A month after the 2015 expedition to T1, Preston develops symptoms of fever, soreness, and sores in his mouth that come and go for the next few months. He also has a bug bite that grows worse over time. Chris Fisher and others from the team have similar bites. They eventually figure out that they have the tropical disease leishmaniasis, a fatal parasitic disease contracted from sand flies. They are treated at the National Institutes of Health (NIH) in Maryland.

Leishmaniasis has been found in ancient dinosaur blood as well as mummies from ancient Egypt and Peru. Preston describes the different strains of leishmaniasis. He and much of the team contract a fatal form of the disease that is difficult to cure and leads to horrible facial disfigurement before death. Preston muses, tongue-in-cheek, that this outbreak among the team and the Honduran soldiers recalls the curse of the monkey god legend, which foretold that anyone who entered the Lost City would die.

Preston arrives at the NIH for diagnosis and treatment. His physician, Dr. Nash, explains the disease and treatment to him in excruciating detail. His prescribed treatment is a drug called amphotericin B, which can cause highly variable and intense side effects.