Polio

Poliomyelitis [from the Greek polio (gray), myelos (brain)] is an acute infection caused by the poliovirus. The symptoms of poliomyelitis are nonspecific, sometimes aseptic meningitis without paralysis (non-paralytic poliomyelitis) and, less often, paralysis of various muscle groups (paralytic poliomyelitis). The diagnosis is clinical, although laboratory diagnostics of poliomyelitis is possible. Treatment of poliomyelitis is symptomatic.

Synonyms: Epidemic infantile paralysis, Heine-Medin disease.

ICD-10 codes

• A80. Acute poliomyelitis.
  • A80.0. Vaccine-associated acute paralytic poliomyelitis.
  • A80.1. Acute paralytic poliomyelitis due to imported wild virus.
  • A80.2. Acute paralytic poliomyelitis caused by wild-type virus.
  • A80.3. Acute paralytic poliomyelitis, other and unspecified.
  • A80.4. Acute nonparalytic poliomyelitis.
  • A80.9. Acute poliomyelitis, unspecified.

What causes polio?

Polio is caused by the poliovirus, which has 3 types. Type 1 most often leads to paralysis, but is less often epidemic in nature. Only humans are the source of infection. It is transmitted by direct contact. Asymptomatic, or minor, infection is related to the paralytic form as 60:1 and is the main source of spread. Active vaccination in developed countries has made it possible to eliminate poliomyelitis, but cases of the disease occur in regions where vaccination is not fully completed, for example, in sub-Saharan Africa and South Asia.

Poliovirus enters the mouth via the fecal-oral route, affects lymphoid tissue as a result of primary viremia, and after a few days secondary viremia develops, culminating in the appearance of antibodies and clinical symptoms. The virus reaches the central nervous system during secondary viremia or through perineural spaces. The virus is found in the nasopharynx and in feces during the incubation period and when symptoms of poliomyelitis appear, persists for 1-2 weeks in the throat and more than 3-6 weeks in feces.

The most severe lesions occur in the spinal cord and brain. Inflammatory components are produced during primary viral infection. Factors predisposing to severe neurological damage include age, recent tonsillectomy or intramuscular injections, pregnancy, impaired B-lymphocyte function, and fatigue.

What are the symptoms of polio?

Polio symptoms may be major (paralytic and non-paralytic) or minor. Most cases, especially in young children, are minor, with subfebrile fever, malaise, headache, sore throat, and nausea lasting 1-3 days. These symptoms of poliomyelitis appear 3-5 days after exposure. There are no neurological symptoms. Polio most often develops without prior minor symptoms, especially in older children and adults. Polio has an incubation period of 7-14 days. Polio symptoms include aseptic meningitis, deep muscle pain, hyperesthesia, paresthesia, and, in active myelitis, urinary retention and muscle spasm. Asymmetric flaccid paralysis develops. The earliest signs of bulbar disorders are dysphagia, nasal regurgitation, and nasal voice. Encephalitis develops rarely, and respiratory failure develops even more rarely.

Some patients develop post-polio syndrome.

How is polio diagnosed?

Non-paralytic poliomyelitis is characterized by normal glucose levels in the cerebrospinal fluid, slightly elevated protein, and cytosis of 10-500 cells/μl, primarily lymphocytes. Polio diagnosis is based on virus isolation from the oropharynx or feces or an increase in antibody titer.

Asymmetric progressive flaccid paralysis of the limbs or bulbar palsy without sensory loss in febrile patients or in febrile unimmunized children or young adults almost always suggests paralytic poliomyelitis. Rarely, a similar picture may be caused by coxsackieviruses of groups A and B (especially A7), various ECHO viruses, and enterovirus type 71. West Nile fever also causes progressive paralysis that is clinically indistinguishable from paralytic poliomyelitis caused by polioviruses; epidemiologic criteria and serologic tests help in the differential diagnosis. Guillain-Barré syndrome causes progressive paralysis, but fever is usually absent, muscle weakness is symmetric, sensory disturbances occur in 70% of patients, and cerebrospinal fluid protein is elevated with normal cell counts.

How is polio treated?

Treatment of poliomyelitis is usually symptomatic, including rest, analgesics, antipyretics if necessary. The possibilities of specific antiviral therapy are being studied.

In active myelitis, one should remember about the possibility of complications associated with prolonged bed rest (e.g., deep vein thrombosis, atelectasis, urinary tract infections), and with prolonged immobilization - contractures. Respiratory failure may require artificial ventilation of the lungs with careful toilet of the bronchial tree.

Treatment of postmyelitis syndrome is symptomatic.

How to prevent polio?

All children should be vaccinated against polio at an early age. The American Academy of Pediatrics recommends vaccination at 2, 4, and 6-18 months, with a booster dose at 4-6 years. Immunity is greater than 95%. The Salk vaccine is preferred over the live-attenuated oral Sabin vaccine; the latter causes paralytic poliomyelitis at an incidence of 1 in 2.4 million doses and is not used in the United States. No severe reactions are associated with the Salk vaccine. Adults are not vaccinated. Unimmunized adults traveling to endemic areas should receive the Salk vaccine as a primary vaccination, two doses given separately at 4 and 8 weeks, and a third dose at 6 or 12 months. One dose is given immediately before travel. Previously vaccinated individuals should receive only one dose of the Salk vaccine. Immunocompromised individuals should not receive the Sabin vaccine.

What is the prognosis for polio?

In non-paralytic forms of poliomyelitis, complete recovery is observed. In paralytic forms, about 2/3 of patients have residual effects, manifested in the form of muscle weakness. Bulbar paralysis resolves more often than peripheral. Mortality is 4-6%, but increases to 10-20% in adults or in patients with developed bulbar paralysis.

Postpolio syndrome is muscle weakness and decreased tone, often associated with fatigue, fasciculitis, and atrophy, that develops years to decades after paralytic poliomyelitis, particularly in older patients and those with severe disease. Damage occurs in previously affected muscle groups. The cause may be related to further cell death in the anterior horn of the spinal cord as a result of aging of the neuronal population damaged by poliovirus infection. Severe poliomyelitis is rare.