Hemorrhagic fevers have been known in Africa since well before the continent was dubbed "the white man's grave," an expression that, when deployed in reference to a region with high rates of premature death, speaks volumes about the differential valuation of human lives. Ebola itself was isolated fully two decades ago (14). Its appearance in human hosts has at times been insidious but more often takes the form of explosive eruptions. In accounting for recent outbreaks, it is unnecessary to postulate a change in filovirus virulence through mutation. The Institute of Medicine lists a single "factor facilitating emergence" for filoviruses: "virus-infected monkeys shipped from developing countries via air" (2).

Other factors are easily identified. Like that of many infectious diseases, the distribution of Ebola outbreaks is tied to regional trade networks and other evolving social systems. And, like those of most infectious diseases, Ebola explosions affect, researchers aside, certain groups (people living in poverty, health care workers who serve the poor) but not others in close physical proximity. Take, for example, the 1976 outbreak in Zaire, which affected 318 persons. Although respiratory spread was speculated, it has not been conclusively demonstrated as a cause of human cases. Most expert observers thought that the cases could be traced to failure to follow contact precautions, as well as to improper sterilization of syringes and other paraphernalia, measures that in fact, once taken, terminated the outbreak (15). On closer scrutiny, such an explanation suggests that Ebola does not emerge randomly: in Mobutu's Zaire, one's likelihood of coming into contact with unsterile syringes is inversely proportional to one's social status. Local élites and sectors of the expatriate community with access to high-quality biomedical services (viz., the European and American communities and not the Rwandan refugees) are unlikely to contract such a disease.

The changes involved in the disease's visibility are equally embedded in social context. The emergence of Ebola has also been a question of our consciousness. Modern communications, including print and broadcast media, have been crucial in the construction of Ebola—a minor player, statistically speaking, in Zaire's long list of fatal infections—as an emerging infectious disease (16). Through Cable News Network (CNN) and other television stations, Kikwit became, however briefly, a household word in parts of Europe and North America. Journalists and novelists wrote best-selling books about small but horrific plagues, which in turn became profitable cinema. Thus, symbolically and proverbially, Ebola spread like wildfire—as a danger potentially without limit. It emerged.

TB is said to be another emerging disease, in which case, emerging is synonymous with reemerging. Its recrudescence is often attributed to the advent of HIV—the Institute of Medicine lists "an increase in immunosuppressed populations" as the sole factor facilitating the resurgence of TB (2)—and the emergence of drug resistance. A recent book on TB, subtitled "How the battle against tuberculosis was won—and lost," argues that "Throughout the developed world, with the successful application of triple therapy and the enthusiastic promotion of prevention, the death rate from tuberculosis came tumbling down" (17). But was this claim ever documented? Granted, the discovery of effective anti-TB therapies has saved the lives of hundreds of thousands of TB patients, many in industrialized countries. But TB—once the leading cause of death among young adults in the industrialized worldw—as already declining there well before the 1943 discovery of streptomycin. In the rest of the world, and in pockets of the United States, TB remains undaunted by ostensibly effective drugs, which are used too late, inappropriately, or not at all: "It is sufficiently shameful," notes one of the world's leading authorities on TB, "that 30 years after recognition of the capacity of triple-therapy . . . to elicit 95%+ cure rates, tuberculosis prevalence rates for many nations remain unchanged" (18). Some estimate that more than 1.7 billion persons are infected with quiescent, but viable, Mycobacterium tuberculosis and, dramatic shifts in local epidemiology aside, a global analysis does not suggest major decreases in the importance of TB as a cause of death. TB has retreated in certain populations, maintained a steady state in others, and surged forth in still others, remaining, at this writing, the world's leading infectious cause of adult deaths (19).

At mid-century, TB was still acknowledged as the "great white plague." What explains the invisibility of this killer by the 1970s and 1980s? Again, one must turn to the study of disease awareness, that is, of consciousness and publicity, and their relation to power and wealth. "The neglect of tuberculosis as a major public health priority over the past two decades is simply extraordinary," wrote Murray in 1991. "Perhaps the most important contributor to this state of ignorance was the greatly reduced clinical and epidemiologic importance of tuberculosis in the wealthy nations" (20). Thus TB has not really emerged so much as emerged from the ranks of the poor (21,22). An implication, clearly, is that one place for diseases to hide is among poor people, especially when the poor are socially and medically segregated from those whose deaths might be considered more important.

When complex forces move more poor people into the United States, an increase in TB incidence is inevitable. In a recent study of the disease among foreign-born persons in the United States, immigration is essentially credited with the increased incidence of TB-related disease (23). The authors note that in some of the immigrants' countries of origin the annual rate of infection is up to 200 times that registered in the United States; moreover, many persons with TB in the United States live in homeless shelters, correctional facilities, and camps for migrant workers. But there is no discussion of poverty or inequality, even though these are, along with war, leading reasons for both the high rates of TB and for immigration to the United States. "The major determinants of risk in the foreign-born population," conclude the authors, "were the region of the world from which the person emigrated and the number of years in the United States."

