Polio Myelitis Lecture Notes PDF

 Overview  Introduction  phases of acute poliomyelitis  Outcomes of poliovirus infection  Epidemiological pattern  Causative organism  Modes of transmission  Diagnosis and laboratory testing  Prevention  Polio Eradication  Know viral poliomyelitis as agent, host &...

 Overview  Introduction  phases of acute poliomyelitis  Outcomes of poliovirus infection  Epidemiological pattern  Causative organism  Modes of transmission  Diagnosis and laboratory testing  Prevention  Polio Eradication  Know viral poliomyelitis as agent, host & enviroment  Identify phases of acute poliomyelitis  Recognize outcomes of poliovirus infection  Familiar with Epidemiological pattern  Identify modes of transmission modes  Evaluate Polio Eradication  Know the diagnosis and laboratory testing  Identify Prevention methods for poliomyelitis  Identify Polio Eradication Programs  Poliomyelitisis a highly infectious disease caused by three serotypes of poliovirus.  Infection with poliovirus results in a spectrum of clinical manifestations from in apparent infection to non-specific febrile illness, aseptic meningitis, paralytic disease, and death.  A viral infection most often recognized by acute onset of flaccid paralysis  The WHO has defined AFP as “any child under 15 years of age with acute onset of focal weakness or paralysis (including GBS)” or any person with paralytic illness at any age when polio suspected, characterized by flaccid (reduced tone), without other obvious causes (e.g. trauma)[  Two phases of acute poliomyelitis can be distinguished: a non-specific febrile illness (minor illness) followed, in a small proportion of patients, by aseptic meningitis and/or paralytic disease (major illness).  The ratio of cases of inapparent infection to paralytic disease ranges from 1:100, 1:1000.  The epidemiological pattern of polio depends upon the degree of the socioeconomic development and health care services of a country.  The pattern of the disease has been considerably modified by widespread immunization.  According to World Health Organization – Regional Office for Eastern Mediterranean (ending on 25/12/2022) No new Wild Poliovirus Type 1 (WPV1) isolates from human or environmental samples reported this week. The cases count in 2022 remains to be 22 cases (2 from Afghanistan and 20 from Pakistan) and the positive environmental samples count in 2022 remains to be 54 (17 in Afghanistan and 37 in Pakistan). VDPV Isolates, EMR countries, 2021 VDPV Isolates, EMR countries, 2022 According to the WHO; Three epidemiological patterns have now been delineated: Countries with no immunization: the virus infects all children, and by age 5 years almost all children develop antibodies to at least one of the 3 types of polio virus. In that pattern paralytic polio cases are frequent in infants. Countries with partial immunization: In these countries, wild polio virus is largely replaced by vaccine virus in the environment. Countries with almost total immunization coverage: in these countries polio is becoming rare, however, sporadic cases do occur rarely.  5 new cases clinically diagnosed in Libya in 1990  Last case with polio had reported in feburary,10,1991 in Darna city , Libya  Poliovirus: belongs to “Picorna” viruses which are small RNA-containing viruses.  Polioviruses have three antigenically distinct types, giving no cross immunity:  Type I: “Leon”; the commonest in epidemics  Type II: “Berlinhide”; the prevailing type in endemic areas.  Type III: “Lansing”; occasionally causes epidemics.  Polioviruses are relatively resistant and survive for a long time under suitable environmental conditions, but are readily destroyed by heat (e.g. pasteurization of milk, and chlorination of water).  Man is the only reservoir of infection of poliomyelitis.  Man: cases and carriers  Cases: all clinical forms of disease  Carriers:all types of carriers (e.g. incubatory, convalescent, contact and healthy) except chronic type. In endemic areas, healthy carriers are the most frequent type encountered.  Pharynx: the virus is found in the oropharyngeal secretions.  Small intestine: the virus finds exit in stools.  Since foci of infection are the throat and small intestines, poliomyelitis spreads by two routes:  Oral-oral infection: direct droplet infection  Faeco-oral infection:  Food-borne (ingestion) infection through the ingestion of contaminated foods. Vehicles include milk, water, or any others that may be contaminated by handling, flies, dust….  Hand to mouth infection.  (polio virus has the ability to survive in cold environments. Overcrowding and poor sanitation provide opportunities for exposure to infection.)  Contact and healthy carriers: about 2 weeks  Cases: the cases are most infectious 7 to 10 days before and after the onset of symptoms. In the feaces, the virus is excreted commonly for 2 to 3 weeks, sometimes as long as 3 to 4 months.  In polio cases, infectivity in the pharyngeal foci is around one week, and in the intestinal foci 6-8 weeks.  Incubation Period: 7-14 days  Age: more than 95% reported in infancy and childhood with over 50% of them in infancy.  Sex: no sex ratio differences, but in some countries, males are infected more frequently than females in a ratio 3:1.  Risk factors: (provocative factors of paralytic polio in individuals infected with polio virus): fatigue, trauma, intramuscular injections, operative procedures, pregnancy, excessive muscular exercise…  Immunity: The maternal antibodies gradually disappear during the first 6 months of life. Immunity following infection is fairly solid, although infection with other types of polio virus can still occur.  Polio infection Inapparent infection Clinical poliomyelitis Abortive polio Involvement of CNS (minor illness) (major illness) Paralytic Non-paralytic polio polio Spinal polio Bulbar polio Bulbospinal polio  Incidence is more than 100 to 1000 times the clinical cases.  No clinical manifestations, but infection is associated with acquired immunity, and carrier state.  I. Abortive polio (minor illness):  The majority of clinical cases are abortive, with mild systemic manifestations for one or two days only, then clears up giving immunity.  II. Involvement of the CNS (major illness):  Affects a small proportion of the clinical cases, and appears few days after subsidence of the abortive stage. It takes two forms: nonparalytic and paralytic polio.  