Spring Viremia of Carp Virus (SVCV) Infection Trials of Pacific Northwest Amphibians.

Spring viremia of carp virus (SVCV) is a rhabdovirus that primarily infects cyprinid finfishes and causes a disease notifiable to the World Organization for Animal Health. Amphibians, which are sympatric with cyprinids in freshwater ecosystems, are considered non-permissive hosts of rhabdoviruses. The potential host range expansion of SVCV in an atypical host species was evaluated by testing the susceptibility of amphibians native to the Pacific Northwest. Larval long-toed salamanders Ambystoma macrodactylum and Pacific tree frog Pseudacris regilla tad-poles were exposed to SVCV strains from genotypes Ia, Ib, Ic or Id by either intraperitoneal injection, immersion, or cohabitation with virus-infected koi Cyprinus rubrofuscus. Cumulative mortality was 100% for salamanders injected with SVCV, 98-100% for tadpoles exposed to virus via immersion, and 0 – 100% for tadpoles cohabited with SVCV-infected koi. Many of the animals that died exhibited clinical signs of disease and SVCV RNA was found by in situ hybridization in tissue sections of immersion-exposed tadpoles, particularly in the cells of the gastrointestinal tract and liver. SVCV was also detected by plaque assay and RT-qPCR testing in both amphibian species regardless of the virus exposure method, and viable virus was detected up to 28 days after initial exposure. Recovery of infectious virus from naïve tadpoles cohabited with SVCV-infected koi further demonstrated that SVCV transmission can occur between classes of ectothermic vertebrates. Collectively, these results indicated that SVCV, a fish rhabdovirus, can be transmitted to and cause lethal disease in two amphibian species. Therefore members of all five of the major vertebrate groups (mammals, birds, reptiles, fish, and amphibians) appear to be vulnerable to rhabdovirus infections.

鲤春季病毒血症病毒（Spring viremia of carp virus, SVCV）为弹状病毒（rhabdovirus），主要感染鲤科鱼类，其所引发的疫病属于世界动物卫生组织（World Organization for Animal Health）规定须通报的疫病。在淡水生态系统中与鲤科鱼类同域分布的两栖动物，被认为是弹状病毒的非容许宿主。本研究通过测试太平洋西北地区本土两栖动物的易感性，评估了SVCV在非典型宿主物种中潜在的宿主范围扩张潜力。研究人员分别采用腹腔注射、浸泡暴露，或与病毒感染的锦鲤（Cyprinus rubrofuscus）共栖的暴露方式，将长趾钝口螈（Ambystoma macrodactylum）幼体及太平洋树蛙（Pseudacris regilla）蝌蚪暴露于基因型为Ia、Ib、Ic或Id的SVCV毒株中。结果显示，经腹腔注射SVCV的钝口螈累积死亡率达100%，经浸泡暴露的蝌蚪累积死亡率为98%~100%，而与SVCV感染锦鲤共栖的蝌蚪累积死亡率区间为0~100%。多数死亡个体表现出典型的疾病临床症状，通过原位杂交（in situ hybridization）技术可在浸泡暴露蝌蚪的组织切片中检测到SVCV RNA，尤以胃肠道与肝脏细胞中的检出信号最为显著。无论采用何种病毒暴露方式，研究人员均可通过噬斑试验（plaque assay）与实时荧光定量逆转录聚合酶链反应（RT-qPCR）在两种两栖动物体内检测到SVCV，且在初始暴露后最长28天仍可分离得到活病毒。从与SVCV感染锦鲤共栖的未接触病毒蝌蚪中成功分离获得传染性病毒，这进一步证实SVCV可在变温脊椎动物的不同类群之间发生传播。综合上述实验结果表明，原本仅感染鱼类的弹状病毒SVCV，可感染两种两栖动物并引发致死性疫病。由此可见，脊椎动物五大主要类群（哺乳类、鸟类、爬行类、鱼类与两栖类）似乎均对弹状病毒感染具有易感性。