Name: 病毒是如何從動物跳到人類身上的？- Ben Longdon (How do viruses jump from animals to humans? - Ben Longdon)
Uploaded: 2021-01-14T08:20:59.000Z
Duration: 5 min 5 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。學這些英文用法：武漢肺炎,新型冠狀病毒,新冠肺炎,COVID-19

the prize pigs were not  looking their best.

Farmers reported feverish hogs with  inflamed eyes and running snouts.

But while fair officials worried  about the pigs,

the Maryland department of health was  concerned about a group of sick fairgoers.

Some had pet the pigs, while others had  merely been near their barns;

but soon, 40 of these attendees would  be diagnosed with swine flu.

More often than not, sick animals  don't infect humans.

But when they do, these  cross-species infections,

have the potential to produce  deadly epidemics.

So how can pathogens from one species  infect another,

Viruses are a type of organic parasite  infecting nearly all forms of life.

To survive and reproduce, they must move through three stages:

contact with a susceptible host,  infection and replication,

As an example, let's look  at human influenza.

First, the flu virus encounters  a new host

and makes its way into  their respiratory tract.

This isn't so difficult, but to survive  in this new body,

the virus must mount a successful  infection

before it's caught and broken down  by an immune response.

viruses have evolved specific interactions with their host species.

Human flu viruses are covered in proteins

adapted to bind with matching receptors  on human respiratory cells.

Once inside a cell, the virus employs  additional adaptations

to hijack the host cell's reproductive  machinery

Now the virus only needs to suppress or evade the host's immune system

long enough to replicate to sufficient  levels and infect more cells.

At this point, the flu can be passed on to its next victim

via any transmission  of infected bodily fluid.

However, this simple sneeze also brings  the virus in contact with pets,

Viruses are constantly encountering  new species and attempting to infect them.

More often than not, this ends in failure.

In most cases, the genetic dissimilarity  between the two hosts is too great.

a lettuce cell would be a foreign and  inhospitable landscape.

But there are a staggering number  of viruses circulating in the environment,

all with the potential to  encounter new hosts.

And because viruses rapidly reproduce  by the millions,

they can quickly develop random mutations.

Most mutations will have no effect,  or even prove detrimental;

but a small proportion may enable the  pathogen to better infect a new species.

The odds of winning this destructive  genetic lottery increase over time,

or if the new species is closely related  to the virus' usual host.

infecting a human might just take  a few lucky mutations.

one of our closest genetic relatives, might barely require any changes at all.

It takes more than time and genetic  similarity

Some viruses come equipped to easily  infect a new host's cells,

but are then unable to evade  an immune response.

Others might have a difficult time  transmitting to new hosts.

For example, they might make the host's  blood contagious,

However, once a host jump reaches  the transmission stage,

the pathogen has twice the odds of  mutating into a more successful virus.

And each new host increases  the potential for a full-blown epidemic.

Virologists are constantly looking for  mutations

that might make viruses such as influenza more likely to jump.

However, predicting the next potential  epidemic is a major challenge.

There's a huge diversity of viruses  that we're only just beginning to uncover.

Researchers are tirelessly studying the  biology of these pathogens.

And by monitoring populations to quickly identify new outbreaks,

they can develop vaccines and containment protocols to stop these deadly diseases.