Polio

What is the history of polio?

Polio is caused by a virus and has been around for thousands of years. There are even Egyptian artifacts portraying individuals with typical features of post-polio paralysis. Polio has been called many different names, including infantile paralysis, debility of the lower extremities, and spinal paralytic paralysis. We now refer to the virus and disease as polio, which is short for poliomyelitis and has Greek derivation: polios (gray), myelos (marrow), and itis (inflammation).
Polio is caused by a very infectious enterovirus, poliovirus (PV), which primarily affects young children and is spread through direct person-to-person contact, with infected mucus, phlegm, feces, or by contact with food and water contaminated by feces of another infected individual. The virus multiplies in the gastrointestinal tract where it can also invade the nervous system, causing permanent neurological damage in some individuals.
Most individuals infected with polio remain asymptomatic or develop only mild flu-like symptoms, including fatigue, malaise, fever, headache, sore throat, and vomiting. In fact, the symptoms, if present, may only last 48-72 hours; however, those individuals will continue to shed virus in their stools for a prolonged period, serving as a reservoir for subsequent infections. About 2%-5% of infected individuals go on to develop more serious symptoms that may include respiratory problems and paralysis. Currently, there is no cure for polio; only vaccination can prevent the spread of the disease, and although in the developed world it is almost unheard of, globally, polio remains a fairly common disease. Originally, international organizations believed it possible to eradicate polio by 2000, though this has been more difficult than initially hoped for.

What causes polio?

The symptoms of polio are caused by the poliovirus, which is a small RNA virus that is spread through contact with the oral mucosa (mouth, nose, etc). Most commonly, the virus attaches to and infects intestinal cells, multiplies, and is excreted in the stool of the infected individual. Rarely, in 2% of the cases, the virus spreads from the gastrointestinal tract to the nervous system and causes paralytic disease.

How is polio spread?

Polio is spread in an "oral-fecal" manner. Person-to-person infection occurs by contact with infected mucus, phlegm, feces, or by contact with food and water contaminated by feces of another infected individual.

What are signs and symptoms of polio?

The signs and symptoms of polio differ depending on the extent of the infection. Signs and symptoms can be divided into paralytic and non-paralytic polio.
In non-paralytic polio which accounts for most individuals infected with polio, patients remain asymptomatic or develop only mild flu-like symptoms, including fatigue, malaise, fever, headache, sore throat, and vomiting. The symptoms, if present, may only last 48-72 hours, though usually they last for one to two weeks.
Paralytic polio occurs in about 2% of people infected with the polio virus and is a much more serious disease. Symptoms occur as a result of nervous system and spinal cord infection and inflammation. Symptoms can include

• abnormal sensation,
• breathing difficulty,
• difficulty swallowing,
• urinary retention,
• constipation,
• drooling,
• headache,
• mood swings,
• muscle pain and spasms, and
• paralysis.

Approximately 5%-10% of patients who develop paralytic polio often die from respiratory failure, since they are unable to breathe on their own. That is why it is imperative that patients receive appropriate medical evaluation and treatment. Prior to the vaccine era and the use of modern ventilators, patients would be placed in an "iron lung" (a negative pressure ventilator, which was used to support breathing in patients suffering from paralytic polio).

How is polio diagnosed?

The diagnosis of polio is a clinical one. History of exposure with no history of previous vaccination is the initial hint. Often, a spinal tap for CSF fluid is done to help distinguish polio from other diseases that initially have similar symptoms (for example, meningitis). After that, viral cultures (taken from throat washings, stools, or CSF fluid) and measurement of polio antibodies support the diagnosis.

How is polio treated?

There is no cure for polio, so prevention is very important. Patients with non-paralytic polio need to be monitored for progression to paralytic polio. Patients with paralytic polio need to be monitored for signs and symptoms of respiratory failure, which may require lifesaving therapies such as respiratory support. In addition, a number of treatments are available to decrease some of the less severe symptoms. There are medications to treat urinary infections and urinary retention and pain management plans for muscle spasms. Unfortunately, there are only supportive measures available to treat the symptoms of paralytic polio. Patients who recover from polio may require physical therapy, leg braces, or even orthopedic surgery to improve physical function.

Is there a vaccine that prevents polio?

The story of polio vaccine is a true medical success story. It is not over yet since polio still causes significant illness in less developed areas of the world such as in India and Africa.
During the last half of the 19th century and into the first half of the 20th century, polio was a global epidemic. Even the future U.S. president, Franklin D. Roosevelt, contracted paralytic polio in 1921. President Franklin D. Roosevelt was quite influential in increasing both public awareness and scientific research dedicated to eradicating the disease. In 1938, after the founding of the National Foundation for Infantile Paralysis (March of Dimes), there was a significant effort to develop a vaccine to prevent polio. This came to fruition in 1955 when Dr. Jonas Salk developed an injectable inactivated polio vaccine (IVP) which was soon distributed and administered to children all over the United States and Canada. The current inactivated polio vaccine has evolved over time, but since 1999, it has been the recommended form of the polio vaccine in developed nations.
In 1961, an oral live virus vaccine against polio (OVP) was developed by Albert Sabin which became available and widely used from 1963 to 1999 in developed countries and to present day in underdeveloped countries. This oral virus vaccine is still recommended to control polio pandemics all over the world due to its ease of administration (no needles needed).
Both vaccines were developed for children since they are the group that generally seemed to be at highest risk. However, the oral vaccine (OVP) should not be given to children who are immunodepressed as they can develop vaccine-associated paralytic poliomyelitis (VAPP).
The newest injected vaccine is an enhanced inactivated polio vaccine that is more immunogenic (produces a strong immune system response) than the previous IVP and is used in the U.S.; it does not cause VAPP. The original OVP (also termed tOVP) was a trivalent oral vaccine (polio viruses types 1-3) but caused a measurable immune response in only about 40%-50% of people who obtained it. Unfortunately, this trivalent oral vaccine was often not immunogenic fast enough to withstand dilution or removal from the gastrointestinal tract by chronic diarrhea that existed in many patients. OVP was modified in 2005 to a monovalent (type 1 polio virus only) termed mOVP1. This change caused the vaccine to be three times more immunogenic than the original trivalent OVP and generated an immune response in over 80% of people who obtained this oral vaccine. This newer oral vaccine is used in many developing countries where no needles or trained personnel are available and where chronic diarrhea further reduces the effectiveness of the original trivalent OVP. Other monovalent OVP (for example, mOVP3, used for the infrequent polio type 3 outbreaks) are occasionally used.
Currently, four doses of inactivated polio vaccine (IPV) are recommended for children when they are 2 months old, 4 months old, 6-18 months old, and finally at 4-6 years of age.
Due to vaccination programs, there have been very few cases of polio in the western hemisphere since the 1970s, and although current worldwide eradication programs continue to be successful, there is still work to be done to eliminate polio in developing countries.