Heartworm Disease Antigen
Heartworm Disease Antigen Diagnostic Tests in Animals
Dogs:
Antigen Tests: These tests are specific and sensitive, detecting heartworm antigen from adult worms. They are nearly 100% specific but can produce false-negative results with low female worm burdens, immature infections, or occasionally due to antigen-antibody complexes.
Microfilaria Testing: Recommended alongside antigen testing to improve diagnostic accuracy, as dogs can be antigen-negative but microfilaria-positive.
Heat Treatment: Improves the sensitivity of ELISA tests in suspected false-negative cases by dissociating immune complexes.
False-Positives: Rare, but possible in low heartworm incidence areas.
Cats:
Challenges: Diagnosis in cats is complex due to often absent clinical signs, low infection incidence, and the prevalence of male-only or immature infections.
Antigen Testing: Less useful in cats due to low worm burdens, male-only infections, and immature infections. False-negative results are common, with sensitivity varying based on worm burden and gender. Heat treatment can increase sensitivity.
Antibody Testing: More effective than antigen testing in cats, detecting exposure to heartworms and aiding in the diagnosis of heartworm-associated respiratory disease (HARD). However, it's less specific for mature infections.
Diagnostic Imaging: Thoracic radiography and echocardiography can assist in diagnosis but are not specific to heartworm disease.
Wolbachia Antigens and PCR: Emerging diagnostic tools showing promise in detecting feline heartworm infections.
Ferrets:
Diagnostic Approach: Similar methods as used in dogs and cats are likely applied, adjusted for ferrets' physiological differences. This may include both antigen testing and diagnostic imaging such as echocardiography.
General Considerations:
Role of Clinical Signs and History: A high index of suspicion is necessary, especially in areas with high heartworm prevalence or in animals with unclear prevention histories.
Combining Tests: Using multiple diagnostic methods increases the likelihood of accurate detection, especially in challenging cases.
Time Factor: The timing of testing is crucial, as it can take months for an animal to test positive following infection.
Continuous Improvements: Diagnostic techniques and test sensitivities are evolving, necessitating ongoing awareness of the latest developments in heartworm diagnostics.
REFERENCES:
Côté, E. Côté’s Clinical Veterinary Advisor Dogs and Cats. 4th Ed. Elsevier. 2020.
Ettinger, SJ. Textbook of Veterinary Internal Medicine. 8th ed. Elsevier. 2017.
American Heartworm Society. "Heartworm Diagnostics: Antigen Tests Alone Aren’t Enough." Available at: .
American Heartworm Society. "The Truth About Testing in Cats."
Courtney, Charles H., and Qi-Yun Zeng. "Comparison of heartworm antigen test kit performance in dogs having low heartworm burdens."
Canine heartworm and heat treatment: An evaluation using a well-based enzyme-linked immunosorbent assay (ELISA) and canine sera with confirmed heartworm infection status."
