Poliomyelitis

Poliomyelitis is an acute communicable disease. It is principally an infection of alimentary tract but affects the central nervous  system leading often to paralysis. You may have seen a number of individuals handicapped for life, as a result of an attack of poliomyelitis in their childhood. With the introduction of immunisation, poliomyelitis is rarely  ever seen in the developed countries where the incidence of the disease has almost approached zero. In India, however. thousands poliomyelitis are reported even today. 

The Disease-- What cause it? who gets it? How and when does it spread? 

Poliomyelitis is caused by a virus which can be seen only under sophisticated microscope. Three types of polio virus-type 1, type 2 and type 3 have been found to be responsible. Type 1 virus shows preponderance both during  epidemic times and non-epidemic times. Polio viruses are resistant to freezing and drying.

Who nets the disease? 

Age : In India, it is essentially a disease of childhood and infancy. About 95 per cent of the cases occur in children below  the age to 5 years and, in  fact, 80 per cent of the cases are seen below the age of 3 years. The most vulnerable age is between 6 months and 3 years In contrast, in about a quarter of the cases it is found in the group 15 yea& and above. 

Sex : Males are more prone to clinical attack of poliomyelitis than females. For every case in females there will be approximately 3 cases of polio in  males. 

Injury : Usually paralytic poliomyelitis is associated with some injury or trauma such as injections, fractures and even surgical operations such as tonsillectomy. 

Season : Seasonal variations are striking. About two thirds of the cases occur during the months of June to September. This approximately corresponds with the monsoon season throughout most  of  the country. 

Standard of living : In contrast to most of the diseases, paralytic poliomyelitis is associated with improved living standards. This is illustrated by increased  incidence of the disease in regions where infant deaths are coming  down. 

How does it is spread? 

Direct contact with secretions from the pharynx (throat) or faeces of infected persons is the  usual method of spread of the disease to the  uninfected persons. In rare instances milk contaminated with viruses has also been a vehicle. Epidemiologic evidence suggests that oral to oral spread (through pharyngeal secretions) is more important, particularly where sanitation is good, than  the spread from faeces (faecal-oral spread). 

Incubation period : Usually it takes 7 to 12 days for a person  to develop infection from the time of first exposure. It can vary, of course, between 3 days to 2 weeks. 

Period of communicability : Polio virus can be demonstrated as early as 36 hours in throat secretions and in the faeces 72 hours after infection. This is true not  only in clinically apparent cases but also in in apparent infection (without any clinical manifestations). The virus can persist in  the throat for about one week and in the case faeces for 3 to 6 weeks or even  longer.  The polio cases are most infectious from one week to 10 days before and after the onset of symptoms. 

Susceptibility : Generally, every individual is susceptible to poliomyelitis. Fortunately, only a few of the infected persons develop paralysis. Second attack of poliomyelitis are rare. Type-specific resistance of long duration is a rule both after clinically recognisable infection or inapparent infection. In other words, persons who are infected with type 1 virus are resistant to type 1 polio reinfection. However, they  can be infected with either type 2 or type 3 virus. Infants born to mothers who are immune (protected) to poliomyelitis have passive immunity which is, of course, temporary. Pregnant women are to be more susceptible to paralytic poliomyelitis than non-pregnant women. 

Symptom and Complications 

Foliomyelitis is m acute viraI illness. Its severity varies inapparent  infection (without any clinical manifestations) to a disease ending in paralysis. The symptoms include fever, headache, upset of the gastrointestinal  tract, malaise and stiffness of neck and  disease may also be accompanied by paralysis. 

Polio  virus enters the body  through the alimentary canal and multiplies initially in the pharynx and  small intestine. It may enter central  nervous system through  the  blood stream resulting in paralysis, particularly of the lower limbs. Sometimes paralysis of muscles of respiration and swallowing can occur which may lead to the death of the patient. 

It is important for you to remember that the number of cases of  inapparent infection may be about a hundred times that of clinical cases. 

Polio virus can be isolated by carrying out sophisticated investigations such as tissue culture from samples of faeces or throat  secretions early in the course of the infection. Such facilities often are not available in  the peripheral hospitals such as primary health centres, taluq or district hospitals. Under these circumstances you have to depend mostly  on clinical diagnosis. 

Complications of poliomyelitis : If respiratory muscles are paralysed the child can die. Similarly if muscles of swallowing are paralysed it may threaten life. Non- paralytic poliomyelitis may lead to aseptic meningitis. About 2-10 per cent of paralytic cases may die. 

Prevention and Management 

Preventive measure of poliomyelitis include: 

a)  Active Immunisation : With the discovery of vaccines, prevention of poliomyelitis has become possible. Active immunisation of all susceptible persons against the 3 types of polio  virus is the simplest method of prevention. All the children, who are at higher risk of catching the disease, should be immunised. 

Two methods of immunisation are available. These include: 

• Immunisation with (a) live polio  vaccine and with (b)  killed polio vaccine. Let us discuss each one of them.  - Live Polio  Vaccine : It is an oral vaccine known as Sabin Vaccine. It is prepared from attenuated (reduced virulence) strains of the three types of polio  virus (trivalent vaccine). In other words,  it is prepared 6om the virus with much less degree of pathogenicity. The primary course of immunisation consists of 3 doses. given by mouth, at an interval of four to eight weeks. An interval of eight weeks between the doses is preferred. The first dose is commonly given around the age of three months, when the first dose of DPT also is given. Booster is given about one year after the third dose. The advantage of oral polio  vaccine (OPV) is that it produces intestinal immunity and this prevents subsequent infection of the alimentary tract with wild strains of polio virus. This vaccine is also relatively  inexpensive. It is useful in controlling epidemics since it produces antibodies to fight virus quickly among the vaccinated. 
• - Killed  Vaccine : It is inactivated vaccine given as injections. It also contains all the three types of polio virus. It also provides protection but is less effective in subsequent alimentary infection. In other words, it does not induce local or intestinal immunity. Hence, mild polio  viruses still can multiply in the intestinal tract of the  vaccinated individual and be a source of infection of others. For primary immunisation, four injections are required. The first three are given at 4 to 6 weeks interval and  the fourth 6-12 months after the third. The first dose can be given at the age of 3 months. One of the major disadvantages of the killed vaccine, particularly  during epidemic of poliomyelitis, is that injections are to be avoided in  epidemic times as they are likely to precipitate paralysis.  Also, immunity is not rapidly achieved with killed vaccine as in the case of oral live vaccine. 

b)  Education : The community should be educated adequately about the dangers of the disease, the mode of spread of the disease and the advantage of immunisation. 

Management of poliomyelitis: There is no specific treatment for poliomyelitis. During acute illness attention should be given to the complications of paralysis. Some patients may require  respiratory assistance.