Department of Pathobiology and Population Sciences, Royal Veterinary College, University of London, Hertfordshire, United Kingdom.
Department of Veterinary Public Health and Preventive Medicine, Faculty of Veterinary Medicine, Ahmadu Bello University, Zaria, Kaduna State, Nigeria.
PLoS Negl Trop Dis. 2021 Jun 2;15(6):e0009458. doi: 10.1371/journal.pntd.0009458. eCollection 2021 Jun.
Toxoplasma gondii parasites present strong but geographically varied signatures of population structure. Populations sampled from Europe and North America have commonly been defined by over-representation of a small number of clonal types, in contrast to greater diversity in South America. The occurrence and extent of genetic diversity in African T. gondii populations remains understudied, undermining assessments of risk and transmission. The present study was designed to establish the occurrence, genotype and phylogeny of T. gondii in meat samples collected from livestock produced for human consumption (free-range chickens, n = 173; pigs, n = 211), comparing with T. gondii detected in blood samples collected from seropositive pregnant women (n = 91) in Benue state, Nigeria. The presence of T. gondii DNA was determined using a published nested polymerase chain reaction, targeting the 529 bp multicopy gene element. Samples with the highest parasite load (assessed using quantitative PCR) were selected for PCR-restriction fragment length polymorphism (PCR-RFLP) targeting the surface antigen 3 (SAG3), SAG2 (5' and 3'), beta-tubulin (BTUB) and dense granule protein 6 (GRA6) loci, and the apicoplast genome (Apico). Toxoplasma gondii DNA was detected in all three of the populations sampled, presenting 30.6, 31.3 and 25.3% occurrence in free-range chickens, pigs and seropositive pregnant women, respectively. Quantitative-PCR indicated low parasite occurrence in most positive samples, limiting some further molecular analyses. PCR-RFLP results suggested that T. gondii circulating in the sampled populations presented with a type II genetic background, although all included a hybrid type I/II or II/III haplotype. Concatenation of aligned RFLP amplicon sequences revealed limited diversity with nine haplotypes and little indication of host species-specific or spatially distributed sub-populations. Samples collected from humans shared haplotypes with free-range chickens and/or pigs. Africa remains under-explored for T. gondii genetic diversity and this study provides the first detailed definition of haplotypes circulating in human and animal populations in Nigeria.
刚地弓形虫寄生虫表现出强烈但具有地理差异的种群结构特征。从欧洲和北美的样本中，通常存在少数克隆类型的过度代表性，而在南美洲则存在更大的多样性。非洲刚地弓形虫种群的遗传多样性的发生和程度仍然研究不足，这影响了对风险和传播的评估。本研究旨在确定在尼日利亚贝努埃州从血清阳性孕妇（n = 91）采集的血液样本中检测到的刚地弓形虫的存在、基因型和系统发育，与从用于人类消费的牲畜（自由放养的鸡，n = 173；猪，n = 211）的肉样本中检测到的刚地弓形虫进行比较。使用针对 529 bp 多拷贝基因元件的已发表的巢式聚合酶链反应确定刚地弓形虫 DNA 的存在。使用定量 PCR 评估寄生虫载量最高的样品选择针对表面抗原 3 (SAG3)、SAG2（5' 和 3'）、β-微管蛋白 (BTUB) 和致密颗粒蛋白 6 (GRA6) 基因座和质体基因组 (Apico) 的聚合酶链反应-限制性片段长度多态性 (PCR-RFLP)。在所有三个抽样人群中均检测到刚地弓形虫 DNA，在自由放养的鸡、猪和血清阳性孕妇中的检出率分别为 30.6%、31.3%和 25.3%。定量 PCR 表明大多数阳性样本中的寄生虫发生较低，限制了一些进一步的分子分析。PCR-RFLP 结果表明，在采样人群中循环的刚地弓形虫呈现 II 型遗传背景，尽管都包含一种混合 I/II 或 II/III 单倍型。对齐的 RFLP 扩增子序列的串联显示出有限的多样性，有 9 个单倍型，几乎没有宿主种特异性或空间分布的亚种群的迹象。从人类收集的样本与自由放养的鸡和/或猪共享单倍型。非洲在刚地弓形虫遗传多样性方面仍未得到充分探索，本研究首次详细定义了在尼日利亚人类和动物群体中循环的单倍型。
