Limitations of Human Knowledge
The majority of the main characters in the book are highly-trained scientists and medical personnel with significant experience with hot agents. Yet, as Preston reveals, their knowledge of filoviruses is woefully incomplete, especially when it comes to their ability to create a preventative vaccine or cure. Preston notes that only three of the seven proteins in filovirus strains have yet to be identified, while even the mystery of Kitum Cave and the source of the Marburg virus is still far from being solved. Ultimately, until science and knowledge can catch up with the filoviruses, there is no option but for individuals like Nancy Jaax and Gene Johnson to continue their research. In the meantime, the role played by both chance and human error will be even more significant in determining the path of a potential outbreak.
Power of Nature
The power of nature is a recurring theme in Preston's descriptions of the various outbreaks of Marburg and Ebola. While human beings may consider themselves to be "master of the earth", Preston argues that nature has the ultimate power, even to the point of determining the course of human evolution. While scientists such as Nancy Jaax and Gene Johnson can strive to understand filoviruses, all humans are ultimately at the mercy of the natural order.
Chance
Chance plays a significant role in determining how a virus spreads and which characters fall victim to it. In every case, the virus strikes indiscriminately, regardless of age, occupation, or personality. This is particularly clear in the scene with Nurse Mayinga and Dr. Isaacson: while both characters treat a patient dying with Ebola Zaire, only Mayinga succumbs to the disease. Preston also takes care to highlight scenarios in which chance seems to be the only thing that prevents an individual from being exposed. When Nancy Jaax is working on Gene Johnson's Ebola experiment, the circumstances are perfectly arranged for her to be infected: the knife cut, the rip in her glove, and the breach in the wrist of her space suit. Yet, Nancy is saved by chance in the form of a thin layer of latex.
Bureaucracy
Particularly in "The Monkey House" and "Smashdown," Preston highlights the various obstacles caused by bureaucratic considerations in dealing with the outbreak at the Reston facility. Preston describes the arguments between various organizations over control and ownership of the problem, as well as highlighting Colonel Peters' job to limit publicity about the operation. In general, these discussions do little to help contain the outbreak at the Reston facility and, in some cases, even increase the potential risk to the general population. The issues with bureaucracy faced by USAMRIID and the C.D.C. are presented in sharp contrast to the steps taken by the government of Zaire in 1976, where bureaucratic discussion is replaced with immediate action to quarantine the hospital and infected villages.
Fear
Fear is the one common denominator between all characters in the book and takes on many forms over the course of the narrative, from fear of death and fear of exposure to fear of the unknown. In scenes where outbreak has already occurred, such as with Ebola Zaire in 1976, Preston is also able to use fear to reveal the inner workings of certain individuals. One example is Dr. Isaacson who is able to conquer her fear and remove her gas mask in order to treat Nurse Mayinga face-to-face. Preston also highlights the importance of fear as a tool to inspire research on hot agents. Because Gene Johnson is terrified of Ebola, even to the point of suffering recurring nightmares about exposure, he is all the more committed to locating the original source of the virus and putting extraordinary safety measures in practice.
Selfishness
Over the course of the book, Preston describes several characters who are fundamentally selfish when faced with a filovirus. Nurse Mayinga, Tom Geisbert, and Peter Jahrling are all potentially exposed to Ebola, but each character chooses to deny the possibility for selfish reasons. Mayinga is determined to travel abroad and is willing to finalize her travel papers in the city, despite potentially exposing dozens of people along the way. Geisbert and Jarhling are similarly self-involved and choose to keep their possible exposure a secret in order to avoid being quarantined in the Slammer. While neither Geibert nor Jahrling is infected, their choice is revealing, particularly when compared to the selfless actions of characters like Dr. Musoke, Dr. Isaacson, and Dr. Breman. Their behavior also indicates a possible mode of outbreak - the human desire to act out of one's self-interest rather than the good of their community.
Human Error
From the use of dirty needles at the Yambuku Mission Hospital and the hospital at Maridi, to the negligence of Hazelton Research Products in knowingly purchasing infected monkeys from the Philippines, human error can be directly connected to the majority of the outbreaks described in the book. Preston also highlights several instances in which negligence could easily have led to an outbreak under different circumstance, such as when dirty needles are left outside the Reston facility or when Dan Dalgard wraps contaminated monkey samples in mere tin foil before sending them to USAMRIID. In every case, Preston makes it clear that the potential for a devastating outbreak can be determined by a single member of the human population.
