Polio is a contagious viral illness that in its most severe form causes nerve injury leading to paralysis, difficulty breathing and sometimes death.

In the U.S., the last case of naturally occurring polio was in 1979. Today, despite a worldwide effort to wipe out polio, poliovirus continues to affect children and adults in parts of Asia and Africa.

The Centers for Disease Control and Prevention (CDC) advises taking precautions to protect yourself from polio if you're traveling anywhere there's a risk of polio.

Adults who have been vaccinated who plan to travel to an area where polio is occurring should receive a booster dose of inactivated poliovirus vaccine (IPV). Immunity after a booster lasts a lifetime.

Although polio can cause paralysis and death, the majority of people who are infected with the virus don't get sick and aren't aware they've been infected.

Nonparalytic polio

Some people who develop symptoms from the poliovirus contract a type of polio that doesn't lead to paralysis (abortive polio). This usually causes the same mild, flu-like signs and symptoms typical of other viral illnesses.

Signs and symptoms, which can last up to 10 days, include:

• Fever
• Sore throat
• Headache
• Vomiting
• Fatigue
• Back pain or stiffness
• Neck pain or stiffness
• Pain or stiffness in the arms or legs
• Muscle weakness or tenderness

Paralytic syndrome

This most serious form of the disease is rare. Initial signs and symptoms of paralytic polio, such as fever and headache, often mimic those of nonparalytic polio. Within a week, however, other signs and symptoms appear, including:

• Loss of reflexes
• Severe muscle aches or weakness
• Loose and floppy limbs (flaccid paralysis)

Post-polio syndrome

Post-polio syndrome is a cluster of disabling signs and symptoms that affect some people years after having polio. Common signs and symptoms include:

• Progressive muscle or joint weakness and pain
• Fatigue
• Muscle wasting (atrophy)
• Breathing or swallowing problems
• Sleep-related breathing disorders, such as sleep apnea
• Decreased tolerance of cold temperatures

When to see a doctor

Check with your doctor for polio vaccination recommendations before traveling to a part of the world where polio still occurs naturally or where oral polio vaccine (OPV) is used, such as Central and South America, Africa and Asia.

Additionally, call your doctor if:

• Your child hasn't completed the vaccine series
• Your child has an allergic reaction to the polio vaccine
• Your child has problems other than a mild redness or soreness at the vaccine injection site
• You had polio years ago and are now having unexplained weakness and fatigue

Poliovirus can be transmitted through direct contact with someone infected with the virus or, less commonly, through contaminated food and water. People carrying the poliovirus can spread the virus for weeks in their feces. People who have the virus but don't have symptoms can pass the virus to others.

Polio mainly affects children younger than 5. However, anyone who hasn't been vaccinated is at risk of developing the disease.

Paralytic polio can lead to temporary or permanent muscle paralysis, disability, bone deformities and death.

The most effective way to prevent polio is vaccination.

Polio vaccine

Most children in the United States receive four doses of inactivated poliovirus vaccine (IPV) at the following ages:

• Two months
• Four months
• Between 6 and 18 months
• Between ages 4 and 6 when children are just entering school

IPV is safe for people with weakened immune systems, although it's not certain just how protective the vaccine is in cases of severe immune deficiency. Common side effects are pain and redness at the injection site.

Allergic reaction to the vaccine

IPV can cause an allergic reaction in some people. Because the vaccine contains trace amounts of the antibiotics streptomycin, polymyxin B and neomycin, it shouldn't be given to anyone who's reacted to these medications.

Signs and symptoms of an allergic reaction usually occur within minutes to a few hours after the shot. Watch for:

• Difficulty breathing
• Weakness
• Hoarseness or wheezing
• Rapid heart rate
• Hives
• Dizziness

If you or your child has an allergic reaction after any shot, get medical help immediately.

Adult vaccination

In the U.S., adults aren't routinely vaccinated against polio because most are already immune, and the chances of contracting polio are minimal. However, certain adults at high risk of polio who have had a primary vaccination series with either IPV or the oral polio vaccine (OPV) should receive a single booster shot of IPV.

A single booster dose of IPV lasts a lifetime. Adults at risk include those who are traveling to parts of the world where polio still occurs or those who care for people who have polio.

If you're unvaccinated or your vaccination status is undocumented, get a series of primary polio vaccination shots — two doses of IPV at four- to eight-week intervals and a third dose six to 12 months after the second dose.

Doctors often recognize polio by symptoms, such as neck and back stiffness, abnormal reflexes, and difficulty swallowing and breathing. To confirm the diagnosis, a sample of throat secretions, stool or a colorless fluid that surrounds your brain and spinal cord (cerebrospinal fluid) is checked for poliovirus.

Because no cure for polio exists, the focus is on increasing comfort, speeding recovery and preventing complications. Supportive treatments include:

• Pain relievers
• Portable ventilators to assist breathing
• Moderate exercise (physical therapy) to prevent deformity and loss of muscle function

Call your primary care doctor if you've recently returned from travel abroad and develop symptoms similar to those that occur with polio. Here's some information to help you get ready for your visit.

What you can do

When you make your appointment, ask if there's anything you need to do in advance. Your doctor may recommend taking steps to reduce the risk of spreading a potentially contagious illness to others. Make a list of:

• Your symptoms, and when they began
• Information about recent exposure to possible sources of infection, including details about international trips, the countries you visited and the dates
• Medical history, including other conditions for which you're being treated; medications, vitamins and supplements you take; and your vaccination history
• Questions to ask your doctor

Take a family member or friend along, if possible, to help you remember the information you're given.

For polio, questions to ask your doctor include:

• Do I have polio?
• What are other possible causes for my symptoms?
• What tests do I need?
• What self-care steps can I take?
• How long is a full recovery likely to take?
• Am I contagious? If so, for how long?
• When can I return to work or school?
• Am I at risk of any long-term complications from polio?

Don't hesitate to ask other questions.

What to expect from your doctor

Your doctor is likely to ask you questions, such as:

• Have your symptoms been continuous or occasional?
• How severe are your symptoms?
• What, if anything, seems to improve your symptoms?
• What, if anything, appears to worsen your symptoms?
• Have you recently been around people with symptoms similar to yours?
• Are you pregnant?