RESEARCH

REFERENCE

AND TRAINING

DIVISION

Vol.No. XLV 29-11-2001 B.No. 18

POLIOMYELITIS

 

Pulse Polio Immunisation programme was launched in India in 1995. Under this programme, every child under the age of five years is given oral polio drops. This backgrounder covers the major aspects of poliomyelitis including its causes, symptoms, epidemiology, treatment and prevention.

 

RESEARCH, REFERENCE AND TRAINING DIVISION

(Ministry of Information and Broadcasting)

Website - www.nic.in/rrtd

E-mail- rrtd_ib@vsnl.com

POLIOMYELITIS

THE DISEASE:

Poliomyelitis (polio) is a highly infectious disease caused by a virus. It invades the nervous system, and can cause total paralysis in a matter of hours. The virus enters the body through mouth and multiplies in the intestine. Initial symptoms are fever, fatigue, headache, vomiting, stiffness in the neck and pain in the limbs. One in 200 infections leads to irreversible paralysis (usually in the legs). Amongst the paralysed patients, 5%-10% die when their breathing muscles become immobilized.

COUNTRIES AT RISK

As long as a single child remains infected with poliovirus, children in all countries are at risk of contracting the disease. The poliovirus can be easily re-imported into a country and can spread rapidly. At the beginning of 2001, up to 20 countries still had ongoing poliovirus transmission (reduced from 30 countries at the beginning of 2000).

There are 10 highest priority countries and they fall into two categories:

POLIO IN INDIA

The states of Assam, Gujarat, Haryana, Orissa, Punjab, Rajasthan and Madhya Pradesh along with the “high burden” states of Uttar Pradesh, Bihar, West Bengal and Delhi, have been conducting the rounds of Intensified Pulse Polio Immunization (IPPI). The four “high burden” states are characterised by the disproportionate number of polio cases that have continued to emerge over the past one year, despite intensification of supplementary immunization activities. All the states in India have been categorised as either “high”,. “middle” or “low burden” states, based on epidemiological data from the National Polio Surveillance Project ( a WHO- Government of India initiative) and the opinion of a group of experts advising the Government of India.

During the IPPI campaign, all children under the age of five receive Oral Polio Vaccine (OPV), irrespective of their previous Immunization status, about 1,70,000 health workers, volunteers, Government functionaries and NGO members conduct house-to-house searches to ensure that not a single child is missed. The next round of IPI this year will be conducted on 2 December 2001.

WHAT CAUSES POLIO?

a) Agent : The causative agents is the polioviruses which have three serotypes 1,2 and 3. Most outbreaks of paralytic polio are due to tpye-1 virus. Polio virus can survive for long periods in the external environment. In a cold environment, it can live in water for 4 months and in faeces for 6 months. It is therefore well-adapted for the faecal-oral route of transmission. However, the virus may be rapidly inactivated by pasteurization, and a variety of physical and chemical agents.

b) Reservoir of Infection : Man is the only known reservoir of infection. Most infections are subclinical. It is the mild and subclinical infections that play a dominant role in the spread of infection; they constitute the submerged portion of the iceberg. It is estimated that for every clinical case, there may be 1000 subclinical cases children and 75 in adults. No animal source has yet been demonstrated.

c) Infectious Material : The virus is found in the faeces and oropharyngeal secretions of an infected person.

d) Period of Communicability : The cases are most infectious 7 to 10 days before and after the onset of symptoms. In the faeces the virus is excreted commonly for 2 to 3 weeks, sometimes as long as 3 to 4 months.

PERSONS AT RISK

Polio mainly affects children under three years of age. In India, polio is essentially a disease of infancy and childhood. About 50 per cent of cases are reported in infancy. The most vulnerable age is between 6 months and 3 years.

 

ENVIRONMENTAL FACTORS

Polio is more likely to occur during the rainy reason. Approximately, 60 per cent of cases recorded in India were during June - September. The environment sources of infection are contaminated water, food and flies. Polio virus survives for a long time in a cold environment. Overcrowding and poor sanitation provide opportunities for exposure to infection.

MODE OF TRANSMISSION

  1. Faecal-Oral Route :This is the main route of spread in developing countries. The infection may spread directly through contaminated fingers where hygiene is poor, or indirectly through contaminated water, milk, foods, flies and articles of daily use.

(b) Droplet Infection : This may occur in the acute phase of disease when the virus occurs in the throat. Close personal contact with an infected person facilitates droplet spread. This mode of transmission may be relatively more important in developed countries where faecal transmission is remote.

