Understanding Poliovirus and Polio Disease: Key Facts and Insights
Poliovirus, a human RNA intestinal virus, causes polio disease with 3 serotypes. It spreads through poor sanitation, affecting the CNS in 3% of cases. Poliomyelitis, or polio, can lead to paralytic complications with significant morbidity and mortality rates.
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3.0 KEY FACTS ABOUT POLIO VIRUS AND POLIO DISEASE National Primary Health Care Development Agency July 2021 Delivered by National Emergency Routine Immunisation Coordination Centre (NERICC)
Session Objectives By the end of this session, participants will be able to explain: What poliovirus is, its mode of transmission and its epidemiology How to diagnose, prevent, and treat poliomyelitis The mechanisms of action of OPV and IPV in the body 2
What is Poliovirus? 1. Polioviruses are human RNA intestinal viruses that cause polio disease. 2. There are 3 serotypes of polioviruses with slightly different capsid proteins (type 1, 2 and 3). 3. They are resistant to inactivation by many common detergents and disinfectants, including soaps, but the viruses are rapidly inactivated by exposure to ultraviolet light. 4. The viral infectivity is stable for months at +4 C and for days at +30 C. 3
Mode of Transmission 1. The virus is transmitted through faeco-oral and oral-to-oral transmissions. 2. Where sanitation is poor, faeco-oral route predominates, whereas oral to oral transmission may be more common where standards of sanitation are even high. 3. In most settings, both patterns of transmissions are likely to occur. 4. The virus then may spread through the pharynx and the gastrointestinal tracts to the bloodstream causing viraemia and enters the central nervous system (CNS) only in about 3% of the infection. 4
Poliomyelitis (Polio) 1. Poliomyelitis or polio otherwise known as infantile paralysis is an acute viral communicable disease caused by any of the three poliovirus serotypes. 2. Most children infected with poliovirus have no symptoms, with viral replication occurring in, and limited to, the gastrointestinal tract or pharynx. 3. Approximately 25% of those infected develop minor symptoms, usually fever, headache and sore throat. 4. The incubation period is usually 7 10 days (range 4 35 days). 5
Poliomyelitis (Polio) cont 1. Paralytic poliomyelitis occurs when poliovirus enters the central nervous system and replicates especially around the spinal cord. 2. The typical clinical manifestation of paralytic poliomyelitis is acute flaccid paralysis (AFP) affecting the limbs, principally the legs. 3. It is usually presenting as asymmetric weakness of the muscles, stiffness of the back and neck and sensation may remain intact. 4. Persistent paralysis and resulting deformities are common complications of polio. 5. The case-fatality rates among paralytic cases range from 5% to 10% in children and from 15% to 30% in adolescents and adults. 6
The case Definition of Acute Flaccid Paralysis (AFP) The WHO case definition of Acute Flaccid Paralysis (AFP) as: Any child under 15 years of age with acute (sudden) onset of weakness or floppiness of one or more limbs or any person of any age with paralytic illness in whom a clinician suspects poliomyelitis . This is confirmed virologically and this involves: Isolation and characterization of poliovirus from the stools of patients with AFP to determine whether the viruses are vaccine-associated, vaccine-derived or wild . 7
Epidemiology 1. In the pre-vaccine era when poliovirus was the leading cause of permanent disability in children. 2. It was estimated that 1 in 200 susceptible individuals infected by polioviruses, develop paralytic poliomyelitis. 3. In 80 s the trends changed and the annual global burden was estimated to be >350,000 with wild poliovirus (WPV) reported in >125 countries in 1988. 4. Based on this alarming cases, the World Health Assembly (WHA) resolved to eradicate poliomyelitis by the year 2000 and the Global Polio Eradication Initiative (GPEI) was established. 8
Epidemiology cont 1. The sustained use of polio vaccines worldwide since 1988 has led to a drastic drop in the global incidence of poliomyelitis by >99% and the number of countries with endemic polio from 125 to just two. 2. Globally, the last case of poliomyelitis caused by naturally circulating WPV type2 (WPV2) occurred in India in 1999. No case due to WPV type3 (WPV3) has been detected since 10th November 2012. 3. However, despite the overall success of the GPEI, Pakistan and Afghanistan remain endemic for transmission of WPV1. 9
Diagnosis The diagnosis of paralytic poliomyelitis is achieved through the following ways: 1. Clinical course based on the case definition and confirmed by Virological testing in the designated laboratories. 2. Other ways include: a. Imaging studies and neurophysiological diagnoses, and b. Residual neurologic deficit 60 days after onset of Symptoms. 10
Treatment No specific antiviral drugs are available for poliomyelitis and most cases of paralytic polio are irreversible. Treatment consists of supportive, symptomatic care during the acute phase. a. These including respiratory support in cases with respiratory muscle paralysis. b. Neuromuscular complications are mitigated by physiotherapy and orthopedic treatment. 11
Protection and Prevention 1. The best and most cost effective method of protection and prevention against polio disease is through vaccination with polio vaccines. a. This is achieved by completing immunization schedule, 2. Other supportive preventive measures include Exclusive breastfeeding during the first 6 months of the child s life, Good nutrition, Environmental sanitation, and handwashing with soap and water 12
Vaccines used in Routine Immunization to combat poliovirus Live attenuated (weakened) oral polio vaccine (OPV) called Sabin The Salk vaccine, or inactivated poliovirus vaccine (IPV) 13
Mechanism of action of OPV and IPV Oral Polio Vaccine When a child ingests OPV, the vaccine active agent enters the child s mouth and gut and replicates. The child then mounts immune responses in three places: 1. Antibody response in the blood that protects against the virus invading the nervous system and causing paralysis. 2. Immune response in the mouth which prevents shedding of virus in oral secretions and spread from those secretions; and 3. Intestinal immunity (also called gut or mucosal immunity), which prevents shedding of the virus in the stool. Inactivated Polio Vaccine IPV is a killed vaccine that stimulates a very good humoral response (antibodies in the blood) in children after vaccination with only 1 or 2 doses. 14
Conclusion 1. Poliomyelitis is viral diseases cause by a poliovirus 2. Children vaccinated with OPV who come into contact with wild poliovirus are less likely to excrete poliovirus in their oral fluids or stool than unvaccinated persons. 3. Individuals vaccinated with IPV alone are protected against paralysis, though they may excrete the virus and allow it to spread. 4. When IPV is administered after a few doses of OPV, the IPV not only enhances protection against paralytic disease but also boosts intestinal immunity, even more than an additional dose of OPV would provide. 5. Combining IPV with bOPV provides the advantages of both vaccines: i.e strong intestinal immunity and antibody protection against the two serotypes in bOPV, types 1 and 3. 6. This combination gives both the child and the child s community the best protection. 15
Thank you 16
