Influenza Viruses by James McSharry, PhD

Summary

In this lecture, Professor James Macari discusses influenza viruses, focusing on their structure and replication process. He explains the difference between low and highly pathogenic strains, the current circulating strains like H5N2 and H5N8, and the 2014 outbreak's link to bird migration. Macari also covers antiviral treatments, including ion channel blockers and neuraminidase inhibitors, and the development of vaccines, highlighting the challenges of creating effective vaccines due to the virus's high mutation rate.

Takeaways

• 🦠 Influenza viruses are negative sense, enveloped RNA viruses that infect various species including birds and humans.
• 🌐 Current circulating strains include H5N2 and H5N8, with geographical spread linked to bird migration.
• 🔬 The virus structure consists of two main surface proteins: Hemagglutinin (H) and Neuraminidase (N), which are crucial for viral attachment and release.
• 🌿 H5N1, which first appeared in China in 1997, has mutated into H5N2 and H5N8, causing significant issues in poultry worldwide.
• 🌡 The severity of influenza can range from mild to deadly, with highly pathogenic strains being more deadly due to their ability to infect various organs.
• 🧬 Influenza viruses are typed into A, B, and C based on the antigenic properties of their nucleoprotein and membrane proteins.
• 💊 Antiviral drugs like amantadine and rimantadine target ion channels of the virus, but resistance is a concern.
• 🌐 The 2009 H1N1 pandemic virus spread globally causing a large number of infections, though not as severe as initially feared.
• 💉 Current vaccines include inactivated vaccines and live attenuated influenza virus vaccines, designed to induce antibodies against specific antigens.
• 🔄 The need for annual flu vaccines arises from the constant mutation of the HA protein, necessitating updates to match circulating strains.
• 🔬 Research is ongoing to develop broadly reactive antibodies and vaccines that could provide protection against all influenza strains.

Q & A

What are influenza viruses?

Influenza viruses are negative sense envelope RNA viruses that contain segmented genomes. They infect various hosts including waterfowl, birds, and occasionally spread to humans and other animals, causing diseases that can range from mild to severe or even deadly.

What are the current circulating influenza viruses?

The current circulating influenza viruses mentioned in the script are H5N2 and H5N8.

How did the H5N1 virus spread globally?

The H5N1 virus appeared in China in 1997 and spread throughout the world, mutating into H5N2 and H5N8, which are causing significant problems in poultry today.

What are the two lipoproteins on the exterior of the influenza virus?

The two lipoproteins on the exterior of the influenza virus are the hemagglutinin (H), which is responsible for attaching the virus to cells, and the neuraminidase (N), which facilitates the release of new virus particles from infected cells.

What is the function of the matrix protein (M1) in the influenza virus?

The matrix protein (M1) in the influenza virus is a major structural protein that lies beneath the viral envelope, providing structural support to the virus particle.

How many ribonucleoproteins are contained within the influenza virus?

There are eight ribonucleoproteins contained within the influenza virus, each associated with a segment of the virus's negative-sense RNA genome.

What are the different types of influenza viruses and how are they classified?

Influenza viruses are classified into types A, B, and C based on the antigenic properties of the nucleoprotein (NP) and the matrix proteins (M). Type A viruses are further subtyped based on the hemagglutinin (HA) and neuraminidase (NA) proteins, with 16 known HA subtypes and 9 known NA subtypes.

What is the significance of the cleavage of the hemagglutinin protein in the pathogenicity of avian influenza viruses?

The cleavage of the hemagglutinin protein is significant in the pathogenicity of avian influenza viruses because it determines how easily the virus can spread within a host. Low pathogenic viruses are cleaved slowly by trypsin-like enzymes, limiting their spread to the respiratory and gastrointestinal tracts. In contrast, highly pathogenic viruses can be cleaved by numerous proteases throughout the body, leading to systemic infection and increased virulence.

What is the replication cycle of the influenza virus?

The replication cycle of the influenza virus begins with attachment to host cell receptors, followed by internalization into the cell's cytoplasm. The viral RNA is then released into the nucleus where it is transcribed into mRNA and replicated. New viral components are assembled and the virus particles are released to infect other cells.

What are the two main classes of antiviral drugs mentioned for treating influenza?

The two main classes of antiviral drugs mentioned for treating influenza are ion channel blockers (like amantadine and rimantadine) and neuraminidase inhibitors (like oseltamivir and zanamivir).

What is the purpose of the live attenuated influenza vaccine (LAIV) and how is it different from the inactivated vaccine?

The live attenuated influenza vaccine (LAIV) contains weakened live viruses that are delivered intranasally, providing a mild form of the infection that stimulates an immune response without causing severe illness. It is different from the inactivated vaccine, which contains killed viruses and is administered intramuscularly, typically with a needle.

Why is a new influenza vaccine developed each year?

A new influenza vaccine is developed each year because the hemagglutinin antigen of type A viruses mutates randomly, leading to different antigens annually. This requires the vaccine to be updated to match the circulating strains and provide effective protection.

Outlines

00:00

🦠 Influenza Virus Basics

The lecture by James Macari introduces influenza viruses as negative sense envelope RNA viruses with segmented genomes. These viruses commonly infect waterfowl and can occasionally spread to humans and other animals, causing diseases ranging from mild to deadly. The current circulating strains are H5N2 and H5N8. The lecture discusses a significant event in 2014 where closely related viruses were detected in Asia, Europe, and North America, possibly linked to bird migration. The structure of the virus is explained, highlighting the hemagglutinin (H) and neuraminidase (N) proteins on its exterior. The process of viral infection, including attachment to cells, entry, and replication, is outlined. Influenza viruses are typed based on the antigenic properties of the nucleic acid protein and membrane proteins, with Type A being the most significant for human infections.