INCUBATION PERIOD

Usually 7 to 14 days (range 3 to 35 days)

CLINICAL SPECTRUM

When an individual susceptible to polio is exposed to infection, one of the following responses may occur (a) INAPPARENT (SUBCLINICAL) INFECTION : this occurs approximately in 95 per cent of poliovirus infections. There are no presenting symptoms. Recognition only by virus isolation or rising antibody titres. (b) ABORTIVE POLIO OR MINOR ILLNESS : Occurs in approximately 4 to 8 per cent of the infections. It causes only a mild or self-limiting illness due to viraemia. The patient recovers quickly. The diagnosis cannot be made clinically. Recognition is only by virus isolation or rising antibody titre. (c) NON-PARALYTIC POLIO : Occurs in approximately 1 per cent of all infections. The presenting features are stiffness and pain in the neck and back. The disease lasts 2 to 10 days. Recovery is rapid. The disease is synonymous with aseptic meningitis. (d) PARALYTIC POLIO : Occurs in less than one per cent of infections. The virus invades CNS and causes varying degrees of paralysis. The predominant sign is asymmetrical flaccid paralysis. A history of fever at the time of onset of paralysis is suggestive of polio, as is the persistence of paralysis beyond 6 weeks. Progressive paralysis, coma or convulsions usually indicate a cause other than polio, as does a very high case fatality rate.

WHAT IS THE TREATMENT ?

There is no specific treatment for polio. Good nursing care from the beginning of illness can minimise or even prevent crippling. Physiotherapy is of vital importance. It can be initiated in the affected limb immediately. It helps the weakened muscles to regain strength. Depending on the severity, the child may have to put on metal calipers. As there is no cure for polio, the best treatment is preventive. A few drops of a powerful vaccine, given multiple times, will protect a child for life.

VACCINES


Immunity against polio can be stimulated in two ways:

Poliovirus infection provides lifelong immunity against the disease, but this protection is limited to the particular type of poliovirus involved (Type 1, 2, or 3). Unfortunately, infection with one type does not protect an individual against infection with the other two types. The development of effective vaccines to prevent paralytic polio was one of the major medical breakthroughs of the 20th century. Two different kinds of vaccine are available:

Both vaccines are highly effective against all three types of poliovirus. There are, however, significant differences in the way each vaccine works.

 


Oral polio vaccine (OPV)

The action of oral polio vaccine (OPV) is two-pronged: OPV produces antibodies in the blood ('humoral' or serum immunity) to all three types of poliovirus. In the event of infection, this will protect the individual against polio paralysis by preventing the spread of poliovirus to the nervous system. OPV also produces a local immune response in the lining ('mucous membrane') of the intestines - the primary site for poliovirus multiplication. The antibodies limit the multiplication of 'wild' (naturally occurring) virus inside the gut, preventing effective infection. This intestinal immune response to OPV is probably the main reason why mass campaigns with OPV can rapidly stop person-to-person transmission of wild poliovirus.

Advantages of Oral Polio vaccine

OPV is an orally applicable vaccine. It does not have to be administered by a trained health worker, can be given by volunteers, and - unlike most other vaccines - does not require sterile injection equipment. The vaccine is relatively inexpensive which is a major consideration when governments have to purchase massive quantities of vaccine for use during National Immunization Days.

The short-term shedding of vaccine virus in the stools of recently immunized children means that in areas where hygiene and sanitation are poor - and the incidence of polio is likely to be high - immunization with OPV can result in the 'passive' immunization of persons within close contact. As discussed above, the unique ability of OPV to induce intestinal, local immunity is probably responsible for the extraordinary effect of OPV mass campaigns in interrupting wild poliovirus transmission. Due to these advantages, OPV remains the vaccine of choice for the eradication of polio, which would not be feasible with inactivated polio vaccine (IPV).

Disadvantages of Oral Polio vaccine

Although OPV is safe and effective, in extremely rare cases (approx. 1 in every 3 million doses of the vaccine) the live attenuated vaccine virus in OPV can cause paralysis - either in the vaccinated child, or in a close contact. Immune deficiency of the recipient may be among the causes. This extremely low risk of vaccine-associated polio (VAPP) is well known, and accepted by most public health programmes in the world because without OPV, hundreds of thousands of children would be crippled every year. Immunization programmes in countries where the risk of wild-virus caused polio has come down to zero are now considering combined immunization schedules using both OPV and IPV.

