The Sickness manifested as a severe mental change on the part of the afflicted. In 1988, one apparent sufferer, Robert, suddenly and uncharacteristically attempted to kill his pregnant fiancée, Danielle Rousseau, seconds after professing his love for her. Claire post-infection became a mentally unstable, paranoid murderer and cradled a boar's skull to replace her baby. Jungle hermit Danielle acted similarly, exhibiting what appeared to be similar paranoid delusions, though she claimed to be the only expedition member to escape the sickness. Danielle personally killed all other members of her expedition and other characters wrote her off as insane. Sayid, after his infection, killed even more readily than usual, and he said he could no longer feel emotions.
In 1988, members of Danielle's team contracted the sickness after exploring beneath the Temple, an area the Man in Black had just entered. The smoke monster once similarly tried to drag Locke underground. Sayid contracted the sickness after dying in the temple spring. He resurrected soon after and credited the Man in Black. Claire's moment of infection is less clear. ("The Little Prince") ("LA X, Part 2") ("Cabin Fever")
Individuals appear to be infected on the Temple grounds. Sayid was at the temple spring, and members of the Bésixdouze expedition were dragged into the Tunnels, within the boundary of the Temple. Claire's manner of infection was not shared, but it is a possibility that infection can only occur at the Temple. ("LA X, Part 2") ("This Place Is Death")
Danielle, who believed the sickness was a contagious illness, thought the Others transmitted it, calling them "carriers". ("Solitary") She also accused Jin of being a carrier, after he witnessed her killing Robert during a time jump.("This Place Is Death") She firmly believed infected people must be killed. When Aaron became sick with a fever and a rash, Danielle told Claire, "I hope your baby's not infected. But if it is, I hope you know what must be done. ("Maternity Leave")
The Others tested individuals for infection by taking their blood and torturing them. They subjected Sayid and Claire to this test. Dogen claimed it measured their level of good and evil.
According to Dogen, infection was irreversible. Rather than trying to cure Sayid, he tried to get Jack to kill him with a poisonous pill. Sayid and Claire, however, both rebelled against the supposed evil within them. ("What Kate Does") ("The Candidate") ("The End")
List of sufferers
|Claire||At some point after the rescue of the Oceanic 6, Claire was brought to the Temple because she was infected.|
|Sayid||Sayid was diagnosed by Dogen by using a complicated machine.|
|Brennan||Infected according to Danielle Rousseau's account.|
|Lacombe||Infected according to Rousseau's account.|
|Robert||Tried to kill Rousseau.|
The series referenced a number of sicknesses possibly unconnected with the Man in Black.
In the 1970s, the DHARMA Initiative inoculated new recruits. Swan residents also used this vaccine, and the Swan mural contained the enigmatic phrase "I am sick." The Others later injected Claire with this vaccine, and several DHARMA stations warned of a quarantine. This vaccine turned out to be a placebo, and the quarantine was a deception to confine workers to stations. ("Live Together, Die Alone, Part 2") ("The Man Behind the Curtain") ("Namaste") A jigsaw puzzle reveals that Kelvin and Radzinsky believed "There is no sickness".
Pregnant women suffered complications unconnected to the sickness. Aaron briefly developed a fever that worried Claire about the sickness, but it cleared up after a few days. Claire later suffered nosebleeds thanks to an artificial implant. ("Maternity Leave") ("One of Us")
Time offshore close to the island caused what Captain Gault called a "heightened case of cabin fever." Brandon behaved erratically and died. Regina behaved listless and eventually killed herself. People traveling to and from the island sometimes suffered from Temporal displacement.