流感是由流感病毒引起的呼吸道传染病，通常在秋冬季节高发.其通过呼吸道飞沫传播，感染过程中引起全身性炎症反应和免疫反应，通常出现发热、头痛、肌肉酸痛等症状。
流感病毒具有高度变异性。根据其核蛋白和基质蛋白的不同，可分为A（甲）、B（乙）、C（丙）、D（丁）四型。丙型流感病毒（Influenza C virus，ICV）是一种较少为人所知的病毒类型，其通常与轻度呼吸道疾病相关，最常出现的症状是发热、流涕和咳嗽。该病毒也与肺炎、毛细支气管炎和支气管炎有关，且ICV感染患者经常出现胃肠炎症状。
尽管ICV主要感染人，但它也在猪、狗和牛中被检测到，并有少数猪传人的报道。自1947年发现ICV以来，由于难以在细胞培养中分离出ICV，其造成的疾病负担描述也较为匮乏，直到最近才有了较为详细的阐述。目前虽然有疫情暴发和家族传播病例的报道，但ICV的季节性特征尚不明确。
ICV是一种有包膜的、负义链RNA病毒，属于正黏病毒科，基因组由7个节段组成，编码9种病毒蛋白。与甲型和乙型流感病毒不同，ICV表面蛋白不是血凝素和神经氨酸酶，而是血凝素-酯酶-融合（HEF）糖蛋白。HEF由第4节段编码，通过促进宿主受体结合、裂解唾液酸以及膜融合，有效地同时发挥血凝素和神经氨酸酶的作用。
此外，人群免疫力可能是导致ICV变异的因素之一。ICV分离株间存在显著的抗原性和遗传多样性，其可划分为六个遗传谱系（C/Taylor、C/Mississippi、C/Aichi、C/Yamagata、C/Kanagawa和C/Sao Paulo），代表六种HEF抗原组，病毒内部基因有两个主要遗传谱系。
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