To understand the complexity of the issues—medical, social, and communicational—that surround the emergence of a disease into public view, consider AIDS. In the early 1980s, the public was informed by health officials that AIDS had probably emerged from Haiti. In December 1982, for example, a physician affiliated with the National Cancer Institute was widely quoted in the popular press stating that "We suspect that this may be an epidemic Haitian virus that was brought back to the homosexual population in the United States" (24). This proved incorrect, but not before damage to Haitian tourism had been done. Result: more poverty, a yet steeper slope of inequality and vulnerability to disease, including AIDS. The label "AIDS vector" was also damaging to the million or so Haitians living elsewhere in the Americas and certainly hampered public health efforts among them (25).

HIV disease has since become the most extensively studied infection in human history. But some questions are much better studied than are others. And error is worth studying, too. Careful investigation of the mechanisms by which immodest claims are propagated (as regards Haiti and AIDS, these mechanisms included "exoticization" of Haiti, racism, the existence of influential folk models about Haitians and Africans, and the conflation of poverty and cultural difference) is an important yet neglected part of a critical epistemology of emerging infectious diseases. Also underinvestigated are considerations of the pandemic's dynamic. HIV may not have come from Haiti, but it was going to Haiti. Critical reexamination of the Caribbean AIDS pandemic showed that the distribution of HIV does not follow national borders, but rather the contours of a transnational socioeconomic order. Furthermore, much of the spread of HIV in the 1970s and 1980s moved along international "fault lines," tracking along steep gradients of inequality, which are also paths of migrant labor and sexual commerce (26).

In an important overview of the pandemic's first decade, Mann and co-workers observe that its course "within and through global society is not being affected—in any serious manner—by the actions taken at the national or international level" (27). HIV has emerged but is going where? Why? And how fast? The Institute of Medicine lists several factors facilitating the emergence of HIV: "urbanization; changes in lifestyles/mores; increased intravenous drug abuse; international travel; medical technology" (2). Much more could be said. HIV has spread across the globe, often wildly, but rarely randomly. Like TB, HIV infection is entrenching itself in the ranks of the poor or otherwise disempowered. Take, as an example, the rapid increase in AIDS incidence among women. In a 1992 report, the United Nations observed that "for most women, the major risk factor for HIV infection is being married. Each day a further three thousand women become infected, and five hundred infected women die" (28). It is not marriage per se, however, that places young women at risk. Throughout the world, most women with HIV infection, married or not, are living in poverty. The means by which confluent social forces, such as gender inequality and poverty, come to be embodied as risk for infection with this emerging pathogen have been neglected in biomedical, epidemiologic, and even social science studies on AIDS. As recently as October 1994—15 years into an ever-emerging pandemic—a Lancet editorial could comment, "We are not aware of other investigators who have considered the influence of socioeconomic status on mortality in HIV-infected individuals" (29). Thus, in AIDS, the general rule that the effects of certain types of social forces on health are unlikely to be studied applies in spite of widespread impressions to the contrary.

AIDS has always been a strikingly patterned pandemic. Regardless of the message of public health slogans—"AIDS is for Everyone"—some are at high risk for HIV infection, while others, clearly, are at lower risk. Furthermore, although AIDS eventually causes death in almost all HIV-infected patients, the course of HIV disease varies. Disparities in the course of the disease have sparked the search for hundreds of cofactors, from Mycoplasma and ulcerating genital lesions to voodoo rites and psychological predisposition. However, not a single association has been compellingly shown to explain disparities in distribution or outcome of HIV disease. The only well-demonstrated cofactors are social inequalities, which have structured not only the contours of the AIDS pandemic, but also the course of the disease once a patient is infected (30–33). The advent of more effective antiviral agents promises to heighten those disparities even further: a three-drug regimen that includes a protease inhibitor will cost $12,000 to $16,000 a year (34).

Ebola, TB, and HIV infection are in no way unique in demanding contextualization through social science approaches. These approaches include the grounding of case histories and local epidemics in the larger biosocial systems in which they take shape and demand exploration of social inequalities. Why, for example, were there 10,000 cases of diphtheria in Russia from 1990 to 1993? It is easy enough to argue that the excess cases were due to a failure to vaccinate (35). But only in linking this distal (and, in sum, technical) cause to the much more complex socioeconomic transformations altering the region's illness and death patterns will compelling explanations emerge (36,37).

Standard epidemiology, narrowly focused on individual risk and short on critical theory, will not reveal these deep socioeconomic transformations, nor will it connect them to disease emergence. "Modern epidemiology," observes one of its leading contributors, is "oriented to explaining and quantifying the bobbing of corks on the surface waters, while largely disregarding the stronger undercurrents that determine where, on average, the cluster of corks ends up along the shoreline of risk" (13). Neither will standard journalistic approaches add much: "Amidst a flood of information," notes the chief journalistic chronicler of disease emergence, "analysis and context are evaporating . . . Outbreaks of flesh eating bacteria may command headlines, but local failures to fully vaccinate preschool children garner little attention unless there is an epidemic" (38).

Research questions identified by various blue-ribbon panels are important for the understanding and eventual control of emerging infectious diseases (39,40). Yet both the diseases and popular and scientific commentary on them pose a series of corollary questions, which, in turn, demand research that is the exclusive province of neither social scientists nor bench scientists, clinicians, or epidemiologists. Indeed, genuinely transdisciplinary collaboration will be necessary to tackle the problems posed by emerging infectious diseases. As prolego-mena, four areas of corollary research are easily identified. In each is heard the recurrent leitmotiv of inequality: