Tellis Anastasia N, Rowe Sam M, Coilparampil Ronald, Jenkins Cheryl, Dart Andrew, Zadoks Ruth N, Regnerus Corey D, Bosward Katrina L
School of Life and Environmental Sciences, Faculty of Science, The University of Sydney, Camperdown, New South Wales, Australia.
Sydney School of Veterinary Science, Faculty of Science, The University of Sydney, Camden, New South Wales, Australia.
Transbound Emerg Dis. 2022 Mar;69(2):793-804. doi: 10.1111/tbed.14051. Epub 2021 Mar 31.
Coxiella burnetii causes coxiellosis in animals and Q fever in humans, a potentially debilitating zoonotic disease commonly transmitted through domestic ruminants. To prevent transboundary spread of C. burnetii, animals may be tested prior to export. In alpacas, this process is complicated by the lack of scientific evidence for C. burnetii infection in the species, and the unique composition of camelid antibodies, which may cause false-positive results in assays developed for ruminants. We evaluated a complement fixation test (CFT; currently recommended for alpacas in New Zealand), an enzyme-linked immunosorbent assay (ELISA) and an immunofluorescence assay (IFA). Positive analytical control samples were generated through vaccination of alpacas with a human Q fever vaccine, whereas negative analytical control samples were sourced from New Zealand (deemed free of C. burnetii). Immunological assays were conducted on 131 alpaca sera submitted for export testing. Test characteristics (sensitivity, specificity, positive and negative predictive values) for CFT, ELISA and IFA were determined using Bayesian latent class analysis. Due to anticomplementary activity, 37 (28.2%) of the CFT results were inconclusive, making CFT unsuitable for routine use. Of the remaining 94 samples, 10.6%, 0% and 7.4% were positive for C. burnetii antibodies based on CFT, ELISA and IFA, respectively, yielding estimated sensitivities of 58%, 26% and 78%, and estimated specificities of 95%, 98% and 95%, with the estimates for sensitivity being imprecise, as evidenced by wide 95% credible intervals. Positive predictive values were similar across assays, albeit very low at the estimated seroprevalence of 5%. Our results indicate that, of the tests available, IFA appears to be the most appropriate for use in alpacas. Higher sensitivity of antibody detection, use of antigen detection assays and availability of samples from individuals with evidence of infection could provide additional insight into the risk of transboundary spread of C. burnetii by alpacas.
伯氏考克斯氏体可导致动物患考克斯氏体病以及人类患Q热，Q热是一种潜在的使人虚弱的人畜共患病，通常通过家养反刍动物传播。为防止伯氏考克斯氏体的跨境传播，动物在出口前可能会接受检测。在羊驼中，由于缺乏该物种感染伯氏考克斯氏体的科学证据，以及骆驼科动物抗体的独特组成，这可能会在为反刍动物开发的检测中导致假阳性结果，使得这一检测过程变得复杂。我们评估了补体结合试验（CFT；目前新西兰推荐用于羊驼）、酶联免疫吸附测定（ELISA）和免疫荧光测定（IFA）。通过用人Q热疫苗给羊驼接种来制备阳性分析对照样本，而阴性分析对照样本则来自新西兰（被认为没有伯氏考克斯氏体）。对提交用于出口检测的131份羊驼血清进行了免疫学检测。使用贝叶斯潜在类别分析确定了CFT、ELISA和IFA的检测特征（敏感性、特异性、阳性和阴性预测值）。由于存在抗补体活性，37份（28.2%）CFT结果无法得出结论，这使得CFT不适合常规使用。在其余94份样本中，基于CFT、ELISA和IFA检测，分别有10.6%、0%和7.4%的样本伯氏考克斯氏体抗体呈阳性，估计敏感性分别为58%、26%和78%，估计特异性分别为95%、98%和95%，敏感性估计值不精确，95%可信区间较宽就证明了这一点。尽管在估计血清阳性率为5%时阳性预测值非常低，但各检测方法的阳性预测值相似。我们的结果表明，在所使用的检测方法中，IFA似乎是最适合用于羊驼的。更高的抗体检测敏感性、使用抗原检测方法以及获取来自有感染证据个体的样本，可能会为羊驼传播伯氏考克斯氏体的跨境风险提供更多见解。
