The U.S. Centers for Disease Control and Prevention (CDC) has issued a warning about a "circulating poliovirus" in over 30 countries.
The "Level 2: Practice Enhanced Precautions" alert was published earlier this week.
"Before any international travel, make sure you are up-to-date on your polio vaccines," the agency said.
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The announcement comes as Americans begin their spring break travels - and countries such as Spain, the United Kingdom and Germany are among those listed in the warning.
Travelers are told they can prevent the illness by making sure that both adults and children are up-to-date on their polio vaccines.
"Adults who previously completed the full, routine polio vaccine series may receive a single, lifetime booster dose of polio vaccine," the CDC recommends.
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This applies to any Americans who are planning on traveling to the countries listed.
The CDC warns that the disease is crippling and can be deadly - impacting the nervous system.
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"Good handwashing practices can help prevent the spread of this disease," the CDC notes.
"Because the virus that causes polio lives in the feces (poop) of an infected person, people infected with the disease can spread it to others when they do not wash their hands well after defecating (pooping)," said the agency.
Travelers are warned they can also be infected if they drink water or eat food contaminated with infected feces.
Dr. Marc Siegel, Fox News senior medical analyst, told Fox News Digital that the "polio vaccine provides lifetime immunity for the vast majority of people who take it. The Salk vaccine is used exclusively in the U.S.," he added, "and it protects against all clinical disease, though you can still carry and shed the virus in your GI tract it doesn't get you sick."
He noted, "It makes sense to have a single booster before traveling to an area where there is polio - one lifetime booster."
The CDC warned that those infected with polio may not feel sick right away.
They may also experience only minor symptoms, such as a "fever, tiredness, nausea, headache, nasal congestion, sore throat, cough, stiffness in the neck and back, and pain in the arms and legs."
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In rare cases, the infection can be fatal if there is a permanent loss of muscle function, causing paralysis.
"Polio can be fatal if the muscles used for breathing are paralyzed or if there is an infection of the brain," the CDC added.
