Emerging Infections
Could Be Next

Mike Field
Staff Writer
Donald Henderson remembers a time when he almost had to change careers.

"I was a young infectious disease epidemiologist working at the Public Health Services' Communicable Disease Center in the 1960s when the U.S. surgeon general declared the war against these diseases to be effectively at an end," he recounted at the first Medical Institutions Humanities Series lecture of the 1996-97 season. "He suggested we should look to heart disease and cancer as the last great frontiers of medicine."

Luckily, Henderson, a former dean of the School of Public Health and now a Hopkins Distinguished Service Professor, decided to stick with what he already knew. From 1966 to 1977 he directed the World Health Organization's smallpox eradication campaign. The last reported case of the one-time pandemic killer was reported the year Henderson left WHO to come to Hopkins. In 1980 worldwide eradication of the disease was certified, marking the first time a major epidemic disease had been erased from the planet.

There was, for a brief period, a growing belief in the industrialized world that the surgeon general had been right: the problems of infectious diseases were nearing their end. "The irony, of course, was that the certification of the eradication of smallpox occurred just months before the first identification of the disease AIDS," he said.

Eventually, it was to be a discovery that would turn the medical world upside down.

Henderson spoke Oct. 9 in East Baltimore's Mountcastle Auditorium as the first in four lectures concerning "The Fourth Horseman: The Culture of Epidemics," sponsored by the Medical Institutions' Office of Cultural Affairs. The series concludes with a two-part colloquium Dec. 4.

In his lecture, titled "The Future of Epidemics," Henderson offered compelling evidence to suggest that the former surgeon general's rosy prediction was not only wrong, it was exactly the opposite of what was beginning already to happen.

"The outbreak of AIDS and some subsequent diseases has caused most of us to rethink our former optimism," he said. "Recall that in 1981, with the identification of AIDS as a communicable disease, there was still a great deal of scientific hubris. In April of 1984 secretary of health and human services Margaret Heckler announced the discovery of the virus and predicted we'd have a vaccine in five years. Robert Gallo outdid her and predicted we'd have it in two."

Henderson stopped to look at his audience, some of whom were shaking their heads at the memory.

"Well here it is 13 years later, we're spending more than $1 billion per year in research, and still there's no vaccine, even in clinical trials. It's not very encouraging."

[Editorial Note: This article was published on October 14, 1996. It is now more than ten years later, so the preceding paragraph should begin, "Well here it is 23 years later . . ."]

This "sobering recognition" led the National Institutes of Health and Rockefeller University to convene a meeting of 45 top researchers and scientists in 1989 to consider the prospects for the outbreak of other infectious diseases. Henderson was invited, in part owing to the work he had done in smallpox eradication.

"One of the things we had to contemplate was the AIDS virus itself," he said. "What if a very small change in the genetic structure had made it a pneumonic disease like influenza--one that is spread very easily--instead of one that can only be transmitted with relative difficulty? With a 10-year incubation period it is entirely conceivable it would have created worldwide devastation."

The subsequent outbreaks of Ebola virus in Sudan and Zaire only highlighted that possibility. Extremely virulent diseases, those outbreaks have registered death rates of 80 to 90 percent, said Henderson.

And the virulence of that disease is not unprecedented, according to the best estimates science can currently make. Although records are extremely sketchy, the bubonic plague that swept Europe from 1346 to 1350 killed from one-third to one-half of the entire population.

"Not only that, but thereafter it would return periodically to kill more," Henderson said. "Population levels are thought to have continued to decline until the end of the century, and it wasn't until 1650--three hundred years later--that Europe regained its former population levels.

The introduction of smallpox into the Americas at the beginning of the age of transoceanic exploration was even more devastating. "Before this, it is estimated the Americas had a population of between 50 and 75 million," he said. "Over the course of 75 years the population declined by somewhere between 75 and 90 percent." In one relatively well-documented case in southern Florida, the native population declined by 95 percent from 1515 to 1620.

"These kinds of population devastation could destroy the fabric of civilization as we know it," he said. "The virulence of microbes, even in this century, should not be underestimated. Consider that during the 20th century alone it is estimated that some 100 million died as a result of armed conflict. Smallpox alone killed at least twice this number, and in the 1918 influenza pandemic alone, an estimated 21 million died."

Even though there is ample precedence for catastrophic infectious diseases, the scientists gathered at the NIH/Rockefeller University meeting still felt uneasy with the concept of a modern outbreak. "It sounded a little too much like an Andromeda-strain scenario," he said, referring to the Michael Crichton book about killer microbes from outer space. "We all got the feeling that somehow this doesn't wash."

One outcome of the meeting was the creation of a National Sciences Academy committee charged with identifying emerging infections that posed possible risks in America. In 1992 the committee stunned many in the scientific community by issuing a report on emerging infections identifying no fewer than 27 viruses, 17 bacteria and 10 protozoa that pose an immediate or near-term threat. Not all are fatal, and few have the kinds of mortality rates associated with some plagues of the past.

But all are becoming increasingly troublesome every year. Infectious diseases such as Lyme disease, racoon rabies, hanta virus pulmonary syndrome and drug-resistant staphylococcus have come from virtually nowhere to become measurable health problems in a matter of only a few years. And the evolving consensus is that more are likely to follow.

Henderson identified five relatively recent developments that act to encourage the spread of infectious diseases, ranging from an increase in international travel to the creation of hundreds of new hospitals that can actually serve as a focus for disease transmission.

"But the single most significant factor has been unprecedented population growth, especially in the densely packed urban areas," he said. "In 1950 there were only two cities, New York and London, with populations of 7.5 million or more. By contrast, by the year 2000 there will be an estimated 30 such population centers, and seven with more than 15 million people."

Moreover, the largest number of these new population centers are located in developing countries, many of them tropical, where hot, moist weather, severe overcrowding and a general absence of clean water, proper sanitation and other public health precautions prove a fertile breeding ground for the rapid spread of disease.

"Epidemics depend on a large population in contact constantly to spread and maintain a high level of infection," Henderson said. "A great deal more has changed in the last 50 years than is generally realized, and change is now ocurring exponentially. The chance of major outbreaks of infectious disease increases yearly. What form these diseases will take, only time will tell."