Rabies is nearly 100 percent fatal once symptoms appear and nearly 100 percent preventable if treated in time, and it has stalked humanity since at least 2000 BC in ancient Mesopotamia. This episode explains how the lyssavirus enters through a bite, quietly replicates in muscle without alerting the immune system, binds acetylcholine receptors at the neuromuscular junction, and hijacks the motor protein dynein to travel up nerves toward the brain. That journey explains why incubation usually runs one to three months and depends on how far the bite is from the head.

Once in the brain, the virus moves outward to the salivary glands. Furious rabies, about 80 percent of cases, brings aggression and hydrophobia: painful throat spasms that stop swallowing and keep saliva loaded with virus. Dumb rabies brings creeping paralysis. The episode covers Louis Pasteur and Émile Roux’s 1885 vaccine, modern post-exposure prophylaxis, Jeanna Giese’s 2004 survival under the Milwaukee Protocol and doubts about it, and the roughly 59,000 deaths each year, 40 percent of them children under 15.

• Why birds largely resist rabies, opossums run too cool, and small rodents rarely carry it
• Domestic dogs causing 99 percent of human cases globally, bats 70 percent in the United States
• India’s stray dogs, a 2001 protection law, and puppy pregnancy syndrome
• Switzerland eliminating rabies with vaccine-laced chicken heads dropped for foxes
• Corneal transplant transmission and Peruvian Amazon residents with natural antibodies