Dhondt André A, Dhondt Keila V, Hochachka Wesley M
Bird Population Studies, Laboratory of Ornithology, Cornell University, Ithaca, New York, 14850, United States of America.
Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, New York, United States of America.
PLoS One. 2015 Apr 16;10(4):e0124820. doi: 10.1371/journal.pone.0124820. eCollection 2015.
Tests for the presence of pathogen DNA or antibodies are routinely used to survey for current or past infections. In diseases that emerge following a host jump estimates of infection rate might be under- or overestimated. We here examine whether observed rates of infection are biased for a non-focal host species in a model system. The bacterium Mycoplasma gallisepticum is a widespread pathogen in house finches (Haemorhous mexicanus), a fringillid finch, but an unknown proportion of individuals of other songbird species are also infected. Our goal is to determine the extent to which detection of M. gallisepticum DNA or antibodies against the bacteria in a non-fringillid bird species is over- or underestimated using black-capped chickadees Poecile atricapillus, a species in which antibodies against M. gallisepticum are frequently detected in free-living individuals. After keeping black-capped chickadees in captivity for 12 weeks, during which period the birds remained negative for M. gallisepticum, four were inoculated with M. gallisepticum and four were sham inoculated in both eyes to serve as negative controls. Simultaneously we inoculated six house finches with the same isolate of M. gallisepticum as a positive control. All inoculated birds of both species developed infections detectable by qPCR in the conjunctiva. For the 6 weeks following inoculation we detected antibodies in all M. gallisepticum-inoculated house finches but in only three of the four M. gallisepticum-inoculated black-capped chickadees. All house finches developed severe eye lesions but none of the black-capped chickadees did. Modeling the Rapid Plate Agglutination test results of black-capped chickadees shows that the rate of false-positive tests would be not more than 3.2%, while the estimated rate of false negatives is 55%. We conclude that the proportion of wild-caught individuals in which we detect M. gallisepticum-specific antibodies using Rapid Plate Agglutination is, if anything, substantially underestimated.
检测病原体DNA或抗体的存在情况通常用于调查当前或过去的感染。在宿主转移后出现的疾病中，感染率的估计可能被低估或高估。我们在此研究在一个模型系统中，观察到的非重点宿主物种的感染率是否存在偏差。鸡败血支原体是家朱雀（一种雀形目雀科鸟类）中广泛存在的病原体，但其他鸣禽物种中感染个体的比例未知。我们的目标是确定使用黑顶山雀（Poecile atricapillus）作为非雀科鸟类物种来检测鸡败血支原体DNA或针对该细菌的抗体时，检测结果被高估或低估的程度，在自由生活的个体中经常检测到针对鸡败血支原体的抗体。将黑顶山雀圈养12周，在此期间鸟类对鸡败血支原体检测呈阴性，然后对4只进行鸡败血支原体接种，4只进行假接种（双眼）作为阴性对照。同时，我们用相同的鸡败血支原体分离株接种6只家朱雀作为阳性对照。两种接种鸟类的结膜中均通过qPCR检测到可检测到的感染。接种后6周内，所有接种鸡败血支原体的家朱雀均检测到抗体，但接种鸡败血支原体的4只黑顶山雀中只有3只检测到抗体。所有家朱雀都出现了严重的眼部病变，但黑顶山雀均未出现。对黑顶山雀快速平板凝集试验结果进行建模表明，假阳性试验率不超过3.2%，而估计的假阴性率为55%。我们得出结论，使用快速平板凝集试验检测野生捕获个体中鸡败血支原体特异性抗体的比例，如果有偏差的话，实际上是被严重低估了。
