Book Review

Virus X: Tracking the new killer plagues; Out of the present and into the future

N Engl J Med 1997; 336:1535-1536May 22, 1997

Article

Virus X: Tracking the new killer plagues; Out of the present and into the future
By Frank Ryan. 430 pp., illustrated. Boston, Little, Brown, 1997. $24.95. ISBN: 0-316-76383-7

I read Virus X: Tracking the New Killer Plagues while flying across the Pacific to study the 40th consecutive epidemic of a viral hemorrhagic fever. This one has killed tens of thousands of children and hospitalized millions of others. I paged quickly through the book to find the story of the dengue virus, a symbiont of subhuman primates that emerged as a “new” virus in the 1950s to become the cause of the most important viral hemorrhagic fever in the world. But the dengue story was told as a footnote to accounts of diseases with higher fatality rates but fewer cases.

Contagiousness and lethality lend drama to each of the real stories of emergence and recognition told here. Above all, this is a technically accurate book, clearly and interestingly written in a calm voice. Those who seek controversy, scandal, or stories of overweening pride or ambition should look elsewhere. Ryan's science detectives are square-jawed and have sparkling eyes. In a succession of brief stories, he recounts the recognition of the hantavirus pulmonary syndrome and the Machupo, Ebola, and human immunodeficiency viruses. Along the way, Ryan spices the narrative with the horrors of smallpox, the 1918 influenza pandemic, plague, flesh-eating bacteria, drug-resistant tuberculosis, and a few others in the microbial bestiary (although he gets Indian pneumonic plague hopelessly wrong).

Most of the major stories are twice told. First, we experience the epidemic from the perspectives of its initial victims, their shocked relatives, and the alternately puzzled and terrified health care workers. Given the high lethality, horrifying symptoms, and rapid downhill clinical course, the people who performed autopsies and collected specimens and dispatched them to diagnostic laboratories were brave and insightful. At the laboratories we are introduced to another group of stalwarts, who have at hand powerful molecular tools for quickly identifying viruses previously unknown to science.

For readers with a general-science background, Virus X contains simple, concise descriptions of the techniques used to identify viral genes (or, for that matter, genes from any species). The polymerase chain reaction is described step by step with enviable clarity.

A unique feature of this book is how it leads toward a grand view of the evolutionary advantages of microbial emergence. Ryan provides evidence that most emerging viruses are nonpathogenic symbionts of one or more vertebrate species but retain seldom-tested cross-species invasiveness and virulence. Symbiosis, in Ryan's view, results when ancient parasitisms evolve. The vertebrate host (or hosts) and virus coevolve in ways that reduce the risk of disease in the host and inhibit the host's destruction of the virus. Ryan notes that the abundance of viral symbionts in nature varies directly with the abundance of host species, as in the case of the Bunyaviruses in rodents in the Brazilian rain forest. The overarching message: the abundance of viral species is a correlate of diversity, not a teleologic force nature designed to prevent human beings from cutting down trees.

The centering point of Virus X is the story of virulence, a reminder of the doomsday scenario in The Andromeda Strain and other science-fiction novels and films. Doomsday for humans might occur when the virulence of an Ebola virus is coupled with the contagiousness of pneumonic plague bacteria for the respiratory tract, or for that matter with the contagiousness of today's measles virus or the 1918 influenzavirus. It turns out that we have already experienced a doomsday scenario. The 1918 pandemic of the influenzavirus, which was extremely contagious by the respiratory route, was lethal in a matter of hours, traveled literally around the world, and killed at least 20 million humans. But it did not eradicate the species.

Ryan's book may leave the reader confused about the term “emergence.” The list of emerging viruses at the end of the book is a virtual Who's Who of viral zoonoses. Emergence in this context can have many meanings: the recognition of a microbial agent through improved diagnostic techniques, which leads to the inevitable “epidemic,” as in the case of human T-cell lymphotropic virus type I; the occurrence in humans of cases of infection by a zoonotic virus that has a clear and unchanging potential to cause human disease, such as Eastern equine encephalitis; and an amplification of such zoonosis, as in the case of Lyme disease. Emergence may also refer to a new outbreak of infection by an organism of known epidemic potential but recently quiescent, as in the case of cholera; the appearance above the threshold of detection of a previously undescribed infectious disease, such as legionnaires' disease; and an old virus with new virulence, such as dengue hemorrhagic fever. Emergence also refers to cross-species infectivity resulting from an unprecedented mutation, as we saw with HIV-1 and the Ebola virus.

Scott B. Halstead, M.D.
Naval Medical Research and Development Command, Bethesda, MD 20889-5606