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.

Cryptococcal meningitis is a cause for cross-reactivity in cerebrospinal fluid assays for anti-Histoplasma, anti-Coccidioides and anti-Blastomyces antibodies.

BACKGROUND/OBJECTIVES: Antibody detection is commonly used for diagnosis of histoplasmosis, and cross-reactions have been recognised due to endemic mycoses but not cryptococcosis. We observed cross-reactions in an anti-Histoplasma antibody enzyme immunoassay (EIA) in the cerebrospinal fluid (CSF) from a patient with cryptococcal meningitis and sought to assess the risk of cross-reactive anti-Histoplasma antibodies in persons with cryptococcal meningitis. METHODS: An anti-cryptococcal antibody EIA was developed to measure CSF antibody response in HIV-infected subjects from Kampala, Uganda and previously healthy, HIV-negative subjects at the National Institutes of Health (NIH) with cryptococcal meningitis. Specimens were tested for cross-reactivity in assays for IgG anti-Histoplasma, anti-Blastomyces and anti-Coccidioides antibodies. RESULTS: Among 61 subjects with cryptococcal meningitis (44 Kampala cohort, 17 NIH cohort), elevated CSF anti-cryptococcal antibody levels existed in 38% (23/61). Of the 23 CSF specimens containing elevated anti-cryptococcal antibodies, falsely positive results were detected in antibody EIAs for histoplasmosis (8/23, 35%), coccidioidomycosis (6/23, 26%) and blastomycosis (1/23, 4%). Overall, 2% (2/81) of control CSF specimens had elevated anti-cryptococcal antibody detected, both from Indiana. CONCLUSIONS: Cryptococcal meningitis may cause false-positive results in the CSF for antibodies against Histoplasma, Blastomyces and Coccidioides. Fungal antigen testing should be performed to aid in differentiating true- and false-positive antibody results in the CSF.

Improved Diagnosis of Acute Pulmonary Histoplasmosis by Combining Antigen and Antibody Detection.

BACKGROUND: Acute pulmonary histoplasmosis can be severe, especially following heavy inoculum exposure. Rapid diagnosis is critical and often possible by detection of antigen, but this test may be falsely negative in 17% of such cases. Antibody detection by enzyme immunoassay (EIA) may increase sensitivity and permit the measurement of immunoglobulin M (IgM) and immunoglobulin G (IgG) classes of antibodies separately. METHODS: Microplates coated with Histoplasma antigen were used for testing of serum from patients with acute pulmonary histoplasmosis and controls in the MVista Histoplasma antibody EIA. Results for IgG and IgM were reported independently. RESULTS: IgG antibodies were detected in 87.5%, IgM antibodies in 67.5%, and IgG and/or IgM antibodies in 88.8% of patients with acute pulmonary histoplasmosis in this assay, while immunodiffusion, complement fixation, and antigen testing showed sensitivities of 55.0%, 73.1%, and 67.5%, respectively (n = 80). Combining antigen and antibody detection increased the sensitivity to 96.3%. CONCLUSIONS: The MVista Histoplasma antibody EIA offers increased sensitivity over current antibody tests while also allowing separate detection of IgG and IgM antibodies and complementing antigen detection. Combining antigen and EIA antibody testing provides an optimal method for diagnosis of acute pulmonary histoplasmosis.

Development of a highly sensitive and specific blastomycosis antibody enzyme immunoassay using Blastomyces dermatitidis surface protein BAD-1.

Serologic tests for antibodies to Blastomyces dermatitidis are not thought to be useful for the diagnosis of blastomycosis, in part due to the low sensitivity of immunodiffusion and complement fixation. Earlier studies have shown that the enzyme immunoassay improves the sensitivity of antibody detection for the diagnosis of blastomycosis. Microplates coated with the B. dermatitidis surface protein BAD-1 were used for testing sera from patients with proven blastomycosis or histoplasmosis and controls. Semiquantification was accomplished by using standards containing human anti-B. dermatitidis antibodies. The antibodies were detected in 87.8% of the patients with blastomycosis by the enzyme immunoassay compared to 15.0% by immunodiffusion. The specificities were 99.2% for patients with nonfungal infections and healthy subjects and 94.0% for patients with histoplasmosis. The results were highly reproducible on repeat testing. When combined with antigen testing, antibody testing improved the sensitivity from 87.8% to 97.6%. Enzyme immunoassay detection of antibodies against BAD-1 is highly specific, has greatly improved sensitivity over immunodiffusion, and may identify cases with negative results by antigen testing. This assay has the potential to aid in the diagnosis of blastomycosis.

Investigation of the efficacy of micafungin in the treatment of histoplasmosis using two North American strains of Histoplasma capsulatum.

Micafungin alone and combined with liposomal amphotericin B was evaluated against two strains of Histoplasma capsulatum. Micafungin was active in vitro against the mold but not the yeast form but was ineffective in vivo. Micafungin appears to be ineffective in treatment of histoplasmosis.

Effect of calcineurin inhibitors on posaconazole blood levels as measured by the MVista microbiological assay.

Calcineurin inhibitors may augment the effects of antifungal drugs in microbiological assays. We examined this interaction in a microbiological assay for posaconazole. No effect was observed. However, concurrent or recently discontinued treatment with other antifungal drugs caused false-positive results, emphasizing a limitation of microbiological assays for antifungal drug level measurement.

Activity of newer triazoles against Histoplasma capsulatum from patients with AIDS who failed fluconazole.

OBJECTIVES: To determine the activity of newer triazoles against strains of Histoplasma capsulatum resistant to fluconazole. METHODS: Susceptibility testing was performed on 17 paired pre- and post-treatment H. capsulatum isolates from patients with AIDS who failed fluconazole. RESULTS: The median MICs of fluconazole, voriconazole, and posaconazole and ravuconazole for the pre-treatment isolates were 1 mg/L, 0.015 mg/L and <0.007 mg/L, respectively. A 4-fold or greater increase in the MIC of fluconazole and voriconazole was observed in 12 and 7 of the post-treatment isolates, respectively; the median fold increases in MIC were 8 and 2.1, respectively. No MIC increases were observed for posaconazole and ravuconazole. One pair of isolates exhibiting reduced susceptibility was examined in more detail. A single amino acid substitution (at tyrosine 136) was identified in the active site of the CYP51 protein from the post-treatment isolate, which is presumed to be responsible for reduced susceptibility to voriconazole and fluconazole, analogous to recent observations in Candida albicans. CONCLUSIONS: These findings support careful monitoring for relapse in patients receiving voriconazole treatment for histoplasmosis, particularly in those who were previously treated with fluconazole.

Antifungal therapy for central nervous system histoplasmosis, using a newly developed intracranial model of infection.

The outcome of central nervous system (CNS) histoplasmosis is often unfavorable. Although fluconazole plays an integral role in treatment of fungal meningitis, its role in the treatment of histoplasmosis is hampered by reduced activity and potential development of resistance. A murine model of CNS histoplasmosis was used to evaluate the hypothesis that a combination of amphotericin B and fluconazole therapy would be superior to amphotericin B monotherapy. Groups of B6C3F(1) mice were infected by injection of Histoplasma capsulatum into the subarachnoid space. The addition of fluconazole hindered the antifungal effect of amphotericin B, as determined by measurement of fungal burden, suggesting antagonism in the brain. Fluconazole was less effective as a single agent than was amphotericin B, despite the greater penetration of fluconazole into brain tissues. The hypothesis that amphotericin B-fluconazole combination therapy would be superior to amphotericin B monotherapy for treatment of CNS histoplasmosis was not supported by this study.