Institute of Virology and Immunology, Vetsuisse Faculty, University of Bern, Bern, Switzerland.
Virol J. 2014 Apr 3;11:65. doi: 10.1186/1743-422X-11-65.
Small ruminant lentiviruses escaping efficient serological detection are still circulating in Swiss goats in spite of a long eradication campaign that essentially eliminated clinical cases of caprine arthritis encephalitis in the country. This strongly suggests that the circulating viruses are avirulent for goats.To test this hypothesis, we isolated circulating viruses from naturally infected animals and tested the in vitro and in vivo characteristics of these field isolates.
Viruses were isolated from primary macrophage cultures. The presence of lentiviruses in the culture supernatants was monitored by reverse transcriptase assay. Isolates were passaged in different cells and their cytopathogenic effects monitored by microscopy. Proviral load was quantified by real-time PCR using customized primer and probes. Statistical analysis comprised Analysis of Variance and Bonferroni Multiple Comparison Test.
The isolated viruses belonged to the small ruminant lentiviruses A4 subtype that appears to be prominent in Switzerland. The 4 isolates replicated very efficiently in macrophages, displaying heterogeneous phenotypes, with two isolates showing a pronounced cytopathogenicity for these cells. By contrast, all 4 isolates had a poor replication capacity in goat and sheep fibroblasts. The proviral loads in the peripheral blood and, in particular, in the mammary gland were surprisingly high compared to previous observations. Nevertheless, these viruses appear to be of low virulence for goats except for the mammary gland were histopathological changes were observed.
Small ruminant lentiviruses continue to circulate in Switzerland despite a long and expensive caprine arthritis encephalitis virus eradication campaign. We isolated 4 of these lentiviruses and confirmed their phylogenetic association with the prominent A4 subtype. The pathological and histopathological analysis of the infected animals supported the hypothesis that these A4 viruses are of low pathogenicity for goats, with, however, a caveat about the potentially detrimental effects on the mammary gland. Moreover, the high proviral load detected indicates that the immune system of the animals cannot control the infection and this, combined with the phenotypic plasticity observed in vitro, strongly argues in favour of a continuous and precise monitoring of these SRLV to avoid the risk of jeopardizing a long eradication campaign.
尽管瑞士开展了一场旨在根除羊关节炎脑炎病毒的漫长行动，基本上消除了该国的临床羊关节炎脑炎病例，但仍有能够逃避有效血清学检测的小反刍动物慢病毒在瑞士山羊中传播。这强烈表明，循环中的病毒对山羊没有毒力。为了验证这一假设，我们从自然感染的动物中分离出循环病毒，并测试了这些田间分离株的体外和体内特征。
病毒从原代巨噬细胞培养物中分离出来。通过逆转录酶测定监测培养上清液中是否存在慢病毒。将分离株在不同的细胞中传代，并通过显微镜观察其细胞病变效应。使用定制的引物和探针通过实时 PCR 定量前病毒载量。统计分析包括方差分析和 Bonferroni 多重比较检验。
分离出的病毒属于小反刍动物慢病毒 A4 亚型，该亚型在瑞士似乎很突出。4 个分离株在巨噬细胞中非常有效地复制，表现出异质表型，其中 2 个分离株对这些细胞表现出明显的细胞病变作用。相比之下，所有 4 个分离株在山羊和绵羊成纤维细胞中的复制能力都很差。外周血中的前病毒载量，尤其是乳腺中的前病毒载量，与之前的观察结果相比出人意料地高。然而，这些病毒似乎对山羊的毒力较低，除了在乳腺中观察到组织病理学变化。
尽管瑞士开展了一场漫长而昂贵的羊关节炎脑炎病毒根除行动，但小反刍动物慢病毒仍在瑞士继续传播。我们从这些慢病毒中分离出 4 种，并证实了它们与主要 A4 亚型的系统发育关联。感染动物的病理和组织病理学分析支持了这样一种假设，即这些 A4 病毒对山羊的致病性较低，但对乳腺有潜在的不利影响。此外，检测到的高前病毒载量表明，动物的免疫系统无法控制感染，再加上体外观察到的表型可塑性，强烈支持对这些 SRLV 进行持续和精确的监测，以避免危及长期根除行动的风险。
