Polio is caused by the aptly named poliovirus. The poliovirus only occurs in humans. Polio is commonly known as a crippling disease that spreads from person to person, causing paralysis of muscles as a result of the virus invading the brain and spinal column of the person infected. It is highly contagious disease that is spread from person to person by several methods or modes of transmission.
Transmission methods include:
▪️Fecal-oral transmission - When the feces of an infected person is introduced (via the mouth) to another person, the disease is transmitted. This commonly occurs when there is contamination of drinking water or food.
▪️Droplet spread - this mode is less common than fecal-oral transmission.
▪️Direct contact
▪️Oral to Oral
▪️Contact with an object (such as a toy) contaminated with an infected person’s stool/feces or saliva/droplet spread, that is put into the mouth.
Once contracted, the contagious virus resides in the infected person’s intestines and throat. There are two kinds of polio, non-paralytic and paralytic.
Non-paralytic polio symptoms go away without any type of intervention, they may include:
▪️Sore throat
▪️Fever
▪️Fatigue
▪️Stomach discomfort
▪️Nausea
▪️Headache
Of the total number of those infected with the polio virus, a smaller number will develop serious symptoms—such as those involving the nervous system. The symptoms, which are considered the most serious may begin mimicking non-paralytic polio but then there is a progression to more serious symptoms such as:
▪️Loss of reflexes
▪️Severe muscle aches
▪️Flaccid paralysis
▪️Paresthesia
▪️Meningitis, which occurs in one in 25 people with polio according to the CDC
▪️Paralysis or weakness in the arms and/or legs, which occurs in about one in 200 people with polio, according to the CDC
▪️Death (from the paralysis of muscles that are required for breathing)
Paralytic polio can cause long-term or permanent paralysis of muscles, disability (such as being unable to walk without crutches), bone deformities, or death.
There is no known effective treatment for polio, other than palliative treatment and prevention of complications. Supportive treatment may include:
▪️Ventilators (to enable normal breathing)
▪️Pain medication
▪️Physical therapy (to prevent loss of muscle function)
𝙿𝚘𝚜𝚝-𝚙𝚘𝚕𝚒𝚘 𝚂𝚢𝚗𝚍𝚛𝚘𝚖𝚎
Post-polio syndrome (PPS) is a condition that can affect polio survivors decades after they recover from their initial poliovirus infection. Unlike poliovirus, PPS is not contagious. PPS affects between 25 and 40 out of every 100 polio survivors.
Symptoms of post-polio syndrome may include:
▪️Muscle or joint weakness and pain which progressively worsens
▪️Fatigue (physical and mental)
▪️Atrophy of muscles (wasting)
▪️Problems swallowing or breathing
▪️Apnea or other sleep-related breathing disorders
▪️Inability to tolerate cold temperatures
Some people with PPS have only minor symptoms, while others develop more visible muscle weakness and atrophy. PPS is rarely life-threatening, but the symptoms can make it difficult for an affected person to function independently.
Although major polio epidemics were unknown before the 20th century, polio survived quietly as an endemic pathogen until the 1900s when major epidemics began to occur in Europe. Soon after, widespread epidemics appeared in the United States. By 1910, frequent epidemics became regular events throughout the developed world primarily in cities during the summer months. At its peak in the 1940s and 1950s, polio would paralyze or kill over half a million people worldwide every year.
In 1908, Vienna MDs Landsteiner and Popper announced that the infectious agent in polio was a virus. They deduced the viral nature of polio by carefully filtering preparations of spinal cord fluid from a person who had died of polio. The filters trapped bacteria so The researchers then concluded that an infectious particle smaller than bacteria caused the disease. Poliovirus itself would not be visible to researchers until the 1950s, when the electron microscope was available.
Early polio vaccine trials were disastrous. Several subjects died of polio, and many were paralyzed, made ill, or suffered allergic reactions to the vaccines. In 1941, researchers discovered that polio wasn't just a disease of the nervous system but also in the digestive system. This finding gave hope that a vaccine could be developed that would produce antibodies to fight the virus in the bloodstream before it reached the nervous system.
In 1949, further research revealed that there were no more than three immunologically different types of polio. This was an important finding because a vaccine would have to produce immunity to all poliovirus types.
Within the quest to develop a vaccine, researchers were investigating the idea of using human immunoglobulin (IgG, or gamma globulin) to protect people from polio. IgG is an antibody preparation made from blood pooled from many people who most likely have antibodies to common infections. Their disease-specific antibodies in the IgG, when injected into a person who had recently or would soon be exposed to the disease, had been shown to provide protection. This type of protection is known as passive immunization. Three clinical trials in 1951-52 showed some likely protective effects of gamma globulin use against polio. Use of the preparation presented several problems, though. Gamma globulin was expensive to produce and it gave only temporary protection. It would need to be used again in each subsequent epidemic. Moreover, physicians relied on gamma globulin for protection against measles, hepatitis, and other diseases for which there were no vaccines. The supply was limited, and the need was great.
A vaccine was still the ideal treatment. In 1954, Jonas Salk conducted a massive clinical trial with his version of a polio vaccine. When the results were studied in 1955 it found that his version of the vaccine was 80-90% effective against paralytic polio. The same day those findings were released to the public, the vaccine was approved for use and vaccinations started immediately. However, within a short amount of time vaccinations were halted after adverse reactions, such as paralysis, were occurring in children. One of the labs in California producing the vaccine were skipping a step that was vital to the safety of the vaccine. Standards were reset and procedures solidified and production started back up.
Jonas Salk's polio vaccine was IPV, an Inactivated Polio Vaccine, and therefore administered via a needle. But there were others who thought they could avoid administration from a needle and hit the digestive system faster if it was given orally.
1959 found the Soviet exploring the polio vaccine orally. Albert Sabin had spent years studying and attenuating the three types of polioviruses so that they were effective in inducing immunity to polio but weak enough not to cause disease. Sabin's oral polio vaccine (OPV) was fed to 10 million Soviet children.
The OPV had several advantages over the Salk vaccine (IPV).
▪️It produced an immune response faster than Salk’s vaccine, which meant that it could be used to respond to an epidemic.
▪️Because it entered the mouth, it traveled through the digestive system in the same manner as the wild virus. Vaccine recipients shed weakened vaccine virus in their stools, which sometimes had the effect of weakly immunizing those around them.
▪️OPV, often delivered on a sugar cube and eaten, was easier to give than the Salk vaccine, which was injected.
The IPV, however, retained one major advantage over the OPV: The killed viruses in IPV cannot revert to virulent forms as can the viruses in OPV.
Other differences between the two vaccines include:
▪️ The OPV does not require a trained health worker to administer it, the IPV does require one.
▪️ The IPV strengthens the immune system and provides further protection from polio. It is for this reason that IPV is usually given in addition to OPV in certain countries.
Sabin's OPV was licensed for use in the United States in 1960, and it protected against Type 1 polio. In 1963 a vaccine would be licensed that protected against all three types, which was the goal.
Salk's IPV vaccine was phased out of use in 1968 and phased back in to use in 1997 when an improved version was developed. By the year 2000, the United States had returned to using Salk's IPV exclusively due to concerns over OPV causing cases of polio. OPV is still used in some parts of the world.
{You can find all the sources I used by clicking here.}
No comments:
Post a Comment