OrthomyxoviridaeOrthomyxoviridaeInfluenza VirusInfluenza Virus

Properties Properties • Spherical Virion ( polymorphic) Spherical Virion ( polymorphic) • 100 nm Size100 nm Size• Segmented –SS-RNA : 7-8 segmentsSegmented –SS-RNA : 7-8 segments• Mostly segment: 1 protein and two Mostly segment: 1 protein and two

segment 2 proteinsegment 2 protein• H & N : Antigenic variationH & N : Antigenic variation• Resistant to room temperature and Resistant to room temperature and

spatially 4ºCspatially 4ºC

Neuraminidase Neuraminidase helps the virus to release itself from the cells

HemagglutininHemagglutininHemagglutinin allows the virus to bind to host cells

RNARNA

Influenza Surface ProteinsInfluenza Surface Proteins

MM22 protein protein (only on type A)(only on type A)

Clinically Relevant Influenza Clinically Relevant Influenza VirusesVirusesType AType A Potentially severe illnessPotentially severe illness

Epidemics and pandemicsEpidemics and pandemicsRapidly changingRapidly changing

Type BType B Usually less severe illnessUsually less severe illnessEpidemicsEpidemicsGenetically more stableGenetically more stable

SubtypeSubtype HumanHuman SwineSwine HorseHorse BirdBirdH1H1H2H2H3H3H4H4H5H5H6H6H7H7H8H8H9H9H10H10H11H11H12H12H13H13H14H14H15H15

Hemagglutinin Subtypes of Hemagglutinin Subtypes of Influenza A VirusInfluenza A Virus

Adapted from Levine AJ. Viruses. 1992;165, with permission.

SubtypeSubtype HumanHuman SwineSwine HorseHorseBirdBirdN1N1N2N2N3N3N4N4N5N5N6N6N7N7N8N8N9N9

Neuraminidase Subtypes of Neuraminidase Subtypes of Influenza A VirusInfluenza A Virus

Adapted from Levine AJ. Viruses. 1992;165, with permission.

Influenza A Virus Constantly Influenza A Virus Constantly ChangesChanges Antigenic driftAntigenic drift

Small changes in H or N proteins that occur Small changes in H or N proteins that occur from year to yearfrom year to year

Antigenic shiftAntigenic shift Acquisition of new H or N protein, possibly from Acquisition of new H or N protein, possibly from

an bird virusan bird virus

Diseases : Diseases : 1- Influenza:Signs and Symptoms1- Influenza:Signs and Symptoms Abrupt onset of symptomsAbrupt onset of symptoms FeverFever Cough with little or no sputumCough with little or no sputum HeadacheHeadache Muscle achesMuscle aches Sore throatSore throat light sensitivity, and eye painlight sensitivity, and eye pain

• PneumoniaPneumoniaElderly, pregnant, and …..Elderly, pregnant, and …..Viral (1:3), most viral & bacterial Viral (1:3), most viral & bacterial

(S.areuse) (2:3)(S.areuse) (2:3)• Reye Syndrome:Reye Syndrome: encephalopathy in encephalopathy in

children (2-16 years) , mortality 10-40% , children (2-16 years) , mortality 10-40% , Influenza A & B, chicken pox ,Influenza A & B, chicken pox ,Salicylic acid compound Salicylic acid compound

Immunity to influenzaImmunity to influenza• PermanatPermanat• Type Related Type Related • Antibody again H & NAntibody again H & N

Treatment Treatment • Amantadine Amantadine • RimantadineRimantadinePreventionPrevention• Vaccination ( 70%)Vaccination ( 70%) Most effective in young, healthy Most effective in young, healthy

peoplepeople Less effective in the elderlyLess effective in the elderly

Influenza Virus VaccineInfluenza Virus Vaccine