MVISTA® Blastomyces Canine Antibody lgG EIA
An 8 year old Pomeranian with a solitary bone lesion had a low positive Blastomyces urine antigen result (0.27 ng/mL). This result is near the cutoff for the assay and the submitting DVM considered the possibility of a false positive result. The patient displayed no other clinical signs of blastomycosis and spent the majority
of her time indoors. A bone biopsy yielded a non-diagnostic result. The MVista® Blastomyces Canine Antibody lgG EIA result was moderately positive (25 units), indicating recent exposure or active infection with Blastomyces. By combining the positive results in both antigen and antibody tests, the DVM made a presumptive diagnosis of blastomycosis and successfully treated the dog with itraconazole.
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
A 2015 study published in JAVMA (1) evaluated the rBAD-1 antibody EIA (precursor to the MVista® Blastomyces Canine IgG Antibody EIA). Antibody results are shown in Fig.1. Specificity was 88% in dogs with histoplasmosis, 95% in healthy dogs from a blastomycosis endemic region and 100% in control dogs with non-fungal pulmonary disease. Antibody EIA was significantly more sensitive compared to the A-antigen AGID antibody assay (95% vs 65%).
Fig. 1. Blastomyces IgG results in EIA units for dogs with blastomycosis, histoplasmosis, other nonfungal disease, or healthy controls. Numbers below the cutoff line indicate negative cases. Note: scale of reporting was different from the current commercial assay.
Although the sensitivity of the MVista® Blastomyces Antigen EIA in dogs is high (2), false-negative results are observed in ~10% of cases. In those cases, empirical treatment is often prescribed without establishing a diagnosis. Adjunctive tests may assist clinicians in diagnosing antigen negative cases. Defining a diagnosis is also problematic in patients with low-level positive (≤1 ng/mL) antigen results, as some of these results may be false positive. This may result in unnecessary, expensive and potentially toxic antifungal therapy. Tests to strengthen the diagnosis in such cases would be useful. Antibody testing for blastomycosis previously had limited utility due to low sensitivity of immunodiffusion methods.
MVista® Blastomyces Antibody lgG EIA
TEST CODE: 330
CPT CODE: N/A
CLINICAL SIGNIFICANCE: IgG antibodies to Blastomyces antigen appear to be associated with active infection, especially in dogs with moderate to high positive (20 EU or greater) results. Antibodies may also be detected in a small percentage of healthy dogs as a result of sub-clinical infection within the last 2 years; however, results of preliminary studies show high specificity of the assay (>90%) in healthy animals from Blastomyces-endemic areas. IgG may be detected in blastomycosis cases with falsely-negative antigen results (especially with localized disease; e.g., ocular or bone infections) and combined antibody and antigen testing increases the overall sensitivity. Intermediate results (8-9.9 EU) typically reflect either rising or falling IgG, and retesting the patient in several weeks may be beneficial.
Serum: Collect serum specimens in serum separator or red top tube. Allow blood to clot for 30 minutes, then centrifuge. Pipette serum into a plastic screw cap vial.
CSF: Sterile transport tube
MINIMUM SPECIMEN REQUIREMENTS
SPECIMEN REJECTION: Any specimen type >14 days old other than serum or CSF
TRANSPORT TEMPERATURE: Refrigerated/Frozen
SHIPPING: Ship on dry ice or frozen packs for next day service. Monday – Friday delivery.
Serum or CSF: Testing is performed on Mondays and Thursdays. Results released the same day.
REFERENCE RANGE: Antibody Not Detected
METHODOLOGY: Enzyme Immunoassay
(1) Mourning AC, Patterson EE, Kirsch EJ, Renschler JS, Wolf LA, Paris JK, Durkin MM and Wheat LJ. 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. J Am Vet Med Assoc 2015 Nov:247(10):1133-38.
(2) Spector D, Legendre AM, Wheat J, et al. Antigen and antibody testing for the diagnosis of blastomycosis in dogs. J Vet Intern Med 2008 Jul;22(4):839-43.