Polio Outbreak in the Republic of Congo: Causes and Response

Introduction to Poliovirus

Poliomyelitis (polio) is caused by a highly contagious enterovirus called the Picorna virus, transmitted through contaminated feces, food, or water that is ingested (Berkow et al., 1997). The Picorna virus is highly stable in fecal matter. Ironically, scientists believe that although the disease dates back at least 3,000 years, in the earliest days when raw sewage was ubiquitous, children developed a protective immunity and outbreaks were rare.

Transmission, Etiology, and Hosts

The virus enters through mucous membranes and lives in the throat and intestines of its human host; there is no animal reservoir. Sometime after infection, the virus spreads to the lymph nodes and blood. Eventually, in fewer than one percent of all cases, the virus penetrates the nervous system through capillary walls and paralyzes motor nerves (CDC, 2010).

Vectors that may transmit the disease are mechanical — insects that are not themselves infected may land on food with contaminated feet, thereby contaminating the food and spreading the illness (CDC, 2010). While some partially immune adults may serve as carriers, the primary hosts are infected children under the age of five. No incidental hosts have been identified (CDC, 2010).

Global Eradication Efforts and the Congo Outbreak

As a result of widespread vaccination programs, polio has nearly been eradicated in most countries. However, reservoirs of the disease still existed in four countries at the time of this writing: Pakistan, India, Nigeria, and China. The Western Hemisphere was declared free of wild poliovirus as of 1994. At one time, the World Health Organization had hopes of completely eradicating the disease by the turn of the 21st century.

Recently, however, a significant outbreak in the Republic of Congo startled scientists (Berkow et al., 1997). Despite no recorded indigenous cases since 2000, the outbreak was confirmed on November 4, 2010. It is highly unusual in that a total of 324 cases of acute flaccid paralysis (AFP) were reported, with 146 recorded deaths as of November 22, 2010. Normally, polio occurs in young children and rarely results in paralysis or death. In response, a massive polio vaccination campaign was launched, estimated to cost in excess of $23 million (PGEI, 2010).

Epidemiology of the 2010 Congo Outbreak

Most of the victims were males between the ages of 15 and 29, an age group for whom the disease is more life-threatening than it is in childhood. The ages and gender of those affected suggest the cause may be insufficient or incomplete immunization, especially since women and girls can develop some immunity through exposure to immunized infants (UN, 2010).

Although only five cases were confirmed as polio at the time of reporting, laboratory testing continued. Of the three known strains of poliovirus, the particular strain causing this outbreak was thought to originate from India, from where it spread to nearby Angola. Previous experience shows that very rapid vaccination efforts can quell an outbreak — in 2006, an outbreak in Namibia was controlled within three months — but the response must be swift and must include all neighboring districts. In addition, surveillance efforts must continue for a full year after vaccination campaigns are complete in order to ensure eradication (PGEI, 2010).

Conclusion and Open Questions

It is interesting to note that some scientists have argued the HIV virus originated in the Congo in 1959 via a polio vaccine, although more recent research suggests this may not be the case (BBC News, 2010). Whether a mutated, more dangerous strain of poliovirus could be emerging remains an open and troubling question for the global public health community.