Donald Henderson remembers a time when he almost had to
"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
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
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,
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
"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
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
"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."