Orthomyxoviridae and Paramyxoviridae Lecture in Microbiology for medical and dental medical students
Orthomyxoviridae and Paramyxoviridae are ss RNA containng viruses Insert Table 25.1 RNA viruses 2
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Influenza virus belongs to family Orthomyxoviridae IV A ssrna consists of 10 genes encoded on 8 separate RNA segments. 3 distinct influenza virus types: A, B, C; type A causes infections. Virus attaches to and multiplies in the cells of the respiratory tract; new viruses are assembled and budded off. 4
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Influenza virus A has glycoprotein spikes: 1. Hemagglutinin (H) 1. 15 different subtypes; 2. most important virulence factor; 3. binds to host cells 2. Neuraminidase (N) 1. 9 subtypes 2. hydrolyzes mucus and assists viral budding and release Both glycoproteins frequently undergo genetic changes decreasing the effectiveness of the host immune response: antigenic drift - constant mutation; gradually change of the aminoacid composition antigenic shift dramatic change, where one of the genes or RNA strands is substituted with a gene or strand from another influenza virus from a different animal host. 6
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Influenza B Not known to undergo antigenic shift Influenza C Known to cause only minor respiratory disease; probably not involved in epidemics 8
Influenza virus causes grippe (flu) Flu is an air-borne infection 9
Influenza A main characteristics Acute, highly contagious respiratory illness Seasonal, pandemics; among top 10 causes of death in U.S.; most commonly among elderly and small children Transmission - respiratory Binds to ciliated cells of respiratory mucosa Causes rapid shedding of cells, stripping the respiratory epithelium; severe inflammation Clinical signs - fever, headache, myalgia, pharyngeal pain, shortness of breath, coughing Complications - weakened host defenses predispose patients to secondary bacterial infections, especially pneumonia. 10
Diagnosis, Treatment and Prevention Diagnosis - Rapid immunofluorescence tests - detect antigens in a pharyngeal specimen; Serological tests - screen for antibody titer Hen embryo innoculation Treatment: control symptoms; Amantadine, Rimantadine, Zanamivir (Relenza) and Oseltamivir (Tamiflu) Flu virus has developed high rate of resistance to amantadine and rimantadine. Specific prophylaxis - annual trivalent vaccine recommended 11
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Which flu viruses will cause grippe in 2017/2018 winter? A/Michigan/45/2015 (Н1N1) А/Hong Kong/4801/2014 (Н3N2) B/Brisbane/60/2008 B/Phuket/3073/2013 13
Paramyxoviruses Paramyxoviruses contain: - Parainfluenza virus - Mumps virus - Morbillivirus (measles virus) - Pnemonovirus (respiratory syncytia virus) Main characteristics: - Respiratory transmission - HN and specialized F spikes in the envelope that initiate cell-to-cell fusion. - Fusion with neighboring cells formation of syncytium or multinucleate giant cells 14
Insert figure 25.5 Effects of paramyxoviruses 15
Parainfluenza - characteristics Widespread as influenza but more benign Respiratory transmission Observed mainly in children Minor cold, bronchitis, bronchopneumonia No specific treatment available; supportive therapy 16
Mumps Epidemic parotitis; self-limited, associated with painful swelling of parotid salivary glands Humans are the only reservoir 40% of infections are subclinical; long-term immunity Incubation 2-3 weeks fever, muscle pain and malaise, classic swelling of one or both cheeks Usually uncomplicated invasion of other organs; in 20-30% of infected adult males, epididymis and testes become infected; sterility is rare Symptomatic treatment Live attenuated vaccine MMR 17
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Measles Caused by Morbillivirus Also known as red measles Very contagious; transmitted by respiratory aerosols Humans are the only reservoir Virus invades respiratory tract Sore throat, dry cough, headache, conjunctivitis, lymphadenitis, fever, oral lesions (Koplik spots) Exanthema 19
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Koplik spots and rash 21
Measles Most serious complication - subacute sclerosing panencephalitis (SSPE), a progressive neurological degeneration of the cerebral cortex, white matter and brain stem. 1 case in a million infections Involves a defective virus spreading through the brain by cell fusion and destroys cells Leads to coma and death in months or years Prevention attenuated viral vaccine MMR 22
Respiratory Syncytial Virus (RSV) Pneumovirus Infects upper respiratory tract and produces giant multinucleated cells Most prevalent cause of respiratory infection in children 6 months or younger; most susceptible to serious disease Pathogenesis - nasal epithelia and eye portal of entry; replicates in nasopharynx Clinical signs - fever, rhinitis, wheezing, otitis, croup Treatment synagis (a monoclonal antibody that blocks attachment and ribavirin 23