50 – 100 millions (death) 1 – 4 millions (death) 1 million (death) 123,000 to 203,000 (death)
Epidemic
H1N1 and H3N2 and influenza B affects 5–15% of the population resulting in 250,000 – 500,000 deaths per year
As a result high transmission barriers yielded few dominant circulating strains in humans!
Biomarkers for zoonotic transmission
Subtypes of HA and NA
Reassortment (Antigenic Shift)
Ecology – Wild aquatic birds, many species, inter-mediators
- Wild aquatic birds (wildfowl and shorebirds) are the natural reservoirs of all influenza A viruses.
Outbreak and sporadic
HPAI H5N1 (Asia, Africa and Europe; 1997 – 5/7, 2014) H7N9 (China; 2013 – 4/8, 2014) H7N2, H7N3 and H7N7 (N. Am and Europe; 2002 – 2004) H9N2 (China; since 1998) H10N7 (Egypt; 2004) H10N8 (China; 2013) H6N1 (Taiwan; 2013)
Enveloped virus with a negative, single-stranded and segmented RNA genome. Viral RNA replicates in nucleus. Re-assortment occurs between members within a given genera, but not different genera.
-Influenza viruses in their natural reservoirs are in evolutionary stasis and do not cause disease.
-Interspecies transmission to new hosts can be followed by rapid virus evolution, creating a potentially pathogenic strain.
Migratory flyways of wild bird populations
Science 2006
Barriers of Zoonotic Transmission
Influenza (from aquatic birds to humans)
420C – 370C Intestinal – Respiratory α-2,3 – α-2,6 Host restriction factors
- Co-infection - Mixing vessels - Live attenuated vaccine and wild type influenza infection -Lab-produced seed virus for vaccine production
Antigenic Drift of H3 HA
(病毒学教学课件）Lecture on influபைடு நூலகம்nza viruses
General Overview
In 1930, Shope isolated the influenza virus, A/Swine/Iowa/15/30 (H1N1) in pig. In 1933 Smith et al. at NIMR in London isolated the first human influenza virus (A/WSN/33).
392/655 99/258 1/90 0/12 0/2 1/1 0/1
Basic Structure
Electron micrographs of influenza A virus
HA
HA HA
M2
New H1N1 influenza viruses
Genome structure of influenza A virus
- Most transfers result in unstable virus lineages, but if a ‘mixing vessel’ (e.g. pig, chicken, quail) is involved a stable lineage may be established.
Orthomyxoviridae family consists of 5 genera:
1) Influenzavirus A 2) Influenzavirus B 3) Influenzavirus C 4) Thogotovirus: Thogoto virus and Dhori virus 5) Isavirus: infectious salmon anemia virus
Name of influenza viruses: A/chicken/Hong Kong/220/97 (H5N1); A/swine/Iowa/15/30 (H1N1); A/Anhui/1/05 (H5N1)
Influenza Epidemiology in Humans
Pandemic
1918 H1N1 1957 H2N2 1968 H3N2 2009 H1N1