ORTHOMYXOVIRUS PARAMYXOVIRUSHusni SamadinLab. Mikrobiologi FK.Unsri/RSMH

OrthomyxovirusInfluenza virus

Influenza A- pandemics and epidemics; humans and animalsInfluenza B- epidemics; human virusInfluenza C- mild respiratory tract infection

Morphology:Segmented, ss genome,helical nucleocapsid with outer lipoprotein envelopeEnvelope contain 2 spikesHemagglutininBinds to cell surface receptors( neuraminic acid/sialic acidNeuramidaseEnzymatic activityInternal antigens- M1 & NP proteins- type specific, shows cross reactivity

The virus envelope contains two glycoproteins:Hemagglutinin (HA) Neuraminidase (NA)Its lined by the matrix (M1) and membrane (M2) pinfluenza A and B viral genomes consists of eight different helical nucleocapsid segments.Each segment contains a negative-sense RNA associated with the nucleoprotein (NP) and the transcriptase (RNA polymerase)All virus proteins are encoded on separate segments, except NS1, NS2, M1, and M2 proteins, which are transcribed from one segment each.

Structure and Replication

The HA has several functions: attachment protein, bind to sialic a. cell receptorspromotes fusion of envelope to cell membranehemagglutinates human RBCsit elicits the protective neutralizing antibody response.

HA & NA of ONLY influenza A virus can undergo major antigenic changes (called: shifts, due to RNA segment reassortment) Minor changes (called: drift, due to gene mutation) occurs in both influenza A & B types.

Antigenic Shift and drift phenomenon of influenza v.:

Antigenic VariationsAntigenic shiftUndergoes reassortmentResults in changes of the H and N antigenPandemics and epidemicsOccurs with influenza A onlyAntigenic driftChange in the amino acid sequence of the H agOccur both in A & B

Influenza Viral replication

Pathogenesis of Influenza virus infectionInfluenza virus first targets and kills mucus-secreting, ciliated, and other epithelial cells, causing the loss of this primary innate defense mechanisms. NA facilitates the development of the infection by cleaving sialic acid residues of the mucus.Virus copies are released at the apical surface of cells (due to insertion of the HA in those sites)..This leads to cell-to-cell spread and transmission to LRT.In LRT, viral infection can cause severe desquamation of bronchial or alveolar epithelium down to a single-cell basal layer or to BM.

As you know, influenza virus is released after ~ 8 h.The infection promotes bacterial adhesion to epithelial cells. Pneumonia may result from a viral pathogenesis or from a secondary bacterial infection. Influenza may also cause a transient or low-level viremia but rarely involves tissues other than the lung. Interferon and cytokine responses are concomitant with the febrile phase of disease. T-cell responses are important for effective recovery and immunopathogenesis. However, influenza infection depresses macrophage and T-cell function, hindering immune resolution. Interestingly, recovery often precedes detection of antibody in serum or secretions !!

MOT: airborne respiratory droplets ( less than 10 um)Survive for short period on surfacesI.P. 18-72 hoursVirus concentration in nasal and tracheal secretions remains high for 24 to 48 hoursSite of infection- epithelial cells of the respiratory tractHumoral Immunity- ( IgG & IgA)protection against reinfection, antibody against HA is important

Symptoms and complications1. Uncomplicated influenzaFever ( 38-40 C)Myalgias, headacheOcular symptoms- photophobia, tears, acheDry cough, nasal d/c2. Pulmonary complications/sequelaeCroup( acute larygotracheobronchitis)Primary influenza pneumoniaSecondary bacterial infection

3. Non pulmonary complicationsMyositisCardiac complicationsEncephalopathyReyes syndromeGuillen-Barre syndrome

Diagnosis1. virus isolationMonkey kidney cell etc.No CPE

2.serologyHemadsorptionPCR

ChemotherapyRimantadine and amantadineZanamavir and oseltamivirRest, liquids and anti febrile agents

Epidemiologic ConcernsStrains of influenza A virus are classified by the following four characteristics: Type (A, B, and C)Place of original isolationDate of original isolationAntigen (HA and NA)

For example, a strain might be designated:

A/Bangkok/1/79 (H3N2) This means that it is an influenza A virus that was first isolated in Bangkok in January 1979 and contains HA (H3) and NA (N2) antigens. For Influenza B virus: same but antigen is not mentioned..why ?

