Polio, also called poliomyelitis, is a serious disease that has affected millions of people around the world. The cause of polio is a virus that enters the body through the mouth and multiplies in the intestines. The polio virus usually affects children and is most commonly spread through contaminated human waste.
The cause of polio is the polio virus replicating by infecting healthy cells with its genetic material. Single viruses lack the components necessary to reproduce on their own and require the complex cells found in plants or animals in order to replicate. After infecting a cell with its genetic material, the cell will create many copies of the virus until its wall bursts and the new virus cells are released into the host. With the polio virus, this replication occurs in the intestines and spreads quickly through the infected person, exiting the body through waste, through which it can contaminate other humans.
Epidemics of the polio virus were common around the world a hundred years ago. The cause of polio was unknown for much of its history, and poor hygiene led to its rapid spread. It was one of the most feared diseases of its time because, though the disease is rarely fatal, in it can cause irreversible paralysis. In approximately one out of every 200 cases, polio causes paralysis of the legs, leaving its victims bound to a wheelchair. Polio can be fatal if the paralysis spreads to the lungs, however.
Polio has been eradicated throughout most of the world, largely due to vaccination efforts. Four doses of the polio vaccine provide near-complete immunity to the disease. Since the cause of polio is a virus that enters the body through material contaminated with human waste, better sanitation has also helped to prevent polio from spreading. While most of the world has eliminated polio, some countries still remain polio-endemic. Between 2009 and 2010, 23 previously polio-free countries were reinfected with the disease when it was imported from high-risk countries.
The polio virus can pass through the human body without causing any symptoms. Early symptoms of the disease can include fever, malaise, vomiting and stiffness and pain in the body. While most cases of the infection will end with these symptoms, 0.5% of cases will result in irreversible paralysis. Occasionally, post-polio syndrome can develop even when there were no symptoms while the body was fighting off the polio disease. Symptoms include malaise, weakness and pain. There is no cure or prevention for post-polio syndrome.