The Medscape Awards in Infectious Diseases: Disease Most Likely to Be Eradicated From Earth

John G. Bartlett, MD

Disclosures

December 18, 2012

Another Award Contender

Polio

Polio represents another amazing chapter in medicine. The virus is unique among enteroviruses in causing necrosis of motor neurons, resulting in paralytic polio. The most dramatic effect was paralysis of respiratory muscles and diaphragm, leading to life dependency on a respirator, or "iron lung" (Figure 2).

Figure 2. Ward with polio patients in iron lungs, 1953. US Food and Drug Administration.

Polio was sporadic in the United States and Europe in the early 1900s and affected primarily infants ("infantile paralysis"). President Franklin D. Roosevelt was confined to a wheelchair for most of his life as a result of this disease. In the early 1950s, paralytic polio became more common, especially in older children and young adults. Polio became a dreaded fear for parents, who often insisted on unrealistic prevention strategies. (When I was growing up, we had to wash silverware before use in restaurants, and all swimming pools were forbidden.)

On April 12, 1955, Dr. Jonas Salk announced the success of the Salk vaccine, which was approved for use 2 hours later. Nine million doses were rapidly distributed. On April 16, 1955, only 4 days after the Salk announcement, journalist Alistair Cooke commented, "Nothing short of the overthrow of the Communist regime in the Soviet Union could bring such rejoicing...as the announcement that the 166-year war against paralytic polio is almost certainly at an end."[4] However, an early setback with the vaccine, an inactivated polio virus, was potentially devastating. On April 25, 1955, it was announced that a batch of vaccine had failed inactivation, resulting in 149 vaccine-associated cases of paralytic polio and 6 deaths.

Despite this setback, the subsequent history of polio eradication was glorious. Seldom in medicine is there such a dramatic response to a medical breakthrough. Rates of paralytic polio plummeted from 17.6/100,000 population in 1955 to 0.4/100,000 in 1962 -- a 40-fold reduction. The last case of naturally occurring indigenously transmitted polio in the United States occurred in 1979.[5]

Initially, polio was largely ignored in the rest of the world, although a 20-nation survey of "lameness" in school children, presumably a consequence of polio, showed rates of 2-11/1000 population -- far higher than the rates reported at the peak of the US epidemic.[6,7]

The major weapons for poliovirus control, used effectively in the United States and Europe, were Salk's trivalent formalin-inactivated polio vaccine, licensed in 1955, and Sabin's 3 live attenuated monovalent oral polio vaccines (OPVs), available in 1962. The subsequent 20-year history of polio science and public health eventually led to the International Symposium on Poliomyelitis Control in 1983 to discuss global eradication.[8] The commitment finally came in 1988, when the World Health Assembly resolved to eradicate polio by 2000.

The plan was a global program, the goal of which was to vaccinate all children in the world by 1990. The strategy was ambitious: 3 doses of OPV for all infants and intensive surveillance for cases supplemented with house-to-house "mop-up vaccinations."[9] By 1997, the number of polio cases in the world had declined from an estimated 600,000 per year before vaccination to 4000, a more than 99% reduction. Since then, incremental gains have produced further reductions to 600-800 cases in about 20 countries in 2011. Most of these are caused by wild-type polio WPV1 or -3, but about 50 cases involve the live-virus vaccine strain.

Despite progress, the current situation is frustrating and reminds us of the statement by Nobel laureate Joshua Lederberg about the human battle against the microbes: "It's our wits vs their genes." Eradication of polio now faces 3 obstacles:[10]

  • Vaccine-derived strains that cause polio;

  • Inadequate immune responses in selected geographic areas; and

  • New epidemics of polio in areas of prior eradication.

The last obstacle is viewed as the most ominous. Countries that were declared polio-free now account for 80% of the 1291 reported cases in 2010. Especially problematic are the "genetically divergent vaccine-derived poliovirus" that caused recent outbreaks in Nigeria, Somalia, and the Republic of the Congo. These can be controlled by use of OPV. However, another problem is chronic excretion of the virus by 65 patients with primary immunodeficiencies in 7 countries. This source of disease can only be controlled by discontinuing OPV.[11]

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