Background Simian T-cell leukemia virus type 1 (STLV-1) is disseminated among various non-human primate species and is closely related to human T-cell leukemia virus type 1 (HTLV-1), the causative agent of adult T-cell leukemia and HTLV-1-associated myelopathy/tropical spastic paraparesis. Notably, the prevalence of STLV-1 infection in Japanese macaques (JMs) is estimated to be > 60%, much greater than that in other non-human primates; however, the mechanism and mode of STLV-1 transmission remain unknown. The aim of this study is to examine the epidemiological background by which STLV-1 infection is highly prevalent in JMs. Results The prevalence of STLV-1 in the JMs rearing in our free-range facility reached up to 64% (180/280 JMs) with variation from 55 to 77% among five independent troops. Anti-STLV-1 antibody titers (ABTs) and STLV-1 proviral loads (PVLs) were normally distributed with mean values of 4076 and 0.62%, respectively, which were mostly comparable to those of HTLV-1-infected humans. Our initial hypothesis that some of the macaques might contribute to frequent horizontal STLV-1 transmission as viral super-spreaders was unlikely because of the absence of the macaques exhibiting abnormally high PVLs but poor ABTs. Rather, ABTs and PVLs were statistically correlated (p < 0.0001), indicating that the increasing PVLs led to the greater humoral immune response. Further analyses demonstrated that the STLV-1 prevalence as determined by detection of the proviral DNA was dramatically increased with age; 11%, 31%, and 58% at 0, 1, and 2 years of age, respectively, which was generally consistent with the result of seroprevalence and suggested the frequent incidence of mother-to-child transmission. Moreover, our longitudinal follow-up study indicated that 24 of 28 seronegative JMs during the periods from 2011 to 2012 converted to seropositive (86%) 4 years later; among them, the seroconversion rates of sexually matured (4 years of age and older) macaques and immature macaques (3 years of age and younger) at the beginning of study were comparably high (80% and 89%, respectively), suggesting the frequent incidence of horizontal transmission. Conclusions Together with the fact that almost all of the full-adult JMs older than 9 years old were infected with STLV-1, our results of this study demonstrated for the first time that frequent horizontal and mother-to-child transmission may contribute to high prevalence of STLV-1 infection in JMs.

中文翻译：

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频繁的水平传播和母婴传播可能导致日本猕猴 STLV-1 感染率高

背景 猿猴 T 细胞白血病病毒 1 型 (STLV-1) 在各种非人灵长类动物中传播，与人类 T 细胞白血病病毒 1 型 (HTLV-1) 密切相关，后者是成人 T 细胞的病原体。白血病和 HTLV-1 相关脊髓病/热带痉挛性下肢轻瘫。值得注意的是，日本猕猴 (JM) 的 STLV-1 感染率估计 > 60%，远高于其他非人类灵长类动物；然而，STLV-1 传播的机制和模式仍然未知。本研究的目的是检查 STLV-1 感染在 JM 中高度流行的流行病学背景。结果 在我们的自由放养设施中饲养的 JMs 中 STLV-1 的流行率达到了 64% (180/280 JMs)，在 5 个独立部队中变化从 55% 到 77%。抗 STLV-1 抗体滴度 (ABT) 和 STLV-1 前病毒载量 (PVL) 分别呈正态分布，平均值分别为 4076 和 0.62%，这与 HTLV-1 感染的人类相当。我们最初的假设是，一些猕猴可能作为病毒超级传播者导致频繁的 STLV-1 水平传播，这是不可能的，因为没有猕猴表现出异常高的 PVL 但 ABT 很差。相反，ABT 和 PVL 具有统计学相关性（p < 0.0001），表明 PVL 的增加导致更大的体液免疫反应。进一步的分析表明，通过检测原病毒 DNA 确定的 STLV-1 流行率随着年龄的增长而显着增加。在 0、1 和 2 岁时分别为 11%、31% 和 58%，这与血清阳性率的结果大体一致，并表明母婴传播的频繁发生。此外，我们的纵向随访研究表明，2011 年至 2012 年期间的 28 名血清阴性 JM 中有 24 名在 4 年后转为血清阳性（86%）；其中，研究开始时性成熟（4岁及以上）猕猴和未成熟猕猴（3岁及以下）的血清转化率相对较高（分别为80%和89%），表明频繁发生水平传播的发生率。结论 再加上几乎所有 9 岁以上的成年 JM 都感染了 STLV-1，