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Global Polio Largely Fading
An Indonesian boy is given polio vaccine in Jakarta, Indonesia. The country kicked off its third nationwide polio immunization campaign in November.
(By Tatan Syuflana -- Associated Press)
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Although polio virus does its damage in the spinal cord, it infects the body through the intestine and spreads most easily in crowded populations with poor sanitation.
In only 1 in 200 infections does it cause paralysis. In other cases, it produces only fever and diarrhea, or no symptoms. Consequently, polio virus can be carried "silently" into a polio-free population and spread before it is recognized.
That is what happened when the Islamic states of northern Nigeria stopped immunizing children in 2003 because of rumors that the oral vaccine caused sterility and was part of a Western campaign against Muslims.
Between January 2003 and July 2005, 18 polio-free countries were reinfected with virus that originated in northern Nigeria.
Analysis of the poliovirus genes -- which accumulate mutations at a steady, known rate -- allowed scientists to trace the route, and even the timing, of the microbe's spread.
Work done at the Centers for Disease Control and Prevention by Olen M. Kew and Mark A. Pallansch showed that virus from northern Nigeria was carried into Chad and several neighboring countries in 2003. From Chad one strain moved to Sudan in late 2003 or early 2004, and from there to Saudi Arabia. From Saudi Arabia it was carried to Indonesia, where on March 13 this year, polio was diagnosed in an infant boy in West Java -- the first Indonesian case since 1995.
Reinfection occurred because these countries had not maintained adequate immunization rates in young children.
During the same period, three other polio-free countries -- Angola, Lebanon and Nepal -- were reinfected with virus that originated in northern India.
In all these countries -- and in northern Nigeria, where politicians and clerics now support polio vaccination -- intensive immunization campaigns have resumed.
Last month, WHO experts confirmed that 10 reinfected African countries -- Benin, Burkina Faso, Cameroon, Central African Republic, Chad, Ivory Coast, Ghana, Guinea, Mali and Togo -- have reported no cases since late June. That strongly suggests virus transmission has been stopped.
The trans-Africa outbreak had many arresting features -- post-9/11 suspicions of the West in Muslim regions, political jockeying in Nigeria and a humanitarian disaster in Sudan that accelerated the spread of the disease.
"What the world wasn't looking at was what was happening in Egypt and India," Aylward said recently in his office in Geneva.
