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 eradicated-- not simply controlled-- 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.
By comparison, polio vaccines must be given in multiple doses and kept cold to maintain their potency. They must be effective against all three strains of the polio virus; the failure of a vaccine to protect against one of the strains led to a 1986 Brazil epidemic involving more than 300 paralytic cases.
The low-cost and easily administered oral polio vaccine is the most widely used polio immunization. But because it is a weakened variant of the natural polio virus, it can on occasion mutate to more virulent forms. As a result, it is associated with a handful of paralysis cases each year in many countries, including the United States.
Smallpox eradication was also facilitated by the fact that people infected with the virus almost always became sick, Chin wrote. In addition, transmission of the virus usually required contact with the respiratory secretions and the skin rash of a smallpox patient. Therefore, the disease could be contained by selectively vaccinating individuals around smallpox patients.
By comparison, infection with the polio virus is usually asymptomatic; only about one in several hundred infected individuals develop paralysis. In addition, the virus can easily be transmitted through food and water contaminated with human feces, as well as close person-to-person contact. By the time a single case of polio paralysis is recognized, infection with the virus is usually widespread.
Because many developing nations lack safe drinking water and sanitary sewage facilities, some polio experts believe that massive immunization programs may keep the virus under control, but not stamp it out.
Some infants, for example, may be exposed before they have had a chance to be adequately immunized. About 20% of the polio cases in the Americas occur in children under age 1 and an additional 60% in children ages 2 to 4.
"The level of hygiene and the use of the vaccine go together," Melnick said. "I don't think you can (eradicate the disease) in a poor village where they don't have (pure) drinking water yet and where they have sewage running through the community."
Pan American Health Organization officials, however, remain cautiously optimistic that they can eliminate the natural polio virus from the Western Hemisphere by the end of 1990.
Despite intensified efforts to discover previously undiagnosed victims, only 782 polio cases were reported throughout the Western Hemisphere in 1987. By comparison, 931 cases were reported in 1986.
At the heart of the strategy are twice yearly "National Vaccination Days" in Brazil, Mexico, Colombia, Venezuela and other Latin American nations that have reported substantial numbers of polio cases in recent years, according to Dr. Ciro de Quadros, a Brazilian, who directs the organization's Washington-based eradication effort.
On the national vaccination days, health workers try to immunize each child up to age 5 against polio and other childhood illnesses such as measles, tetanus and whooping cough, irrespective of how many vaccine doses a child may have received before. Often, the days are accompanied by highly publicized festivities, including television appearances by national leaders, parades and music.
Contaminated Food, Water
Many Latin American countries are reporting childhood immunization rates for three doses of the oral polio virus of 70% to 85% or more. In addition, public health officials hope that even unvaccinated children will benefit from such campaigns. This is because the weakened polio virus used in the vaccine can be spread through contaminated food and water as well, perhaps triggering immunity in more children.
Other key aspects of the $500-million campaign are improved surveillance to promptly detect suspected polio cases and improved laboratory facilities to distinguish other paralytic diseases that can mimic polio, such as other viral infections and the Guillain-Barre syndrome.
Johns Hopkins' Henderson, who chairs the campaign's technical advisory committee, said the eradication effort "did not begin as aggressively and effectively as we thought it would." Now, however, he said the prospects for success by the end of 1990 are "not bad."
"All of the (necessary) activities are well under way," Henderson said. Later this year, "we will have a much better fix on where we are."
CONTROLLING SMALLPOX AND POLIO SMALL POX
1796--First smallpox vaccination administered in England by Dr. Edward Jenner. Vaccine used inoculations of a related virus causing "cowpox."
1920--First worldwide smallpox statistics show more than 100,000 cases each year in the United States.
1958--The Soviet Union makes first proposal that the World Health Organization (WHO) undertake global smallpox eradication.
1967--WHO launches intensified program for smallpox eradication. The virus still causes an estimated 10 to 15 million cases each year, and about two million deaths.
1969--Last smallpox case in the United States.
1977--Last case of smallpox in the wild detected, in Somalia.
1980--WHO certifies eradication of smallpox throughout the world.
1908--Discovery of the polio virus by researchers in Vienna, including Dr. Karl Landsteiner.
1951--Dr. Jonas Salk begins to develop the inactivated polio vaccine at the University of Pittsburgh.
1952--21,269 cases of paralytic polio reported in the United States, one of the worst polio epidemic years since 1900.
1955--Announcement of success with the Salk polio vaccine is followed by mass polio immunizations of children throughout the country.
1963--Mass immunizations begin with the oral polio vaccine, developed by Dr. Albert B. Sabin.
1981--Last known naturally-transmitted case of paralytic polio in the United States.
1985--Pan American Health Organization launches campaign to eradicate polio from the Western Hemisphere by the end of 1990.
ERADICATING POLIO IN THE AMERICAS
POLIO IN THE U.S. 1951 TO PRESENT Polio, a once-feared killer, is being targated for elimination as a serious disease around the world. Cases in the United States declined markedly in the 1950s after Jonas Salk developed the inactivated polio vaccine; mass immunization among children followed. Even larger declines followed introduction of the oral vaccine that was developed by Albert B. Sabin. Source: U.S. Centers for Disease Control
POLIO IN THE AMERICAS 1961 TO PRESENT POLIO IN LATIN AMERICA, 1987
El Salvador 55
Source: Pan American Health Organization
POLIO AROUND THE WORLD WORLDWIDE
Estimated Cases 250,000
Reported Cases 29,807
% of Children Immunized by Age 1 50%
Source: World Health Organization. 1985 r eported cases and immunization, except for the Americas which are 1987.
REGIONS OF THE WORLD
% of Children Immunized Reported by Age 1 Cases Africa 29% 1,847 Americas 66% 782 Mideast 47% 3,604 Europe 86% 264 S.E. Asia 29% 19,575 W. Pacific 78% 3,735