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35971 - Epidemiology of Poliomyelitis Poliomyelitis Dr...

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Unformatted text preview: Epidemiology of Poliomyelitis Poliomyelitis Dr. Rasha Salama PhD Community Medicine and Public Health Suez Canal University Egypt Poliomyelitis Poliomyelitis First described by Michael Underwood in First 1789 1789 First outbreak described in U.S. First in 1843 in 21,000 paralytic cases reported in the U. S. 21,000 in 1952 in Global eradication in near future Introduction Introduction A viral infection most often recognized by acute onset of flaccid paralysis. Infection with poliovirus results in a spectrum of Infection clinical manifestations from inapparent infection to non-specific febrile illness, aseptic meningitis, paralytic disease, and death. Poliomyelitis is a highly infectious disease caused by three serotypes of poliovirus. 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 100:1 to 1000:1. paralytic Outcomes of poliovirus infection Asymptomatic Aseptic menigitis 0 20 Minor non-CNS illness Paralytic 40 60 Percent 80 100 Epidemiological pattern Epidemiological The epidemiological pattern of polio The 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. immunization. According to the WHO; Three epidemiological patterns have now been delineated: patterns – Countries with no immunization: the virus infects all Countries 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. frequent – Countries with partial immunization: In these Countries countries, wild polio virus is largely replaced by vaccine virus in the environment. vaccine – Countries with almost total immunization coverage: in Countries these countries polio is becoming rare, however, sporadic cases do occur rarely. Poliomyelitis—United States, 1950-2005* 25000 Inactivated vaccine Cases 20000 15000 10000 Live oral vaccine 5000 Last indigenous case 0 1950 1956 1962 1968 1974 1980 1986 1992 1998 2004 *2005 provisional total Causative organism Causative Poliovirus: belongs to “Picorna” viruses which are small Poliovirus: RNA-containing viruses. RNA-containing Polioviruses have three antigenically distinct types, Polioviruses giving no cross immunity: giving – 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 Polioviruses time under suitable environmental conditions, but are readily destroyed by heat (e.g. pasteurization of milk, and chlorination of water). and Reservoir of infection Reservoir Man is the only reservoir of infection of Man poliomyelitis. Man: cases and carriers Man: Cases: all clinical forms of disease Carriers: all types of carriers (e.g. incubatory, Carriers: convalescent, contact and healthy) except chronic type. In endemic areas, healthy carriers are the most frequent type encountered. are Foci of infection Foci Pharynx: the virus is found in the Pharynx: oropharyngeal secretions. oropharyngeal Small intestine: the virus finds exit in Small stools. stools. Modes of transmission Modes Since foci of infection are the throat and small intestines, Since poliomyelitis spreads by two routes: poliomyelitis Oral-oral infection: direct droplet infection Faeco-oral infection: – Food-borne (ingestion) infection through the ingestion of Food-borne contaminated foods. Vehicles include milk, water, or any others that may be contaminated by handling, flies, dust…. that – Hand to mouth infection. (polio virus has the ability to survive in cold environments. Overcrowding and poor sanitation provide opportunities for exposure to infection.) exposure Period of infectivity Period Contact and healthy carriers: about 2 weeks Cases: the cases are most infectious 7 to 10 days before Cases: 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. long In polio cases, infectivity in the pharyngeal foci is around In one week, and in the intestinal foci 6-8 weeks. one Incubation Period: 7-14 days Susceptibility Age: more than 95% reported in infancy and childhood with over 50% of them in infancy. with Sex: no sex ratio differences, but in some countries, Sex: 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. of Sequelae of polio infection Polio infection Inapparent infection Clinical poliomyelitis Abortive polio (minor illness) Involvement of CNS (major illness) Paralytic polio Non-paralytic polio Spinal polio Bulbar polio Bulbospinal polio Inapparent infection Inapparent Incidence is more than 100 to 1000 times Incidence the clinical cases. No clinical manifestations, but infection is associated with acquired immunity, and carrier state. carrier Clinical poliomyelitis Clinical Abortive polio (minor illness): I. The majority of clinical cases are abortive, with mild The systemic manifestations for one or two days only, then clears up giving immunity. Some abortive cases may be so mild to pass unnoticed. Manifestations: Manifestations: – – – Moderate fever Upper respiratory manifestations: pharyngitis and sore throat