Acute poliomyelitis is a viral disease that may cause paralysis due to an attack on the motor nerve cells in the spinal cord. Three immunologically distinct types of poliovirus have been identified, and infection by one type will not confer immunity against potential future infections by the other two types. Successful inoculation with either the oral poliovirus vaccine (Sabin) or the inactivated poliovirus vaccine (Salk) provides immunity against all three subtypes of poliovirus (see Vaccines, Polio).
The poliovirus enters the body through the mouth and resides in the gastrointestinal tract, and in some cases, becomes blood-borne and invades the central nervous system (CNS). The manifestations of the infection can range from an asymptomatic infection, that results in the development of antibodies to the infecting strain of poliovirus, to a severe paralytic illness. Well over 95% of polio infections result in no corresponding paralysis (World Health Organization, 1954).
Abortive poliomyelitis is a brief systemic illness often limited to one or more of the following symptoms: sore throat, headache, vomiting, and fever, in which clinical or laboratory signs pointing to CNS involvement fail to develop.
Paralytic poliomyelitis is a major illness in which severe muscle weakness, or paralysis of one or more muscles, develops. After the acute stage and over the next few months, some paralyzed muscles recover (see Pathology). The location of paralysis depends on where the virus caused injury or death of motor nerve cells in the spinal cord. Spinal paralytic poliomyelitis affects the muscles of the legs, arms, and back. Also affected may be the muscles of the thorax, including the intercostals, and the diaphragm with its motor nerve cells located just below the brainstem. Paralysis in these areas interferes with breathing. Bulbar paralytic poliomyelitis, responsible for the vast majority of deaths, results from paralysis of muscle groups innervated by cranial nerves, including those of the soft palate and pharynx, face, tongue, and paralysis of the respiratory center of the brain (World Health Organization, 1954).
Nonparalytic poliomyelitis is also an example of the major illness, with involvement of the CNS, as manifested by spinal-fluid changes or appropriate clinical signs, such as fever, headache, vomiting, neck, back, trunk, or limb pain, and stiffness of the neck or back, but in which acute or residual muscle paralysis does not occur (Paul, 1955). It is only diagnosed during epidemics in those symptomatic individuals known to have associated closely with someone with a confirmed case of poliomyelitis. Due to the indiscriminate use of the term “nonparalytic poliomyelitis,” the Expert Committee on Poliomyelitis, in 1958, recommended the elimination of the term, replacing it with “aseptic meningitis syndrome” (World Health Organization, 1958).
Encephalitic manifestations, such as coma and tremors, are also observed in some cases of acute poliomyelitis.
Fewer than five cases of acute poliomyelitis have been reported in the United States in the last decade, but between 500 and 1,000 cases per year are occurring around the world, mostly in developing countries. No case of wild poliovirus has been reported in the Western Hemisphere since 1991.
The Global Polio Eradication Initiative (GPEI) was founded in 1988 and includes the WHO, Rotary International, the CDC, Bill and Melinda Gates Foundation, and Gavi, the Vaccine Alliance. Their website, www.polioeradication.org, has historical and up-to-date information about cases of confirmed polio.
References
Paul, J.R. (1955). Epidemiology of poliomyelitis. In Poliomyelitis (pp. 14-15). Geneva: World Health Organization.
World Health Organization Technical Report Series, No. 81 (1954). Expert committee on poliomyelitis, first report (pp. 7-8). Geneva: World Health Organization.
World Health Organization Technical Report Series, No. 145 (1958). Expert committee on poliomyelitis, second report (pp. 14-15). Geneva: World Health Organization.