Smallpox and Ebola Viruses as Agents of Bioterrorism
National Institute of Allergy and Infectious Diseases, NIH
About the Lecture
Smallpox virus was one of the most fearsome pathogens of all time; in the 20th century alone, it was responsible for over 100 million deaths. The naturally occurring disease was eradicated from the planet by the World Health Organization through an intensive vaccination campaign. Yet the threat of smallpox looms large, because of its potential to be used as a weapon of bioterrorism. Intensive vaccination will probably not control a deliberate release, and the vaccine has serious side effects for immunocompromised individuals. Thus an improved vaccine and antiviral drugs are urgently needed to counter the threat. How does one study an eradicated disease? An interagency group has developed a primate model using authentic smallpox virus in closely controlled studies at the Centers for Disease Control. Through evaluation of infected primates, we now have insight into the nature of the “toxemia” clinicians used to describe fatal smallpox decades ago. By comparison with other exotic and lethal viral infections, Ebola in particular, we have identified some common threads of pathogenesis which provide targets for generic intervention into entire classes of viral agents with bioterrorist potential.
About the Speaker
PETER JAHRLING is Scientific Adviser and Senior Research Scientist at the United States Army Medical Research Institute of Infectious Diseases (USAMRIID). He is Head of the WHO collaborating centre on arbovirus and hemorrhagic fever virus research at USAMRIID, a member of the Committee on Return of Biological Samples of the National Research Council, CDC/NIH Guest Editor for Biosafety in Microbiological and Biomedical Laboratories, 3rd and 4th editions, and Chairman, Subcommittee on Laboratory Safety, American Committee on Arthropod-borne Viruses.
President Robert Hershey called the 2,192nd meeting of the Philosophical Society of Washington to order in the Powell Auditorium of the Cosmos Club at 8:16 pm April 22, 2005.
The minutes of the 2,191st meeting were read and approved.
Mr. Hershey introduced the speaker of the evening, Mr. Peter Jahrling. Mr. Jahrling is chief scientist of the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health. Mr. Jahrling spoke on “Smallpox and Ebola Viruses as Agents of Bioterrorism.”
Emerging infections arise, Mr. Jahrling said, by unnatural means. New organisms have always arisen or evolved as a result of adaptation or environmental pressures. New pressures come from the extension of civil engineering into new geography, international travel, political instability, natural disasters (often involving sanitation), war and famine and displaced persons that result from them, and intentional release. Only the last is the action of terrorists. The reality of bioterrorism did not sink in until anthrax attacks of 2001.
In the past 10 - 15 years, new viruses that have broken out include the
Hantavirus Outbreaks in the U.S.,
Ebola-related Reston Filovirus,
Andes Virus - Argentina,
Ebola - Ivory Coast, Zaire, Gabon, Uganda, Sudan,
SARS – China, Canada, (world-wide?),
Monkeypox, almost indistinguishable from smallpox,
Marburg Virus (Angola) –presently ongoing,
Influenza H5N1 (poised to emerge)
Mr. Jahrling said he never wanted to work with ebola. There is no treatment for it, it is fatal, and results in a gruesome death.
He gave several examples of how tricky and dangerous it is to work with these viruses. One of them was the dying golden tamarinds at the National Zoo. It turned out to be a virus which was being transmitted to the tamarinds by the baby mice the caretaker was feeding them. The tamarinds were being bred and some of the infected ones had been scheduled to be shipped to Brazil. It was a narrow escape that they were not.
Monkeypox came to the United States in a shipment of Giant Gambian rats. Here they were cohoused with prairie dogs, and the prairie dogs were sold as pets in the Midwest. Humans were infected by prairie dog bites. A disturbing fact was that it was extant in the country for about 30 days, even though the symptoms look very much like smallpox, before it was reported to appropriate authorities. It infected 30 people in 15 states. It was just fortunate that it happened to be a weak strain of the monkeypox virus.
Smallpox was declared dead in 1980. The campaign to defeat it was successful because it has no natural reservoir; it has only one natural host, humans. Its last vestiges were wiped out in Africa by identifying cases and then sending in teams to vaccinate everyone the infected person came in contact with.
At that time, however, the Soviet Union was manufacturing it. They were making 20 tons of smallpox every six months. They were planning to put it in the nose cones of missiles to wipe out any survivors of a nuclear war. That was Russian military doctrine. They say they don't do it any more, and Mr. Jahrling believes that, but we can only wonder if all that material has been effectively destroyed, although the evidence he has seen has not been very alarming. They also produced anthrax, and an accidental release of that killed 80 people downstream.
There was an outbreak of smallpox in Kazakhstan in 1971. It originated in the Russian smallpox factory on an island in the Aral Sea. The man who communicated it had been vaccinated, but for some reason the vaccination was ineffective.
He described a planning exercise called “Dark Winter.” It assumes 3000 people are exposed to smallpox in simultaneous attacks on three shopping centers in different states. Since 42% of the population have never been vaccinated, and assuming that each case exposes ten others and that only 15 million doses of vaccine are available, by the fourth generation of the disease, in nine weeks, three million people would have caught smallpox and one million would have died. The exercise demonstrated two important points: the lack of vaccines limits management options in dealing with diseases, and the United States lacks the resources to deal with a mass outbreak of smallpox, or indeed any contagious bioterrorism agent. As an interim policy, the best they could do is targeted vaccination of contacts. Asymptomatic contacts would be monitored but not isolated. Any delay in vaccination would increase mortality greatly.
Smallpox, he concludes, is a very credible agent of terrorism. Ring vaccination would be only a partial solution to a large or multi-centered attack. Mass vaccination, it appears, works better than targeted vaccination, largely because of the time required to find the people at risk.
There is surprisingly little material around to show what smallpox looks like. They do have a preserved human arm and, of course, there are old pictures.
They are working to develop an animal model of the disease. People in moon suits have infected monkeys in labs of the Centers for Disease Control. Another answer is variola in monkeys. It looks much like smallpox and its spread appears to be very similar. It appears that they are not contagious until they are obviously sick.
They did a study of the effectiveness of cidofovir against variola. A massive variola exposure resulted in death for all the controls. Three of the six treated animals survived, but they were the ones treated at 24 hours after infection. The three treated at 12 hours all died.
An aerosol attack was not very effective. It takes too much variola material to infect monkeys through the air.
He showed some pictures of monkeys with variola and of humans with smallpox. Both are pretty scary. His description was “Really ugly.” The infection produces nasty, boil-like sores all over, inside and out. Mr. Jahrling concluded that effective countermeasures against smallpox terrorism can be developed through research by an international community of scientists. They will presumably include better vaccines, antiviral drugs, and methods to distribute and use them.
Mr. Hershey made the usual announcements. Finally, at 9:46 pm, he adjourned the 2,192nd meeting to the social hour.
Weather: misty to sprinkly
Ronald O. Hietala,