Evaluation of an enzyme immunoassay for antibodies to a recombinant Blastomyces adhesin-1 repeat antigen as an aid in the diagnosis of blastomycosis in dogs

UTILITY OF URINE ANTIGEN TESTING FOR DIAGNOSIS OF BLASTOMYCOSIS IN NONDOMESTIC FELIDS

Blastomycosis caused by the fungus Blastomyces dermatitidis has been reported to cause disease in numerous species of nondomestic felids. Diagnosis of blastomycosis in domestic species often relies on the combination of clinical signs, radiographic findings, and commercial urinary antigen testing. In this report, the sensitivity, specificity, and positive and negative predictive values for urine blastomyces antigen testing for use in nondomestic felids were examined and compared with findings on postmortem examination. The study showed a sensitivity of 100%, specificity of 91.86%, positive predictive value of 50%, and negative predictive value of 100% for urine antigen testing. Furthermore, radiographic and hematologic findings were compared with those of animals diagnosed with blastomycosis. Radiographic evidence consistent with blastomycosis was found in those animals diagnosed via urine antigen testing, but no significant differences in plasma biochemistry parameters between diseased and nondiseased animals were found. This study provides evidence that a positive blastomycosis antigenuria test result should be combined with other diagnostic methods to confirm the presence of infection with B. dermatitidis, whereas a negative antigenuria test result is 100% effective in predicting the absence of disease.

Blastomycosis: A Review of Mycological and Clinical Aspects

Blastomycosis is caused by a thermally dimorphic fungus that thrives in moist acidic soil. Blastomyces dermatitidis is the species responsible for most infections in North America and is especially common in areas around the Great Lakes, the St. Lawrence Seaway, and in several south-central and southeastern United States. Other Blastomyces species have more recently been discovered to cause disease in distinct geographic regions around the world. Infection almost always occurs following inhalation of conidia produced in the mold phase. Acute pulmonary infection ranges from asymptomatic to typical community-acquired pneumonia; more chronic forms of pulmonary infection can present as mass-like lesions or cavitary pneumonia. Infrequently, pulmonary infection can progress to acute respiratory distress syndrome that is associated with a high mortality rate. After initial pulmonary infection, hematogenous dissemination of the yeast form of Blastomyces is common. Most often this is manifested by cutaneous lesions, but osteoarticular, genitourinary, and central nervous system (CNS) involvement also occurs. The diagnosis of blastomycosis can be made by growth of the mold phase of Blastomyces spp. in culture or by histopathological identification of the distinctive features of the yeast form in tissues. Detection of cell wall antigens of Blastomyces in urine or serum provides a rapid method for a probable diagnosis of blastomycosis, but cross-reactivity with other endemic mycoses commonly occurs. Treatment of severe pulmonary or disseminated blastomycosis and CNS blastomycosis initially is with a lipid formulation of amphotericin B. After improvement, therapy can be changed to an oral azole, almost always itraconazole. With mild to moderate pulmonary or disseminated blastomycosis, oral itraconazole treatment is recommended.

Negative Antigenuria in a Dog with Suspected Central Nervous System Localized Blastomycosis

A 7 yr old female spayed mixed-breed dog was presented for a 1 wk history of neck pain and pelvic limb weakness. Examination revealed nonambulatory paraparesis and thoracolumbar hyperesthesia. MRI revealed extensive intramedullary T2-weighted/short tau inversion recovery hyperintensity and diffuse severe T1-post contrast meningeal enhancement of the thoracolumbar spinal cord. An L5-L6 cerebrospinal fluid sample revealed a suppurative pleocytosis (81% neutrophils, total protein 4362.5 mg/dL and nucleated cell count 352,000/μL). While awaiting the results of infectious disease testing, the dog was treated for suspected meningoencephalitis of unknown etiology with corticosteroids, cyclosporine, and a cytarabine arabinoside infusion. The dog neurologically declined and was started on broad-spectrum antibiotics. The dog continued to decline despite antibiotics, and infectious disease titers subsequently revealed serum antibody positivity for blastomycosis. The dog was then referred to a multispecialty referral hospital and was treated with amphotericin B followed by fluconazole. Prednisone was continued at anti-inflammatory doses. Urine blastomycosis antigen testing was submitted for subsequent disease monitoring but was negative. Five months after presentation the dog was clinically doing well with no identifiable neurologic deficits. This case demonstrates that neurologic blastomycosis may have negative urine antigen concentrations in some dogs and that other diagnostic modalities should be pursued when central nervous system fungal disease is suspected.

Mandibular Blastomycosis in a 5-Year-Old Dog

A case of localized oral mandibular blastomycosis is described in a five-year-old dog. Complete resolution of clinical signs and oral radiographic changes were seen following itraconazole therapy at 5 mg/kg/day for four and a half months. The patient remained free of Blastomyces at the one year follow up based on the Mira Vista Blastomyces urine antigen test by EIA (Enzyme Immunoassay)^a. A literature review of localized blastomycosis cases in humans and dogs was performed, available diagnostic tests evaluated, and treatment comparisons made.

Ocular findings in cats with blastomycosis: 19 cases (1978-2019)

OBJECTIVE

To document ocular findings in cats with blastomycosis.

ANIMALS

35 cats with blastomycosis.

PROCEDURES

Medical records from 1978 through 2019 were reviewed to identify cats with confirmed Blastomyces infection. Cats were grouped as having or not having ocular involvement. Clinical signs, histopathologic findings, and response to treatment were evaluated.

