Lecture 14 - Influenza viruses

What is the structure of Influenza virus type A?

-Single strand

-Negative sense

-8 segments of RNA

Where do Influenza viruses replicate?

In the nucleus

How do Influenza viruses enter and uncoat?

-Enter through receptor-mediated endocytosis

-Uncoat by fusing to endosomal membrane

What are the two glycoproteins found on a virus envelope?

-Hemagglutinin (HA)

-Neuraminidase (NA)

What is the function of Hemagglutinin (HA)? How many types are there?

-Binds sialic acid on host cells to allow for entry (host specific)

-18 types

What type of sialic acids do birds have? Humans? Pigs?

-Birds: a-2.3 sialic acids

-Humans: a-2.6 sialic acid

-Pig: a-2.5 sialic acid

What is the function of Neuraminidase (NA)? How many different proteins are there?

-Cleaves sialic acid and allows virus to uncoat

-11 different proteins

Which glycoprotein is most susceptible to viral antibodies and has the highest rate of mutation?

Hemagglutinin (HA)

What is antigenic drift?

Accumulation of non-lethal point mutations by nucleotide substitutions (usually involves HA and NA)

What are the antigenic consequences of antigenic drift?

-Progressive accumulation of mutations within one subtype

-Change in antigenic epitopes

-Escape from antibodies (can cause recurrent infections)

What is coinfection?

Genome segment exchanges between two viruses

What are the antigenic consequences of coinfection?

-New strain of flu (may be highly virulent)

-No immunity to new strain

-May lead to new zoonotic diseases

What is the reservoir for influenza A virus?

Aquatic birds

In respiratory epithelium, is apical or basolateral release of a pathogen more virulent?

Basolateral side

What type of virus are all influenza vaccines?

Inactivated

What are the clinical symptoms of canine influenza virus (CIV = H3N8)

Cough, runny nose, fever, rarely pneumonia

What is the diagnosis of canine influenza virus (CIV - H3N8)?

-Serum samples (HI and neutralization tests)

-Swabs for virus isolation or RT-PCR

What is the control for canine influenza virus (CIV - H3N8)?

Vaccines

What is the infection rate and incubation period for equine influenza (H3N8 and H7N7)?

-Incubation: 3-5 days

-Infection rate: 100% in unvaccinated horses

What are the clinical signs of equine influenza?

Fever, dry cough, runny nose, bronchitis

How is equine influenza diagnosed?

Clinical signs, serology, detection of viral antigens in secretion, RT-PCR, virus isolation

What are the differential diagnoses for equine influenza?

-Equine herpesvirus (EHV-4)

-Equine arteritis virus (EAV)

-Equine rhinovirus

What is the control for equine influenza?

Quarantine, disinfection, vaccination

What are the clinical signs of swine influenza (SIV = H1N1, H1N2)?

Runny nose, lethargy, “goose honk” cough, reduced appetite

What is the diagnosis for swine influenza (SIV = H1N1, H1N2)?

Clinical signs, RT-PCR, virus isolation

How is swine influenza (SIV = H1N1, H1N2) controlled?

Vaccines (only lasts a few months)

What is the difference with HA protein cleavage sequences in LPAI compared to HPAI?

-LPAI: HA extracellularly cleaved by trypsin (protease)

-HPAI: HA intracellular cleaved by furin

What antigenic types of influenza are circulating in wild birds?

All 18 types of HA and all 11 types of NA

What antigenic types of influenza are circulating in humans?

H1N1, H3N2, and Influenza B and C

What antigenic types of influenza are circulating in swine?

H1N1, N3N2

What antigenic types of influenza are circulating in equine??

H3N8

What antigenic types of influenza are circulating in dogs?

H3N8, H3N2

What HA proteins are circulating in HPAI?

H5, 7, and 9

What antigenic types of influenza are circulating in Bovine?

H5N1