Gastrointestinal manifestations: vomiting, abdominal pain, Gastrointestinal and diarrhea. and Clinical poliomyelitis (cont.) Clinical II. Involvement of the CNS (major illness): Affects a small proportion of the clinical cases, and Affects appears few days after subsidence of the abortive stage. It takes two forms: nonparalytic and paralytic polio. It Nonparalytic polio is manifested by fever, headache, Nonparalytic 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. occur. The case either recovers or passes to the paralytic The stage, and here the nonpralytic form is considered as a “preparalytic stage”. “preparalytic Clinical poliomyelitis (cont.) Clinical Paralytic poliomyelitis: Paralysis usually appears within 4 days after the Paralysis preparalytic stage (around 7-10 days from onset of disease). disease). The case shows fever, headache, irritability, and The different paralytic manifestations according to the part of the CNS involved, with destruction of the motor nerve cells, but not the sensory nerve cells. cells, Forms: spinal, bulbar, and bulbospinal. Spinal polio Spinal Different spinal nerves are involved, due Different to injury of the anterior horn cells of the spinal cord, causing tenderness, weakness, and flaccid paralysis of the corresponding striated muscles. corresponding The lower limbs are the most commonly The affected. affected. Bulbar polio Bulbar Nuclei of the cranial nerves are involved, Nuclei causing weakness of the supplied muscles, and maybe encephalitis. maybe Bulbar manifestations include dysphagia, nasal Bulbar voice, fluid regurgitation from the nose, difficult chewing, facial weakness and diplopia chewing, Paralysis of the muscles of respiration is the Paralysis most serious life-threatening manifestation. most Bulbospinal polio Bulbospinal Combination of both spinal and bulbar Combination forms forms Complications and case fatality Respiratory complications: pneumonia, pulmonary edema edema Cardiovascular complications: myocarditis, cor Cardiovascular pulmonale. pulmonale. Late complications: soft tissue and bone deformities, Late osteoporosis, and chronic distension of the colon. osteoporosis, Case fatality: varies from 1% to 10% according to the Case form of disease (higher in bulbar), complications and age ( fatality increases with age). fatality Case definition Case The following case definition for paralytic poliomyelitis has been approved by CDC (1997) poliomyelitis Clinical case definition Acute onset of a flaccid paralysis of one or more Acute limbs with decreased or absent tendon reflexes in the affected limbs, without other apparent cause, and without sensory or cognitive loss. cause, Case classification Case Probable: A case that meets the clinical case definition. Probable: case Confirmed: A case that meets the clinical case definition and in Confirmed: which the patient has a neurologic deficit 60 days after onset of initial symptoms, has died, or has unknown follow-up status. initial Confirmed cases are then further classified based on epidemiologic and laboratory criteria. Only confirmed cases are included in the Morbidity and Mortality Weekly Report (MMWR) . Morbidity Indigenous case: Any case which cannot be proved to be Indigenous imported. imported. Imported case: A case which has its source outside the country. A Imported case person with poliomyelitis who has entered the country and had onset of illness within 30 days before or after entry onset Diagnosis and laboratory testing Diagnosis Laboratory studies, especially attempted Laboratory poliovirus isolation, are critical to rule out or confirm the diagnosis of paralytic poliomyelitis. poliomyelitis. Virus isolation The likelihood of poliovirus isolation is highest from stool specimens, specimens, intermediate from pharyngeal swabs, and very low from blood or spinal fluid. blood Diagnosis and laboratory testing (cont.) (cont.) Serologic testing A four-fold titer rise between the acute and four-fold convalescent specimens suggests poliovirus infection. Cerebrospinal fluid (CSF) analysis Cerebrospinal The cerebrospinal fluid usually contains an The increased number of leukocytes—from 10 to 200 cells/mm3 (primarily lymphocytes) and a mildly elevated protein, from 40 to 50 mg/100 ml. Prevention General prevention: General Health promotion through environmental Health sanitation. sanitation. Health education (modes of spread, Health protective value of vaccination). protective Prevention Seroprophylaxis by immunoglobulins: Seroprophylaxis Not a practical way of giving protection Not because it must be given either or before or very shortly after exposure to infection. or (0.3 ml/kg of body weight). (0.3 prevention prevention Active immunization: – Salk vaccine (intramuscular polio trivalent Salk killed vaccine). killed – Sabin vaccine (oral polio trivalent live Sabin attenuated vaccine). attenuated Inactivated Polio Vaccine Inactivated Contains 3 serotypes of vaccine virus Grown