Answer:
In chapter 25 of the novel "I Am Legend" by Richard Matheson, Robert Neville discovers that the dog he has been trying to capture and cure of its illness has been killed by a spear, which he suspects was thrown by a member of the new society of vampires that has emerged in the post-apocalyptic world.
Later in the chapter, Neville himself becomes ill with a high fever and intense pain in his throat. He realizes that he has contracted the same illness as the dog, which he refers to as "vampiris". The illness is characterized by a rapid onset, high fever, intense thirst, and degeneration of the body's tissues.
The doctors that Neville consults with speculate that the illness may have been caused by a virus or bacteria that has mutated in response to the nuclear radiation that was released during the war. They also suggest that the illness may have been spread through the bites of infected animals or insects. However, they are ultimately unable to determine the exact cause of the illness, as they are unable to study it in depth due to the danger posed by the infected individuals.
Step-by-step explanation: