B.14,15,34,35 It is important to
remember that long-term therapy and reevaluation are
essential because recurrence is possible.15
A mare with C. coronatus granulomatous tracheitis was
successfully treated with iodide therapy (44 mg/kg IV of
20% sodium iodide for 7 days; then 1.3 mg/kg PO of
EDDI q12h for 4 months, then q24h for 1 year, then
once per week). Excessive lacrimation was an occasional
adverse effect of the iodide but resolved if therapy was
discontinued for 1 day.9
C. coronatus cultured from a nasal mass in one horse
was found to be resistant in vitro to ketoconazole and
itraconazole.36 Treatment with itraconazole (3 mg/kg
PO q24h for 41 ⁄2 months) was ineffective.36 Oral fluconazole was successful in treating two pregnant mares
with nasal conidiobolomycosis.2 One mare was administered 2 mg/kg PO q12h for 8 weeks; the other mare was
treated at currently recommended dosages (a loading
dose of 14 mg/kg followed by 5 mg/kg q24h PO)19 for 6
weeks. The lesions in the second horse were more extensive but resolved more rapidly than those in the horse
treated with the lower dose.2 Intralesional injection of
azole antifungals, such as miconazole or fluconazole, to
treat conidiobolomycosis has not been reported but
CompENdium EQuiNE
Figure 5. Cytologic smear of a biopsy sample of a nasal
mass from a horse. C. neoformans show their characteristic
wide, nonstaining capsule (large arrow) and narrow-based budding
(small arrow). (modified Wright’s stain; bar = 40 μm)
could be considered when parenteral treatment is not
economically feasible.3 A vaccine using C. coronatus antigen from broth cultures was unsuccessful in treating
seven horses with conidiobolomycosis. 3 Similar
immunotherapy has been very successful in treating
horses with pythiosis.37
Cryptococcosis
Cryptococcosis is commonly caused by C. neoformans
(var neoformans and var gattii)—a ubiquitous, saprophytic, round, basidiomycetous yeast-like fungus (5 to
10 µm in diameter) with a large heteropolysaccharide
capsule (1 to 30 µm in diameter) that does not take up
common cytologic stains (Figure 5). The capsule, which
forms a clear halo when stained with India ink, is
immunosuppressive and antiphagocytic. Capsular antigens that are secreted into the host’s body fluids bind
opsonizing antibodies before they reach the organism.
Equine cryptococcosis occurs at a relatively high frequency in Western Australia,6 and there is an epidemiologic relationship between C. neoformans var gattii and
the Australian river red gum tree (Eucalyptus camaldulensis) as well as between C. neoformans var neoformans
and avian (particularly pigeon) excreta.6 Cytologic or
histopathologic identification is very reliable for diagnosis because of the characteristic morphology of the
yeast. Differentiation of various cryptococcal species is
possible based on culture characteristics, serologic identification, DNA sequencing, or immunohistochemical
may 2008
Fungal infections of the upper Respiratory Tract CE
215
staining.38 Serologic testing with latex agglutination to
identify cryptococcal capsular antigen has been useful in
the diagnosis of equine cryptococcosis, with resolution
of lesions being correlated with declining serum titers.7
Cryptococcosis in horses is primarily associated with
pneumonia, rhinitis (Figure 6), meningitis, and abortion.
Reports of successful medical treatment are rare.7,39
Pseudallescheriosis
Pseudallescheria boydii is a saprophytic ascomycete
(the telomorph is Scedosporium apiospermum). Infection
with P. boydii most commonly involves the extremities;
in human patients, it is known as Madura foot. Hyphae
of Fusarium or Aspergillus spp within tissue cannot be
differentiated unless they are cultured. P. boydii cultured
from the nasal cavity and the sinus of a horse with
chronic, malodorous nasal discharge was susceptible in
vitro to miconazole, ketoconazole, natamycin, and
clotrimazole (Figure 7). After debridement and flushing of the plaque, 5 g of 2% miconazole cream was
infused twice daily for 4 weeks through lavage tubing
that had been passed into the nasal passage through a
hole drilled in the frontal bone and sinuses. Sodium
iodide was administered systemically for 4 days followed by potassium iodide for 14 days. The nasal cavity
was free of infection 30 and 60 days after treatment
had been initiated.28
Nasal mycosis caused by P. boydii has been reported in
two other horses, both of which were euthanized.40,41 In
one horse, an attempt was made to curette the nasal
Figure 6. Endoscopic image of a mycotic granuloma
caused by C. neoformans in the nasal passages of a horse.
