Poliomyelitis

Poliovirus enters through the fecal-oral route, typically via contaminated food or water. Once ingested, the virus replicates in the mucosal lining of the throat and intestines, particularly in lymphoid tissues like the tonsils and Peyer's patches. Most infections remain asymptomatic at this stage, with the virus contained in the gastrointestinal tract.

Abortive poliomyelitis occurs in over 90% of cases, causing minor nonspecific symptoms like fever, headache, and sore throat. Paralytic poliomyelitis, affecting fewer than 2% of infections, results from viral invasion of the central nervous system and destruction of motor neurons in the anterior horn of the spinal cord, causing flaccid, asymmetric paralysis.

After primary viremia, poliovirus disseminates through the bloodstream and reaches the central nervous system. The virus may also travel via retrograde axonal transport from peripheral nerves. Once in the spinal cord, it replicates in anterior horn cells, destroying motor neurons that control muscle movement and resulting in sudden onset flaccid paralysis.

The inactivated poliovirus vaccine (IPV), developed by Jonas Salk in 1955, is injected and induces systemic immunity, preventing paralytic disease but not transmission. The oral poliovirus vaccine (OPV), developed by Albert Sabin in 1961, is live attenuated, induces mucosal immunity, and effectively interrupts fecal-oral transmission but carries a rare risk of vaccine-derived paralytic poliomyelitis.

Nonparalytic poliomyelitis occurs in about 1–2% of infections when the virus invades the central nervous system but does not destroy motor neurons. It presents with meningeal irritation signs including neck stiffness and muscle spasms, similar to viral meningitis, without the flaccid paralysis characteristic of paralytic poliomyelitis.

Bulbar poliomyelitis occurs when poliovirus affects the cranial nerve motor nuclei in the brainstem, impairing respiratory and swallowing functions. This severe form can compromise breathing, sometimes necessitating mechanical ventilation for survival, making it one of the most critical complications of paralytic poliomyelitis.

Poliovirus is a small, non-enveloped, positive-sense RNA virus belonging to the Picornaviridae family and Enterovirus genus. It causes poliomyelitis, a disease that primarily affects the nervous system. The virus is highly stable in the gastrointestinal tract, facilitating transmission through contaminated food and water.