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The many-headed hydra is always out there’
While much fear and consternation swirls around the possibilities of bioterrorism, it is wise to remember that the greatest biological killers occur naturally in the form of emerging and reemerging infections.
"The worst bioterrorist can actually be nature itself," said Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health in Bethesda, MD. Fauci spoke on the subject recently in San Diego at the Interscience Conference on Antimicrobial Agents and Chemotherapy. "A classic, truly emerging disease, HIV, originated in sub-Sahara Africa. A reemerging disease, West Nile virus, landed in the East Coast of the United States and is now permeating our entire country. [There are] multiple different types of antibiotic-resistant tuberculosis, malaria, staphylococcus, enterococcus — all emerging and reemerging diseases. It is a continuing spectrum. Just this past summer we had an extraordinary outbreak in Madagascar of flu with a very, very high case fatality rate. Again, it just reminds us of what’s out there."
Yet the fear factor is strikingly different between bioterrorism and natural disease, though the patient outcomes may be far worse with the latter. The anthrax attacks disrupted government and instilled widespread fear, but the death toll was five people. Compare that to West Nile virus, which has infected 2,200 people and killed 108 of them since it first appeared in North American in 1999. Endemic in some parts of the world, the virus is a classic example of a reemerging microbe, Fauci noted. Having now reached the West Coast of the United States after first appearing in New York, West Nile virus is digging into new niches and at times causing a "polio-like" syndrome. "[We are seeing] that it is transmitted by organ transplantation and likely by blood transfusion. More recently genetic elements of West Nile were isolated from the breast milk of an infected mother," Fauci said.
The death toll of natural occurring epidemics has been staggering. "The flu pandemic of 1918 killed [more than] 25 million people worldwide, 750,000 in the United States," he said. "HIV/AIDS — 60 million people thus far infected, 20 million of whom are dead. The projections are that 45 million more people will be infected in the next 10 years and [there will be] 75 million deaths in the next 20 years." While bioterrorism scenarios remain the prime topic of discussion, the world actually flirted with a huge biological disaster when the avian flu strain H5N1 emerged in Hong Kong a few years ago. Stamped out quickly by public health officials, the unusual strain had the potential to achieve pandemic status.
"The  flu pandemic is a most extraordinary stamp on our history," Fauci said. "Those of us in the field of public health and emerging disease, if there’s one thing that we’re concerned about, it’s the next flu pandemic. That’s something that would be naturally occurring if it does occur — hopefully, naturally occurring — but it will be something that could have an impact that totally transcends some of the [bioterrorism] things that we’re talking about. We saw little blips of that with the avian flu strain that first emerged in Hong Kong, but that was jumped on by the [Centers for Disease and Prevention] and the Chinese authorities in a manner that actually interrupted what potentially could have been a catastrophe."
In addition, diseases of zoonotic origin such as HIV constantly threaten to "jump species" and become an infecting agent in humans. "So it was not surprising that [HIV] happened, but what it resulted in is an enormous pandemic that is ranking among the worst in history."
In contrast, natural occurring viral hemorrhagic fevers (e.g., Ebola, Marburg, and Lhasa) are more a threat to health care workers treating victims than the general population, he added. "Although Ebola is a terrible disease, the most vulnerable people are the physicians, nurses, and health care providers who take care of [the infected] — not the people who are out in the community," he said. "Because by the time someone gets to the point of spreading Ebola, they’re generally so sick they can’t get out of bed. So it’s a big horror’ microbe but not necessarily [a risk] of spreading from person to person." That transmission factor may make Ebola a less likely choice as a bioterror weapon, "but then there are other ways of spreading disease," Fauci warned. The intersection between natural infection and bioterrorism occurs most dramatically with smallpox, an ancient scourge that has been eradicated in nature but lives on as a prospect of war. There are few microbes that rival the impact on civilization of smallpox, which has been identified in DNA analysis on the mummy of the Pharaoh Ramses. In the context of world history, the last few smallpox-free decades are strikingly brief.
"Back as early as the early 1900s, there were a lot of cases in the United States — almost 50,000 cases from 1900 to 1904," he said. "Importantly, the last reported case in the United States was in 1949, and we stopped vaccinating in 1972."