Drake Jason, Gruntmeir Jeff, Merritt Hannah, Allen Lynn, Little Susan E
Novartis Animal Health, Greensboro, NC, USA.
Department of Veterinary Pathobiology, Center for Veterinary Health Sciences, Oklahoma State University, Room 250 74078 McElroy Hall, Stillwater, OK, USA.
Parasit Vectors. 2015 Feb 4;8:68. doi: 10.1186/s13071-015-0698-4.
Dogs with chronic inflammation, including those with heartworm being managed with macrocyclic lactones and doxycycline (slow kill, SK), may develop immune complexes that block detection of Dirofilaria immitis antigen on commercial tests.
To determine if SK could result in development of false-negative antigen tests, we collected serum samples from dogs that had been diagnosed with heartworm by antigen detection, with or without confirmation by detection of D. immitis microfilariae, placed on monthly macrocyclic lactones and doxycycline, and that later tested negative on an antigen test, and then tested them for antigen of D. immitis before and after treatment to disrupt immune complexes.
Serum samples from a total of 15 dogs managed with SK were negative for antigen prior to heating on commercial assay (DiroCHEK, Zoetis) by colorimetric detection and spectrophotometry, but after heat treatment, 8/15 (53.3%) samples converted to positive. Review of the medical records of each dog indicated that, after the heartworm diagnosis, only 7/15 (46.7%) dogs appeared to receive preventive monthly as prescribed, including 3 dogs that had detectable antigen after heating the sample and 4 dogs that did not have detectable antigen after heating. Whole blood was available from 9 dogs; microfilariae of D. immitis were detected in 1 sample.
These data suggest that immune complex formation in dogs infected with heartworm and managed with SK can induce false negative antigen test results, misleading veterinarians and owners about the efficacy of this approach. Moreover, compliance with preventive administration appears poor, even after a heartworm diagnosis. The presence of persistent microfilaremia in at least one dog has implications for resistance selection.
患有慢性炎症的犬只，包括那些正在使用大环内酯类药物和强力霉素进行治疗（慢杀法，SK）的心丝虫病犬只，可能会形成免疫复合物，从而在商业检测中阻断犬恶丝虫抗原的检测。
为了确定慢杀法是否会导致抗原检测出现假阴性结果，我们收集了通过抗原检测确诊为心丝虫病的犬只的血清样本，这些犬只无论是否通过检测犬恶丝虫微丝蚴得到确认，均每月接受大环内酯类药物和强力霉素治疗，且后来抗原检测呈阴性，然后在治疗前后对它们进行犬恶丝虫抗原检测，以破坏免疫复合物。
共有15只采用慢杀法治疗的犬只的血清样本，在使用商业检测方法（DiroCHEK，硕腾公司）进行比色检测和分光光度法检测时，加热前抗原检测呈阴性，但热处理后，8/15（53.3%）的样本转为阳性。对每只犬的病历审查表明，在心丝虫病诊断后，只有7/15（46.7%）的犬只似乎按规定每月接受预防治疗，其中包括3只样本加热后仍可检测到抗原的犬只和4只样本加热后未检测到抗原的犬只。9只犬可获得全血样本；其中1份样本检测到犬恶丝虫微丝蚴。
这些数据表明，感染心丝虫并采用慢杀法治疗的犬只中，免疫复合物的形成可导致抗原检测出现假阴性结果，从而在该治疗方法的疗效方面误导兽医和犬主。此外，即使在心丝虫病诊断后，预防用药的依从性似乎也很差。至少有一只犬持续存在微丝蚴血症，这对耐药性选择具有影响。
