Tuesday, October 23, 2007

What makes Polio a dreaded disease?

The scariest thing about polio is that 95 percent of people infected with the polio virus do not exhibit any symptoms. Yet while they themselves do not display any symptoms, they can still spread the polio virus and cause others to develop polio.

The Poliovirus can strike at any age, but affects mainly children younger than three. It is spread by poor sanitation and infected drinking water. Early symptoms are fever, fatigue, headache, vomiting, stiffness and pain in the neck and limbs.

The poliovirus attacks the central nervous system, leaving victims with fever, permanent muscle weakness, paralysis and, in extreme cases, death from asphyxiation.The virus generally enters the body through the mouth and multiplies in the intestine. The polio virus in the nervous system can cause total paralysis in a matter of hours.

Polio is caused by three poliovirus serotypes-- Poliovirus type 1 (PV1 or Mahoney), PV2 (Lansing), and PV3 (Leon). Out of these Type-2 poliovirus appears to have has been eliminated.

Treatment of Polio focuses on providing relief of polio symptoms as the body fights the poliovirus. This is called supportive care.

If there is one disease that illustrates the value of vaccination, it is Polio. Typically the fight against Polio starts with building up the body’s immune system to fight the disease through immunization. Under the Global Polio Eradication Initiative -- the largest public health initiative the world has ever known, 130 million children around the world are immunized before the age of five.

When it comes to immunization there are only two options – oral drops (OPV) or injectable vaccine (IPV). Among these, the oral polio vaccine developed by Polish American scientist Dr. Sabin, has been preferred in many countries because it is administered orally -- usually on a sugar cube. This also does not require a highly trained person to administer the dose i.e. two drops in the mouth.

Dr. Sabin believed that the polio viruses lived in the small intestines. So he developed a mutant form that could not reproduce the disease, but would displace more lethal forms of the virus. Rather than subject another person to risk, Dr. Sabin ingested the mutant virus himself to prove its effectiveness.

The Salk vaccine on the other hand needs to be injected with a needle. These injections require administration by trained medical personnel. There is also resistance among poor, illiterate people to get their children “pricked by needles”.

One of shortcomings of the oral vaccine is that the attenuated virus used in the vaccine may revert to pathogenicity, causing paralysis in one out of every 750,000 to 2.5 million people vaccinated, depending on the source. Rarely, a strain of poliovirus in OPV may genetically change and circulate among a population. These are known as vaccine-derived polioviruses (VDPV) and knowledge on them is growing.

On the other hand,IPV is not a 'live' vaccine - the polio virus is inactivated - and immunization with IPV carries no risk of vaccine-associated polio paralysis. The injectable vaccine contains three viral strains in the following proportions: 40 units of type 1; 8 units of type 2; and 32 units of type 3. Generally speaking, the oral vaccine contains one live, attenuated strain of each type.

Because of these reasons alone in countries where the risk of wild-virus caused polio has come down to zero immunization programmes are now considering combined immunization schedule using both OPV and IPV.

In countries where there is only one type of virus in circulation (generally type 1, but also type 3), the WHO recommends using a monovalent vaccine). Monovalent oral polio vaccines (OPV) – targeted at poliovirus types 1 or 3 – appears to work faster than traditional trivalent OPV to build immunity.

Friday, October 19, 2007

Mission: Polio Free Planet Earth

For nearly 6,000 years now, since the time of the Ancient Egyptians, Polio (also known as poliomyelitis or infantile paralysis) has been one of the most dreaded diseases crippling and maiming mostly children, with a frightening randomness. Records on Paranoiac stele show that the disease existed in Egypt more than 3000 years ago. Withered and deformed limbs of Egyptian mummies are an evidence for this. An Egyptian stele (stone slab) dating back to the 18th paranoiac dynasty (16th - 13th centuries B.C.) shows a priest leaning on a staff, his right leg withered and dangling. His foot is in the equines position, which is a typical sign of polio.

Till as late as 1700's, however, existence of polio remained a mystery even in medical science. The first clinical description of polio dates as far back as 1789 when British physician Michael Underwood referred to it as "debility of the lower extremities."

Polio remained the No 1 most notorious diseases in the 20th century till AIDS arrived on the horizon. Even today the crippling virus accounts for nearly 20 million disabled and paralyzed people in six of the world's poorest nations.

A major breakthrough in the fight against Polio came in 1948 when a research group headed by John Enders at the Children's Hospital Boston successfully cultivated the poliovirus in human tissue in the laboratory. This development greatly facilitated vaccine research and ultimately allowed for the development of vaccines against polio. Enders and his colleagues, Thomas H. Weller and Frederick C. Robbins, were awarded Nobel Prize for Medicine in 1954

A turning point in the history of polio came with the introduction of an inactivated polio vaccine (IPV) in 1955. This contained an inactivated or "killed" version of the virus. This vaccine had to be administered by injection. On April 12, 1955, Dr Jonas Salk, developed a vaccine to prevent polio. This was followed by launch of the oral polio vaccine (OPV) by Dr Albert B. Sabin in 1961. Unlike the injectible form, the oral polio vaccine containing a live attenuated, or weakened, version of the virus. This Sabin vaccine had to be given orally.

Another significant landmark in the fight against polio came in 1988, with the launch of the Global Polio Eradication Initiative. This initiative was instrumental in curtailing the toll of polio paralysis from an estimated 350,000 cases worldwide to fewer than 500 in 2001. Thanks to the hard work of millions of volunteers, the commitment of governments everywhere and the dedication of international partners, nearly four million people have been spared crippling lifelong disability. This was a sharp contrast from the times when wild polio virus was paralyzing more than 1000 children every day in more than 125 countries across five continents. Today polio is largely confined to Nigeria, India, Pakistan, Niger, Afghanistan and Egypt.

But the battle for a polio free world seems to be far from over. The lethality of Polio can be judged from the fact that even today there is no treatment, anywhere in the world. Polio is caused by poliovirus. Till date there is no antibiotic or medicines which can completely and effectively kill the polio virus.