Genome Science laboratory, College of Veterinary Medicine and Biomedical Sciences, Sokoine University of Agriculture, Morogoro, Tanzania.
Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Berlin, Germany.
Transbound Emerg Dis. 2020 Mar;67 Suppl 1:79-87. doi: 10.1111/tbed.13405.
The infection and treatment (ITM) procedure remains the only available method of immunization against Theileria parva infection. One constraint to deployment is the perception that the carrier state induced by ITM could result in enhanced disease problems. More than one million cattle have been ITM vaccinated in pastoralist systems in Tanzania over the last 2 decades. We present the results of a longitudinal study of six groups of cattle in Maasai villages in northern Tanzania exposed to natural tick challenge for between 2 weeks and 14 years post-vaccination. The p104 nested PCR revealed a higher frequency of T. parva carriers among vaccinates (30%) compared with controls (8%) (OR = 4.89, p = .000), with the highest frequency of carriers found in calves vaccinated 6 months previously, although carrier state was also detected in cattle vaccinated >10 years prior to the study. Variable number tandem repeat genotype analysis revealed 6 MS7 alleles with sizes ranging from 150 bp to 500 bp, but only two alleles were detected in cattle vaccinated >4 years earlier, relative to five alleles detected in recently vaccinated cattle and controls. In terms of heterozygosity, diversity was maximal in calves vaccinated within the last 2 weeks (h = 0.776) but lowest in cattle vaccinated 4 years earlier (h = 0.375). The analysis suggested close genetic relatedness of parasites in vaccinated and unvaccinated groups and up to 96% of variation was within rather than between the groups. These results confirm that ITM leads to a long-term T. parva carrier state in cattle and the detection of vaccine component VNTR in co-grazing unvaccinated cattle suggests potential vaccine transmission by ticks. However, vaccination stocks did not totally replace local genotypes, at least in cattle populations. These findings should mitigate concerns that ITM modifies T. parva field populations in a way that enhances disease in the medium term.
感染和治疗（ITM）程序仍然是唯一可用的预防泰勒虫病感染的免疫方法。部署的一个限制因素是，人们认为 ITM 诱导的携带状态可能导致更严重的疾病问题。在过去的 20 年里，坦桑尼亚的牧民系统中已经有超过 100 万头牛接受了 ITM 疫苗接种。我们介绍了在坦桑尼亚北部马赛村庄进行的一项纵向研究的结果，该研究涉及六组在接种疫苗后暴露于自然蜱挑战的牛，暴露时间从 2 周到 14 年不等。p104 巢式 PCR 显示，与对照组（8%）相比，接种疫苗的牛中携带 T. 泰勒虫的频率更高（30%）（OR=4.89，p=0.000），在接种疫苗 6 个月前的小牛中发现的携带率最高，但在研究前 10 多年接种疫苗的牛中也检测到携带状态。可变数量串联重复基因型分析显示有 6 个 MS7 等位基因，大小从 150bp 到 500bp 不等，但在接种疫苗>4 年前的牛中只检测到两个等位基因，而在最近接种疫苗的牛和对照组中检测到 5 个等位基因。就杂合度而言，在最近 2 周内接种疫苗的小牛中最大（h=0.776），而在接种疫苗>4 年前的牛中最低（h=0.375）。分析表明，接种疫苗和未接种疫苗的牛群中的寄生虫密切相关，高达 96%的变异是在群体内而不是群体间发生的。这些结果证实，ITM 导致牛中长期的 T. 泰勒虫携带状态，并且在共同放牧的未接种疫苗的牛中检测到疫苗成分 VNTR 表明蜱可能传播疫苗。然而，疫苗库存并没有完全取代当地的基因型，至少在牛群中是这样。这些发现应该减轻人们的担忧，即 ITM 会以一种在中期增强疾病的方式改变泰勒虫的田间种群。