RESULTS

21 of the 35 (60%) cats with confirmed blastomycosis had ocular abnormalities. Two of 21 cats with ocular abnormalities also had systemic hypertension and were excluded. Of the remaining 19 cats, 15 (79%) had bilateral ocular signs. Ten (53%) cats had inflammatory ocular lesions, and 9 (47%) had neuro-ophthalmic abnormalities. Six of the 19 (32%) cats appeared to be completely blind, and 5 (26%) appeared to be unilaterally blind. For the 10 cats with inflammatory ocular lesions, the most common lesions were anterior uveitis (9/20 eyes), active chorioretinitis (6/20 eyes), and retinal detachment (4/20 eyes). For the 9 cats with neuro-ophthalmic abnormalities, the most common abnormalities were a negative menace or tracking response (10/18 eyes) and negative pupillary light response (4/18 eyes).

CLINICAL RELEVANCE

Results suggested that ocular involvement is common in cats with blastomycosis and that both inflammatory lesions and neuro-ophthalmic abnormalities can be seen. Blastomycosis should be considered in the differential diagnosis for cats with anterior uveitis, posterior segment inflammation, or neuro-ophthalmic abnormalities, and a complete ophthalmic examination should be performed in all cats with confirmed or suspected blastomycosis.

Retrospective analysis of the effects of Blastomyces antigen concentration in urine and radiographic findings on survival in dogs with blastomycosis

Background

The Blastomyces antigen concentration in urine (BACU) test is used to diagnose blastomycosis and monitor treatment in dogs. It is unknown if a higher BACU is associated with shorter survival.

Objectives

To determine if the magnitude of BACU before treatment is associated with survival in dogs with blastomycosis.

Animals

Fifty‐two dogs with blastomycosis.

Methods

Retrospective case review. BACU, radiographic lung severity (RLS) score (0‐4 scale), and survival time up to 1 year after diagnosis were obtained through medical record review of dogs with Blastomyces dermatitidis.

Results

The overall survival was: discharge, 87%; 1 week, 85%; 2 months, 74%; and 6 months, 69%. BACU correlated with RLS score (r_s = 0.33, P = .02). BACU and RLS scores were lower in survivors to 2 months than nonsurvivors (average BACU difference of 2.5 ng/mL, 95% confidence interval [CI]: 0.2‐4.8 ng/mL, P = .04; median RLS difference of 2; range, 0‐4, P = .02). Dogs with BACU <5 ng/mL and dogs with mild (0‐1) RLS scores had a greater proportion surviving than those with BACU >5 ng/mL (P = .03) and dogs with severe (3‐4) RLS scores (P = .04). All dogs with a BACU <5 ng/mL or mild RLS score were alive at last follow‐up (median, 365 days; range, 44‐365 days). In all, 68.1% of other dogs survived to 2 months (95% CI, 54.8%‐84.8%).

Conclusions and Clinical Importance

Dogs with lower BACU and RLS scores have improved survival; however, it is unclear what specific cutoffs should be used for prognosis.

Novel canine anti-Coccidioides immunoglobulin G enzyme immunoassay aids in diagnosis of coccidioidomycosis in dogs

The diagnosis of coccidioidomycosis (CM) in dogs is typically based on clinical presentation, serology, and (less frequently) spherule identification. Agar gel immunodiffusion (AGID) is the most commonly employed serological method, but AGID is slow (requiring up to a week for titer). A Coccidioides antigen enzyme immunoassay (EIA) is also available; however, sensitivity is low in CM dogs. An antibody EIA was developed to detect canine immunoglobulin G (IgG) reacting to Coccidioides antigens. Serum was evaluated from dogs with pathology proven CM and/or AGID positive CM, as well as dogs with histoplasmosis, blastomycosis, non-fungal infections, or healthy dogs. A standard curve was used to convert optical density (OD) values into EIA units (EU). Serum and urine samples from CM dogs were also tested in the antigen EIA. Sensitivity and specificity for IgG were 89.2% and 97.2%, respectively, upon evaluation of dogs with proven or probable CM and control dogs. Cross-reactivity was observed in 7.7% and in 6.4% of dogs with histoplasmosis or blastomycosis, respectively. The antigen EIA alone was insensitive (33.8%). Combined IgG and antigen testing increased sensitivity to 93.2%, as three dogs were IgG-negative but had detectable serum or urine antigen. In 22 dogs with proven CM, sensitivity was statistically similar for antibody EIA and AGID (86% and 73%; P = .487). The MiraVista® canine Coccidioides antibody IgG EIA may aid in the diagnosis of CM by improving turnaround time with comparable sensitivity to AGID. Serial or concurrent testing by antibody and antigen EIAs may be beneficial when screening dogs for CM.

Fungal Infections of the Central Nervous System in Small Animals: Clinical Features, Diagnosis, and Management

Small animal mycoses vary geographically. Different clinical presentations are seen in animals with infection of the central nervous system (CNS), including multifocal meningoencephalomyelitis, intracranial lesions that accompany sinonasal lesions, rapidly progressive ventriculitis, or solitary granuloma of the brain or spinal cord. Systemic, nasal, or extraneural clinical signs are common but, especially in granuloma cases, do not always occur. Surgery may have a diagnostic and therapeutic role in CNS granuloma. There have been recent advancements in serology. Fluconazole, voriconazole, and posaconazole cross the blood-brain barrier, but voriconazole is neurotoxic to cats. Liposomal and lipid-encapsulated formulations of amphotericin B are preferred.