Validation of immune complex dissociation methods for use with heartworm antigen tests

Area of Science:

• Veterinary diagnostics
• Parasitology
• Immunology

Background:

• Canine Dirofilaria immitis infections are diagnosed using antigen testing.
• Original heartworm antigen tests used immune complex dissociation (ICD) to release antibody-bound antigen.
• ICD methods were discontinued due to assay reagent improvements but may still be valuable.

Purpose of the Study:

• To evaluate various ICD methods for detecting heartworm antigen using microtiter plate ELISA.
• To assess the performance of ICD methods in diagnosing heartworm in pet dogs.

Main Methods:

• Compared pepsin ICD with heat (with/without EDTA) and acid treatments.
• Evaluated pepsin ICD using the PetChek® Heartworm Test on canine serum/plasma.
• Assessed samples from dogs with discrepant results and dogs undergoing pre-adulticide treatment.

Main Results:

• All four ICD methods successfully released complexed antigen.
• Pepsin and acid ICD required significantly less serum (50 μL) compared to heat treatment (≥600 μL).
• Pepsin ICD identified antigen in 10% of dogs with initially discrepant results; treatment reduced antigen levels, which were recovered by ICD.

Conclusions:

• ICD is a valuable tool for diagnosing canine heartworm in cases with discrepant results or intermittent preventive use.
• Heartworm therapies can reduce antigen production and promote immune complexing, leading to false-negative antigen tests.
• Confirming positive heartworm antigen test results before initiating therapy is essential.