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

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1. 0:06One morning in France in 1885, a dog attacked 9-year-old Joseph Meister,
2. 0:13biting him in 14 places.
3. 0:15He survived— but his mother realized he was probably now infected with rabies,
4. 0:20an almost certain death sentence.
5. 0:23She rushed him to Paris,
6. 0:25knowing his life depended on a rumored experimental medicine.
7. 0:30Today, without proper intervention, rabies remains deadly in almost all cases,
8. 0:36making it the most lethal infectious disease.
9. 0:39However, modern advances have afforded us a much deeper understanding
10. 0:43of the mechanisms that make rabies so dangerous and treatment-resistant,
11. 0:48and have revealed the best methods to save lives.
12. 0:52Rabies is caused by the roughly 20 virus species in the Lyssavirus genus,
13. 0:57all of which attack the mammalian nervous system.
14. 1:01Lyssavirus rabies, the most abundant, can infect any mammal.
15. 1:06Lyssaviruses mainly persist long term in bat populations.
16. 1:10Besides bats, rabies virus has also adapted to carnivores
17. 1:13like foxes, raccoons, and skunks,
18. 1:16and most human rabies infections come from dogs.
19. 1:20Infection begins with the transfer of virus-laden saliva
20. 1:24into the new host's tissue.
21. 1:26This could happen with a deep bite wound or a simple lick to certain spots.
22. 1:31Once inside its new host,
23. 1:33the virus particles, called virions, set out for the brain.
24. 1:38If the infection site is closer to the head,
25. 1:40things may escalate faster.
26. 1:42Rabies virions may lay low for days, weeks, months, or in rare cases, years,
27. 1:48replicating without causing any immediate symptoms.
28. 1:52Virions also suppress certain immune responses,
29. 1:55making it harder to clear an infection locally.
30. 1:58Meanwhile, the virions begin to travel,
31. 2:01entering local nerve cells
32. 2:02and exploiting the existing transport mechanisms along their axons,
33. 2:06traveling up to 100 millimeters a day.
34. 2:10Their protected position here in the nerve cells
35. 2:12helps shield the virions from the host’s immune system.
36. 2:16Once they’ve made it to the central nervous system,
37. 2:19the infection enters a new, devastating stage.
38. 2:22Clinical symptoms develop as rabies virions rapidly proliferate,
39. 2:27spreading into the peripheral nervous system and its connective tissues.
40. 2:31First, the escalating infection registers with flu-like symptoms.
41. 2:35Where a different neurological infection might cause inflammation
42. 2:39that opens the blood-brain barrier and incites an immune response,
43. 2:43rabies viruses do not,
44. 2:45so immune cells and therapies cannot easily or quickly reach them there.
45. 2:50Then, as the disease damages the nervous system,
46. 2:52things take one of two turns.
47. 2:55In paralytic rabies,
48. 2:56symptoms like a vacant expression, weakness, and paralysis set in.
49. 3:01Furious rabies, meanwhile,
50. 3:03is associated with hyperactivity, uncontrolled movements,
51. 3:07hallucinations, aggression, and paralysis.
52. 3:11As virions accumulate in the salivary glands,
53. 3:14the host secretes excess saliva.
54. 3:16The infection also often causes hydrophobia in people,
55. 3:20where throat spasms make swallowing water painful and difficult,
56. 3:23further concentrating the virus in the saliva
57. 3:26and increasing the odds of transmission.
58. 3:29Some hosts are especially effective at transmitting the virus;
59. 3:33humans, however, aren’t,
60. 3:35and rarely transmit rabies themselves,
61. 3:37for example, in cases of tissue or organ transplantation.
62. 3:42Regardless of whether transmission occurs,
63. 3:44this period of acute illness is almost always followed by coma and death.
64. 3:49Once symptoms have begun, there is currently no cure for rabies.
65. 3:53However, we do have highly effective preventative methods
66. 3:57if they’re delivered early enough—
67. 3:59and Joseph Meister was the first to benefit.
68. 4:03For years, French scientist Louis Pasteur and colleagues
69. 4:06had been trying to develop a rabies vaccine.
70. 4:09They collected the spinal cords of rabies-virus-infected rabbits,
71. 4:13dried them to weaken the virus,
72. 4:15and injected the resulting mixtures into dogs and other animals.
73. 4:19Meister’s mother got him to Pasteur two days after the attack.
74. 4:23He received a course of inoculations, and though the procedure was risky,
75. 4:27he beat the odds,
76. 4:28becoming the first rabies-vaccinated person to survive.
77. 4:33Today, two series of vaccinations are available:
78. 4:37pre- and post-exposure prophylaxis.
79. 4:40Each is highly effective at preventing rabies virus infections
80. 4:44from reaching the central nervous system,
81. 4:46before symptoms develop and the virus has done irreparable harm.
82. 4:50The very few people known to have survived rabies after the onset of symptoms
83. 4:55have done so due to intensive care,
84. 4:57usually sustaining neurological damage in the process.
85. 5:01Around 59,000 people are still estimated to die of rabies annually,
86. 5:06though the number is sadly suspected to be higher
87. 5:09due to insufficient medical access in rabies-burdened areas.
88. 5:14Scientists are still looking into new therapies.
89. 5:16But the way rabies virions elude the immune system and damage cells
90. 5:21makes the infection extremely difficult to treat.
91. 5:24And because the Lyssavirus has so many natural hosts,
92. 5:27it's impossible to eradicate the disease.
93. 5:30This makes preventative measures especially essential.
94. 5:34Even unconfirmed, potential exposures—
95. 5:37like the mere presence of a bat in one’s house while they’ve been sleeping—
96. 5:41warrant serious medical investigation.