Epidemiology and control of poliomyelitis.

Introduction Poliomyelitis is an infectious disease of viral origin. It is classically associated with muscular paralysis, particularly of the lower limbs. In areas where the disease is common, as many as 1 % of young children may develop paralytic disease (PAHO, 1994). The paralysis results from damage to the motor neurone in the spinal cord, and is flaccid in nature and asymmetrical in distribution. In general, less than one percent of all infected individuals develop paralytic illness (Hull, 1995), and in a few cases the disease presents with bulbar paralysis and respiratory involvement. In about 10% of infected individuals the presentation is that of mild illness with symptoms of headache, sore throat and fever, while in most people it is a case of inapparent (subclinical) infection. Thus, in most cases of poliomyelitis an unequivocal diagnosis of the infection cannot be made without the aid of serological examinations. Overall the estimated ratios of inapparent to apparent infections range between 100:1 and 1,000:1 depending on the strain of the polio virus (PAHO, 1994). Case-fatality rate varies between 2% and 20% among paralytic cases, but may be as high as 40% in cases where there is bulbar or respiratory involvement. Since the development of effective polio vaccine inactivated polio vaccine (IPV) in 195 5 by Salk and oral polio vaccine (OPV) in 1961 by Sabin efforts have been directed towards the effective control of the disease in many parts of the world, with some positive results such as the eradication of the disease in Cuba since 1963 (Czaplicki, 1989), and the dramatic reduction in the incidence of the disease in the USA and other developed countries (Hinman et al, 1987). The 1988 declaration of the World Health Assembly to the effect of global eradication of the disease by the year 2000 had given further impetus to control activities, and generated interest in the development of simple, but effective, strategies for the disease on a global level. As part of the continuing effort towards global eradication, the World Health Organization (WHO) recently declared the theme of the 1995 World Health Day as ’Target 2000: A World Without Polio’. In order to meet this