Why is getting bitten by a rabid animal so dangerous? - Charles Rupprecht

0:06 One morning in France in 1885,

0:09 a dog attacked 9-year-old Joseph Meister, 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.

1:06 Lyssaviruses mainly persist long term in bat populations.

1:10 Besides bats, rabies virus has also adapted to carnivores like foxes,

1:14 raccoons, and skunks, and most human rabies infections come from dogs.

1:20 Infection begins with the transfer of virus-laden

1:23 saliva 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, the virus particles,

1:34 called virions, set out for the brain.

1:38 If the infection site is closer to the head, things may escalate faster.

1:42 Rabies virions may lay low for days, weeks, months,

1:46 or in rare cases, years, 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 and exploiting

2:03 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, things take one of two turns.

2:55 In paralytic rabies, symptoms like a vacant expression,

2:59 weakness, and paralysis set in.

3:01 Furious rabies, meanwhile, is associated with hyperactivity,

3:06 uncontrolled movements, hallucinations, aggression, and paralysis.

3:11 As virions accumulate in the salivary glands, 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;

3:33 humans, however, aren’t, and rarely transmit rabies themselves, for example,

3:38 in cases of tissue or organ transplantation.

3:42 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 if they’re

3:58 delivered early enough— 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, 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

4:43 virus infections 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

4:53 the onset of symptoms 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

5:08 higher 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

5:20 and damage cells 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— like the mere presence of a bat

5:39 in one’s house while they’ve

5:40 been sleeping— warrant serious medical investigation.