Rhinosporidiosis
Rhinosporidium seeberi rarely causes polypoid growths
in the nasal, vaginal, and ocular mucous membranes of
horses.44–46 On gross examination, mottled small white
foci may be interspersed throughout the granuloma.46
We are not aware of any reports of treatment of R. seeberi in the literature.
Coccidioidomycosis
Coccidioides immitis is a soil saprophyte that grows in
semiarid areas with sandy, alkaline soils.47 In the environment, C. immitis exists as a mycelium with thick-walled,
Clinical signs of fungal diseases include nasal discharge, respiratory noise,
facial distortion, or airway obstruction with upper respiratory tract granulomas. Guttural pouch
mycosis may cause intermittent serosanguineous nasal discharge or epistaxis.
plaques, which was followed by topical treatment via a
surgically placed drain that was flushed daily with dilute
povidone-iodine for 10 days, followed by natamycin
solution for 2 weeks. No improvement was noted, and
the horse was euthanized.41 P. boydii has also been isolated from the pharynx of two of 60 healthy donkeys and
uterine fluid from horses with chronic uterine infection.42,43 Miconazole, itraconazole, ketaconazole, and
voriconazole are active in vitro against P. boydii, which
generally responds poorly to amphotericin B. Topical
miconazole is effective for superficial lesions.41
may 2008
barrel-shaped arthroconidia. Inhaled arthroconidia can
enlarge to form nonbudding spherules, which incite an
inflammatory reaction. Most infections are pulmonary or
systemic and have been reviewed elsewhere.47 Localized,
recurring nasal granulomas have also been reported.48–50
Nasal masses can be very slowly progressive. One horse
developed a coccidioidal ethmoid mass 6 years after
moving from Texas to a nonendemic area.48 The mass
was surgically removed; 5 years later, the clinical signs
recurred and the horse was euthanized because of the
extensiveness of the lesions.49
CompENdium EQuiNE
216
CE Fungal infections of the upper Respiratory Tract
Figure 7. Nasal and nasopharyngeal masses due to P. boydii in a quarter horse gelding with chronic, malodorous nasal
discharge. (Courtesy of R. Reid Hanson, Auburn university)
mucosanguineous nasal discharge and the most rostral
mass within the external nares.
P. boydii fungal plaque as observed by
endoscopic examination.
Adhesions caused by P. boydii in the
nasopharynx as observed by endoscopic
examination.
C. immitis is difficult to culture. However, serology is
very useful in diagnosing infection, and decreasing titers
are associated with clinical improvement.47 Oral itraconazole and fluconazole have been used to treat osseous
and pulmonary coccidioidomycosis.51,52 Nasopharyngeal
lesions can be treated surgically or medically, and longterm reevaluation is recommended.
Aspergillosis
Aspergillosis in horses has been reviewed.11 Aspergillus spp
have broad (2 to 4 µm in diameter), septate hyphae with
parallel sides and acute right-angled branching. They have a
propensity for vascular invasion. A definitive diagnosis can
be made by culture or staining using immunohistochemistry or immunofluorescence (Fusarium spp and P. boydii
appear similar on histologic examination53,54). Serologic
diagnosis has occasionally been useful5,11 but is often unreliable. Aspergillus spp are very common in the environment,
especially in moldy feed and bedding.5 Aspergillus spp are
the most common cause of guttural pouch mycosis (see
below) and can also cause plaques in the nasopharynx.35
In two horses, mycotic rhinitis was treated successfully
with itraconazole (3 mg/kg PO q24h for 120 days,
which achieved concentrations that exceeded the minimum inhibitory concentration for the organism). 36
Additional successful treatments in two horses included
topical natamycin (25 mg in 100 ml of saline) flushed
via an endoscope as well as nystatin powder insufflated
up the affected nostril. Another horse was treated sucCompENdium EQuiNE
Figure 8. Endoscopic image of guttural pouch mycosis.
