Latif Abdalla A, Troskie P Christo, Peba Seeland B, Maboko Boitumelo B, Pienaar Ronel, Mans Ben J
School of Life Sciences, University of KwaZulu-Natal, Durban, Westville, South Africa.
Epidemiology, Parasites and Vectors, Agricultural Research Council-Onderstepoort Veterinary Research, Onderstepoort 0110, South Africa.
Vet Parasitol Reg Stud Reports. 2019 Dec;18:100331. doi: 10.1016/j.vprsr.2019.100331. Epub 2019 Aug 21.
East Coast fever (Theileria parva infection in cattle) was eradicated from South Africa in the mid-1900. However, another form named Corridor disease (CD), associated with T. parva carrier buffaloes exists and outbreaks have increased in endemic areas. The occurrence of a CD carrier state in cattle under field situations has not been demonstrated but remains a subject of controversy. The current study investigated the T. parva carrier state following a severe outbreak in cattle introduced onto a game ranch. Monitoring of the outbreak included clinical signs, mortality, microscopy, serology, real-time PCR and xenodiagnoses. The herd of cattle received block treatment using oxytetracyclines (OTC) by the farmer during the outbreak. Cattle were sampled early during the outbreak and twice within the following 75 days. All buffaloes were tested for a T. parva carrier state. Two batches of questing adult R. appendiculatus were collected at the time of disease occurrence and a year later. These ticks were fed on susceptible cattle under controlled conditions and monitored for disease transmission. Ticks infected with a buffalo-derived stock of T. parva were fed on one bovine under controlled conditions and simultaneously injected with OTC, simulating the infection and treatment method of vaccination and was used as a positive control. Clean R. appendiculatus nymphs were fed on four recovered PCR positive cattle from the outbreak and on the positive control animal. The adult ticks were tested for infectivity by xenodiagnoses on susceptible bovines. For the initial outbreak the CD prevalence was 62.3% with a mortality rate of 29.5%. However, the outbreak was contained by block OTC treatment of the herd since only 3.4% cattle subsequently died until the end of the investigations. Adult ticks fed on one field bovine and the laboratory established T. parva carrier both transmitted fatal infections to susceptible cattle. Ticks fed on two field cattle transmitted T. taurotragi and one failed to transmit any infection. Questing adult R. appendiculatus collected during the outbreak transmitted fatal CD to two bovines while ticks collected a year later transmitted T. taurotragi. These findings demonstrated the effectiveness of disease control either by cattle treatment using OTC simulating the ITM or by intensive cattle dipping following the outbreak or by both interventions. The potential risk of creating carrier cattle by OTC treatment during CD outbreaks should be considered, supporting the continued control measures of segregation of cattle and buffalo herds.
东海岸热（牛泰勒虫感染）于20世纪中叶在南非被根除。然而，另一种名为走廊病（CD）的疾病与携带泰勒虫的水牛有关，且在流行地区疫情有所增加。牛在野外情况下携带CD病原体的情况尚未得到证实，但仍是一个有争议的话题。本研究调查了引入野生动物牧场的牛群发生严重疫情后泰勒虫的携带状态。对疫情的监测包括临床症状、死亡率、显微镜检查、血清学、实时PCR和接种诊断。在疫情期间，农场主使用土霉素（OTC）对牛群进行了分组治疗。在疫情早期以及随后的75天内对牛进行了两次采样。对所有水牛进行了泰勒虫携带状态检测。在发病时和一年后收集了两批成年肩突硬蜱。将这些蜱在受控条件下喂食易感牛，并监测疾病传播情况。用源自水牛的泰勒虫毒株感染的蜱在受控条件下喂食一头牛，并同时注射OTC，模拟疫苗接种的感染和治疗方法，用作阳性对照。将清洁的肩突硬蜱若虫喂食疫情中4头PCR检测呈阳性且已康复的牛以及阳性对照动物。通过对易感牛进行接种诊断来检测成年蜱的感染性。对于最初的疫情，CD患病率为62.并在随后的75天内对牛进行了两次采样。对所有水牛进行了泰勒虫携带状态检测。在发病时和一年后收集了两批成年肩突硬蜱。将这些蜱在受控条件下喂食易感牛，并监测疾病传播情况。用源自水牛的泰勒虫毒株感染的蜱在受控条件下喂食一头牛，并同时注射OTC，模拟疫苗接种的感染和治疗方法，用作阳性对照。将清洁的肩突硬蜱若虫喂食疫情中4头PCR检测呈阳性且已康复的牛以及阳性对照动物。通过对易感牛进行接种诊断来检测成年蜱的感染性。对于最初的疫情，CD患病率为62.3%，死亡率为29.5%。然而，通过对牛群进行分组OTC治疗，疫情得到了控制，因为直到调查结束，只有3.4%的牛随后死亡。以一头野外牛和实验室确定的泰勒虫携带者为食的成年蜱都将致命感染传播给了易感牛。以两头野外牛为食的蜱传播了水牛头巴贝斯虫，一头未能传播任何感染。在疫情期间收集的成年肩突硬蜱将致命的CD传播给了两头牛，而一年后收集的蜱传播了水牛头巴贝斯虫。这些发现证明了通过使用OTC模拟隔离治疗法治疗牛、或在疫情爆发后进行密集浸浴、或两种干预措施结合来控制疾病的有效性。应考虑在CD疫情期间通过OTC治疗产生携带病原体牛的潜在风险，这支持了继续采取牛群和水牛群隔离的控制措施。 3%，死亡率为29.5%。然而，通过对牛群进行分组OTC治疗，疫情得到了控制，因为直到调查结束，只有3.4%的牛随后死亡。以一头野外牛和实验室确定的泰勒虫携带者为食的成年蜱都将致命感染传播给了易感牛。以两头野外牛为食的蜱传播了水牛头巴贝斯虫，一头未能传播任何感染。在疫情期间收集的成年肩突硬蜱将致命的CD传播给了两头牛，而一年后收集的蜱传播了水牛头巴贝斯虫。这些发现证明了通过使用OTC模拟隔离治疗法治疗牛、或在疫情爆发后进行密集浸浴、或两种干预措施结合来控制疾病的有效性。应考虑在CD疫情期间通过OTC治疗产生携带病原体牛的潜在风险，这支持了继续采取牛群和水牛群隔离的控制措施。
