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Polio Vaccine IPV When to Get Vaccinated

Polio Vaccine IPV When to Get Vaccinated

Poliomyelitis, infectious viral disease that sometimes results in paralysis. The infection chiefly affects children

and young adults and is caused by any one of three related viruses called polioviruses. In more than 95 percent of cases, the infection may pass without creating severe or even noticeable illness because the body’s immune system neutralizes the invading virus and protects against future infection. In a small percentage of cases the virus penetrates to the central nervous system, infecting cells that control muscle function. Such infection can result in permanent paralysis of limbs. In its most perilous form, the infection attacks the brain, creating complications that sometimes result in death.
The term poliomyelitis derives from Greek words referring to inflammation (itis) of the gray (polios) matter of the spinal cord (myelos). The shortened term polio is commonly used by the public and medical professionals, and the disease has also been referred to as infantile paralysis.

According to figures from the World Health Organization (WHO), approximately 7,100 cases of polio were reported throughout the world in 1999. Experts suspect that misdiagnosis and underreporting may make these numbers inaccurate. Thus, the actual number of polio cases may be roughly five times the reported figure—perhaps more than 20,000 cases, occurring primarily in Africa, the Middle East, and South Asia.

While still a health threat in many parts of the world, polio also represents one of the greatest medical success stories of the 20th century. The number of polio cases found worldwide today constitutes a 90 percent reduction from the number of cases reported in the late 1980s. Most health experts credit this achievement to a mass vaccination program called the Global Polio Eradication Initiative that WHO initiated in 1988 to eradicate polio worldwide by the year 2005.

In the United States and Canada, polio has been effectively eliminated, with fewer than ten cases reported in each country per year. This statistic contrasts strikingly with those from the first half of the 20th century, when epidemic polio was one of the most dreaded and feared diseases in North America. The first large-scale outbreak in the United States occurred in 1916, when over 37,000 cases were reported in 26 states, resulting in 6,000 deaths. Each year thereafter the number of polio cases in the United States averaged about 38,000 per year, including about 21,000 paralytic cases each year. In Canada the epidemic peaked in 1953, resulting in one of the highest national polio rates ever recorded in the world.

Fearing infection during epidemics in the first half of the 20th century, some people avoided beaches, public pools, theaters, fairs—any place of public gathering. Occasionally schools were closed until epidemics subsided. In response to the public’s fear of this disease, in 1938 President Franklin Delano Roosevelt (who had himself lost the use of both legs to polio) founded the National Foundation for Infantile Paralysis. Now known as the March of Dimes Birth Defects Foundation, the organization raised millions of dollars for polio research and the support of victims.

The discovery in the 1950s of vaccines that protect against poliovirus infection eventually led to successful polio vaccination programs in North America, Latin America, and Europe. By the early 1990s, WHO declared the western hemisphere free of polio. But the struggle to eradicate polio continues in many developing nations. Furthermore, health officials stress that vaccination programs must be maintained in areas considered polio free. They warn that the virus could easily become dangerous again in populations of children who have not acquired immunity, the body’s ability to resist infection from the polio virus. This danger was chillingly demonstrated in 1979 when an outbreak of paralytic polio erupted among unvaccinated members of an Amish sect in Pennsylvania and Maryland.

HOW POLIO DEVELOPS,

The three types of poliovirus belong to the virus family known as picornaviruses. This name derives from a combination of the words pico, meaning "small," and RNA, indicating that the viruses contain a core of the genetic material known as ribonucleic acid, or RNA. Three types of poliovirus have been identified: Type 1 (also known as Brunhilde), Type 2 (Lansing), and Type 3 (Leon). Type 1 is the most common form and the one most closely associated with polio’s more severe, paralytic progression. A person who develops immunity from exposure to one poliovirus type will not have immunity against the other polioviruses.

Poliovirus typically enters the body through the mouth and multiplies in the tonsils and lymph nodes of the upper respiratory tract. Infection proceeds from the mouth into the gastrointestinal tract through the stomach to the intestines. The virus multiplies in the intestines and is shed from the body in feces, often resulting in further infections. For example, a parent can become infected by an infant during diaper changes, or improper waste disposal can lead to contamination of a water supply. These infections, in turn, will spread the virus more widely.

Large quantities of poliovirus multiply in intestinal tissue known as Peyer’s patches, where cells of the body’s lymphatic system are concentrated. Passage of the virus into the body’s lymphatic system stimulates the production of antibodies. These specialized immune-system defenders, in time, will destroy the viral intruder. From the lymphatic system, the virus typically invades the bloodstream.

Types of Polio Disease,

Once the virus enters the bloodstream, the virus may cause one of four types of illnesses marked by varying severity. Some infections result in abortive poliomyelitis, a mild form of the disease characterized by fever, headache, sore throat, fatigue, nausea, and vomiting. This short-lived form of the illness lasts only from hours to a few days. In more than 95 percent of cases, the disease gets no worse. Sometimes, however, the virus may invade the nervous system, causing more severe forms of the disease.

Some poliovirus infections of nerve cells, or neurons, result in nonparalytic poliomyelitis. In addition to the fever and other symptoms seen in abortive poliomyelitis, nonparalytic poliomyelitis causes pain and stiffness in the neck and back. This infection typically produces aseptic meningitis—an inflammation of the membranes that surround the brain and spinal cord. As with abortive poliomyelitis, however, symptoms from nonparalytic polio usually subside within a few days without causing permanent damage.

In perhaps 1 or 2 percent of cases a more disabling form of the disease occurs, called paralytic poliomyelitis. In this form viral infection of neurons in the spinal cord may cause temporary damage to these cells—or permanent destruction. The muscles activated by the involved neurons become painful, and muscular weakness in the arms and legs may develop, sometimes followed by paralysis. The muscles affected and the degree of damage that occurs depend on the area of the spinal cord that has been invaded and on the number of neurons involved. Any limb or combination of limbs may be affected—one leg, one arm, or both legs and both arms. In children under 5 years of age paralysis of one leg is most common. In adults paralysis of all four limbs—a condition known as quadriplegia—is more common. In some cases muscles that control breathing are affected, requiring that the patient be placed on artificial respiration, in which breathing is controlled mechanically. Roughly 2 to 5 percent of infants with paralytic polio die. For adults the disease is even deadlier, causing death in 15 to 30 percent of cases.

In the most serious cases of polio infection the virus attacks the brain, causing bulbar poliomyelitis. Various nerves in the head and face, including those that send signals to the ears, eyes, and the muscles controlling chewing and swallowing, may be affected. Sometimes the virus affects the part of the brain that controls breathing and heartbeat, resulting in death.

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