(Courtesy of John Schumacher, Auburn university)
cessfully with natamycin solution via an indwelling
facial catheter in the caudal maxillary sinus.1
Guttural Pouch Mycosis
There are several excellent, detailed reviews of guttural pouch mycosis.11,55,56 Mycotic infection of the guttural pouch generally occurs on the dorsal wall of the
medial compartment or on the lateral wall of the lateral
compartment (Figure 8). Mycotic ulcerations are typimay 2008
Fungal infections of the upper Respiratory Tract CE
217
Figure 10. Photomicrograph of a histologic section
showing Aspergillus spp in a fatal case of guttural pouch
mycosis. The hyphae of Aspergillus spp are septate and show
dichotomous branching. (Hematoxylin–eosin stain; bar = 30 μm;
courtesy of Arno Wünschmann, university of minnesota)
Figure 9. Fatal guttural pouch mycosis in a quarter
horse mare that had a 2-week history of intermittent,
unilateral epistaxis. The mare had been referred for arterial
coil embolization. An acute, profuse hemorrhagic episode
occurred, and the mare died in 7 minutes.
cally located over the internal carotid artery and less
commonly located over the external carotid artery or
maxillary artery. Plaques can vary in size and can expand
to cover the entire roof of the pouch. Infection may
erode through the median septum into the neighboring
pouch, causing bilateral infection.
Horses generally have intermittent mucopurulent to
serosanguineous nasal discharge or epistaxis.56 Erosion
of the internal carotid artery or, less commonly, the
external carotid artery or maxillary artery can result in
fatal hemorrhage (Figure 9). If guttural pouch mycosis
associated with epistaxis is untreated, 50% of affected
horses will die.55 Bouts of epistaxis are unpredictable,
but several usually occur before a fatal bleeding episode.
Endoscopy or placement of lavage catheters carries a
significant risk for dislodging fungal plaques or previously formed clots, which can result in further hemorrhage. Secondary neurologic abnormalities may result if
thrombi from the internal carotid artery dislodge and
embolize to the brain, causing subsequent cerebral dysfunction. Inflammation can affect cranial nerves that
traverse the guttural pouch, leading to the development
may 2008
CompENdium EQuiNE
of laryngeal hemiplegia, dysphagia, facial paralysis, or
Horner’s syndrome.
Guttural pouch mycosis is most often caused by
218
CE Fungal infections of the upper Respiratory Tract
Aspergillus spp, particularly A. nidulans (Figure 10).
Infections with Mucor, Penicillium, Paecilomyces,
Chrysosporium, Rhizopus, and Alternaria spp have also
been reported. Surgical arterial occlusion by either balloon catheter technique or transarterial coil is the preferred treatment for guttural pouch mycosis; there is
little evidence for the necessity of adjunctive medical
therapy56,57 (e.g., oral or topical thiabendazole; topical
nystatin, natamycin, miconazole, or enilconazole; oral or
systemic iodides).
If surgical options are not available, topical medications can be applied via an indwelling catheter (a temporary Chamber’s catheter or long-term commercial
guttural pouch catheter) that is advanced through the
guttural pouch opening. Medications may also be
sprayed directly on the lesion through the biopsy portal
of a flexible endoscope. The dorsal location of the
lesions makes treatment difficult, and there is always the
risk for fatal hemorrhage.
