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Why is getting bitten by a rabid animal so dangerous? - Charles Rupprecht - Video học tiếng Anh
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Why is getting bitten by a rabid animal so dangerous? - Charles Rupprecht
Why is getting bitten by a rabid animal so dangerous? - Charles Rupprecht
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0:06
One morning in France in 1885, a dog attacked 9-year-old Joseph Meister,
0:13
biting him in 14 places.
0:15
He survived— but his mother realized he was probably now infected with rabies,
0:20
an almost certain death sentence.
0:23
She rushed him to Paris,
0:25
knowing his life depended on a rumored experimental medicine.
0:30
Today, without proper intervention, rabies remains deadly in almost all cases,
0:36
making it the most lethal infectious disease.
0:39
However, modern advances have afforded us a much deeper understanding
0:43
of the mechanisms that make rabies so dangerous and treatment-resistant,
0:48
and have revealed the best methods to save lives.
0:52
Rabies is caused by the roughly 20 virus species in the Lyssavirus genus,
0:57
all of which attack the mammalian nervous system.
1:01
Lyssavirus rabies, the most abundant, can infect any mammal.
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Lyssaviruses mainly persist long term in bat populations.
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Besides bats, rabies virus has also adapted to carnivores
1:13
like foxes, raccoons, and skunks,
1:16
and most human rabies infections come from dogs.
1:20
Infection begins with the transfer of virus-laden saliva
1:24
into the new host's tissue.
1:26
This could happen with a deep bite wound or a simple lick to certain spots.
1:31
Once inside its new host,
1:33
the virus particles, called virions, set out for the brain.
1:38
If the infection site is closer to the head,
1:40
things may escalate faster.
1:42
Rabies virions may lay low for days, weeks, months, or in rare cases, years,
1:48
replicating without causing any immediate symptoms.
1:52
Virions also suppress certain immune responses,
1:55
making it harder to clear an infection locally.
1:58
Meanwhile, the virions begin to travel,
2:01
entering local nerve cells
2:02
and exploiting the existing transport mechanisms along their axons,
2:06
traveling up to 100 millimeters a day.
2:10
Their protected position here in the nerve cells
2:12
helps shield the virions from the host’s immune system.
2:16
Once they’ve made it to the central nervous system,
2:19
the infection enters a new, devastating stage.
2:22
Clinical symptoms develop as rabies virions rapidly proliferate,
2:27
spreading into the peripheral nervous system and its connective tissues.
2:31
First, the escalating infection registers with flu-like symptoms.
2:35
Where a different neurological infection might cause inflammation
2:39
that opens the blood-brain barrier and incites an immune response,
2:43
rabies viruses do not,
2:45
so immune cells and therapies cannot easily or quickly reach them there.
2:50
Then, as the disease damages the nervous system,
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things take one of two turns.
2:55
In paralytic rabies,
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symptoms like a vacant expression, weakness, and paralysis set in.
3:01
Furious rabies, meanwhile,
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is associated with hyperactivity, uncontrolled movements,
3:07
hallucinations, aggression, and paralysis.
3:11
As virions accumulate in the salivary glands,
3:14
the host secretes excess saliva.
3:16
The infection also often causes hydrophobia in people,
3:20
where throat spasms make swallowing water painful and difficult,
3:23
further concentrating the virus in the saliva
3:26
and increasing the odds of transmission.
3:29
Some hosts are especially effective at transmitting the virus;
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humans however aren’t
3:35
and rarely transmit rabies themselves,
3:37
for example, in cases of tissue or organ transplantation.
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Regardless of whether transmission occurs,
3:44
this period of acute illness is almost always followed by coma and death.
3:49
Once symptoms have begun, there is currently no cure for rabies.
3:53
However, we do have highly effective preventative methods
3:57
if they’re delivered early enough—
3:59
and Joseph Meister was the first to benefit.
4:03
For years, French scientist Louis Pasteur and colleagues
4:06
had been trying to develop a rabies vaccine.
4:09
They collected the spinal cords of rabies-virus-infected rabbits,
4:13
dried them to weaken the virus,
4:15
and injected the resulting mixtures into dogs and other animals.
4:19
Meister’s mother got him to Pasteur two days after the attack.
4:23
He received a course of inoculations, and though the procedure was risky,
4:27
he beat the odds,
4:28
becoming the first rabies-vaccinated person to survive.
4:33
Today, two series of vaccinations are available:
4:37
pre- and post-exposure prophylaxis.
4:40
Each is highly effective at preventing rabies virus infections
4:44
from reaching the central nervous system,
4:46
before symptoms develop and the virus has done irreparable harm.
4:50
The very few people known to have survived rabies after the onset of symptoms
4:55
have done so due to intensive care,
4:57
usually sustaining neurological damage in the process.
5:01
Around 59,000 people are still estimated to die of rabies annually,
5:06
though the number is sadly suspected to be higher
5:09
due to insufficient medical access in rabies-burdened areas.
5:14
Scientists are still looking into new therapies.
5:16
But the way rabies virions elude the immune system and damage cells
5:21
makes the infection extremely difficult to treat.
5:24
And because the Lyssavirus has so many natural hosts,
5:27
it's impossible to eradicate the disease.
5:30
This makes preventative measures especially essential.
5:34
Even unconfirmed, potential exposures—
5:37
like the mere presence of a bat in one’s house while they’ve been sleeping—
5:41
warrant serious medical investigation.
