How do viruses jump from animals to humans? - Ben Longdon
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0:08 - 0:11At a Maryland country fair in 2017,
-
0:11 - 0:14the prize pigs were not
looking their best. -
0:14 - 0:19Farmers reported feverish hogs with
inflamed eyes and running snouts. -
0:19 - 0:22But while fair officials worried
about the pigs, -
0:22 - 0:28the Maryland department of health was
concerned about a group of sick fairgoers. -
0:28 - 0:32Some had pet the pigs, while others had
merely been near their barns; -
0:32 - 0:38but soon, 40 of these attendees would
be diagnosed with swine flu. -
0:38 - 0:41More often than not, sick animals
don’t infect humans. -
0:41 - 0:45But when they do, these
cross-species infections, -
0:45 - 0:47or viral host jumps,
-
0:47 - 0:50have the potential to produce
deadly epidemics. -
0:50 - 0:54So how can pathogens from one species
infect another, -
0:54 - 0:58and what makes host jumps so dangerous?
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0:58 - 1:03Viruses are a type of organic parasite
infecting nearly all forms of life. -
1:03 - 1:07To survive and reproduce, they must move
through three stages: -
1:07 - 1:11contact with a susceptible host,
infection and replication, -
1:11 - 1:15and transmission to other individuals.
-
1:15 - 1:18As an example, let’s look
at human influenza. -
1:18 - 1:21First, the flu virus encounters
a new host -
1:21 - 1:24and makes its way into
their respiratory tract. -
1:24 - 1:27This isn’t so difficult, but to survive
in this new body, -
1:27 - 1:31the virus must mount a successful
infection -
1:31 - 1:34before it’s caught and broken down
by an immune response. -
1:34 - 1:36To accomplish this task,
-
1:36 - 1:40viruses have evolved specific interactions
with their host species. -
1:40 - 1:43Human flu viruses are covered in proteins
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1:43 - 1:49adapted to bind with matching receptors
on human respiratory cells. -
1:49 - 1:54Once inside a cell, the virus employs
additional adaptations -
1:54 - 1:56to hijack the host cell’s reproductive
machinery -
1:56 - 1:59and replicate its own genetic material.
-
1:59 - 2:04Now the virus only needs to suppress
or evade the host’s immune system -
2:04 - 2:08long enough to replicate to sufficient
levels and infect more cells. -
2:08 - 2:12At this point, the flu can be passed on to
its next victim -
2:12 - 2:16via any transmission
of infected bodily fluid. -
2:16 - 2:21However, this simple sneeze also brings
the virus in contact with pets, -
2:21 - 2:23plants, or even your lunch.
-
2:23 - 2:29Viruses are constantly encountering
new species and attempting to infect them. -
2:29 - 2:31More often than not, this ends in failure.
-
2:31 - 2:37In most cases, the genetic dissimilarity
between the two hosts is too great. -
2:37 - 2:39For a virus adapted to infect humans,
-
2:39 - 2:43a lettuce cell would be a foreign and
inhospitable landscape. -
2:43 - 2:48But there are a staggering number
of viruses circulating in the environment, -
2:48 - 2:51all with the potential to
encounter new hosts. -
2:51 - 2:55And because viruses rapidly reproduce
by the millions, -
2:55 - 2:58they can quickly develop random mutations.
-
2:58 - 3:02Most mutations will have no effect,
or even prove detrimental; -
3:02 - 3:08but a small proportion may enable the
pathogen to better infect a new species. -
3:08 - 3:13The odds of winning this destructive
genetic lottery increase over time, -
3:13 - 3:18or if the new species is closely related
to the virus’ usual host. -
3:18 - 3:20For a virus adapted to another mammal,
-
3:20 - 3:24infecting a human might just take
a few lucky mutations. -
3:24 - 3:27And a virus adapted to chimpanzees,
-
3:27 - 3:33one of our closest genetic relatives,
might barely require any changes at all. -
3:33 - 3:36It takes more than time and genetic
similarity -
3:36 - 3:38for a host jump to be successful.
-
3:38 - 3:42Some viruses come equipped to easily
infect a new host’s cells, -
3:42 - 3:46but are then unable to evade
an immune response. -
3:46 - 3:50Others might have a difficult time
transmitting to new hosts. -
3:50 - 3:53For example, they might make the host’s
blood contagious, -
3:53 - 3:55but not their saliva.
-
3:55 - 3:59However, once a host jump reaches
the transmission stage, -
3:59 - 4:01the virus becomes much more dangerous.
-
4:01 - 4:04Now gestating within two hosts,
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4:04 - 4:09the pathogen has twice the odds of
mutating into a more successful virus. -
4:09 - 4:14And each new host increases
the potential for a full-blown epidemic. -
4:14 - 4:17Virologists are constantly looking for
mutations -
4:17 - 4:21that might make viruses such as influenza
more likely to jump. -
4:21 - 4:26However, predicting the next potential
epidemic is a major challenge. -
4:26 - 4:31There’s a huge diversity of viruses
that we’re only just beginning to uncover. -
4:31 - 4:35Researchers are tirelessly studying the
biology of these pathogens. -
4:35 - 4:39And by monitoring populations to quickly
identify new outbreaks, -
4:39 - 4:45they can develop vaccines and containment
protocols to stop these deadly diseases.
- Title:
- How do viruses jump from animals to humans? - Ben Longdon
- Speaker:
- Ben Longdon
- Description:
-
View full lesson: https://ed.ted.com/lessons/how-do-viruses-jump-from-animals-to-humans-ben-longdon
At a Maryland country fair in 2017, farmers reported feverish hogs with inflamed eyes and running snouts. While farmers worried about the pigs, the department of health was concerned about a group of sick fairgoers. Soon, 40 of these attendees would be diagnosed with swine flu. How can pathogens from one species infect another, and what makes this jump so dangerous? Ben Longdon explains.
Lesson by Ben Longdon, directed by Cabong Studios.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 04:47
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