Intranasal 2% miconazole has been used in the resolution of four cases of guttural pouch mycosis.23 In two
cases, 70 mg of injectable miconazole solution was
diluted in 10 mL of normal saline; in two other cases,
400 mg of warmed gynecologic miconazole cream was
infused into the guttural pouch once daily for 1 week,
then every other day for 2 weeks. Treatment using the
gynecologic cream was continued twice per week for an
additional 3 weeks. All horses recovered uneventfully.23
Although enilconazole is not available in the United
States, it has been used topically as a 0.9% or 1.7% solution to successfully treat four cases of guttural pouch
mycosis caused by Rhizopus, Aspergillus, Penicillium,
Mucor, Chrysosporium, and Alternaria spp.25,26
Systemic treatment of guttural pouch mycosis has
also been successful using itraconazole and topical
enilconazole.24 Itraconazole (5 mg/kg PO for 3 weeks)
was administered, and topical enilconazole (60 mL)
was later sprayed directly onto the mycotic lesion using
endoscopic guidance for 2 weeks.24 Medical therapy
may be a more economically feasible treatment option
than surgical arterial occlusion and can be considered
when neurologic deficits are present in the absence of
epistaxis.
CONCLUSION
Conidiobolomycosis, aspergillosis, cryptococcosis,
coccidioidomycosis, and pseudallescheriosis are the most
commonly reported causes of fungal granulomas in the
equine respiratory tract. Infection with other organisms
CompENdium EQuiNE
is possible, and new etiologies will likely be reported in
the future. Determination of the specific fungal agent
influences the choice of the antifungal in medical management but may be irrelevant in surgical intervention.
Drugs available for systemic therapy are becoming more
affordable (especially fluconazole), but it has not been
determined whether medical therapy with a sole agent is
more or less efficacious or cost effective than are combinations of surgical debulking, intralesional injection,
and/or the use of systemic antifungals.
REFERENCES
1. Greet TRC. Nasal aspergillosis in 3 horses. Vet Rec 1981;109:487-489.
2. Taintor J, Crowe C, Hancock S, et al. Treatment of conidiobolomycosis with
fluconazole in two pregnant mares. J Vet Intern Med 2004;18:363-364.
3. Taintor J, Schumacher J, Newton J. Conidiobolomycosis in horses. Compend
Contin Educ Pract Vet 2003;25:872-876.
4. Rezabek GB, Donahue JM, Giles RC, et al. Histoplasmosis in horses. J Comp
Pathol 1993;109:47-55.
5. Guillot J, Sarfati J, de Barros M, et al. Comparative study of serological tests
for the diagnosis of equine aspergillosis. Vet Rec 1999;145:348-349.
6. Riley CB, Bolton JR, Mills JN, et al. Cryptococcosis in 7 horses. Aust Vet J
1992;69:135-139.
7. Begg LM, Hughes KJ, Kessell A, et al. Successful treatment of cryptococcal
pneumonia in a pony mare. Aust Vet J 2004;82:686-692.
8. Kaufman L, Mendoza L, Standard PG. Immunodiffusion test for serodiagnosing subcutaneous zygomycosis. J Clin Microbiol 1990;28:1887-1890.
9. Steiger RR, Williams MA. Granulomatous tracheitis caused by Conidiobolus
coronatus in a horse. J Vet Intern Med 2000;14:311-314.
10. Moore BR, Reed SM, Kowalski JJ, et al. Aspergillosis granuloma in the
mediastinum of a nonimmunocompromised horse. Cornell Vet 1993;83:97104.
11. Blomme E, Del Piero F, La Perle KMD, et al. Aspergillosis in horses: a
review. Equine Vet Educ 1998;10:86-93.
12. Gubbins PO. Fungal infections. In: Fink MP, Abraham E, Vincent J-L,
Kochanek PM, eds. Textbook of Critical Care. 5th ed. Philadelphia: Elsevier
Saunders; 2005;1345-1357.
13. Chandna VK, Morris E, Gliatto JM, et al. Localized subcutaneous cryptococcal granuloma in a horse. Equine Vet J 1993;25:166-168.
