DiGangi Brian A, Dworkin Carly, Stull Jason W, O'Quin Jeanette, Elser Morgan, Marsh Antoinette E, Groshong Lesli, Wolfson Wendy, Duhon Brandy, Broaddus Katie, Gingrich Elise N, Swiniarski Emily, Berliner Elizabeth A
Department of Small Animal Clinical Sciences, University of Florida, College of Veterinary Medicine, PO Box 142275, Gainesville, FL, 32614, USA.
Present address: ASPCA, PO Box 142275, Gainesville, FL, 32614, USA.
Parasit Vectors. 2017 Nov 9;10(Suppl 2):483. doi: 10.1186/s13071-017-2443-7.
The diagnosis and management of canine heartworm disease is a growing concern for shelter veterinarians. Although the accuracy of commercial antigen test kits has been widely studied, recent reports have renewed interest in antigen blocking as a causative factor for false "no antigen detected" results. The objectives of this study were to determine the prevalence of false "no antigen detected" results in adult dogs entering shelters in northern, southern, and western regions of the country and to identify historical and clinical risk factors for such results.
Serum samples were evaluated for Dirofilaria immitis antigen using a commercially available point-of-care ELISA; samples in which no antigen was detected underwent a heat treatment protocol and repeat antigen testing. Whole blood samples underwent Knott testing to identify the presence of microfilariae. Historical and clinical findings were analyzed using exact logistic regression.
A total of 616 samples were analyzed. Overall prevalence of positive antigen test results (prior to heat treatment) was 7.3% and frequency of false "no antigen detected" results due to antigen blocking (ie, samples with no antigen detected prior to heat treatment and positive after heat treatment) was 5.2%. Among dogs that had no detectable antigen on the initial tests, dogs that had microfilariae detected via modified Knott testing (OR = 32.30, p-value = 0.013) and dogs that previously received a heartworm preventive (OR = 3.81, p-value = 0.016) had greater odds of antigen blocking than dogs without these factors. Among dogs that were heartworm positive, those without microfilariae detected had greater odds of antigen blocking than dogs with this factor (OR = 11.84, p-value = 0.0005). Geographic region of origin was significantly associated with occurrence of antigen blocking (p = 0.0036); however, blocking occurred in all regions sizably contributing to heartworm diagnoses. Of the 74 dogs found to be infected with heartworms in this study, 39.2% (29) had no detectable antigen prior to heat treatment.
Heat treatment of serum samples should be considered to improve diagnostic test accuracy, particularly in dogs that reportedly received a heartworm preventive prior to antigen testing regardless of region of origin.
犬心丝虫病的诊断和管理日益受到收容所兽医的关注。尽管商业抗原检测试剂盒的准确性已得到广泛研究，但最近的报告重新引发了人们对抗原阻断作为导致假“未检测到抗原”结果的一个因素的兴趣。本研究的目的是确定在该国北部、南部和西部地区进入收容所的成年犬中假“未检测到抗原”结果的发生率，并确定导致此类结果的历史和临床风险因素。
使用市售的即时检测酶联免疫吸附测定法（ELISA）评估血清样本中的犬恶丝虫抗原；对未检测到抗原的样本进行热处理方案并重复抗原检测。对全血样本进行Knott检测以确定是否存在微丝蚴。使用精确逻辑回归分析历史和临床发现。
共分析了616个样本。阳性抗原检测结果（热处理前）的总体发生率为7.3%，由于抗原阻断导致的假“未检测到抗原”结果（即热处理前未检测到抗原且热处理后呈阳性的样本）的发生率为5.2%。在初次检测未检测到可检测抗原的犬中，通过改良Knott检测检测到微丝蚴的犬（比值比[OR]=32.30，p值=0.013）和先前接受过心丝虫预防治疗的犬（OR=3.81，p值=0.016）比没有这些因素的犬发生抗原阻断的几率更高。在感染心丝虫的犬中，未检测到微丝蚴的犬比有此因素的犬发生抗原阻断的几率更高（OR=11.84，p值=0.0005）。来源地理区域与抗原阻断的发生显著相关（p=0.0036）；然而，所有地区都发生了抗原阻断，这在很大程度上影响了心丝虫的诊断。在本研究中发现感染心丝虫的74只犬中，39.2%（29只）在热处理前未检测到可检测抗原。
应考虑对血清样本进行热处理以提高诊断测试的准确性，特别是在据报道在抗原检测前接受过心丝虫预防治疗的犬中，无论其来源地区如何。
