Looking for an Ebola Vaccine
Viral infection has been a scourge to humankind since before recorded time. The 1918 influenza pandemic led to the death of over 20 million people; smallpox was a virulent killer for thousands of years; the fear of polio, the crippler of Pres. Franklin D. Roosevelt, cleared American public pools and school playgrounds in the 1950s. The hope against viruses remains vaccines. For polio, the saviors were doctors Jonas Edward Salk and Albert Bruce Sabin, both of whom developed polio vaccines, while the collective efforts of the medical establishment worldwide led to the eradication of smallpox. Now the National Institute of Allergy and Infectious Diseases in Bethesda, Md., has announced a potential vaccine breakthrough against one of the modern world's most feared viral foes, Ebola.
Ebola is a virus of the family Filoviridae and has only one known relative, the rare and less deadly Marburg virus. Thus far four species of the Ebola virus have been identified: Ebola-Ivory Coast, Ebola-Sudan, Ebola-Zaire, and Ebola-Reston, which was made famous by Richard Preston's nonfiction book The Hot Zone. While all the species of the virus can cause illness in primates, Ebola-Reston seems to be benign to humans. The occurrences of Ebola-Ivory Coast infections have been too few to determine a credible mortality rate. Only the Sudan and Zaire species have been determined to cause highly lethal human infections; their morality rates range from 50% for Ebola-Sudan to 90% for Ebola-Zaire. Death from the Sudan and Zaire species is often presaged by a terrifying hemorrhagic fever (Ebola HF), which is characterized by the dissolving of internal organs and diffuse bleeding through virtually every orifice of the victim's body. A May 6, 2003, World Health Organization report on a recent outbreak of Ebola HF in the Congo records 143 reported infections, leading to 128 deaths.
One of the most frightening aspects of Ebola HF is its virulence against health-care workers. Since transmission of Ebola is closely associated with direct contact with blood or fluids from an infected victim, the disease often cruelly attacks those most concerned for the victim--the family and attending doctors and nurses. In some early Ebola outbreaks in Africa, health-care workers abandoned their posts and patients, fleeing in terror after observing the gruesome death of their colleagues.
Now there is news that offers hope in the fight against Ebola. As reported in the August 2003 issue of Nature, conspicuously positive results were obtained in experimental Ebola vaccine trials on monkeys. Generally, vaccines must be used for pre-exposure immunization only, because so much time is needed for the body to produce a therapeutically sufficient concentration of antibodies in the vaccinated individual. One exception to this rule, however, is the smallpox vaccine, which produces antibodies in a patient quickly enough to sometimes halt an ongoing infection.
Similarly, the new Ebola vaccine seems to have provided an unusually quick onset of protection in the test monkeys. If the same holds true in human cases, health-care workers might be able to contain ongoing outbreaks with a procedure called "ring vaccination." In such a scenario, all who have had recent contact with the infected victim would be inoculated, preventing them from passing on the infection and stopping the outbreak from spreading. Because vaccine tests in primates generally translate well to humans, researchers predict human testing could begin in 2004. If trials begin this early, the time line for producing an Ebola vaccine could be reduced by as much as a decade, thus escalating the provision of protection to health-care workers, residents of affected areas in Africa, and potential targets of Ebola bioterrorism.
Many thorny issues remain to be worked out, however. For instance, researchers question how effective the vaccine may be for persons with already impaired immune systems, such as those suffering from the human immunodeficiency virus (HIV). This issue is of no small significance, since outbreaks of Ebola are associated with African regions where HIV infection has reached epidemic proportions. Additionally, the vaccine has been created by grafting Ebola genetic material to an adenovirus, which belongs to the viral family associated with the common cold. Since colds are, in fact, quite common, 45% of the American public already displays antibodies to adenoviruses.
The general prevalence of adenovirus immune system resistance, extrapolated to the world's population, could compromise the effectiveness of an adenovirus-based Ebola vaccine. Also of concern is the fact that the vaccine may work only once in an individual recipient and that there is no data on the duration of antiviral protection after a single inoculation. Nevertheless, research continues, and the prospects for containing deadly Ebola outbreaks look positive.
Ebola is a virus of the family Filoviridae and has only one known relative, the rare and less deadly Marburg virus. Thus far four species of the Ebola virus have been identified: Ebola-Ivory Coast, Ebola-Sudan, Ebola-Zaire, and Ebola-Reston, which was made famous by Richard Preston's nonfiction book The Hot Zone. While all the species of the virus can cause illness in primates, Ebola-Reston seems to be benign to humans. The occurrences of Ebola-Ivory Coast infections have been too few to determine a credible mortality rate. Only the Sudan and Zaire species have been determined to cause highly lethal human infections; their morality rates range from 50% for Ebola-Sudan to 90% for Ebola-Zaire. Death from the Sudan and Zaire species is often presaged by a terrifying hemorrhagic fever (Ebola HF), which is characterized by the dissolving of internal organs and diffuse bleeding through virtually every orifice of the victim's body. A May 6, 2003, World Health Organization report on a recent outbreak of Ebola HF in the Congo records 143 reported infections, leading to 128 deaths.
One of the most frightening aspects of Ebola HF is its virulence against health-care workers. Since transmission of Ebola is closely associated with direct contact with blood or fluids from an infected victim, the disease often cruelly attacks those most concerned for the victim--the family and attending doctors and nurses. In some early Ebola outbreaks in Africa, health-care workers abandoned their posts and patients, fleeing in terror after observing the gruesome death of their colleagues.
Now there is news that offers hope in the fight against Ebola. As reported in the August 2003 issue of Nature, conspicuously positive results were obtained in experimental Ebola vaccine trials on monkeys. Generally, vaccines must be used for pre-exposure immunization only, because so much time is needed for the body to produce a therapeutically sufficient concentration of antibodies in the vaccinated individual. One exception to this rule, however, is the smallpox vaccine, which produces antibodies in a patient quickly enough to sometimes halt an ongoing infection.
Similarly, the new Ebola vaccine seems to have provided an unusually quick onset of protection in the test monkeys. If the same holds true in human cases, health-care workers might be able to contain ongoing outbreaks with a procedure called "ring vaccination." In such a scenario, all who have had recent contact with the infected victim would be inoculated, preventing them from passing on the infection and stopping the outbreak from spreading. Because vaccine tests in primates generally translate well to humans, researchers predict human testing could begin in 2004. If trials begin this early, the time line for producing an Ebola vaccine could be reduced by as much as a decade, thus escalating the provision of protection to health-care workers, residents of affected areas in Africa, and potential targets of Ebola bioterrorism.
Many thorny issues remain to be worked out, however. For instance, researchers question how effective the vaccine may be for persons with already impaired immune systems, such as those suffering from the human immunodeficiency virus (HIV). This issue is of no small significance, since outbreaks of Ebola are associated with African regions where HIV infection has reached epidemic proportions. Additionally, the vaccine has been created by grafting Ebola genetic material to an adenovirus, which belongs to the viral family associated with the common cold. Since colds are, in fact, quite common, 45% of the American public already displays antibodies to adenoviruses.
The general prevalence of adenovirus immune system resistance, extrapolated to the world's population, could compromise the effectiveness of an adenovirus-based Ebola vaccine. Also of concern is the fact that the vaccine may work only once in an individual recipient and that there is no data on the duration of antiviral protection after a single inoculation. Nevertheless, research continues, and the prospects for containing deadly Ebola outbreaks look positive.
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