Respiratory viruses Categories of Respiratory Viruses Orthomyxoviridae: Influenz
Boyd, Sammy, Host has reference to this Academic Journal, PHwiki organized this Journal Respiratory viruses Categories of Respiratory Viruses Orthomyxoviridae: Influenza virus Paramyxoviridae : Parainfluenza virus; Mumps virus; Measles; Respiratory syneytical virus Togaviridae: Rubella Virus Coronaviridae: Corona Virus; SARS virus Adenoviridae : human Adenovirus picornaviridae: Rhino Virus; Reoviridae: Influenza virus Orthomyxoviridae: Influenza virus Influenza is a disease caused by Influenza virus ,a member of the Orthomyxoviridae.
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Genome of Influenza virus 8 negative sense RNA nucleocapsid segments The ‘RNP’ (RNA + nucleoprotein) is in a helical as long as m with the 3 polymerase polypeptides associated with each segment. The segmented genome promotes genetic diversity caused by mutation in addition to reassortment of segments on infection with two different strains Virion spherical/ovoid, 80-120nm diameter, The inner side of the envelope is lined by the matrix protein, stable type-specific. Virion The outer surface of the particle consists of a lipid envelope from which project prominent glycoprotein spikes of two types, the haemagglutinin, ~135Å trimer (HA), in addition to neuraminidase, ~60Å tetramer (NA).
Haemagglutinin (HA) Encoded by RNA segment 4 Can agglutinate red blood cells – hence the nomenclature Cleavage by host-cell protease is required (resulting in HA1 in addition to HA2) as long as infection to occur Hemagglutinin glycoprotein is the viral attachment protein in addition to fusion protein , in addition to it elicits neutralizing , protective antibody responses Neuraminadase (NA) Encoded by RNA segment 6 Enzyme that uses neuraminic (sialic) acid as a substrate Important in releasing mature virus from cells ORTHOMYXOVIRUSES M1 protein helical nucleocapsid (RNA plus NP protein) HA – hemagglutinin polymerase complex lipid bilayer membrane NA – neuraminidase type A, B, C : NP, M1 protein sub-types: HA or NA protein
Influenza virus A Replication Influenza transcribe in addition to replicates its genome in the target cell nucleus assemble in addition to buds from the plasma membrane Influenza virus
Antigen Soluble antigens: include ribonucleoprotein in addition to M protein which are much stable in antigenicity. Surface antigens: include HA in addition to NA which are much variable in antigenicity. Types Influenza viruses are divided into 3 groups determined by the ribonucleoprotein (RNP) antigen in addition to M antigen: Group A – This group is the cause of epidemics in addition to p in addition to emics in addition to has an avian intermediate host (IH) Group B – This group causes epidemics in addition to has no IH Group C – This group does not cause epidemics in addition to causes mild disease TYPE A ++++ yes yes yes shift, drift yes sensitive sensitive 2 severity of illness animal reservoir human p in addition to emics human epidemics antigenic changes segmented genome amantadine, rimantidine zanamivir surface glycoproteins TYPE B ++ no no yes drift yes no effect sensitive 2 TYPE C + no no no (sporadic) drift yes no effect (1)
Subtypes According to antigenicity of HA in addition to NA, influenza virus is divided into subtypes such as HnNm( H1N2, et al ) Variation in addition to Epidemiology Antigenic drift: median or small epidemic. Antigenic shift:large scale epidemic. Antigenic Shift Of Influenza virus Reassortment of genes is a common feature of Influenza A, but not B or C When two different “A” viruses infect the same cell, their RNA segments can become mixed during replication New viruses produced in this way may survive due to a selective advantage within the population
Antigenic Drift of Influenza Virus Constant mutations in the RNA of influenza which lead to polypeptide mutations Changes are less dramatic than those induced by Shift If these mutations affect HA or NA they may cause localized epidemics Epidemic
where do new HA in addition to NA come from 13 types HA 9 types NA all circulate in birds pigs avian in addition to human where do new HA in addition to NA come from why do we not have influenza B p in addition to emics so far no shifts have been recorded no animal reservoir known
Resistence The particles are relative labile ,not resistant to drying, etc. Pathogenesis Influenza is characterised by fever, myalgia, headache in addition to pharyngitis. In addition there may be cough in addition to in severe cases, prostration. There is usually not coryza(runny nose) which characterises common cold infections. Infection may be very mild, even asymptomatic, moderate or very severe Transmission Source of infection: patients in addition to carriers. AEROSOL 100,000 TO 1,000,000 VIRIONS PER DROPLET 18-72 HR INCUBATION
Aerosol Inoculation Of virus NORMAL TRACHEAL MUCOSA 3 DAYS POST-INFECTION 7 DAYS POST-INFECTION SYMPTOMS FEVER HEADACHE MYALGIA() COUGH RHINITIS() OCULAR SYMPTOMS
Important Characteristics Rhinoviruses are picornaviruses similar to enteroviruses but differ from them in having a buoyant density in cesium chloride of 1.40 g/ml in addition to in being Acid-labile Rhinoviruses are isolated commonly from the nose in addition to throat but very rarely from feces. These viruses cause upper respiratory tract infections, including the common cold Reovirus () Important Characteristics Virion: Icosahedal, 60-80nm in diameter, double capsid shell Genome: dsRNA Envelope: none Diseases: Acute respiratory tract infection in addition to Gastrointestinal infections
Boyd, Sammy Host
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