Poliomyelitis is an enteroviral infection that can manifest in 4 different forms: inapparent infection, abortive disease, nonparalytic poliomyelitis, and paralytic disease. Before the 19th century, poliomyelitis occurred sporadically. During the 19th and 20th centuries, epidemic poliomyelitis was more frequently observed, reaching its peak in the mid 1950s. The worldwide prevalence of this infection has decreased significantly since then because of aggressive immunization programs. Eradication of this disease during the present decade is a top priority for the World Health Organization (WHO). [1, 2] See the image below.
See 11 Travel Diseases to Consider Before and After the Trip, a Critical Images slideshow, to help identify and manage several infectious travel diseases.
Poliovirus is an RNA virus that is transmitted through the oral-fecal route or by ingestion of contaminated water. Three serotypes are able to cause human infection. The incubation period for poliovirus is 5-35 days. The viral particles initially replicate in the nasopharynx and GI tract and then invade lymphoid tissues, with subsequent hematologic spread. After a period of viremia, the virus becomes neurotropic and produces destruction of the motor neurons in the anterior horn and brainstem. The destruction of motor neurons leads to the development of flaccid paralysis, which may be bulbar or spinal in distribution.
No cases of wild-type poliovirus infection have been reported in the United States since 1979. Until 1998, an average of 8-10 cases associated with the vaccine virus were reported every year. Since the institution of an all-inactivated poliovirus vaccine (IPV) policy in the routine immunization schedule, the number of vaccine-associated cases has significantly decreased. Four cases of vaccine-derived poliovirus were identified in 2005 among unvaccinated children in an Amish community in Minnesota. [3, 4]
The global incidence of poliovirus infection has decreased by more than 99% since 1988. Although no outbreaks had been reported in the western hemisphere since 1991, the Pan American Health Organization reported an outbreak in Haiti and the Dominican Republic in 2001. Since 2001, no additional outbreaks of disease caused by wild poliovirus have been reported in the Americas. Clusters of wild-type disease are still found in some areas in Africa and Southeast Asia.
As of 2014, significant progress has been made towards poliomyelitis eradication in India, which is now considered a nonendemic area. [5, 6] Pakistan, Afghanistan, and Nigeria are 4 countries in which indigenous transmission of wild poliovirus still occurs. However, importation of wild poliovirus into countries previously considered free of poliomyelitis continues to be a problem, especially in Africa. [7, 8] In addition, there have been recently confirmed cases of poliomyelitis in Syria and Iraq caused by wild poliovirus type 1 (WPV1). 
Concern for importation of cases from Afghanistan and Pakistan into Israel has resulted in a change in their routine polio immunization to include at least one dose of oral vaccine. In 2014, India began requiring a dose of oral polio vaccine for anyone coming from countries where polio is still seen, particularly Afghanistan and Pakistan. 
Mortality is more frequently observed in cases of paralytic poliomyelitis and is associated with complications such as respiratory failure. No deaths due to wild-type poliovirus have been reported in the United States since 1979.
Although most cases of poliomyelitis (90-95%) are inapparent, 5-10% of patients who acquire this infection develop symptoms.
Males and females of pediatric age are affected with equal frequency.
Poliovirus affects mainly children. However, individuals of any age (especially those who are immunocompromised) may also develop the disease.
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