The summer season is fast approaching, a season very much anticipated by vacationers and sun-worshippers. However, health experts worldwide are busier during this season because various dreaded diseases abound during the hot and humid days of April and May. One of them is poliomyelitis, commonly known as polio, a systemic infectious disease that can affect the central nervous system and cause paralysis in its most severe form.
Just when local health authorities thought that polio has already been successfully eradicated in our country, three cases of what are believed to be due to a mutant strain of wild polio are reported. And parents are again hounded by fear that their children might get the disease.
The term poliomyelitis comes from the Greek words polio which means gray and myelin or marrow which refers to the spinal cord. Polio had its most noticeable impact on humanity during the latter part of the 19th century when an epidemic was recorded in the Western Hemisphere, from the United States to as far as Norway in northern Europe. But polio had caused widespread paralysis as early as the ancient Egyptian period. Proof of this is a stone engraving depicting paralytic poliomyelitis dating back over 3,000 years.
There are three different types of polioviruses, all members of the enterovirus family, which infect the human intestinal tract. These strains of viruses are quite stable and have the capacity to remain infectious for long periods of time both in water and in food. Infection produces lifelong immunity to the disease.
The virus may enter the body through the nose or mouth, and it travels to the intestines where it multiplies. The virus can remain in the mouth and throat for about three weeks, and in the intestines for up to eight weeks.
As soon as it enters the intestines, the virus multiplies rapidly. It will then invade the nearby lymphatic system and enters the bloodstream to gain access to the central nervous system composed of the brain and spinal cord. In some cases, the virus infects a nerve in any part of the body and eventually spreads along that nerve to be able to find its way into the brain.
After a few days, most infected individuals are asymptomatic but some patients develop flu-like symptoms such as headache, nausea, vomiting and fever. At this stage, the patient is highly capable of transmitting the disease to others.
When the poliovirus has successfully invaded the brainstem – the stalk of brain that connects the two cerebral hemispheres with the spinal cord – the patient may begin to have trouble breathing and swallowing food. This can be fatal if the brainstem is affected because the brain’s control of vital bodily functions such as heart rate and blood pressure may be disturbed.
Some poliovirus patients develop severe headache and pain and stiffness of the neck and back. This is mainly attributed to inflammation of the meninges, three layers of tissue that cover both the spinal cord and brain. This syndrome is commonly called "aseptic meningitis." The patient may still be able to recover completely from this illness within several days.
A small percentage of poliovirus sufferers develop the so-called "major illness." They develop symptoms such as headache, backache and neck pain. The major symptoms are due to invasion of the motor nerves, which are responsible for movement of the muscles. This causes severe inflammation and the eventual destruction of the motor nerves.
Due to the destruction of motor nerves, the muscles do not receive any messages from the brain or spinal cord. In the process, muscles become weak and paralyzed. The eventual "wasting" of the muscle will eventually result in atrophy, a condition wherein muscles substantially decrease in size.
The Salk vaccine is an injection of chemically killed poliovirus that allows one’s immune system to recognize the virus and eliminate it once an active virus enters one’s body.
The Sabin vaccine, also called the "oral polio vaccine (OPV)," is given by mouth. It contains weak but live viruses of each of the three polio serotypes. Once inside the body, the virus replicates in the patient’s intestinal tract and induces immunity.
Both oral and injectable polio vaccines are effective in preventing polio when used according to recommendations. The oral polio vaccine is more popular among developing nations, like India, Pakistan and the Philippines since it is cheaper and more convenient to administer.
"There is a need to launch a massive anti-polio campaign to cast a wider net of protection and finally stop the transmission of the virus strain," says Health Secretary Manuel Dayrit.
In the global front, the prognosis for the eradication of the poliovirus is convincingly positive. Dr. Gro Harlem Brundtland, the current director-general of the World Health Organization (WHO), envisions a polio-free world in her speech at the 2001 Geneva Convention. With the successful eradication of the poliovirus in almost all countries, except the 10 countries in sub-Saharan Africa and South Asia, Brundtland believes that the global certification target of polio-free world by 2005 is truly in sight.
(The Charter Bureau is a non-stock, non-profit research foundation based at the Manila Sanitarium Hospital. It advocates healthy lifestyle practices in the prevention and treatment of common medical problems. Dr. Castillo is a member of its board of trustees.)