Maddie's Shelter Medicine Program, College of Veterinary Medicine, University of Florida, 2015 SW 16th Avenue, Gainesville, FL, 32610, USA.
Zoetis Petcare, 10 Sylvan Way, Parsippany, NJ, 07054, USA.
Parasit Vectors. 2021 Apr 26;14(1):224. doi: 10.1186/s13071-021-04715-4.
Various heartworm (HW) diagnostic testing modalities detect products of, or reactions to, different life cycle stages of Dirofilaria immitis. Microfilariae (Mf) can be directly visualized in blood, antigen (Ag) from immature and adult heartworms may be detected on commercial assays, and antibody (Ab) tests detect the host immune response to larval stages. Ag and Mf tests are commonly used in dogs, which frequently carry adult HW infections, but Ab tests have only been validated for use in cats. In some HW-infected dogs, Ag is blocked by immune complexing leading to false-negative results. Heat-treatment (HT) to disrupt these complexes can increase the sensitivity of HW Ag tests. The aim of this study was to compare different methods for diagnosing HW infection in dogs at high risk using individual and paired diagnostic tests, including an exploration of using Ab tests designed for cats to test canine samples.
One hundred stray adult (≥ 2-year-old) dogs in Florida shelters were tested using Mf, HW Ag, and HW Ab tests (feline HW Ab tests currently not commercially validated/approved for use in dogs); two versions of each test platform were used.
Fourteen dogs tested positive using point-of-care (POC) Ag tests; an additional 2 dogs tested positive with microtiter well assay, and an additional 12 dogs tested positive using HT Ag testing. For individual tests, Ag test sensitivity/specificity compared to HT Ag was 50-57%/100%, and Ab tests were 46-64%/82-94%. Sensitivity estimates for individual tests were higher when comparing to non-HT Ag. Pairing POC Ag tests with Mf tests improved sensitivity without loss of specificity, while pairing POC Ag and Ab tests modestly increased sensitivity at the expense of specificity.
Screening dogs for HW infection using both POC Ag and Mf detection, which is recommended by the American Heartworm Society, improved diagnostic performance in this study compared to single Ag test use, but may have missed more than one in four infected dogs. The need to improve access to highly accurate, rapid, and inexpensive large-scale HW testing for dogs in animal shelters remains largely unmet by current testing availability. The development of practical and validated protocols that incorporate heat or chemical treatment to disrupt Ag-Ab complexes in POC testing or decreasing the cost and time required for such testing in reference laboratories might provide solutions to this unmet need. Similar studies performed in countries where the prevalence of parasites such as D. repens or A. vasorum is different to the USA could potentially yield very different positive predictive values for both HT and non-HT Ag tests.
各种心丝虫（HW）诊断检测方法可检测犬心丝虫不同生命周期阶段的产物或反应。微丝蚴（Mf）可直接在血液中观察到，未成熟和成年心丝虫的抗原（Ag）可在商业检测中检测到，抗体（Ab）检测则可检测宿主对幼虫阶段的免疫反应。Ag 和 Mf 检测常用于常携带成年 HW 感染的犬，但 Ab 检测仅在猫中得到验证。在一些感染心丝虫的犬中，Ag 被免疫复合物阻断，导致假阴性结果。热处理（HT）可破坏这些复合物，从而提高 HW Ag 检测的敏感性。本研究的目的是使用个体和配对诊断检测比较高风险 HW 感染犬的不同方法，包括探索使用专为猫设计的 Ab 检测来检测犬样本。
佛罗里达州收容所的 100 只流浪成年（≥2 岁）犬使用 Mf、HW Ag 和 HW Ab 检测（目前尚未商业化验证/批准用于犬的猫心丝虫 Ab 检测）进行检测；每种检测平台使用两种版本。
14 只犬使用即时检测（POC）Ag 检测呈阳性；另外 2 只犬微量滴定板检测呈阳性，另外 12 只犬使用 HT Ag 检测呈阳性。与 HT Ag 相比，单独检测的 Ag 检测敏感性/特异性为 50-57%/100%，Ab 检测为 46-64%/82-94%。与非 HT Ag 相比，个体检测的敏感性估计值更高。将 POC Ag 检测与 Mf 检测配对可提高敏感性而不降低特异性，而将 POC Ag 和 Ab 检测配对则可适度提高敏感性，代价是特异性降低。
本研究使用美国心脏worm 学会推荐的 POC Ag 和 Mf 检测筛查 HW 感染犬，与单独使用 Ag 检测相比，提高了诊断性能，但可能漏诊了超过四分之一的感染犬。目前的检测方法无法满足动物收容所中犬类对高度准确、快速且廉价的大规模 HW 检测的需求。开发实用且经过验证的方案，包括对 POC 检测中的 Ag-Ab 复合物进行热处理或化学处理，或降低参考实验室进行此类检测的成本和时间，可能是解决这一未满足需求的方法。在寄生虫流行率与美国不同的国家（如 D. repens 或 A. vasorum）进行类似的研究，可能会对 HT 和非 HT Ag 检测的阳性预测值产生非常不同的影响。
