Impact of heat treatment on antigen detection in sera of Angiostrongylus vasorum infected dogs

Detection and cross-reaction of Dirofilaria repens using a commercial heartworm antigen test kit

Antigen enzyme-linked immunosorbent assay tests are widely used for the diagnosis of heartworm infection in dogs. While commercially-available heartworm antigen tests have high sensitivity and specificity, false-negative test results can occur in dogs with low worm burdens, female-only infections, or prior to patency. The use of immune complex dissociation (ICD) methods have demonstrated increased sensitivity in the detection of Dirofilaria immitis antigens and the reversal of false-negative antigen results. However, there are concerns pertaining to false-positive antigen results due to infections of other nematode parasites, especially post-ICD. Therefore, this study evaluated the effect of heat-treatment on serum samples of dogs experimentally-infected with Dirofilaria repens during the course of infection, to assess for potential cross-reactivity on heartworm antigen tests. Archived serum samples from three dogs experimentally-infected with D. repens were utilized. All samples were tested for cross-reactivity pre- and post-heat-treatment using the DiroCHEK® Heartworm Antigen test kit throughout infection (day -9 through 404 days post-infection; dpi). All heat-treated samples tested false-positive starting at 164 dpi and continuing through 404 dpi, thereby testing positive prior to patency. No cross-reactivity was observed for any dog at any time point prior to heat-treatment. Our results suggest that the ICD method decreased the specificity of heartworm antigen tests and caused cross-reactivity of serum from dogs experimentally infected with D. repens. In conclusion, heat-treatment of serum in areas co-endemic for D. repens and D. immitis has limited clinical value, and should be used with caution.

Antibody immobilization technique using protein film for high stability and orientation control of the immobilized antibody

The development of antibody immobilization techniques is essential for creating antibody-based biomaterials. Although numerous methods for antibody immobilization have been demonstrated, low stability and disordered orientation of the immobilized antibody remain an important problem. In this work, an original antibody immobilization technique using a protein film, which achieved a high stability and orientation control of the immobilized antibody, has been described. In this method, an antibody-immobilized albumin film was prepared by adding the cross-linked albumin solution to the substrate, where antibodies were attached in uniform orientation, followed by subsequent drying, and detaching the formed film from the substrate by heating at 120 °C in a dry state. Antibodies in the film showed high antigen-binding capacity, at a level comparable to the oriented immobilized antibody using protein G. The stability of antibodies in the film was found to be significantly high; their antigen-binding capacity was completely retained even after storage at 40 °C in a dry state for one month. Thus, this approach provides useful information to immobilize the antibody on solid surfaces while controlling its orientation and increasing its stability.

Angiostrongylosis in dogs with negative fecal and in-clinic rapid serological tests: 7 Cases (2013-2017)

BACKGROUND

Angiostrongylosis is considered as emerging disease in dogs in Belgium. Detection of first-stage larvae in feces using the Baermann method has an imperfect sensitivity.

OBJECTIVES

Investigation of efficacy of noninvasive blood and fecal diagnostic tests in comparison with PCR on bronchoalveolar lavage (BAL) material in a small series of coughing or dyspnoeic dogs naturally infected with Angiostrongylus vasorum.

ANIMALS

Seven dogs with angiostrongylosis.

METHODS

Retrospective study. Dogs with cough, exercise intolerance and dyspnea of 2- to 8-week duration. Diagnostic methods used included Baermann analysis, AngioDetect rapid assay, ELISAs for detection of circulating antigen and specific antibodies and qPCR on BAL material.

RESULTS

Baermann analysis, AngioDetect rapid assay, antigen ELISA, antibody ELISA, and qPCR on BAL material were positive in 3/7, 2/7, 3/6, 6/6, and 7/7 dogs, respectively. ELISA for antibodies or qPCR on BAL material were essential for definitive diagnosis in 3 dogs. Relative sensitivities of AngioDetect rapid assay, Baermann analysis, and ELISA for antigen detection were lower than 50% compared with ELISA for antibodies or qPCR on BAL material.

CONCLUSION AND CLINICAL IMPORTANCE

In this small clinical series, Baermann analysis and AngioDetect rapid assay failed to confirm the diagnosis in some dogs. Therefore, ELISA for antibody detection and qPCR on BAL material should strongly be considered in clinically suspected dogs when antigen detection methods (AngioDetect or ELISA) and Baermann analysis are negative.