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Polio, Surveillance and Observation - 2002-11-22

This is the third in a five-part series on global polio eradication, based on interviews in Washington, in Atlanta at the Centers for Disease Control and Prevention, and at National Immunization Days in northern Nigeria.

Polio, a highly infectious viral disease, is preventable but not curable. Vaccines have halted its spread in much of the world. Thanks to the efforts of a global campaign to stop the disease, the World Health Organization predicts a polio-free world by 2005.

Surveillance and reporting play a major role in the eradication effort. During National Immunization Days in Nigeria, teams of vaccinators knock on every door in the country. In a small farming hamlet in northern Nigeria, no one refused the vaccine. Houses were marked with chalk symbols to show where children have been vaccinated, or where the vaccinators must return.

Vaccinators also checked for symptoms of new cases. This is how surveillance teams track the virus. And this is also how Nigeria, after three years without a new case, will eventually be certified by the World Health Organization as polio-free.

World Health Organization epidemiologist Ali Takai was one of two surveillance officers in the northern state of Kano, a high-risk area. Alerted by an observant local informant, he hurried to the countryside to examine a child. He stopped first at a cold storage facility, located within one of the hospitals, to collect the vaccine carrier and ice-packs, ready to go into the child's house.

Based on what he saw, he would order laboratory tests that either confirmed the presence of the wild polio virus or showed a case of acute flaccid paralysis, an adverse reaction to the oral polio vaccine. The latter occurs in only one out of every three million doses of the oral vaccine, and the condition is not contagious.

A two-hour drive and a walk through a dense field of guinea corn put Dr. Takai at the feet of a tiny little girl. She lived in a small village of mud huts nestled in the shade of ancient trees. Dr. Takai gently bent down to examine the naked child, who was frightened and crying.

"The left hand is weak. Likewise the left leg. The weakness is flaccid, not spastic, therefore consistent with an acute flaccid paralysis case," observed Dr. Takai. "So, this case is based on the clinical presentation of an acute flaccid paralysis, or polio, for which we now have to collect the stool sample and send it to the laboratory to see whether we are going to isolate wild polio virus or not." The child was two years old, and only the day before had received her second dose of oral polio vaccine.

Should the stool specimen prove to contain the wild virus, it would be sent to a special polio reference laboratory like the one Olen Kew directs at the Centers for Disease Control and Prevention in the United States. The CDC laboratory in Atlanta genetically sequences the virus and tracks its transmission.

Mr. Kew said the information helps answer some important questions about the spread of the disease. "Where are the communities sustaining continuous circulation of the wild polio virus? Where should the immunization team put their best efforts?" he asked. "Helping the WHO and immunization teams [know] where you can shut the tap off at the source is a key function of the laboratory network. Recognition where the reservoirs [of wild polio] are can help save resources. Rather than running all over the country and trying to immunize children everywhere in special sub-national activities we sometimes call 'mop-up campaigns,' the activities can be targeted to those areas that present the greatest risk for continued risk for the wild virus."

Mr. Kew said in this way, laboratory data helps decision-makers guide the eradication process, both nationally and internationally. "When it becomes clearer that communities of one country harbor the virus which could be carried to neighboring countries, that can build some support for the countries still struggling with polio on the part of its neighbors," he said. "What kind of support can be given to the neighboring countries to help them finish the job?"

What are the laboratories' challenges? "Certainly there are funding challenges, and retention of well-trained staff is certainly is an issue," he said. "That I think in the short term is the single greatest challenge to hold this network together and to keep engaged these very talented people who have a lot of experience working with epidemiologists and program people."

The polio laboratory network is the most comprehensive for any disease. It includes 127 national laboratories, 15 regional reference laboratories, and six global specialized reference laboratories like the one in Atlanta. Olen Kew said the polio eradication initiative has established new global partnerships and tied the laboratory surveillance work more closely with public officials and health workers in the field.

In part 4, we'll examine the impact of polio through the eyes of a victim.

Photos for this series provided by Rosanne Skirble