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A killer in close up
殺手在敲門
You can do a lot of damage with just seven genes
七個基因，禍害無窮
EBOLA is a simple virus, but also a subtle one. The stringy looking particles consist of a genome wrapped up in two layers of protein. This long, thin package, along with a large protein called a polymerase, is packed into a membrane that is studded with a glycoproteins—that is, proteins with sugar stuck to them.
埃博拉病毒看似簡單，實則精妙。由兩層蛋白質包裹著由基因組組成的絲狀體，形成長而薄的包膜，包膜上布滿醣蛋白顆粒，所謂醣蛋白就是糖分子附著在蛋白質上。
When the virus infects a cell the polymerase makes copies of the genome and the cell is tricked into using these to make the proteins that the virus needs. These include two, called VP35 and VP24, which stymie interferons, a class of molecule that alerts the immune system to infection. VP35 prevents interferons from being made; VP24 stops their cries for help from being heard. The sugars on the virus's outside make it hard for other parts of the immune system to get to grips with; to confuse things more, the virus makes infected cells produce more glycoprotein than it needs for its coat, with the surplus simply secreted into the bloodstream. Antibodies which would otherwise attack the virus stick to this decoy protein instead.
當埃博拉病毒感染細胞時，病毒的聚合酶就復制基因組，并誘使細胞使用這些基因組制造病毒所需要的蛋白質。這種蛋白質有兩種類型，分別叫做VP35和VP24，它們阻礙干擾素發揮作用，干擾素是一類能向免疫系統發出警示作用的細胞因子。VP35阻止細胞干擾素形成，VP24則阻礙免疫系統接受干擾素的警示信息。病毒外附著的糖分子阻止免疫系統的其他部分捕獲該病毒；更麻煩的是，病毒使得被感染的細胞生成超過其表皮需要量的醣蛋白，于是，這些過剩的醣蛋白直接代謝入血液。于是，抗體只能附著在這些作為誘餌的醣蛋白上面，而不會攻擊病毒。
Immune cells which the virus attacks in the bloodstream early on carry the infection to the liver, the spleen and lymph nodes. Symptoms may manifest themselves in a day or two or may wait weeks (see chart). Eventually the virus's spread triggers an immune overreaction known as a cytokine storm. Blood-vessel walls become leaky, blood pressure and core temperature drop, organs fail and the body goes into shock. Various combinations of those and other symptoms kill about 70% of those who get ill.
血液中先前被病毒攻擊的免疫細胞攜帶感染元進入肝臟、脾臟和淋巴結。癥狀可能會在1天、2天或者等上1周后顯示出來。最后，病毒的傳播引發了免疫過載，這稱為“細胞素風暴”。于是，血管壁開始滲漏，血壓和體核溫度下降，導致器官衰竭，身體休克。這些作用結合其它癥狀使得70%的患者死亡。
Some of the sick weather the storm, but most who survive infection do so by never getting to its direst straits. Some do not succumb at all: a study of people who had direct contact with patients during outbreaks in Gabon in 1996 showed that some had definitely been infected, but never fallen ill.
一些病人能挨過細胞素風暴，但是能在感染后活下來的人大多數靠的是沒有遇到殺招，但有一類人根本就是命硬：一項針對1996年在加蓬爆發期間和病人直接接觸的人群的研究表明：一些人絕對受到了感染，但從沒有生病。翻譯：沈竹 校對：徐牧之
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