Utility of antigen testing for the diagnosis of ocular histoplasmosis in four cats: a case series and literature review

Invasive Fungal Infections and Oomycoses in Cats: 1. Diagnostic approach

CLINICAL RELEVANCE

In contrast to superficial fungal infections, such as dermatophytosis, invasive fungal infections (IFIs) are characterised by penetration of tissues by fungal elements. Disease can spread locally within a region or can disseminate haematogenously or via the lymphatics. The environment is the most common reservoir of infection. Since fungal spores are airborne, indoor cats are also susceptible to IFIs. Some environmental fungi are ubiquitous and present globally, while others are endemic or hyperendemic within specific geographic regions. Zoonotic pathogens include Microsporum canis, Sporothrix schenckii and Sporothrix brasiliensis.

AIM

In the first of a two-part article series, the approach to the investigation of feline IFIs and oomycoses is reviewed. As well as tips for diagnosis, and information on the ecological niche and distribution of fungal pathogens, the review covers clinical presentation of the most common IFIs, including cryptococcosis, histoplasmosis, blastomycosis, coccidioidomycosis, sporotrichosis, phaeohyphomycosis, aspergillosis and dermatophytic pseudomycetoma, as well as the oomycoses pythiosis, lagenidiosis and paralagenidiosis. In Part 2, the spectrum of activity, mechanisms of action, pharmacokinetic and pharmacodynamic properties and adverse effects of antifungal drugs are reviewed, and the treatment and prognosis for specific IFIs and oomycoses are discussed.

EVIDENCE BASE

The review draws on published evidence and the authors' combined expertise in feline medicine, mycology, dermatology, clinical pathology and anatomical pathology.

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.

Invasive fungal rhinitis with adnexal involvement caused by Histoplasma capsulatum in a cat from a non-enzootic location

Case summary

This report describes a cat with a rare form of histoplasmosis: invasive rhinitis with adnexal involvement, mimicking disease more commonly caused by cryptococcosis or aspergillosis. This case is especially noteworthy as it was from an area where histoplasmosis is not enzootic.

Relevance and novel information

Invasive fungal rhinitis causes significant morbidity in cats. Diagnostic investigation of more common pathogens includes detection of fungal antigen (Cryptococcus) or antifungal antibodies (Aspergillus). This case demonstrates that histoplasmosis can present as chronic nasal disease in cats. Histoplasma antigen testing provides a non-invasive diagnostic option. Moreover, this case serves as a reminder that histoplasmosis can affect cats anywhere, even in non-enzootic areas.

Evaluation of a novel monoclonal antibody-based enzyme immunoassay for detection of Histoplasma antigen in urine of dogs

Background

Commercially available, noninvasive testing options for histoplasmosis are limited outside of the United States.

Objectives

To describe the diagnostic performance of a novel Histoplasma antigen enzyme immunoassay (IM EIA) for the diagnosis of histoplasmosis in dogs.

Animals

Twenty dogs with histoplasmosis, 79 dogs without histoplasmosis, and 11 unclassified dogs providing 202 urine samples.

Methods

This a prospective study using stored urine samples. Samples were analyzed with the IM EIA and with the commercially available Histoplasma antigen EIA (MV EIA). Dogs were classified based on final proven diagnosis and performance of the IM EIA was described and compared with the MiraVista enzyme immunoassay (MV EIA).

Results

The diagnostic sensitivity (DSe), specificity (DSp), and accuracy (DAc) of the IM EIA were 70% (51%‐89%), 99% (97%‐100%), and 93% (81%‐100%), respectively. The DSe, DSp, and DAc for the MV EIA were 95% (85%‐100%), 99% (97%‐100%), and 98% (95%‐100%), respectively. The area under the receiver operator characteristic curve was significantly smaller for IM EIA (0.87) as compared with MV EIA (0.97, P = .03). This was primarily due to 6 false negative IM EIA results, 4 from dogs with disease localized to the gastrointestinal tract. The MV EIA was positive in 5/6 of these dogs.

Conclusions and Clinical Importance

The IM EIA might be useful for the diagnosis of disseminated histoplasmosis in dogs, but clinical usefulness will be limited in dogs with histoplasmosis localized to the GI tract.

Mediastinal histoplasmosis with cardiac involvement in a cat

Histoplasmosis is the second most common fungal infection reported among domestic felines in the United States. Dissemination of the organism after inoculation is common and affected organ systems include the respiratory tract, gastrointestinal tract, reticuloendothelial organs, skeletal system, integument, and ocular system. However, histoplasmosis presenting as a discrete granulomatous mass identified on echocardiogram has never been reported in the veterinary literature. Here, we describe the first case of feline histoplasmosis presenting as a granuloma with cardiac involvement. The patient, a 6-year-old male neutered domestic longhair feline, was referred for tachypnea and dyspnea. A mass in the cranial mediastinum abutting the heart was diagnosed via two-dimensional echocardiography. Cytology of fine needle aspirates from the mass revealed round yeast structures consistent with Histoplasma spp. The patient was treated with oral fluconazole therapy, and subsequent rechecks have shown marked improvement in clinical parameters, lesion size, and antigen concentrations.

Disseminated histoplasmosis with ocular adnexal involvement in seven cats

OBJECTIVE

To describe the clinical features, diagnosis, and treatment of disseminated histoplasmosis with conjunctival and/or nictitating membrane involvement in cats.

