International Livestock Research Institute, Nairobi, Kenya.
Vet Parasitol. 2010 Mar 25;168(3-4):223-30. doi: 10.1016/j.vetpar.2009.11.006. Epub 2009 Nov 13.
In areas with a low incidence of infection due to unimodal presence of ticks, Theileria parva has been observed to induce a disease with relatively low pathology. This is followed by a carrier state, rather than death and therefore provides a better chance of transmission of the parasite back to the tick vector since in unimodal conditions, the different tick stages occur at different times. One isolate from such an area in Zambia, T. parva Chitongo, was compared for virulence with T. parva Muguga, isolated from an area exhibiting a continuous presence of all vector stages in East Africa. To reduce any variation due to infection dose, an in vitro standardized dose was used to initiate infection of groups of three local zebu cattle with each isolate. Parameters of virulence measured were prepatent period, fever, survival (based on ECF index), parasitosis, piroplasm parasitaemia and hematological parameters. Our results suggest that T. parva Chitongo developed a slightly later onset (1-2 days) and lower levels of parasitosis in the lymph node, causing less and later mortality. Comparison of the in vitro rate of transformation confirmed that the time needed to transform an infected lymphocyte took 4 days longer for T. parva Chitongo than T. parva Muguga. Elucidating the mechanism responsible for the lower virulence of T. parva Chitongo could be useful for designing an attenuated vaccine.
在感染率较低的地区，由于 tick 的单一存在，观察到 Theileria parva 会引起相对较轻的病理学疾病。随后是携带状态，而不是死亡，因此寄生虫更有可能传播回 tick 媒介，因为在单一条件下，不同的 tick 阶段会在不同的时间发生。从赞比亚的一个这样的地区分离出的一株 T. parva Chitongo，与从东非连续存在所有媒介阶段的地区分离出的 T. parva Muguga 进行了毒力比较。为了减少由于感染剂量引起的任何差异，使用体外标准化剂量来启动每组 3 头当地瘤牛感染每种分离株。测量的毒力参数包括潜伏期、发热、存活（基于 ECF 指数）、寄生性、巴贝斯虫寄生虫血症和血液学参数。我们的结果表明，T. parva Chitongo 的发病时间略晚（1-2 天），淋巴结中的寄生性较低，导致死亡率较低且较晚。体外转化率的比较证实，T. parva Chitongo 感染淋巴细胞转化所需的时间比 T. parva Muguga 长 4 天。阐明 T. parva Chitongo 较低毒力的机制可能有助于设计减毒疫苗。
