Prime detection of Dirofilaria immitis: understanding the influence of blocked antigen on heartworm test performance
Open accessAbstract
Detection of circulating antigen of Dirofilaria immitis has been a mainstay of identifying heartworm infection in clinical practice for the past three decades. Several validated commercial antigen tests have very good sensitivity, specificity, and positive predictive values, especially when used in patients for which heartworm infection is likely. In some dogs and cats infected with heartworm, antigen may not be available for detection although present in the patient sample; heat pretreatment of these samples reveals the antigen, changing the false negative to positive. This phenomenon was documented in the literature in the 1980s but subsequently overlooked by the heartworm research community for many years. In this review, we provide a summary of the current understanding of the role of heat reversal in diagnosing heartworm infection. This additional diagnostic step is most important for patients in which heartworm infection is likely, such as dogs or cats in an endemic area with an inconsistent history of heartworm preventive use, or dogs with a prior diagnosis of heartworm infection that were recently treated. To illustrate the concept, we share a summary of results from canine samples tested at the state veterinary diagnostic laboratory in Oklahoma, USA in 2017 by modified Knott test and by commercial antigen test before and after heat treatment of samples; in this sample set, heat treatment changed all D. immitis microfilaria-positive but antigen-negative samples to antigen-positive. Pet dogs with a history of consistent preventive use are unlikely to become positive with heat pretreatment; for that reason, routine pretreatment of all samples tested in a veterinary practice is not recommended. We also review known causes of false negative and false positive results on heartworm antigen tests that, although uncommon, can complicate accurate diagnosis in individual patients. Together, this review provides a primer to aid understanding of strategies that can enhance accurate diagnosis of heartworm infection in veterinary practice and clinical research.
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Treatment with macrocyclic lactones can lead to the formation of antigen-antibody complexes in some patients, masking the antigen and resulting in false-negative test results.
“As treatment with macrocyclic lactones can lead to the formation of antigen-antibody complexes in some patients, masking the antigen and resulting in false-negative test results, ELISA antigen-testing was repeated in negative samples, using heated serum [41,42].”
From The Incidence of Dirofilaria immitis in Shelter Dogs and Mosquitoes in Austria (2021) · cites this paper as [42]
Heat pretreatment of feline and canine serum or plasma samples improves the sensitivity of these commercial antigen assays in cats (and dogs) carrying only a few adult female worms by releasing antigens blocked within circulating immune complexes.
“heat pretreatment of feline and canine serum or plasma samples improves the sensitivity of these commercial antigen assays in cats (and dogs) carrying only a few adult female worms by releasing antigens blocked within circulating immune complexes.”
From Dirofilarioses in cats: European guidelines from the ABCD on prevention and management (2020) · cites this paper as [51]
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- Authors
- Little, S., Saleh, M., Wohltjen, M., & Nagamori, Y.
- Affiliations
- Oklahoma State University (US)
- Corresponding author
- Little, Susan
- Venue
- Parasites & Vectors
- Published
- 2018-03-20
- Volume
- 11
- Issue
- 1
- Pages
- 186-186
- ISSN
- 1756-3305 (ISSN-L)
- PMC
- PMC5859648
- OpenAlex
- W2804718140
- Cited by
- 93
- References
- 55
- Citations by year
- 2026: 8 · 2025: 6 · 2024: 12 · 2023: 18 · 2022: 11 · 2021: 13 · 2020: 19 · 2019: 5 · 2018: 1
- FWCI
- 1.39
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Licence
- Locations
- Parasites & Vectors (publishedVersion, cc-by)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion)
- Funders
- Oklahoma State University
- Bayer Animal Health
- Topics
- Health Sciences › Medicine › Infectious Diseases › Parasitic Diseases Research and Treatment
- Health Sciences › Veterinary › Small Animals › Helminth infection and control
- Health Sciences › Medicine › Public Health, Environmental and Occupational Health › Research on Leishmaniasis Studies
- Keywords
- Dirofilaria immitis, heartworm infection, thermal pretreatment, false-negative results, dogs, cats, sensitivity and specificity
- MeSH terms
- Animals, Antigens, Helminth, Cats, Dirofilaria immitis, Dirofilariasis, Dog Diseases, Dogs, Enzyme-Linked Immunosorbent Assay, False Negative Reactions, False Positive Reactions, Hot Temperature, Reagent Kits, Diagnostic, Sensitivity and Specificity
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