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Sources: Clarke T. Polio’s last stand. Nature. 2001;409:278-280; Polio eradication: The end game. Nat Med. 2001;7:131; Watanabe M. Polio outbreak threatens eradication program. Nat Med. 2001;7:135.
Fifty years ago, poliomyelitis was the most dreaded infection that annually affected children and relatively young adults worldwide. The virus itself resides in the intestinal track of nonimmune persons and includes 3 distinct antigenic types, allowing it rarely to strike twice. Both antipolio vaccines discussed below, however, protect against all three types. Highly active viruses can kill large spinal anterior horn cells, thereby precipitating varying degrees of permanent muscular paralysis. A fraction of neurological victims also suffer potentially fatal attacks of acute brain stem encephalitis, which temporarily disrupts autonomic pathways as well as the ponto-medullary regulation of blood pressure, heart rate, breathing, swallowing, and bladder function.
By 1949, Enders and associates managed to cultivate the polio virus in tissue culture, a step awarded by the Nobel prize. Jonas Salk developed his killed virus inactivated poliomyelitis vaccine (IPV) in 1954. A year later Albert Sabin meticulously developed a vaccine comprised of alive, but attenuated non-paralytogenic, and delivered as orally polio viruses (OPV). Administration of the oral vaccination was far more easy to achieve and less costly. Used widely by the World Health Organization (WHO) and the Pan American Health Organization (PAHO), the OPV vaccine has been highly successful in reducing the incidence of poliomyelitis in 2nd and 3rd world countries around the globe. Thanks to these efforts, the disease has almost disappeared in the North and South Americas, Northern Europe, and Asia, plus almost the entire Pacific Asian coast, islands and continents. Global annual incidence of polio dropped from 320,000 p.a. before the advent of polio vaccination to a present ± 2000 p.a. Most of these latter cases come from Central Africa and Southwest Asia.
Against the above background, a small epidemic of acute paralytic poliomyelitis appeared last summer in the Dominican Republic and Haiti, both of which share the island of Hispaniola. Seven of the 9 paralyzed children were traced to a single mutant antibody of OPV pattern. By accident or staleness, this must have emerged from recipients who previously received either insufficient or too old vaccine, or have generated a wild mutant oral polio vaccine. The CDC suggests that the rogue OPV virus in the Dominican Republic may have kindled for 2 (or more) years before the present epidemic, spreading the diseased mutation via person to person from intestinal contents. Supporting this concept is that Clarke found that only 20% of Dominican children had ever even had one of the three OPV doses, an amount not sufficient to provide immunity. The remaining children and, presumably, adults never received preventive inoculation.
No fatalities have been reported, but Nature indicates that in the WHO international program, OPV vaccinations have occasionally had random hitches that averaged 1 case of paralytic polio for every 1/750,000 inoculated persons. Watanabe also indicates that Donald Henderson, Chairman of the Technical Advisory Group Program of Immunization of the Americas, says there are an additional 39 suspected cases in Hispaniola. Whether paralytic is not commented upon.
Information from inner China several years ago suggested a small outbreak of persons presumably taking too little OPV. Watanabe also indicates that Mortality and Morbidity Weekly in its January 26 issue refers to an outbreak associated with OPV distribution in Egypt some years ago. Affected were a total of 32 polio cases in 1988 and 1993. Analysis suggests that a potentially malignant OPV virus may have been growing insidiously in the intestines of the affected population for as long as 11 years.
WHO and PAHO for many years have been struggling in efforts to eradicate poliomyelitis in the way that small pox apparently has been permanently conquered. Nature Medicine’s editor, however, has cautions. Although the present breakthroughs of patients given OPV have involved only small numbers of paralytic disease, stronger mutations might cause larger and more frequent epidemics. He implies that if OPV can’t block generating stronger mutations, there may come a day when such a mutation reproduces the acute severe crippling or killing illness that once came from wild viruses.
(Editor’s Note: When to be inoculated for poliomyelitis. Adults: For those younger than 40 years and never previously inoculated against poliomyelitis, take 2 doses of IVP sc 1 month apart and a third 6-12 months later. If urgent and anticipating immediate trips into Sub-Saharan Africa or Southwest Asia, take a single boost of either OPV or IVP even if either was completely or incompletely obtained several months or years earlier. For adults, see Cecil Textbook of Medicine, 21st ed. 2000: 44. For children’s vaccination, consult Merck Manual, Centennial Edition. 1999:2342.)