Influenza is spread via airborne droplets expelled during talking, breathing, and coughing. Influenza virus can survive on surfaces for a dayChildren especially at school- are most susceptible population.A patient is contagious before symptoms and long time after.Categories at highest risk for serious complications are: ChildrenImmunosuppressedElderlyPersons with heart and lung diseasesSmokers.

Mortality: > 90% occurs in elderly patients.

New influenza A strains are generated through mutation and reassortment. influenza A is able to infect and replicate in humans, birds, and pigs (zoonose).Co-infection of a cell with different strains of influenza A virus allows genomic segments to randomly reassort and form a new viral antigenic make-up, virulence property, or host scope.An exchange of the HA gp may generate a new virus that can infect an immunologically nave human population. For example, an H5N1 duck virus and an H3N2 human virus infected pigs, reassortants were isolated from the pig, and the resulting virus was able to infect humans. There is concern that a reassortant between the avian, very virulent H5N1 (that can pass directly from bird to human) and a human influenza virus might generate a pandemic.

PROPERTIES OF ORTHOMYXOVIRUS AND PARAMYXOVIRUS

PropertyorthomyxovirusparamyxovirusvirusesInfluenza A,B,CMeasles,mumps, RSV,& parainfluenzagenomeSegmented Non segmentedVirion RNA polymeraseyesyesCapsidhelicalhelicalEnvelopeyesyessizeSmaller(110 nm)Larger( 150 nm)Surface spikesH&N diff. spikesH&N same spikesGiant cell formationnoyes

Envelope spikes

VirusHNFusion proteinMeasles virus+-+mumps+++RSV--+Parainfluenza+++

ParamyxovirusNon segmented, ss genome; helical capsid with outer lipoprotein envelope

Envelope spikes: H & N and fusion protein

MEASLES VIRUSSingle serotype

H- target of neutralizing Ab

Humans are the natural host

PathogenesisReceptor: CD46 on surface of macrophagesRash-cytotoxic T cells attacking the virus infected vascular endothelial cells in the skinCMI- neutralizing the virus during viremic phaseMOT: droplet inhalationHematogenous transplacental

ClinicalIncubation : 7-13 daysProdrome- high fever, 3C & P- infectiousKoplicks spots- buccal mucosa across the molars- grains of salt surrounded by red haloRashes appears-starts below the ears and spread throughout the body undergoes brawny desquamation

ComplicationsEncephalitisBacterial pneumoniaGiant cell pneumonia- defective CMIAtypical measles- older inactivated mealsesSSPE-subacute sclerosing panencephalitis

Mumps virusH and N + fusion protein on envelope spikesInternal nucleocapsid protein- S Antigen- detected in complement fixation testHumans are the natural hostthermolabile

Mumps

Nasal or URT epithelial cells- blood-salivary glands, testes,ovaries, pancreas, meninges and kidneysShed in the saliva 2 days before to 9 days after the onset of salivary gland swelling(+) virus in urine up to 14 days after onset of symptoms

Clinical

1/3 of patients subclinical50% with swelling of the salivary glandsPain and anorexiaComplicationsOrchitis-postpubertal-unilateral, bilateral-sterilityaseptic meningitisOophoritis-5%Pancreatitis- 4%

Immunity

Ab vs HN glycoprotein- correlate with immunityAb vs S Ag- appear earliest, gone w/in 6 monthsPassive immunity from mother to offspring- protection during 1st 6 months of life

Diagnosis1. cell cultureSpecimen-saliva, spinal fluid or urineMonkey kidney cellCPE- cell rounding and giant syncytia formation2. serology- 4 fold rise in Ab titer in HI or CFAb vs S antigen- current infectionAb Vs V antigen- past infection

Prevention: vaccine, attenuated vaccine

Respiratory Syncytical VirusMost important cause of pneumonia and bronchiolitis in infantsFusion proteins- syncytia formationHumans and chimpanzees- natural host2 serotype: A & BMOT: respiratory droplet

Clinical 1. infants- bronchiolitis, pneumonia2. young children- otitis media3. older children and adults- common coldDiagnosis: immunofluorescenceIsolation in cell culture- + CPEserology

TreatmentAerosolized RibavirinRibavirin + hyperimmune globulins

PreventionNO VACCINEPalivizumab-prophylaxis, monoclonal ab vs. fusion protein

Parainfluenza VirusSurface spikes: H & N same spike, fusion on different spikeBoth humans and animals infected

Four serotypes: 1, 2, 3 & 4

MOT: respiratory droplet

No viremiaClinical:1&2- major cause of croup; children < 6 y/oLaryngitisPneumoniaCommon cold- 4PharyngitisOtitis media