14. French DD, Haynes PF, Miller RI. Surgical and medical management of
rhinophycomycosis (conidiobolomycosis) in a horse. JAVMA 1985;186:11051107.
15. Zamos DT, Schumacher J, Loy JK. Nasopharyngeal conidiobolomycosis in a
horse. JAVMA 1996;208:100-101.
16. Prades M, Brown MP, Gronwell R, et al. Body fluid and endometrial concentrations of ketaconazole in mares after intravenous injection or repeated gavage. Equine Vet J 1989;21:211-214.
17. Nappert G, VanDyck T, Papich M, et al. Successful treatment of a fever associated with consistent pulmonary isolation of Scopulariopsis sp in a mare.
Equine Vet J 1996;28:421-424.
18. Clode AB, Davis JL, Salmon J, et al. Evaluation of concentration of voriconazole in aqueous humor after topical and oral administration in horses. Am J
Vet Res 2006;67(2):296-301.
19. Latimer FG, Colitz CMH, Campbell NB, et al. Pharmacokinetics of fluconazole following intravenous and oral administration and body fluid concentrations of fluconazole following repeated oral dosing in horses. Am J Vet
Res 2001;62:1606-1611.
may 2008
Fungal infections of the upper Respiratory Tract CE
219
20. Jeu L, Piacenti FJ, Lyakhovetskiy AG, et al. Voriconazole. Clin Ther
2003;25:1321-1381.
46. Blackford J. Superficial and deep mycoses in horses. Vet Clin North Am Equine
Pract 1984;6:47-58.
21. Fleming RV, Walsh TJ, Anaissie EJ. Emerging and less common fungal
pathogens. Infect Dis Clin North Am 2002;16:915-933.
47. Ziemer EL, Pappagianis D, Madigan JE, et al. Coccidioidomycosis in horses:
15 cases (1975-1984). JAVMA 1992;201:910-916.
22. Davis JL, Salmon JH, Papich MG. Pharmacokinetics of voriconazole after
oral and intravenous administration to horses. Am J Vet Res 2006;67:170-175.
23. Giraudet AJ. Medical treatment with miconazole in four cases of guttural
pouch mycosis. J Vet Intern Med 2005;19:485.
24. Davis EW, Legendre AM. Successful treatment of guttural pouch mycosis
with itraconazole and topical enilconazole in a horse. J Vet Intern Med
1994;8:304-305.
25. Vannieuwstadt RA, Kalsbeek HC. Guttural pouch mycosis: local treatment
with an indwelling through-the-nose-catheter with enilconazole. Tijdschr
Diergeneesk 1994;119:3-5.
26. Carmalt JL, Baptiste KE. Atypical guttural pouch mycosis in three horses.
Pferdeheilkunde 2004;20:542.
27. Plumb D. Veterinary Drug Handbook. 4th ed. Ames: Iowa State University
Press; 2002.
28. Davis PR, Meyer GA, Hanson RR, et al. Pseudallescheria boydii infection of
the nasal cavity of a horse. JAVMA 2000;217:707-709.
29. Scott DW, Miller WH. Fungal skin diseases. In: Scott DW, ed. Equine Dermatology. Philadelphia: WB Saunders; 2003:311-312.
30. Embertson RM. Upper airway conditions in older horses, broodmares and
stallions. Vet Clin North Am Equine Pract 1991;7:149-164.
31. Miller RI, Campbell RSF. The comparative pathology of equine cutaneous
phycomycosis. Vet Pathol 1984;21:325-332.
48. Reed SM, Boles CL, Dade AW, et al. Localized equine nasal coccidioidomyces granuloma. J Equine Med Surg 1979;3:119-123.
49. Hodgin EC, Conaway H, Ortenburger AI. Recurrence of obstructive nasal
coccidioidal granuloma in a horse. JAVMA 1984;184:339-340.
50. Pappagianis D. Epidemiology of coccidioidomycosis. In: McGinnis MR, ed.
Current Topics in Medical Mycology. New York: Springer-Verlag; 1988:199238.
