Polio is spreading

28 October 2008

Today’s NY Times reports that cases of wild polio (as opposed to vaccine-induced polio) are appearing in new countries, and increasing numbers are occurring in countries that are endemic for the disease. Article link here. A disease is ‘endemic’ in a country when it is maintained without introduction from other countries.

Polio is considered to be endemic in four countries: Nigeria, India, Afghanistan, and Pakistan. The reasons for the continued presence of the disease in these countries are complex. Armed conflict in Afghanistan and Pakistan has prevented adequate immunization. The outbreak in Nigeria is a consequence of the government’s decision to halt immunization several years ago. Administration of polio vaccine has since been resumed, but the spread of type 1 poliovirus still occurs. In India, repeated immunization in western Uttar Pradesh often fails to prevent infection, for obscure reasons.

The number of cases of polio in these four countries has risen since the same time last year. In India, there have been 486 cases so far this year, compared with 326 by this time in 2007. The same increases are seen in Pakistan (81 vs. 16), Nigeria (728 vs. 210), and Afghanistan (22 vs. 12).

Unfortunately, the disease is also spreading to other countries. For example, two cases have been reported in Ghana, which had not reported the disease since 2003. Overall there have been 1406 cases reported globally this year, compared with 635 by this time in 2007. More details can be found at polioeradication.org.

The reason for the increased case count is unknown, especially because WHO sponsored immunization programs continue at an aggressive rate.

Remember, for every reported case of polio, there are likely at least 100-200 individuals harboring the virus without showing symptoms of paralysis. These asymptomatic infections are important for the transmission of the infection.