Vaccines: Preventing Illness, Saving Lives
The role of animal research in vaccine development for humans and animals
AN IMPORTANT CONTEMPORARY ISSUE:
Developing and producing vaccines to protect against bioterrorism
The tragic events of September 11, 2001, have fundamentally changed how the United States views the threat of biological attacks. Biological weapons, composed of either bacteria, viruses, or microbial toxins, can be used against civilian and farm animal populations to terrorize and harm our way of life. Medical experts estimate that these agents, some of which are stockpiled at various sites around the world, pose a very real threat. Consequently, the U.S. and other countries continue to carry out research on a variety of dangerous microbes in order to develop vaccines (and other biologicals) to counteract terrorism and combat natural outbreaks of highly contagious diseases.
Indeed, actions to address the threat of deliberately introducing a disease causing agent into a population have taken on a new urgency. This topic is the current focus of national planning efforts by agencies of the federal government responsible for protecting the public, e.g., the Department of Health and Human Services, including the National Institutes of Health, the Food and Drug Administration, and the Centers for Disease Control and Prevention; the Department of Defense; and the National Academy of Sciences. The common goal is to prepare for and respond to acts of bioterrorism.
Category A: Among the 20 or so potential bioweapons, smallpox, anthrax, and plague have generated the highest level of worry. These are followed by botulism, tularemia, and hemorrhagic fevers. A committee of experts has judged that these agents pose a high risk to national security because they have the potential for major public health impact, the greatest number of deaths and economic losses, and psychological damage. Other agents considered to be of somewhat lesser importance have been placed in Category B and Category C. They will not be discussed in this brochure. (See article -November 2000, New Frontiers: Biowarfare, Bioterrorism: Are We Prepared?)
Vaccines to Combat Bioterrorism - Category A Agents.
Smallpox (Variola major). This virus is considered one the most dangerous potential weapons. It causes fever and a rash on the face, neck and arms progressing to pustular lesions and scabs. Death results in 30 percent of cases. This disease was effectively eradicated in the late 1970s, and vaccination has not been required since 1972. The smallpox virus is contained in a few research laboratories. Since 1983, the U.S. has about 200 million doses of the Dryvax vaccine. Fortunately, the vaccine has retained its potency and recent tests indicate that it can be diluted ten-fold and still confer protection.
Until now, vaccination has been recommended only for persons who are at high risk for infection because the vaccine can cause serious complications such as fever and severe local reactions, some of which can be life threatening to some groups, such as persons with immune deficiencies. Whether the federal government should make smallpox vaccine widely available in the current situation is still under debate, but a panel of medical experts has concluded that nationwide vaccination for Americans is too risky. Advance smallpox vaccination would reduce the number of people ultimately infected in an attack by bioterrorists, but itself would cause some serious side effects and a small number of deaths, raising a question about the ethical consequences of wholesale immunization.
While a newer vaccine is under development, it is not ready for use at this time. The virus must be produced in cell culture using FDA approved reagents and tested for safety and efficacy in appropriate animal models, a process that may take at least two years.
Anthrax (Bacillus anthracis). The bacterium causing anthrax produces stable spores that remain viable and infective in the soil for years. The spores are easily aerosolized increasing their ability to be inhaled by people. Anthrax occurs naturally in hoofed animals and uncommonly infects humans who have contact with contaminated animal products. Its potential as a biological weapon has been recognized for many years. Inhaled spores germinate and release toxins that cause pulmonary disease. Unless the victim gets early antibiotic treatment, the disease is almost always fatal. Experts estimate that spores sprayed into the air could be dispersed over long distances infecting and killing thousands of people. Research on monkey models advanced to the development of anthrax vaccines in 1970. The currently available vaccine has been used to vaccinate some U.S. military personnel; however; it is not available for civilian use. Anthrax assaults delivered in mailed letters in 2001 have led to significant interest in the development of new vaccines as counter-measures for combating this problem. Scientists are seeking new knowledge of how the anthrax organism causes disease in order to develop strategies for new vaccine candidates that require fewer doses.
Plague (Yersinia pestis). As early as 541 AD, bubonic plague swept Egypt and the rest of the world, killing between 50 and 60 percent of the population. In 1346, a second plague, known as the "Black Death" killed millions. The bubonic form of the plague is spread to humans by fleas found on infected rats. It is so named because it causes the swelling of lymph glands in the armpits and groin called "buboes." The pneumonic form of plague is easily readily transmitted from person-to-person through face-to-face contact and is therefore considered a dangerous biological weapon. Early antibiotic administration is essential for successful treatment. There are ongoing research efforts to find and develop a vaccine to protect against this highly dangerous disease. Vaccination with the killed vaccine reduces the severity of the disease but does not prevent the pneumonic form.
Botulism (Clostridium botulinum). This bacterium produces a highly lethal toxin that binds to nerve endings and paralyzes muscle. Ordinarily, people are exposed to the toxin after eating contaminated food. Treatment consists of the administration of antitoxins produced in horses. Botulinum toxoid is available in limited quantities and is only used to protect laboratory workers.
Tularemia (Francisella tularensis). This bacterial agent causes fever, headache, chills, aches, and sore throat, symptoms that worsen and lead to incapacitation and ultimately, death. Airborne tularemia has been recognized for some time as a potential biological weapon because it is highly infectious and easy to disseminate. During the cold war, both the East and West created strains that are resistant to antibiotics. The U.S. has a live, attenuated vaccine, which until recently has only been used to immunize laboratory workers who might be exposed to the disease; however, the vaccine is not effective after exposure.
Hemorrhagic Fever Viruses (Filoviruses-Ebola and Marburg). Ebola hemorrhagic fever is one of the most virulent viral diseases known, killing its victims 50-90% of the time. The natural reservoir of the Ebola virus is the rain forests of Africa and Asia, but scientists have not yet learned how outbreaks occur. Up to now, most human infections have resulted from contact with nonhuman primates who are infected from the natural reservoir. No vaccine or specific treatment exists; however, researchers are attempting to develop a DNA vaccine using selected genes of the virus.
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