Nonparalytic polio is manifested by fever, headache, nausea, vomiting, and abdominal pain. Signs of meningeal irritation (meningism), and aseptic meningitis (pain and stiffness in the neck back and limbs) may also occur.  The case either recovers or passes to the paralytic stage, and here the nonpralytic form is considered as a “preparalytic stage”.  Paralytic poliomyelitis:  Paralysis usually appears within 4 days after the preparalytic stage (around 7-10 days from onset of disease).  Forms: spinal, bulbar, and bulbospinal.  Different spinal nerves are involved, due to injury of the anterior horn cells of the spinal cord, causing tenderness, weakness, and flaccid paralysis of the corresponding striated muscles.  The lower limbs are the most commonly affected.  Nuclei of the cranial nerves are involved, causing weakness of the supplied muscles, and maybe encephalitis.  Bulbar manifestations include dysphagia, nasal voice, fluid regurgitation from the nose, difficult chewing, facial weakness and diplopia  Paralysis of the muscles of respiration is the most serious life-threatening manifestation.  Combination of both spinal and bulbar forms  Respiratory complications: pneumonia, pulmonary edema  Cardiovascular complications: myocarditis, cor pulmonale.  Late complications: soft tissue and bone deformities, osteoporosis, and chronic distension of the colon.  Case fatality: varies from 1% to 10% according to the form of disease (higher in bulbar), complications and age ( fatality increases with age).  Suspected case: any case of acute-onset flaccid paralysis (AFP), including Guillain-Barré syndrome, in a person under 15 years of age for any reason other than severe trauma, or paralytic illness in a person of any age in which polio is suspected.  Probable case: a case in which AFP is found, and no other cause for the paralysis can be identified immediately. The classification of "probable case" is also temporary; within 10 weeks of onset the case  Confirmed case: a case with acute paralytic illness, with or without residual paralysis, and isolation of wild poliovirus from the stools of either the case or its contacts.  Laboratory studies, especially attempted poliovirus isolation, are critical to rule out or confirm the diagnosis of paralytic poliomyelitis.  Virus isolation  The likelihood of poliovirus isolation is highest from stool specimens,  intermediate from pharyngeal swabs, and very low from blood or spinal fluid.  Serologictesting  A four-fold titer rise between the acute and convalescent specimens suggests poliovirus infection.  Cerebrospinal fluid (CSF) analysis  The cerebrospinal fluid usually contains an increased number of leukocytes (primarily lymphocytes) and a mildly elevated protein  A. General prevention  Health promotion through environmental sanitation. Health education (modes of spread, protective value of vaccination).  B. specific protection  1. passive immunization  2. active immunization  C. Tertiary prevention:  Intervention to prevent further complication happen   Seroprophylaxis by immunoglobulins:  Not a practical way of giving protection because it must be given either or before or very shortly after exposure to infection.  IPV  Use standard IPV schedule if possible (0, 1-2 months, 6-12 months)  May separate doses by 4 weeks if accelerated schedule needed  WHO  Previously complete series administer one dose of IPV  Incomplete series administer remaining doses in series no need to restart series  Increased risk in persons >18 years  Increased risk in persons with immunodeficiency  No procedure available for identifying persons at risk of paralytic disease  5-10 cases per year with exclusive use of OPV  Most cases in healthy children and their household contacts  In any country, a single case of poliomyelitis must now be considered a public health emergency, requiring an extensive supplementary immunization response over a large geographic area. 1) Report to local health authority: Obligatory case report of paralytic cases as a Disease under surveillance by WHO, Class 1. 2) Isolation: Enteric precautions in the hospital for wild virus disease; of little value under home conditions because many household contacts are infected before poliomyelitis has been diagnosed. 3)Concurrent disinfection: Throat discharges, feces and articles soiled therewith. Terminal cleaning. 4) Protection of contacts: Immunization of familial and other close contacts is recommended; the virus has often infected susceptible close contacts by the time the initial case is recognized. 5) Investigation of contacts and source of infection 6) Specific treatment: None; however, Physical therapy is used to attain maximum function after paralytic poliomyelitis.  National health administrations are expected to inform WHO immediately of individual cases and to supplement these reports as soon as possible with details of the nature and extent of virus transmission.  Planning a large-scale immunization response must begin immediately and, if epidemiologically appropriate, in coordination with bordering countries. Once a wild poliovirus is isolated, molecular  epidemiology can often help trace the source. Countries should submit monthly reports  on case of poliomyelitis AFP cases and AFP surveillance performance to their respective WHO offices. International travelers visiting areas of high  prevalence must be adequately immunized.  Overcrowding of non-immune groups and collapse of the sanitary infrastructure pose an epidemic threat.  WHO is a partner in the Global Polio Eradication Initiative, the largest private-public partnership for health, which has reduced polio by 99%. Polio now survives only among the world's poorest and most marginalized communities, where it stalks the most vulnerable children. The Initiative's goal is to reach every last child with polio vaccine and ensure a polio- free world for future generations. **The reasons why polio can be eradicated are:  polio only affects humans, and there is no animal reservoir  an effective and inexpensive vaccine exists, called Oral PolioVirus (OPV)  immunity against polio is life-long  the virus can only survive for a very short time in the environment  As long as a single child remains infected, children in all countries are at risk of contracting polio. Failure to eradicate polio from these last remaining strongholds could result in as many as 200 000 new cases every year, within 10 years, all over the world.  In most countries, the global effort has expanded capacities to tackle other infectious diseases by building effective surveillance and immunization systems.