Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany.
Department of Translational Genetics, The Cyprus Institute of Neurology and Genetics, Nicosia, Cyprus.
mSphere. 2018 Jul 25;3(4):e00171-18. doi: 10.1128/mSphere.00171-18.
Polar bears in captivity can be exposed to opportunistic pathogens not present in their natural environments. A 4-month-old polar bear () living in an isolated enclosure with his mother in the Tierpark Berlin, Berlin, Germany, was suffering from severe abdominal pain, mild diarrhea, and loss of appetite and died in early 2017. Histopathology revealed severe hepatic degeneration and necrosis without evidence of inflammation or inclusion bodies, although a viral infection had been suspected on the basis of the clinical signs. We searched for nucleic acids of pathogens by shotgun high-throughput sequencing (HTS) from genomic DNA and cDNA extracted from tissue and blood. We identified a novel and assembled a nearly complete genome from the shotgun sequences. Quantitative PCR (qPCR) revealed that viral DNA was present in various concentrations in all tissues examined and that the highest concentrations were found in blood. Viral culture did not yield cytopathic effects, but qPCR suggested that virus replication was sustained for up to three passages. Positive immunofluorescence staining confirmed that the virus was able to replicate in the cells during early passage. Phylogenetic analysis demonstrated that the virus is highly divergent compared to other previously identified members and basal to most known viral clades. The virus was found only in the 4-month-old bear and not in other captive polar bears tested. We surmised, therefore, that the polar bear was infected from an unknown reservoir, illustrating that adenoviral diversity remains underestimated and that cross-species transmission of viruses can occur even under conditions of relative isolation. Cross-species transmission of viral pathogens is becoming an increasing problem for captive-animal facilities. This study highlights how animals in captivity are vulnerable to novel opportunistic pathogens, many of which do not result in straightforward diagnosis from symptoms and histopathology. In this study, a novel pathogen was suspected to have contributed to the death of a juvenile polar bear. HTS techniques were employed, and a novel was isolated. The virus was present in both the tissue and blood samples. Phylogenetic analysis of the virus at both the gene and genome levels revealed that it is highly divergent to other known mastadenoviruses. Overall, this study shows that animals in isolated conditions still come into contact with novel pathogens, and for many of these pathogens, the host reservoir and mode of transmission are yet to be determined.
圈养的北极熊可能会接触到其自然环境中不存在的机会性病原体。2017 年初，一只生活在德国柏林动物园隔离围栏中和母亲在一起的 4 个月大的北极熊，出现严重腹痛、轻度腹泻、食欲不振的症状，并死亡。组织病理学检查显示严重的肝变性和坏死，没有炎症或包涵体的证据，尽管根据临床症状怀疑是病毒感染。我们从组织和血液中提取的基因组 DNA 和 cDNA ，通过高通量测序（HTS）来寻找病原体的核酸。我们鉴定了一种新的腺病毒，并从 shotgun 序列中组装了一个近乎完整的基因组。定量 PCR（qPCR）显示，在所有检查的组织中均以不同浓度存在病毒 DNA，在血液中浓度最高。病毒培养未产生细胞病变效应，但 qPCR 表明病毒复制可维持多达 3 个传代。阳性免疫荧光染色证实病毒在早期传代过程中能够在细胞中复制。系统发育分析表明，与其他已鉴定的腺病毒成员相比，该病毒高度分化，并且在大多数已知病毒进化枝的基础上。该病毒仅在 4 个月大的北极熊中发现，而在其他受测试的圈养北极熊中未发现。因此，我们推测北极熊是从未知的宿主感染的，这表明腺病毒的多样性仍然被低估，并且即使在相对隔离的条件下，病毒也可以跨物种传播。病毒病原体的跨物种传播对于圈养动物设施来说是一个日益严重的问题。本研究强调了圈养动物易受新的机会性病原体的影响，其中许多病原体的症状和组织病理学检查并不能明确诊断。在本研究中，一种新的病原体被怀疑导致了一只幼年北极熊的死亡。我们使用高通量测序技术，分离出一种新的腺病毒。该病毒存在于组织和血液样本中。病毒的基因和基因组水平的系统发育分析表明，它与其他已知的腺病毒高度分化。总的来说，本研究表明，处于隔离状态的动物仍然会接触到新的病原体，对于其中许多病原体，宿主库和传播方式仍有待确定。
