poliomyelitis

poliomyelitis. Poliomyelitis is an acute infectious disease caused by the poliovirus, a member of the genus Enterovirus. The virus invades the central nervous system, particularly targeting motor neurons in the spinal cord and brainstem, which can lead to irreversible paralysis. While most infections are asymptomatic, the disease has historically been a major cause of disability and was a source of widespread fear before the development of effective vaccines. Global eradication efforts, led by organizations like the World Health Organization and UNICEF, have dramatically reduced its incidence.

Signs and symptoms

The clinical presentation ranges from inapparent infection to severe paralysis and death, categorized into several forms. Abortive poliomyelitis, a minor illness, presents with nonspecific symptoms like fever, headache, and sore throat, resembling other common viral infections. In non-paralytic poliomyelitis, patients may experience symptoms of aseptic meningitis, such as stiffness in the neck, back, and legs. The most severe form, paralytic poliomyelitis, occurs when the virus attacks motor neurons, leading to asymmetric flaccid paralysis that often affects the legs; bulbar polio involves the brainstem and can impair swallowing, speech, and respiration. A small percentage of survivors may develop post-polio syndrome decades later, characterized by new muscle weakness and fatigue.

Cause and transmission

The disease is caused by three serotypes of poliovirus (types 1, 2, and 3), which are highly contagious human enteroviruses. The virus primarily spreads via the fecal-oral route, often through contaminated water or food in areas with poor sanitation; it can also spread, less commonly, via the respiratory droplet route. The virus replicates in the oropharynx and the intestinal tract before potentially invading the nervous system. Humans are the only natural reservoir and host for the virus, which has facilitated targeted public health strategies. Epidemics were historically common in the United States and Europe during the summer and autumn months.

Diagnosis and prevention

Diagnosis is confirmed by isolating the virus from specimens such as stool, cerebrospinal fluid, or throat swabs, or by detecting specific antibodies in the serum. The development and deployment of vaccines are the cornerstone of prevention. The inactivated polio vaccine, developed by Jonas Salk and first used widely in 1955, is administered by injection. The oral polio vaccine, developed by Albert Sabin using live, attenuated virus, became a critical tool for mass vaccination campaigns due to its ease of administration and ability to induce intestinal immunity. Global initiatives like the Global Polio Eradication Initiative, launched in 1988, have relied on these vaccines to drive cases to near-zero, though challenges remain in regions like Afghanistan and Pakistan.

Treatment and prognosis

There is no antiviral cure; management focuses on supportive care, alleviating symptoms, and preventing complications. During the acute phase, rest and analgesics are recommended. For paralytic cases, interventions may include physical therapy to maintain muscle function and prevent deformities, and the use of assistive devices like braces or wheelchairs. In severe bulbar cases, historical treatment often required the use of an iron lung or other forms of mechanical ventilation to support breathing. The prognosis depends on the form of the disease: non-paralytic cases typically recover completely, while paralytic cases may suffer permanent disability. Mortality is highest in bulbar polio due to respiratory failure.

Epidemiology and history

The disease likely existed for millennia but emerged as a major epidemic threat in the late 19th and early 20th centuries in industrialized nations, with notable outbreaks in New York City and Copenhagen. The development of vaccines transformed the landscape; the United States saw its last wild case in 1979. The eradication campaign has been remarkably successful, with wild poliovirus type 2 declared eradicated in 2015 and type 3 in 2019. As of the early 2020s, wild poliovirus type 1 remains endemic only in parts of Afghanistan and Pakistan. Continued vigilance is required to address vaccine-derived polioviruses and achieve the goal of global certification of eradication by the World Health Assembly.

Category:Virus-related cutaneous conditions Category:Eradicated diseases Category:World Health Organization essential medicines