Awad Hoyam, Gadalla Amal A H, Postigo Milagros, Al-Hamidhi Salama, Tageldin Mohammed H, Skariah Sini, Sultan Ali A, Johnson Eugene H, Shiels Brian, Pain Arnab, Thompson Joanne, Babiker Hamza A
Department of Biochemistry, College of Medicine and Health Sciences, Sultan Qaboos University, AlKhoud 123, Muscat, Oman.
Division of Population Medicine, School of Medicine, College of Biomedical Sciences, Cardiff University, Cardiff, UK.
Sci Rep. 2020 Nov 13;10(1):19802. doi: 10.1038/s41598-020-76844-2.
Mixed species infections of Theileria spp. are common in nature. Experimental and epidemiological data suggest that mixed species infections elicit cross-immunity that can modulate pathogenicity and disease burden at the population level. The present study examined within-host interactions, over a period of 13 months during natural infections with two Theileria spp., pathogenic (T. lestoquardi) and non-pathogenic (T. ovis), amongst a cohort of naive sheep in Oman. In the first two months after exposure to infection, a high rate of mortality was seen among sheep infected with T. lestoquardi alone. However, subsequently mixed-infections of T. lestoquardi and T. ovis prevailed, and no further death occurred. The overall densities of both parasite species were significantly higher as single infection vs mixed infection and the higher relative density of pathogenic T. lestoquardi indicated a competitive advantage over T. ovis in mixed infection. The density of both species fluctuated significantly over time, with no difference in density between the very hot (May to August) and warm season (September to April). A high degree of genotype multiplicity was seen among T. lestoquardi infections, which increased with rising parasite density. Our results illustrate a potential competitive interaction between the two ovine Theileria spp., and a substantial reduction in the risk of mortality in mixed parasite infections, indicating that T. ovis confers heterologous protection against lethal T. lestoquardi infection.
泰勒虫属的混合物种感染在自然界中很常见。实验和流行病学数据表明，混合物种感染会引发交叉免疫，这种免疫可以在种群水平上调节致病性和疾病负担。本研究在阿曼一群未感染过的绵羊中，对两种泰勒虫属物种（致病性的小泰勒虫和非致病性的绵羊泰勒虫）自然感染期间的13个月内，研究了宿主体内的相互作用。在接触感染后的头两个月，仅感染小泰勒虫的绵羊中出现了高死亡率。然而，随后小泰勒虫和绵羊泰勒虫的混合感染占了上风，且没有再发生死亡。与混合感染相比，单一感染时两种寄生虫物种的总体密度均显著更高，致病性小泰勒虫相对较高的密度表明其在混合感染中比绵羊泰勒虫具有竞争优势。两种物种的密度随时间波动显著，在非常炎热的季节（5月至8月）和温暖季节（9月至次年4月）之间密度没有差异。在小泰勒虫感染中观察到高度的基因型多样性，其随着寄生虫密度的增加而增加。我们的结果说明了两种绵羊泰勒虫属物种之间潜在的竞争相互作用，以及混合寄生虫感染中死亡率风险的大幅降低，表明绵羊泰勒虫赋予了对致死性小泰勒虫感染的异源保护。
