Department of Veterinary Microbiology & Pathology, Washington State University, Pullman, WA, USA.
School of Biological Sciences, University of Nairobi, Nairobi, Kenya.
Transbound Emerg Dis. 2020 Mar;67 Suppl 1:56-67. doi: 10.1111/tbed.13325.
The infection and treatment (ITM) live vaccination method for control of Theileria parva infection in cattle is increasingly being adopted, particularly in Maasai pastoralist systems. Several studies indicate positive impacts on human livelihoods. Importantly, the first detailed protocol for live vaccine production at scale has recently been published. However, quality control and delivery issues constrain vaccination sustainability and deployment. There is evidence that the distribution of T. parva is spreading from endemic areas in East Africa, North into Southern Sudan and West into Cameroon, probably as a result of anthropogenic movement of cattle. It has also recently been demonstrated that in Kenya, T. parva derived from cape buffalo can 'breakthrough' the immunity induced by ITM. However, in Tanzania, breakthrough has not been reported in areas where cattle co-graze with buffalo. It has been confirmed that buffalo in northern Uganda national parks are not infected with T. parva and R. appendiculatus appears to be absent, raising issues regarding vector distribution. Recently, there have been multiple field population genetic studies using variable number tandem repeat (VNTR) sequences and sequencing of antigen genes encoding targets of CD8+ T-cell responses. The VNTR markers generally reveal high levels of diversity. The antigen gene sequences present within the trivalent Muguga cocktail are relatively conserved among cattle transmissible T. parva populations. By contrast, greater genetic diversity is present in antigen genes from T. parva of buffalo origin. There is also evidence from several studies for transmission of components of stocks present within the Muguga cocktail, into field ticks and cattle following induction of a carrier state by immunization. In the short term, this may increase live vaccine effectiveness, through a more homogeneous challenge, but the long-term consequences are unknown.
控制牛泰勒虫病感染的感染和治疗（ITM）活疫苗接种方法越来越多地被采用，尤其是在马赛牧民系统中。几项研究表明对人类生计有积极影响。重要的是，最近刚刚发表了第一个关于大规模生产活疫苗的详细方案。然而，质量控制和交付问题限制了疫苗的可持续性和部署。有证据表明，牛泰勒虫的分布正在从东非的流行地区向北扩散到南苏丹，向西扩散到喀麦隆，这可能是由于牛的人为迁移。最近还表明，在肯尼亚，来自海角水牛的 T. parva 可以“突破” ITM 诱导的免疫力。然而，在坦桑尼亚，与水牛共同放牧的地区没有报告突破。已经证实，乌干达北部国家公园的水牛没有感染 T. parva，而且似乎没有 R. appendiculatus，这引发了有关媒介分布的问题。最近，已经使用可变数串联重复（VNTR）序列和编码 CD8+ T 细胞反应靶标的抗原基因测序进行了多项现场种群遗传研究。VNTR 标记通常显示出高度的多样性。在 Muguga 鸡尾酒中存在的抗原基因序列在牛可传播的 T. parva 种群中相对保守。相比之下，来自水牛源 T. parva 的抗原基因存在更大的遗传多样性。还有几项研究的证据表明，在免疫诱导携带状态后，Muguga 鸡尾酒中存在的成分会通过接种传播到现场蜱和牛中。从短期来看，这可能会通过更均匀的挑战来提高活疫苗的有效性，但长期后果尚不清楚。