51. Foley JP, Legendre AM. Treatment of coccidioidomycosis osteomyelitis with
itraconazole in a horse: a brief report. J Vet Intern Med 1992;6:333.
52. Higgins JC, Leith GS, Pappagianis D, et al. Successful treatment of Coccidioides immitis pneumonia with fluconazole in two horses. J Vet Intern Med
2005;19:482-483.
53. Tunev SS, Ehrhart EJ, Jensen HE, et al. Necrotizing mycotic vasculitis with
cerebral infarction caused by Aspergillus niger in a horse with acute typhlocolitis. Vet Pathol 1999;36:347-351.
54. Thirion-Delalande C, Guillot J, Jessen HE, et al. Disseminated acute concomitant aspergillosis and mucormycosis in a pony. J Vet Med 2005;52:121125.
55. Hardy J, Leveille R. Diseases of the guttural pouches. Vet Clin North Am
Equine Pract 2003;19:123-158.
32. Chaffin MK, Schumacher J, McMullan WC. Cutaneous pythiosis in the
horse. Vet Clin North Am Equine Pract 1995;11:91-103.
56. Lepage OM, Perron MF, Cadore JL. The mystery of fungal infection in the
guttural pouches. Vet J 2004;168:60-64.
33. Grooters AM, Leise BS, Lopez MK, et al. Development and evaluation of an
enzyme-linked immunosorbent assay for the serodiagnosis of pythiosis in
dogs. J Vet Intern Med 2002;16:142-146.
57. Leveille R, Hardy J, Robertson JT, et al. Transarterial coil embolization of the
internal and external carotid and maxillary arteries for prevention of hemorrhage from guttural pouch mycosis in horses. Vet Surg 2000;29:389-397.
34. McMullan WC, Joyce JR, Hanselka DV, et al. Amphotericin-B for treatment
of localized subcutaneous phycomycosis in horses. JAVMA 1977;170:12931298.
35. Hanselka DV. Equine nasal phycomycosis. Vet Med Small Anim Clin
1977;72:251-253.
36. Korenek NL, Legendre AM, Andrews FM. Treatment of mycotic rhinitis
with itraconazole in three horses. J Vet Intern Med 1994;8:224-227.
37. Newton J, Schumacher J. Pythiosis. In: Robinson NM, ed. Equine Current
Therapy. 4th ed. Philadelphia: WB Saunders; 1997:396-397.
38. Lester SJ, Kowalewich NJ, Bartlett KH, et al. Clinicopathologic features of an
unusual outbreak of cryptococcosis in dogs, cats, ferrets, and a bird: 38 cases
( January to July 2003). JAVMA 2004;225:1716-1722.
39. Boulton CH, Williamson L. Cryptococcal granuloma associated with jejunal
intussusception in a horse. Equine Vet J 1984;16:548-551.
ARTICLE #2 CE TEST
CE
This article qualifies for 2 contact hours of continuing
education credit from the Auburn University College of
Veterinary Medicine. Subscribers may take individual
CE tests or sign up for our annual CE program.
Those who wish to apply this credit to fulfill state relicensure
requirements should consult their respective state
authorities regarding the applicability of this program.
CE subscribers can take CE tests online and get real-time
scores at CompendiumEquine.com.
40. Johnson GR, Schiefer B, Pantekoek JFCA. Maduromycosis in a horse in
Western Canada. Can Vet J 1975;16:341-344.
41. Brearley JC, McCandlish IAP, Sullivan M, et al. Nasal granuloma caused by
Pseudallescheria boydii. Equine Vet J 1986;18:151-153.
42. El-Allawy T, Atria M, Amer A. Mycoflora of the pharyngeotonsillar portions
of clinically healthy donkeys in Assuit. Assuit Med Vet 1977;4:63-69.
43. Carter ME, Menna ME. Petriellidium boydii from the reproductive tracts in
mares. N Z Vet J 1975;23:13.
44. Myers DD, Simon J, Case MT. Rhinosporidiosis in a horse. JAVMA
1964;145:345-347.
