Influenza Virus: Biological Properties 3在线视频

As what we have discussed last time,
我们上次讨论过

Influenza A viruses are divided into
甲型流感病毒可以

subtypes based on HA and NA.
根据HA和NA分成不同的亚型

Can humans be infected by
人类会被甲型流感病毒

all the subtypes?
所有的亚型感染吗？

The answer is no.
答案是否定的

There are only some subtypes
只有部分甲型流感病毒的亚型

as H 1, 2, 3 and N 1, 2
例如H1,H2,H3以及N1,N2

which can infect human beings
可以感染人类

and can be transmitted from person
同时易于在人与人之间

to person easily.
传播

These subtypes
这些亚型

are human influenza viruses.
是人流感病毒

Wild aquatic birds are carriers
野生水鸟可以携带

of the full variety
甲型流感病毒

of influenza virus A subtypes,
的几乎所有亚型

except subtype H17N10 and H18N11
除了H17N10和H18N11两种

which have only been found in bats.
是只在蝙蝠中发现的亚型

Aquatic ducks are considered
水鸟可以被认为是

as natural reservoir for new human
新型人甲型流感病毒的

influenza A virus subtypes,
天然储存库

since they contain almost
水禽携带了

all the subtypes,
绝大部分的病毒亚型

and never get diseases.
且从未因此患病

And they will migrate every year,
它们每年都会迁徙

that could spread the virus
从而可以将病毒

to different places of the world.
传播到世界各地

Some subtypes are highly pathogenic.
有些亚型是高致病性的

This map shows you the outbreak
这张图展示了在2005到2016年期间，

of highly pathogenic avian influenza
家禽中高致病性禽流感病毒

in poultry 2005-2016.
的爆发情况

They were the highly pathogenic
H5和H7

flu viruses,
是具有高致病性

H5 and H7,
禽流感病毒亚型

which killed many poultry.
可以杀死许多家禽

So the next question is:
因此我们的下一个问题是

could the highly pathogenic
这些高致病性

avian flu virus be transmitted
禽流感病毒

to humans?
可以感染人类吗？

Usually, it is not easy.
通常来说，这并不是件容易的事

Because the human flu viruses bind to
因为人流感病毒

sialic acid α-2,6 linked receptors,
结合在唾液酸α-2，6残基型的流感病毒受体上，

whereas bird flu virus bind to
而禽流感病毒结合在

α-2,3 linked receptors.
α-2，3残基型流感病毒受体上

And the epithelial cells
而人类呼吸道的

of human respiratory tract
上皮细胞

mainly express α-2,6 linked receptors,
主要表达α-2，6残基型受体，

making difficult for the avian flu virus
所以会使禽流感病毒很难

infect humans.
感染人类

But in fact,
但实际上

humans can be infected by
人类是可以被

avian influenza virus.
禽流感病毒感染的

This table is from WHO website,
世界卫生组织官网的表格

which shows us the cumulative number
显示了已被证实的

of confirmed human cases
人类感染禽流感病毒H5N1

for avian flu virus H5N1.
病例的累计数据

From 2003 to 2020,
从2003年到2020年，

there are 861 cases,and 455 deaths.
累计有861起病例，其中455例死亡

The mortality is about 52.8%,
死亡率接近52.8%，

very high.
这是一个非常高的数字

And humans can also be infected
并且人类也能够被另外一种

by another highly pathogenic flu virus
高致病性禽流感病毒H7N9

H7N9.
所感染

The mortality is 28%.
这种病毒的致死率是28%

Question is why humans
但问题在于为什么

can be infected by avian flu virus?
人类可以被禽流感病毒感染呢？

Here we shows you some investigations.
这些是一些相关研究结果

This paper shows us H7N9
这篇论文告诉我们

influenza viruses interact with
H7N9流感病毒作用于

α-2,3 linked sialic acids and bind
唾液酸α-2，3残基型受体

weakly to α-2,6 linked sialic acids.
同时可以微弱地结合在唾液酸α-2，6残基型受体上

That means the viruses can bind to
这意味着这种病毒

the human receptor.
能与人类的受体结合

And some investigation shows the cells
还有一些研究显示

in deeper respiratory tract
在呼吸道深处

also express α-2,3 linked receptors.
也可以表达α-2，3连接的受体

These enable the avian viruses
这使禽流感病毒

to invade humans but difficult
能够感染人类

