A decade after smallpox was eradicated as a human disease, polio, the feared crippler of children, is being targeted for a similar fate.
The task is likely to be far more daunting than the conquest of smallpox and faces uncertain prospects for success. Improved polio vaccines, improved sanitary conditions and better health services may all be necessary
Many Western nations, including the United States, appear to have eliminated the natural polio virus. But the virus is still responsible for about 250,000 cases of paralysis worldwide each year, primarily in Africa and Asia, as well as minor or inapparent illnesses in perhaps 25 million additional children.
Nevertheless, global polio eradication is receiving increasing attention. Mass immunization campaigns in Brazil, Mexico and other Latin American nations have dramatically curtailed polio cases. Within the next 2 1/2 years, public health officials hope to eliminate the natural polio virus from the Western Hemisphere and all of Europe.
A clarion call for eradicating polio worldwide by the end of the century, first sounded by a group of international experts on child health in March, is expected to be a focus of discussion later this week at the annual Geneva meeting of the World Health Assembly, the 166-member nation governing body of the World Health Organization.
"The progress achieved in immunization is so heartening that people are now willing to consider this," said Dr. Ralph H. Henderson, the director of the WHO's expanded program on immunization. "It would be a lovely gift from this century to the next if we could move in without either smallpox or polio."
But a strong note of caution was sounded by Dr. Donald A. Henderson, the dean of Johns Hopkins University School of Hygiene and Public Health in Baltimore and previously the director of the WHO's smallpox eradication unit.
"I am not enthusiastic about setting a goal (for global polio eradication) that is just not obtainable," Johns Hopkins' Henderson said in a recent interview. He said international public health officials were "seriously discredited" by the abysmal failure of a 1955 World Health Assembly initiative to eradicate malaria, as were American public health officials by the failure of a 1977 initiative to eradicate measles in the United States.
"A target date of 1995 (for polio eradication) is totally unrealistic," Dr. Donald Henderson added. "We might set the year 2000 . . . but without a better vaccine we can't do it." Similar concerns are shared by Joseph L. Melnick, chairman of the department of virology at Baylor College of Medicine in Houston and a leading polio researcher. The year 2000 is a "romantic" and "worthy" goal, he said, but "that is not the right time frame."
For an infectious disease to be \o7 eradicated--\f7 not simply \o7 controlled--\f7 the natural transmission of the germ that causes it must cease entirely. Then this result must be verified over several years.
Once eradication is confirmed, all control efforts against a germ, such as mass immunizations, can be discontinued as has been the case with the smallpox vaccine. This is because the germ is no longer present either in human beings or in the environment.
Guinea Worm Disease
The germs most likely to be eradicated are those that infect only humans and that will not recur after the initial infection.
These germs include smallpox and polio. (In 1986, the World Health Assembly also set a goal of eradicating guinea worm disease, which causes painful skin ulcers. It occurs in rural areas of the Indian subcontinent and Africa, where the worm contaminates drinking water.)
The smallpox virus causes an illness marked by high fever, exhaustion and a blister-like rash. As recently as 1967, it was responsible for about 10 million to 15 million cases and 2 million deaths in developing countries each year, primarily in Asia and Africa.
In October, 1977, after an intensive international effort, the last case of naturally transmitted smallpox was discovered--in a 23-year-old hospital cook in Somalia in Africa. Over a period of several years, a global commission painstakingly certified smallpox eradication. Ten years later, samples of the virus exist only in high-security laboratories in Moscow and at the U.S. Centers for Disease Control in Atlanta.
The prospects for polio and smallpox eradication were authoritatively compared in a 1984 article in the Reviews of Infectious Diseases by Dr. James Chin of the California Department of Health Services, who is now an official with the WHO's Global Program on AIDS.
According to Chin, a key to the successful smallpox eradication drive was an effective one-dose vaccine using the vaccinia, or cowpox, virus. This vaccine retained its potency even when stored at body temperature for up to 30 days.