PROCEDURE

Medical records from seven cats with naturally acquired disseminated histoplasmosis and conjunctival and/or nictitating membrane lesions were reviewed for signalment, clinical findings, diagnostic results, treatment, and outcome.

RESULTS

Breeds included domestic shorthair (n = 5), Maine Coon (n = 1), and Siamese mix (n = 1) with four spayed females and three castrated males. Conjunctival abnormalities were identified in four cats, and nictitating membrane lesions were identified in four cats; one cat had both a conjunctival and nictitating membrane lesion. Cytologic evaluation of lesions identified Histoplasma capsulatum organisms in two of four cases sampled, and histopathologic evaluation identified H capsulatum in both cases in which a sample was submitted. Histoplasmosis antigen testing was positive in three of four submitted samples. Initial treatment for all cats included fluconazole (median dose: 26 mg/kg/d). Median duration of follow-up was 11 months (range: 1-108 months; n = 4). Resolution of ocular adnexal lesions was achieved in three cats. Two cats had relapse of disease, one of which was subsequently euthanized. One cat with concurrent feline immunodeficiency virus (FIV) infection died one month after diagnosis of histoplasmosis.

CONCLUSIONS

Histoplasmosis should be a differential diagnosis for ocular adnexal inflammatory lesions in cats.

Clinical features of cats diagnosed with coccidioidomycosis in Arizona, 2004-2018

OBJECTIVES

The goal of this study was to describe the clinical presentation, diagnosis and treatment of coccidioidomycosis in cats residing in a region endemic for Coccidioides species.

METHODS

A retrospective review of records was performed at both primary and tertiary care veterinary practices in Tucson and Phoenix, Arizona, USA. Data collected included signalment, clinical signs, physical examination findings, diagnostic test results, treatment and outcome.

RESULTS

Fifty-one feline cases were identified from six veterinary hospitals. Cats presented with clinical signs and laboratory abnormalities similar to what has been seen in dogs, including respiratory illness (n = 20/51), neutrophilia (n = 24/31), monocytosis (n = 17/31) and hyperglobulinemia (n = 16/30). However, cats at diagnosis were typically significantly ill, with 31/51 having disseminated infection, most commonly to the skin (n = 22). Additionally, 43/44 cats that had serum antibody tests performed were positive, and median titer at diagnosis was 1:32 (range 1:4 to ⩾1:256). Serum antibody titers were significantly reduced (P ⩽0.001) in cats that responded to treatment compared with cats that did not clinically improve. Forty of 46 cats that were treated with oral fluconazole responded and did not require additional therapy. Fourteen cats developed recurrent disease and all but one had antifungal therapy successfully reinstituted.

CONCLUSIONS AND RELEVANCE

Coccidioidomycosis is a disease of concern for cats residing in the regions endemic for Coccidioides species. Disease is most often disseminated at the time of diagnosis, possibly due to delays in presentation for care and recognition of the infection. Suspicion of disease, serum chemistries, blood cell counts, presence of antibody and imaging aid in the diagnosis of coccidioidomycosis in cats. Serum antibody reduction during treatment frequently correlated with an adequate response to medication. Consideration of coccidioidomycosis as a cause of illness will lead to earlier diagnosis and potentially better treatment outcomes in cats.

Pretreatment Histoplasma capsulatum urine enzymatic immunoassay concentrations do not correlate with outcome but may be influenced by renal function in cats with histoplasmosis

OBJECTIVES

The objective of this study was to determine if urine Histoplasma antigen (HAg) enzyme immunoassay (EIA) concentrations at the time of diagnosis and prior to the administration of antifungal agents are predictive of outcome for cats infected with Histoplasma capsulatum and to determine if compromised renal function affects urine HAg EIA measurements.

METHODS

Medical records at four institutions were searched to identify cats diagnosed with histoplasmosis between April 2012 and December 2015. Pretreatment urine Histoplasma EIA values were recorded, along with patient signalment, serum creatinine concentration, urine specific gravity, site(s) of infection and survival data.

RESULTS

Pretreatment urine HAg EIA measurements were available for 50 cats, and ranged from 0-19.1 ng/ml (median 6.3 ng/ml). Thirty-five cats were alive at day 180, 12 had died or were euthanized (median survival time 24 days; range 2-124 days) and three were lost to follow-up. The median urine HAg EIA at the time of diagnosis for cats alive at 6 months was 5 ng/ml (range 0-19.1); this was similar to findings for the non-survivors (median 7.29 ng/ml; range 0.78-19.1; P = 0.54). Surviving cats were significantly younger (mean age 6.9 years) than non-survivors (mean age 9.9 years; P = 0.03) but median body weights (3.8 kg vs 3.6 kg) and rates of pulmonary involvement (22/35 vs 9/12) were similar for the two groups. Median urine HAg EIA concentration was lower in cats with evidence of renal compromise than cats with acceptable renal function (0.54 ng/ml vs 7.2 ng/ml; P <0.013).

CONCLUSIONS AND RELEVANCE

Urine HAg EIA concentrations at the time of diagnosis are not predictive of outcome in cats with histoplasmosis and should not be used as a prognostic indicator in this species. Renal function may influence urine HAg EIA concentrations in cats; further investigation is needed to see if concurrent kidney disease impacts test sensitivity.