to be transmitted from person to person.
但难以在人与人之间传播

Now, the next question is:
那么，下一个问题是

can the avian flu virus acquire
禽流感病毒是否可以获得

the ability to transmit fast
在人与人之间

and easily between humans?
轻易而快速的传染能力呢？

Let's see another host, swine.
让我们来看另一个宿主，猪

We usually consider the swine
我们经常会把猪

as the intermediate host.
作为中间宿主

Swine may express both α-2,3
猪呼吸道上皮细胞可以同时表达

and α-2,6 linked sialic acid receptors
α-2，3和α-2，6

on its epithelial cells.
两种受体

So when human flu virus and avian
所以当人流感病毒和禽流感病毒

flu virus infect swine at the same time,
同时感染猪的时候

what will happen?
会发生什么呢？

Yes, the gene reassortment.
是的，基因重配

The brand new progeny virus has
新生的子代病毒

the chance to be highly pathogenic
有机会获得高致病性

and transmissible in humans easily.
而变得能够在人群中轻易传播

Because of the reassortment
因为分段基因组的

of segmented genomes,
基因重配

there will be a major antigenic change,
会导致抗原性的明显改变

and that could cause worldwide
就可以引起

pandemic of the disease.
疾病的全球流行

This is antigenic shift.
这就是抗原转换

Here is an example.
这里举一个例子

2009 human H1N1 caused the flu pandemic.
2009年人类H1N1型流感病毒引起流感的肆虐

We can see from this diagram,
从这张图我们可以看出

the virus contains some segments
这个病毒包含着

from swine flu virus,
一些节段来自于猪流感病毒

some from human
一些节段来自于人流感病毒

and some from avian flu virus.
还有一些来自于禽流感病毒

And the gene reassortment occurred
而且基因重配导致1990，2000和2009年的

in 1990, and 2000, and 2009.
流感爆发

The 2009 virus was a very new virus,
2009年的病毒是一种全新的病毒

that acquired the ability to transmit
它获得了在人之间传播的能力

between humans and no one in the world
并且世界上没有一个人

had the immunity to the new virus.
对这种全新的病毒有免疫力

So the virus led to a pandemic.
所以这个病毒可以导致流感的爆发

But fortunately,
不过幸运的是

the mortality was not that high.
这个病毒的致死率并没有那么高

Let's summarize now.
现在让我们来总结一下

Point mutation of the HA and NA genes,
HA和NA基因的点突变

results in minor antigenic changes,
导致抗原性的微小变化

which are called antigenic drift.
被称为抗原漂移

This process occurs every 2 to 3 years,
这个过程每2到3年发生一次

causing local outbreaks of influenza
并引起区域性

A and B infections (seasonal epidemic).
A型和B型流感病毒的爆发（季节性流感）

Gene reassortment
基因重配

results in major changes.
可以导致抗原的明显变化

Antigenic shift is often associated with
抗原转换往往

the occurrence of worldwide pandemic.
和世界范围的流行有关

Antigenic shift occurs only with
通常只有甲型流感病毒

the influenza A virus.
可以发生抗原转换

Influenza B is predominantly
乙型流感病毒

a human virus and does not undergo
一般只感染人

antigenic shift.
很少发生抗原转换

Summary of the structure & composition
总结一下流感病毒的

of flu virus.
结构和组成

Virion: spherical, 80-120 nm in diameter.
病毒体：球形，直径在80到120nm之间

Genome: -ssRNA,
基因组：单负链RNA

8 (7) separated fragments.
8（或7）个节段

Proteins: structural proteins and NS.
蛋白质：结构蛋白和NS

Envelope:
包膜：

contains viral hemagglutinin (HA)
有病毒的血凝素（HA）

and neuraminidase (NA).
和神经氨酸苷酶（NA）

The main characteristics
主要的特点是

is genetic reassortment.
可以进行基因重配

Now let's answer this question:
现在来回答这个问题

will a killer pandemic
未来还会发生像1918年那样的

like the 1918 flu come again?
致死性流感的全球大流行吗？

What is your answer?
你的答案是什么？

That may come again,
有可能会再度发生

because the viruses will change
因为病毒的抗原性

the antigenicity definitely.
肯定会发生变化

Now break time.
好了，让我们休息一下

See you soon.
稍后再见