45. Lengfelder KD, Pospischil A. Rhinosporidiosis in the horse: histological and
electron microscopic study of a case. Zentralbl Veterinarmed B 1980;27:326339.
may 2008
1. Which statement about fungal cell structure is
incorrect?
a. Fungal cell walls are composed of chitins, glucans, and
mannans.
b. Fungal cell membranes contain ergosterol.
c. Fungi are prokaryotes, as are bacteria.
d. Fungi growing in decaying matter are usually present
in the mycelial form.
e. dimorphic fungi can change between forms, depending on environmental conditions.
CompENdium EQuiNE
220
CE Fungal infections of the upper Respiratory Tract
2. Which statement about guttural pouch mycosis
is incorrect?
a. Horses usually present with episodic mucopurulent
to serosanguineous nasal discharge.
b. Fatal epistaxis can occur if there is erosion into an
artery.
c. The most common cause is Aspergillus spp.
d. Fungal plaques frequently involve the retropharyngeal
lymph nodes on the ventral wall of the medial compartment of the guttural pouch.
e. Cranial nerve dysfunction can lead to the development of laryngeal hemiplegia, dysphagia, facial paralysis, or Horner syndrome.
3. Which statement about antifungals is correct?
a. Amphotericin B is an azole antifungal.
b. intravenous amphotericin B can be nephrotoxic.
c. The use of compounded itraconazole is recommended to reduce costs of therapy.
d. miconazole is an inexpensive, safe, and effective intravenous antifungal.
e. Ketoconazole has good oral bioavailability.
4. Which statement about infection with C. coronatus is incorrect?
a. C. coronatus is a round, basidiomycetous yeast-like
fungus with a large heteropolysaccharide capsule.
b. Hyphae of C. coronatus are thin-walled, highly septate,
and irregularly branched.
c. The lesions typically have large numbers of eosinophils
and fewer macrophages, neutrophils, plasma cells, and
lymphocytes surrounding the hyphae.
d. infection generally results in granulomatous lesions in
the nasal passages, trachea, or soft palate.
e. Successful resolution has been obtained with intralesional amphotericin B, oral fluconazole, and oral itraconazole.
5. Which statement about C. neoformans is incorrect?
a. Cytologic or histopathologic identification is very
reliable for diagnosis because of characteristic morphology.
b. Resolution of cryptococcal lesions is correlated with
decreasing serum titers.
c. Cryptococcosis in horses is primarily associated with
pneumonia, rhinitis, meningitis, and abortion.
CompENdium EQuiNE
d. Successful medical treatment of cryptococcosis has
never been reported in horses.
e. C. neoformans has a large heteropolysaccharide capsule that is immunosuppressive and antiphagocytic.
6. An epidemiologic association among the Australian river red gum tree, bird droppings, and
_________ has been described.
a. Alternaria spp
b. Aspergillus spp
c. C. coronatus
d. C. neoformans
e. P. boydii
7. Guttural pouch mycosis is most often caused by
infection with
a. Aspergillus spp.
b. C. neoformans.
c. Alternaria spp.
d. P. boydii.
e. C. coronatus.
8. The preferred surgical treatment of guttural
pouch mycosis is
a. arterial occlusion by balloon catheter or transarterial
coil.
b. curettage via Viborg’s triangle.
c. stylohyoid ostectomy.
d. jugular vein occlusion.
e. trephination via the nasomaxillary sinus into the
pouch as well as topical therapy.
9. Aspergillus spp typically have
a. thin-walled, highly septate hyphae with irregular
branching.
b. broad, septate hyphae with parallel sides and acute,
right-angled branching.
c. narrow, nonseptate hyphae with tapering sides.
d. round, yeast-like cells with a large heteropolysaccharide capsule.
e. nonencapsulated cells with broad-based budding.
10. Which azole antifungal is toxic if administered
systemically?
a. itraconazole
b. fluconazole
c. ketaconazole
d. miconazole
e. voriconazole
may 2008