Transplacental transmission of Anaplasma marginale in beef cattle chronically infected in southern Brazil

In this study, we have investigated the incidence of transplacental transmission of Anaplasma marginale in chronically infected cows with no history of acute anaplasmosis during gestation. In addition, we evaluated various techniques for detection of transplacental transmission ofA. marginale. Blood samples were collected from 30 cows at three different periods: at the time of artificial insemination, at gestational diagnosis, and after calving. Also, blood was collected from the newborn calves, including one sample before colostrum intake, and another three days after birth. A. marginale-specific antibodies were detected in 100% of the cows with an indirect fluorescent antibody test (IFAT), and in 97% of them, using an indirect enzyme-linked immunosorbent assay (ELISA). Also, we observed that all of the three-day-old newborn calves were seropositive by IFAT. According to polymerase chain reaction, 63.3% of the cows were carriers of A. marginale, as well as 6.7% of the newborn calves. This represented a transplacental transmission rate of 10.5%. Furthermore, a correlation of 93.3% was observed between the two serodiagnostic techniques, demonstrating that both ELISA and IFAT can be used in epidemiological surveys of A. marginale. These results confirm the occurrence of transplacental transmission of A. marginale in chronically infected cows and suggest the importance of this transmission route in areas of enzootic instability.本研究针对妊娠期间无急性无形体病病史的慢性感染边缘无形体（Anaplasma marginale）母牛，探究了其边缘无形体经胎盘传播的发生情况。此外，本研究评估了多种用于检测边缘无形体经胎盘传播的技术。研究人员于三个不同时段从30头母牛采集血液样本：人工授精时、妊娠诊断时以及产犊后。同时，从新生犊牛采集血液样本，包括初乳摄入前的一份样本，以及出生后三日的另一份样本。通过间接荧光抗体试验（indirect fluorescent antibody test, IFAT）可在所有受试母牛样本中检出边缘无形体特异性抗体，而采用间接酶联免疫吸附试验（indirect enzyme-linked immunosorbent assay, ELISA）的检出率为97%。此外，研究观察到，所有三日龄新生犊牛的IFAT血清学检测均呈阳性。经聚合酶链式反应（polymerase chain reaction, PCR）检测，63.3%的母牛为边缘无形体携带者，新生犊牛的携带者比例为6.7%，据此推算经胎盘传播率为10.5%。进一步分析显示，两种血清学检测技术的符合率达93.3%，表明ELISA与IFAT均可应用于边缘无形体的流行病学调查。上述结果证实了慢性感染母牛存在边缘无形体经胎盘传播的情况，并提示该传播途径在地方流行性不稳定区域中的重要性。