Poliovirus, part of the enterovirus * group, makes its home in the gastrointestinaltract, but when the viral infection spreads it can destroy nerve cells known as motor neurons, which make muscles work. The damaged motor neurons cannot rebuild themselves, and as a result the body's muscles no longer function correctly.
Poliovirus infections are broken down into four types: asymptomatic (a-simp-toh-MA-tik), abortive, nonparalytic (non-pair-uh-LIH-tik), and paralytic (pair-uh-LIH-tik). Most cases of polio cause no symptoms (asymptomatic) or only minor symptoms (abortive), such as sore throat, vomiting, or other symptoms resembling those of the flu. Nonparalytic polio has more severe symptoms, including stiff neck due to meningitis and muscle stiffness in the back and legs. Paralytic polio, the rarest but most severe form of the disease, attacks the central nervous system (the part of the nervous sysem that includes the brain and spinal cord) and can cause muscle weakness, spasms, and paralysis.
Types of paralytic polio include spinal, bulbar (BUL-bar), and bulbospinal (bul-boh-SPY-nul). The spinal type is most common, affecting the muscles of the legs, trunk, and neck. The bulbar form involves nerves of the brain stem * and can cause problems with breathing, talking, and swallowing. Bulbospinal polio is a combination of the first two types.
Polio essentially has been wiped out in the United States and many other developed countries since the introduction of a polio vaccine in 1955. Before that, polio occurred in epidemic * form, with more than 21,000 paralytic cases (mostly children) in the United States in 1952 alone. The last cases of naturally occurring polio infection (known as "wild polio") acquired in the United States were reported in 1979. In the following two decades, only 152 cases of polio were reported, most of them vaccine-associated paralytic polio (VAPP), a rare complication that strikes 1 in 2 million to 3 million people who receive the oral (by mouth) polio vaccine (OPV). The last case of VAPP was recorded in 1999, and children now receive a vaccine containing an inactivated form of the virus that cannot cause polio. Although wild polio has not been found in the United States for more than two decades, it is still present in parts of Africa and Asia.
Poliovirus is extremely contagious and can pass easily from person to person. The virus typically is found in feces * and can be transmitted when people come into contact with infected matter from bowel movements and unknowingly touch the mouth or nose without washing their hands first. The virus can live in feces for weeks, making the spread of infection difficult to control. It also can spread through contact with tiny drops of fluid from a sick person's mouth or nose or by drinking contaminated water. After entering the mouth or nose, the virus multiplies in the throat or gastrointestinal tract and eventually can invade the bloodstream. The infection is most contagious 7 to 10 days before symptoms begin and for the same period after they appear. The virus spreads more readily in areas with poor sanitation.
There is no cure for polio. Easing a patient's symptoms is the best treatment for the disease. Controlling pain and muscle spasms and watching for progression of muscle weakness so supportive care can be given are the main parts of treatment. Abortive cases and many nonparalytic cases of polio usually are helped by rest, fluids, and pain medication. Moist heat on muscles can ease stiffness. Antibiotics may be prescribed to treat bacterial infections that can occur in patients with polio, such as urinary tract infections * .
Patients with severe cases of polio, particularly the paralytic form, often require hospitalization. In the 1940s and 1950s, patients were placed inside metal tanks called "iron lungs" that assisted their breathing. Although medical technology has progressed since then, many people who have polio still need machines called ventilators * to assist breathing as they recover, as well as additional supportive care. Patients with paralytic polio may need physical therapy, crutches, leg braces, or surgery to help them regain their strength and movement.
The polio vaccine is the best way to prevent the disease; its use has eliminated polio from the Western Hemisphere. Jonas Salk developed the first vaccine in 1955. It is known as inactivated poliovirus vaccine (IPV), because the poliovirus used to make the vaccine was "killed," or inactivated. Several years later, Albert Sabin developed an oral polio vaccine, which was given in the form of drops that could be swallowed. These drops contained a live, but weakened, virus.*