Karachi - where four female health workers were shot yesterday is one of a number of areas in Pakistan where wild poliovirus is being spread.

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Last year there were just 205 cases of naturally occurring poliovirus compared with 650 cases in 2011 and a staggering 350, 000 a quarter of a century ago.

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Iraq has been polio-free for more than two years, and it is not likely that the cultures in the incubators contained wild poliovirus, according to the report.

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But people may need additional protection if they are traveling to high-risk countries, handle poliovirus specimens in a laboratory or have close contact with a person who has polio.

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When poliovirus infects your body, it affects nerve cells called motor neurons particularly those in your spinal cord that carry messages (electrical impulses) between your brain and your muscles.

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