on monkey kidney (Vero) cells Inactivated with formaldehyde Contains 2-phenoxyethanol, neomycin, Contains streptomycin, polymyxin B streptomycin, Oral Polio Vaccine Oral Contains 3 serotypes of vaccine virus Grown on monkey kidney (Vero) cells Contains neomycin and streptomycin Shed in stool for up to 6 weeks following Shed vaccination vaccination Inactivated Polio Vaccine Inactivated Highly effective in producing Highly immunity to poliovirus immunity >90% immune after 2 doses >99% immune after 3 doses Duration of immunity not known with Duration certainty certainty Oral Polio Vaccine Oral Highly effective in producing Highly immunity to poliovirus immunity 50% immune after 1 dose >95% immune after 3 doses Immunity probably lifelong Salk versus Sabin vaccine Salk IPV (Salk) OPV (Sabin) killed formolised virus killed Given SC or IM Induces circulating antibodies, but Induces not local (intestinal immunity) not Prevents paralysis but does not Prevents prevent reinfection prevent Not useful in controlling epidemics More difficult to manufacture and is More relatively costly relatively Does not require stringent conditions Does during storage and transportation. Has a longer shelf life. longer live attenuated virus live given orally given immunity is both humoral and intestinal. induces antibody quickly intestinal. Prevents paralysis and prevents Prevents reinfection reinfection Can be effectively used in controlling Can epidemics. epidemics. Easy to manufacture and is cheaper Requires to be stored and Requires transported at subzero temperatures, and is damaged easily. and Polio Vaccination Schedule Age Vaccine 2 months IPV 4 months IPV 6-18 months IPV 4-6 years* IPV Minimum Interval --4 wks 4 wks 4 wks *the fourth dose of IPV may be given as early as 18 weeks of age Polio Vaccination of Unvaccinated Adults Unvaccinated IPV Use standard IPV schedule if possible (0, 1-2 Use months, 6-12 months) months, May separate doses by 4 weeks if accelerated May schedule needed schedule Polio Vaccination of Previously Vaccinated Adults Vaccinated Previously complete series – administer one dose of IPV Incomplete series – administer remaining doses in series – no need to restart series Polio Vaccine Adverse Reactions Polio Rare local reactions (IPV) No serious reactions to IPV have been No documented documented Paralytic poliomyelitis (OPV) Vaccine-Associated Paralytic Polio Vaccine-Associated Increased risk in persons >18 years Increased Increased risk in persons with immunodeficiency No procedure available for identifying persons at risk No of paralytic disease of 5-10 cases per year with exclusive use 5-10 of OPV of Most cases in healthy children and their household Most contacts contacts Polio Vaccine Polio Contraindications and Precautions Severe allergic reaction to a vaccine Severe component or following a prior dose of vaccine vaccine Moderate or severe acute illness Polio Vaccine Polio Contraindications and Precautions Severe allergic reaction to a vaccine Severe component or following a prior dose of vaccine vaccine Moderate or severe acute illness B. Control of patient, contacts and the immediate environment: 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) Quarantine: Of no community value. 5) Protection of contacts: Immunization of familial and other close contacts is recommended but may not contribute to immediate control; the virus has often infected susceptible close contacts by the time the initial case is recognized. 6) Investigation of contacts and source of infection: Occurrence of a single case of poliomyelitis due to wild poliovirus must be recognized as a public health emergency prompting immediate investigation and planning for a large-scale response. A thorough search for additional cases of AFP in the area around the case assures early detection, facilitates control and permits appropriate treatment of unrecognized and unreported cases. 7) Specific treatment: None; however, Physical therapy is used to attain maximum function after paralytic poliomyelitis. C. Epidemic measures: 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. D. Disaster implications: Overcrowding of non-immune groups and collapse of the sanitary infrastructure pose an epidemic threat. E. International measures: Poliomyelitis is a Disease under surveillance by WHO and is targeted for eradication by 2005. 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. E. International measures (cont.): 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. Polio Eradication Polio Last case in United States in 1979 Western Hemisphere certified polio free in 1994 Last isolate of type 2 poliovirus in India in Last October 1999 October Global eradication goal Wild Poliovirus 1988 Wild Wild Poliovirus 2004 Poliomyelitis Eradication is a crucial issue of discussion in “group discussion” session!! “group Please go and read about it Thank You Thank ...
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