Orthomyxoviridae Flashcards
Know characteristics of Orthomyxo family
What is common on composition of the genome of Orthomyxoviridae family?
6-8 segments of linear negative-sense single-stranded RNA, 10-14.6kb overall size
What genus compose the Orthomyxoviridae family?
Influenzavirus A, Influenzavirus B, Influenzavirus C, Thogotovirus (tick borne disease in livestock and humans), Quaranjavirus (ticks and birds), and Isavirus (Salmon anemia virus). Influenzavirus D in equine and bats is waiting classification
Which virus and year where the latest outbreaks for pandemic influenza?
H5N1 in 1997 and H1N1 in 2009
Who are the hosts of low pathogenic influenza A viruses?
Aquatic birds of Order Anseriformes and Charadriiformes: ducks, shorebirds, gulls
Where do Influenza A viruses replicate in wild birds and how is it excreted?
Replicates in intestine and upper respiratory epithelium without causing disease, and is excreted in feces and oral secretions
Which is the most common hemmagglutinin subtype in each species: humans, swine, and equine?
Humans: H1, H2, H3,
Swine: H1, H3,
Equine: H3, H7
How many HA and NA subtypes exist?
HA: 1 to 16
NA: 1 to 9
How do you name the influenza viruses?
Virus type (A,B,C), host if not human, geographic origin, strain number, year of sample collection, HA and NA subtype (example:
A/equine/Miami/1/1963 (H3N8) prototypic equine influenza
A/swine/Iowa/15/1930(H1N1) prototypic swine influenza
A/Hong Kong/1/1968(H3N2) human pandemic of 1968
What is a clade and give an example using an Influenza A virus?
A taxonomic group comprising a single common ancestor and all descendants of that ancestor.
It is used for H5N1 to relate the evolutionary changes in isolates. Started in A/Goose/Guangdong/1/1996(H5N1) but spread to China. Now there are 30 clades. 2.1,2.2, 2.1.3
What are the properties and main proteins of the Orthomyxovirus virion?
Pleomorphic, filamentous (spherical in lab), 80-120nm in diameter. Lipid envelop with NA segments, with two kinds of spikes (influenza A and B; homotrimers of the HA GP, and homotetramers of the NA GP). Envelope is lined with M1 and M2, and genome is surounded by nuceloprotein (NP). Also associated with viral RNA polymerase complex (prot PB1, PB2, and PA).
What is the function of the genome of all viruses that have a negative sense RNA genome?
- Template for synthesis of messenger RNAs
2. Template for synthesis of positive sense replicative intermediate RNA, template for progeny genomic RNA synthesis
What is unique about the infuenza virus RNA replication site?
It occurs in the nucleus of the cells
Explain the molecular determinants of pathogenesis of influenza A viruses based on the HA protein that differentiates a HPAI with a LPAI.
The HA protein (HA0) needs to be cleaved postranslationally so the virus is infectious. The HA0 from HPAI viruses has several basic aa at the HA cleavage site or long insertions of aa. LPAI have a single arginine at a short cleavage site. The proteases that cleave the single arginine are tissue restricted, and access to protease determines tissue tropism (resp or GI tract). Virus is noninfectious and activation is extracell. The HA0 of HPAI can be cleaved by furins of the trans-golgi network. So the HA is cleaved intracell and fully infectious virions are released from infected cells. NS1 protein is important also to block interferon, and PB2 of the polymerase complex important for RNA replication and synthesis.
How are avian influenza viruses classified?
High pathogenicity avian influenza (H5 or H7 with an intravenous pathogenicity index IVPI greater than 1.2) and low pathogenicity avian influenza
