But the vaccinia virus is only distantly related to the variola virus that causes smallpox.

但牛痘病毒与引起天的天病毒关系疏远。

Throughout Europe, it was known as variola, meaning " spotted."

整欧洲将其称为“痘斑”，意为 “斑点”。

The immune system will forever remember variola, making  you immune forever.

免疫系统会永远记住天病毒，让你终身免疫。

Smallpox is a highly contagious disease that is caused by two forms of the variola virus.

天两种形式的天病毒引起的高度传染性疾病。

At some point a critical threshold is reached and variola starts its attack for real.

在某时刻，一关键阈值被达到，天病毒开始真正发起攻击。

And so, with little resistance variola spreads  everywhere and infects billions of your cells all over your body.

于，天病毒无阻碍地扩散到全身，感染你体内数十亿的细胞。

How could variola be so incredibly deadly for  so long and how could we have forgotten its horror so quickly?

天病毒为何能如此致命地肆虐这么久，而我们又为何能如此迅速地忘记它的恐怖？

Variolation probably worked because it introduced  the variola in a part of the body the virus wasn't prepared for, disabling most of its nasty  tricks.

种痘可能有效因为它将天病毒引入了病毒没有准备好的身体部位，从而破坏了它大部分的恶劣手段。

Other systems would usually help  - like the complement system, a sort of mobile minefield that can destroy viruses but  variola also manages to shut this down too.

其他系统通常也会提供帮助——比如补体系统，这一种移动的地雷阵，能够摧毁病毒，但天病毒也能将其关闭。

Although Jenna did not know it, cowpox is caused by the vaccinia virus, which can be transmitted to humans and is closely related to the variola virus responsible for smallpox.

尽管詹纳并不知情， 牛痘痘病毒引起的，这种病毒能传染给人类， 并与负责引发天的痘病毒密切相关。

Pus and cellular junk fills it up as  your body swells up with hundreds of lesions, all over your skin and inside, even on your organs,   all filled with billions of variola viruses.

脓液和细胞碎片充满了这些病灶，你的身体会肿胀并布满数百病灶，遍布你的皮肤内外，甚至在器官上，里面都充满了数十亿的天病毒。

As immune cells begin cleaning up dead  cells, eating viruses and killing infected cells , variola infects a crucial cell of  your immune system: Your Dendritic cells, intelligence cells that gather information  and leave the battlefield to get help.

当免疫细胞开始清理死亡细胞、吞噬病毒并杀死受感染细胞时，天病毒会感染你免疫系统中的一关键细胞：你的树突状细胞，这些情报细胞负责收集信息并离开战场去寻求帮助。