Identification of a novel alphavirus related to the encephalitis complexes circulating in southern Brazil

In early 2017, an outbreak caused by an unknown and supposedly viral agent in the Marilena region of southern Brazil was investigated. Since the etiological agent causing the outbreak was not identified from human samples, mosquitoes from this region were collected. Three out of 121 mosquito pools collected from the region tested positive for alphavirus in molecular tests. Next generation sequencing results revealed the presence of a novel alphavirus, tentatively named here as Caainguá virus (CAAV). DNA barcoding analyses indicated that different species of <i>Culex</i> are hosts for CAAV. This new virus was basal to the New World encephalitic alphaviruses in a comprehensive and robust phylogenetic approach using complete genomes. Viral particles were observed in the cytosol and inside of intracellular compartments of cells in mosquito-derived cell cultures. Despite being noninfectious in vertebrate derived cell cultures, primary culturing of CAAV in human mononuclear cells suggests monocytes and lymphocytes as CAAV targets. However, the epidemiological link of CAAV on the human outbreak should be further explored.

2017年初，巴西南部马里莱纳地区暴发了一起由未知疑似病毒病原体引发的疫情，相关调查随即开展。由于未能从人类样本中鉴定出本次疫情的病原体，研究人员采集了该地区的蚊虫样本。在该地区采集的121组蚊虫混合样本中，有3组在分子检测中呈甲病毒（alphavirus）阳性。下一代测序（next generation sequencing）结果显示，样本中存在一种新型甲病毒，研究团队暂将其命名为卡因瓜病毒（Caainguá virus，CAAV）。DNA条形码（DNA barcoding）分析表明，不同种类的库蚊（Culex）均可作为CAAV的宿主。基于完整基因组的全面且稳健的系统发育分析显示，该新型病毒处于新世界嗜脑性甲病毒的进化基部。在蚊虫来源的细胞培养物中，研究人员在细胞胞质及胞内区室内观察到了病毒粒子。尽管该病毒在脊椎动物来源的细胞培养物中无感染性，但在人单核细胞中的原代培养实验显示，单核细胞与淋巴细胞为CAAV的靶标细胞。不过，CAAV与本次人类暴发疫情之间的流行病学关联仍有待进一步探究。