Moredun Research Institute, Pentlands Science Park, Midlothian, EH26 0PZ, UK.
Department of Preventive Veterinary Medicine and Animal Health, School of Veterinary Medicine, University of São Paulo, São Paulo, SP, CEP 05508-000, Brazil.
Parasit Vectors. 2019 Mar 14;12(1):104. doi: 10.1186/s13071-019-3372-4.
Toxoplasma gondii is a zoonotic parasite of global importance. The outcome of infection in humans can depend on a number of factors including the infecting stage of the parasite, inoculating dose and virulence of the infecting strain. Molecular epidemiological studies have demonstrated an abundance of atypical strains of T. gondii in South America, many of which have been associated with more severe sequelae of infection. The aim of this study was to compare the virulence of T. gondii strains isolated in the Caribbean to a virulent Brazilian strain and an avirulent European strain.
One hundred and twenty Swiss CD-1 mice were split into 8 groups of 15 mice and each group was inoculated with 200 tachyzoites of one of 8 isolates, comprising ToxoDB genotypes #1, #141, #265, #13, #3 and #6. Five mice per group were euthanized at day 8 post-inoculation (p.i.) and parasite burden was determined in heart, lungs and eyes using quantitative PCR. Lungs and brain were also examined by histopathology and immunohistochemistry. The remaining 10 mice per group were part of a survival experiment to assess virulence. DNA was extracted from tachyzoites of each of the 8 T. gondii isolates and genotyped at four ROP gene loci, including ROP5, ROP16, ROP17 and ROP18 to look for association with markers of virulence.
Infection with ToxoDB genotype #13 from the Caribbean resulted in 100% of mice being euthanized which was comparative to infection with the virulent Brazilian strain (ToxoDB genotype #6). Significantly higher parasite burdens were recorded in the lungs and eyes of mice infected with ToxoDB genotypes #13 and #6. Genotyping of ROP loci revealed that the virulent Caribbean isolates had a different ROP18/ROP5 allelic profile (3/1) to the virulent Brazilian isolate (1/3); however, the avirulent Caribbean isolate (ToxoDB genotype #1) had the same ROP18/ROP5 profile as the avirulent European isolate (ToxoDB #3) (both 2/2). Caribbean isolates of intermediate virulence (ToxoDB #141 and #265) all had the same ROP18/ROP5 allelic profile (2/2).
Isolates from the Caribbean with ToxoDB genotype #13 were acutely virulent for mice and comparable to a known virulent Brazilian isolate. The ROP protein allelic profile of the virulent Caribbean and Brazilian isolates differed indicating that perhaps other factors are involved in predicting virulence. Understanding virulence is important for predicting disease outcome in humans and may also aid vaccine design as well as drug discovery.
刚地弓形虫是一种具有全球重要性的动物源性寄生虫。人类感染的结果可能取决于许多因素，包括寄生虫的感染阶段、接种剂量和感染菌株的毒力。分子流行病学研究表明，南美洲存在大量非典型刚地弓形虫菌株，其中许多与感染的更严重后果有关。本研究旨在比较加勒比地区分离的刚地弓形虫菌株与一种毒力较强的巴西株和一种弱毒的欧洲株的毒力。
将 120 只瑞士 CD-1 小鼠分为 8 组，每组 15 只小鼠，每组接种 200 个速殖子的 8 个分离株之一，包括 ToxoDB 基因型 #1、#141、#265、#13、#3 和#6。每组 5 只小鼠于接种后第 8 天（p.i.）处死，用定量 PCR 法测定心脏、肺和眼睛中的寄生虫负荷。用组织病理学和免疫组织化学法检查肺和脑。每组其余 10 只小鼠参与生存实验，以评估毒力。从 8 株刚地弓形虫分离株的速殖子中提取 DNA，在 4 个 ROP 基因座（ROP5、ROP16、ROP17 和 ROP18）进行基因分型，以寻找与毒力标志物的关联。
感染加勒比地区的 ToxoDB 基因型 #13 的小鼠 100%被安乐死，与感染毒力较强的巴西株（ToxoDB 基因型 #6）相当。感染 ToxoDB 基因型 #13 和#6 的小鼠肺部和眼睛中的寄生虫负荷明显更高。ROP 基因座的基因分型显示，毒力较强的加勒比分离株的 ROP18/ROP5 等位基因谱（3/1）与毒力较强的巴西分离株（1/3）不同；然而，弱毒的加勒比分离株（ToxoDB 基因型 #1）与弱毒的欧洲分离株（ToxoDB #3）具有相同的 ROP18/ROP5 谱（均为 2/2）。中等毒力的加勒比分离株（ToxoDB #141 和 #265）均具有相同的 ROP18/ROP5 等位基因谱（2/2）。
加勒比地区 ToxoDB 基因型 #13 的分离株对小鼠具有急性毒力，与已知的毒力较强的巴西分离株相当。毒力较强的加勒比和巴西分离株的 ROP 蛋白等位基因谱不同，表明可能有其他因素参与预测毒力。了解毒力对于预测人类疾病结局很重要，也可能有助于疫苗设计和药物发现。
