In the fourth part of the book, the narrative shifts to the summer of 1993 and the author’s own visit to Mount Elgon and Kitum Cave. At the beginning of his journey, Preston notes that the road he is taking to Mount Elgon is part of the Kinshasa Highway, also known as the “AIDS highway.” The road cuts through the middle of Africa and, as the author recalls from his childhood, was a rarely used dirt road until it was paved in the 1970s. Soon afterward, the AIDS virus started to appear in the towns running parallel to the highway.
For the trip to Mount Elgon, Preston hires Robin MacDonald as his guide. A professional hunter and safari guide, MacDonald is unconcerned about the threat of the Marburg virus inside Kitum Cave. He laughingly assures Preston that, if necessary, he will roll Preston up in a tent and drop him off at the entrance to Nairobi Hospital. However, more seriously, MacDonald notes that he has a gallon of bleach in his Land Rover.
In addition to Robin’s wife, Carrie, and their two sons, the expedition to Kitum Cave includes three professional safari men and two of Preston’s close friends. Unbeknownst to his friends, Preston has prepared a list of instructions in case he breaks with the Marburg virus after visiting the cave. At the end of the first day, the group reaches the town of Kitale at the base of Mount Elgon. They decide to make camp in the same meadow where Charles Monet had camped more than 13 years before.
The next morning, the expedition hikes to the mouth of Kitum Cave. Because of problems with poachers from Uganda, the group is escorted by an armed guard, per government order. As they approach the cave, the author realizes that everything he sees is a potential transmitter for the Marburg virus: every moth, every insect, even the stinging nettles. The trail leading to the cave is also covered with animal dung, another possible host for the virus, and the author becomes increasingly nervous about his mission.
Before entering the cave, Preston puts on a neutral-pressure body suit with a hood and respirator, as well as gloves and boots. He closes all of the seals in his suit with sticky tape. As Preston finishes suiting up, one of the professional safari men named Okuku asks how many people have died in the cave. Preston admits that two people have died, but both deaths happened several days after they visited the cave. Okuku remembers hearing about an expedition of American scientists who came to the cave in the late 1980s.
Preston finally begins his journey into the cave. Aided by a map drawn by an elephant expert who studied Kitum Cave, Preston passes through a zone of bat roosts to a dry, dusty area with remnants of a petrified rainforest. With each step, he wonders if he is inadvertently stepping on or through the hidden source of the Marburg virus. When Preston reaches the back wall of the cave, he turns off his light and briefly stands in the darkness, trying to feel if he can sense the presence of a viral predator.
Back outside the cave, Preston removes his makeshift space suit and immediately experiences the uncanny fear that he has been exposed to the filovirus. He tries to remind himself of the many people who have entered Kitum Cave without ever developing the Marburg virus. Finally, he remembers the advice of Joe McCormick, who told him that the only treatment for exposure to a filovirus is a bottle of scotch.
In the final few pages of the book, Preston visits the abandoned monkey facility in Reston, Virginia. As he looks through the glass door, he can see the airlock corridor used by Jerry Jaax’s SWAT team and a bucket that carried bleach for the decontamination team. Other than a few cobwebs and creeping vines, the building shows no signs of life, not even of the ancient organism it once hosted. However, Preston knows that the virus will be back.
At this point in the book, the reader is introduced to Richard Preston as a character on his own journey through the world of the filoviruses. While Preston has been largely limited to third person narrative up to this point, he now provides the reader with his own perspective of Kitum Cave, as well as background about his time in Africa as a child. As a result, this section serves as a sort of nonfiction epilogue to the rest of the narrative. As the bulk of the story has already been told, Preston uses this opportunity to offer his own conclusions about the filoviruses and their role in the natural order.
In his description of the Kinshasa Highway, Preston presents human technology as another cause for the progression of disease. Since the paving of the road in the 1970s, travel through the middle of Africa became possible, which in turn allowed for a more efficient route for the AIDS virus. While Preston has spent the majority of the book on the filoviruses, he admits that AIDS poses a far greater threat to the human species. However, because the virus can be slow-moving with symptoms that are less dramatic than the filoviruses, it has not been viewed with the proper amount of concern.
By putting on the space suit and entering Kitum Cave, Preston steps into the role played by Nancy Jaax, Gene Johnson, and the other scientists in The Hot Zone who confront their fear of hot agents for the sake of research. Preston’s decision is particularly significant because, like Jaax and Johnson, he actually understands the danger of what he is doing by entering a hot zone. He is not an unknowing victim like Charles Monet or Peter Cardinal, but rather an active participant in the risk to his own life.
Preston’s motivation for entering the cave seems tenuous – instead of looking for a cure for Marburg, he is researching for the sake of his book. Yet, despite his reasons, Preston enters Kitum Cave with the same amount of courage required to work at Level 4. For the first time, he as the author can fully understand the experiences of the characters he includes in his book. His action also allows the reader to grasp the threat of the hot zone as he experiences Kitum Cave for himself.
Significantly, Preston does not enter Kitum Cave with the sole purpose of stepping into the mindset of the scientists of his book. He is interested in assuming the mindset of the hot agent itself. With each step in the cave, he tries to discern the source of the virus, even to the point of turning off his light and trying to “feel” its presence. Preston does not reveal whether or not he feels anything, but he is clearly affected by his experience after emerging from the cave. Just as Tom Geisbert and Peter Jahrling must wait for the entirety of Ebola’s incubation period to know whether or not they are infected, Preston can only wait to see if he develops a headache. This personal episode of terror is an affecting way to end a book about human folly and threats larger than mankind.