Inactivated Polio Vaccine (IPV)

Inactivated polio vaccine (IPV) needs to be injected and works by producing protective antibodies in the blood (serum immunity) - thus preventing the spread of poliovirus to the central nervous system. However, it induces only very low levels of immunity to poliovirus locally, inside the gut. As a result, it provides individual protection against polio paralysis but, unlike OPV, cannot prevent the spread of wild polio virus.

Advantages of Inactivated Polio Vaccine

IPV is not a 'live' vaccine - the polio virus is inactivated - and immunization with IPV carries no risk of vaccine-associated polio paralysis. Immunization with IPV triggers an excellent response of the immune system in most IPV recipients.

Disadvantages of Inactivated Polio Vaccine

Unlike the oral vaccine, IPV confers only very little immunity in the intestinal tract. When a person immunized with IPV is infected with wild poliovirus, virus can still multiply inside the intestines and be shed in stool -- risking continued circulation. For this reason, OPV is the vaccine of choice wherever a polio outbreak needs to be contained, even in countries which rely exclusively on IPV for their routine immunization programme

Other disadvantages of IPV include the price (over five times that of OPV), the cost of the syringe, and the need for trained health workers to administer the vaccine using sterile injection procedures.

 

THE GLOBAL POLIO ERADICATION INITIATIVE

Strategies:

There are five main activities necessary to realize polio eradication, the global certification target of 2005, and eventual cessation of polio immunization:

Before a region can be certified polio-free, immunization and high quality surveillance need to continue for a number of years after the last polio case has been detected. Laboratory stocks must be contained before the world can be certified polio-free.

The target date for certification of the world as polio-free is 2005.

ERADICATION


The Global Eradication of Polio --- A Polio-Free World in 2005

In May 1988, at its annual meeting in Geneva, the World Health Assembly, the governing body of the World Health Organization (WHO), resolved to eradicate polio from the world.

The global eradication of polio involves both halting the incidence of the disease and the worldwide eradication of the virus that causes it - poliovirus.

Rationale for Polio Eradication

Polio is one of the few diseases (others include measles and guinea worm disease) that can be eradicated. Polio can be eradicated because:

The polio eradication strategy is based on the premise that poliovirus will die out if it is deprived of its human host through immunization. The strategy is similar to that used for smallpox eradication in 1977; smallpox is the only disease so far to have been eradicated

 

 

CHALLENGES FACED IN POLIO ERADICATION

Polio eradication faces three main challenges:

Access: Securing access to all children, especially those in conflict-affected countries, is crucial.

Funding: Necessary financial resources must be secured to purchase oral polio vaccine (OPV), plan and implement national immunization days and mop-up campaigns, and cover surveillance and laboratory costs.

Political commitment: Sustaining political commitment from the highest levels of government is particularly challenging in the face of a disappearing disease. In polio- endemic countries, personal monitoring by health is key to improving the quality of activities. In polio-free countries, political commitment is needed for sustaining certification-standard surveillance and achieving laboratory containment of poliovirus.

In addition, priority reservoir countries require a special effort, including extra national immunization days and house-to-house mop-up campaigns. Certification-standard surveillance is needed to find the last cases in every country and evaluate the status for certification.

Once polio is eradicated, the laboratories of the world will be the only remaining location of the virus. As an increasing number of countries become polio-free, the virus needs to be safely and securely stored in laboratories to ensure no inadvertent release occurs after eradication.

IMPACT OF THE GLOBAL POLIO ERADICATION INITIATIVE

Since the global initiative began in 1988, Rotary International estimates that three million people in the developing world, who would have been paralysed, are walking because they have been immunized against polio. Nearly two billion children worldwide have been immunized during national immunization days in the last five years. In 2000, 550 million children were reached as part of these efforts.

Tens of thousands of public health workers have been trained to investigate cases of paralysis and manage immunization programmes.

On an average, one out of every 250 people in a country are involved in polio immunization campaigns. Tens of millions of volunteers have been trained to deliver OPV and vitamin A.

In 2000, over 50 countries gave vitamin A during polio national immunization days, preventing over 2,40,000 childhood deaths.

Cold chain, transport and communications systems for immunization have been strengthened.

A polio laboratory network of 148 polio laboratories has been established.

FUTURE BENEFITS OF POLIO ERADICATION

The savings of polio eradication, once immunization stops, are estimated to be US$ 1.5 billion per year – funds that can be used to address other public health priorities.

In many countries polio eradication is expanding the capacity to tackle other diseases by building effective disease reporting and surveillance systems, training epidemiologists and establishing a global laboratory network.

No child, regardless of race, sex, ethnicity, economic status or religious belief, need ever fear or suffer from this crippling disease.

 

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