Polio is a disease caused by infection with the poliovirus. The virus spreads by:
Direct person-to-person contact
Contact with infected mucus or phlegm from the nose or mouth
Contact with infected feces
The virus enters through the mouth and nose, multiplies in the throat and intestinal tract, and then is absorbed and spread through the blood and lymph system. The time from being infected with the virus to developing symptoms of disease (incubation) ranges from 5 to 35 days (average 7 to 14 days). Most people do not develop symptoms.
Lack of immunization against polio
Travel to an area that has had a polio outbreak
As a result of a global vaccination campaign over the past 25 years, polio has largely been eliminated. The disease still exists in some countries in Africa and Asia, with outbreaks occurring in groups of people who have not been vaccinated. For an updated list of these countries, visit the website: www.polioeradication.org.
There are 3 basic patterns of polio infection: subclinical infections, nonparalytic, and paralytic. Most people have subclinical infection, or may not have any symptoms.
Post-polio syndrome is a complication that develops in some people, usually 30 or more years after they are first infected. Muscles that were already weak may get weaker. Weakness may also develop in muscles that were not affected before.
When to Contact a Medical Professional
Call your provider if:
Someone close to you has developed poliomyelitis and you haven't been vaccinated.
You develop symptoms of poliomyelitis.
Your child's polio immunization (vaccine) is not up to date.
Polio immunization (vaccine) effectively prevents poliomyelitis in most people (immunization is over 90% effective).
Romero JR, Modlin JF. Poliovirus. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 8th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 173.
Silver JK. Post-poliomyelitis syndrome. In: Frontera WR, Silver JK, Rizzo Jr TD, eds. Essentials of Physical Medicine and Rehabilitation. 2nd ed. Philadelphia, PA: Elsevier Saunders; 2008:chap 137.
Simoes EAF. Polioviruses. In: Kliegman RM, Stanton BF, St Geme JW III, Schor NF, eds. Nelson Textbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 249.
Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School; Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.