05:00

🔬 Pathogenicity and Replication

This section delves into the pathogenicity of avian influenza viruses, explaining how low pathogenic strains are slowly cleaved by trypsin-like enzymes, limiting infection to the respiratory and gastrointestinal tracts. In contrast, highly pathogenic strains can be cleaved by numerous proteases, allowing for systemic infection and greater deadliness. The replication cycle of influenza viruses is detailed, starting with attachment to host cells, followed by internalization, replication in the nucleus, and eventual release of new virus particles. The role of antivirals in treating influenza is also discussed, including ion channel blockers like amantadine and rimantadine, and neuraminidase inhibitors such as oseltamivir (Tamiflu) and zanamivir, which prevent the release of new viruses from infected cells.

10:00

💊 Antiviral Treatments and Vaccines

The paragraph discusses various antiviral drugs used to treat influenza, including ion channel blockers and neuraminidase inhibitors. It also mentions experimental compounds like DAS181, which removes sialic acid from respiratory tract glycoproteins to control infection, and T-705, an RNA-dependent RNA polymerase inhibitor. The current state of influenza vaccines is explored, including inactivated vaccines and live attenuated vaccines. The vaccines aim to induce antibodies against the type-specific hemagglutinin antigen but face challenges such as the need for annual updates due to viral mutations and varying effectiveness. The development of broadly reacting antibodies and universal vaccines is an active area of research.

15:00

🛡 Vaccine Development and Challenges

This section discusses the evolution of influenza vaccine production, moving from traditional methods to recombinant technology that uses plasmids of viral genes to create new vaccines. The challenges of vaccine development are highlighted, including the need for annual updates due to mutations in the hemagglutinin antigen of Type A viruses. The paragraph also covers the discovery of broadly reacting antibodies that target the conserved central region of the hemagglutinin, which could potentially lead to the development of universal vaccines. The lecture concludes with a discussion on the importance of continued research in influenza vaccine development.

Keywords

💡Influenza

Influenza, commonly known as the flu, is a contagious respiratory illness caused by the influenza virus. In the video, the focus is on the influenza virus, its types, and its impact on human and animal health. Influenza viruses are responsible for seasonal epidemics and occasional pandemics, as discussed with the mention of the 2009 H1N1 pandemic.

💡Negative sense envelope RNA viruses

This refers to the type of viruses that influenza belongs to. They have a lipid envelope and a negative sense RNA genome, meaning the RNA is complementary to the mRNA. The video explains that these viruses infect various hosts, including birds and humans, and can cause diseases ranging from mild to severe.

💡Segmented genomes

Influenza viruses possess segmented genomes, which means their genetic material is divided into separate pieces. This characteristic allows for genetic reassortment, contributing to the virus's ability to evolve and adapt, as mentioned in the context of the H5N1 mutation into H5N2 and H5N8.

💡Hemagglutinin (H)

Hemagglutinin is a glycoprotein found on the surface of the influenza virus. It plays a critical role in the virus's ability to bind to and enter host cells. The video describes it as the 'blue knob' that attaches the virus to sialic acid receptors on the cell surface, illustrating its importance in viral infection.

💡Neuraminate (N)

Neuraminate, or neuraminidase, is another surface glycoprotein of the influenza virus that helps the virus to be released from infected cells. The video mentions that neuraminidase inhibitors, such as Tamiflu, work by blocking this protein's function, preventing the virus from spreading.

💡Antigenic properties

Antigenic properties refer to the ability of a virus to stimulate an immune response and the characteristics that define its recognition by the immune system. The video explains that influenza viruses are typed based on the antigenic properties of the hemagglutinin and neuraminidase proteins, which are crucial for vaccine development.

💡Replication cycle

The replication cycle of influenza viruses is detailed in the video, starting with attachment to the host cell, followed by entry, replication, assembly, and release of new viral particles. Understanding this cycle is key to grasping how antiviral drugs target different stages of the virus's life cycle.

💡Antivirals

Antivirals are medications used to treat viral infections. The video discusses various antiviral drugs, such as ion channel blockers (amantadine) and neuraminidase inhibitors (Tamiflu), which are used to treat influenza by inhibiting specific stages of the virus's replication cycle.

💡Vaccines

Vaccines are preventive measures against influenza, and the video discusses different types of vaccines, including inactivated vaccines and live attenuated vaccines. The development of vaccines is tied to the antigenic properties of the virus, and the video highlights the challenges of creating effective vaccines due to the virus's high mutation rate.

💡Broadly reacting antibodies

Broadly reacting antibodies are a focus of vaccine research mentioned in the video. These antibodies have the potential to target multiple strains of the virus, offering a more universal approach to influenza vaccination. They are directed towards conserved regions of the hemagglutinin protein, which do not mutate as frequently as the globular head.

💡Pandemic

A pandemic refers to a widespread infectious disease affecting a large number of people across multiple geographic regions. The video mentions past pandemics, such as the 1918 influenza pandemic, and the potential for new influenza viruses, like H5N1, to cause pandemics due to their ability to infect humans and animals.

Highlights

Influenza viruses are negative sense envelope RNA viruses with segmented genomes.

Influenza viruses infect a variety of hosts including waterfowl and can occasionally infect humans.

The current circulating influenza viruses are H5N2 and H5N8.

Influenza viruses can spread through bird migration, as seen in the 2014 outbreak.

H5N1 appeared in China in 1997 and has since mutated into other strains causing problems in poultry.

The structure of the influenza virus includes two lipoproteins, hemagglutinin (H) and neuraminidase (N).

The M1 protein is a matrix protein, and the M2 protein is an ion channel involved in virus release.

Influenza viruses contain eight ribonucleoproteins with negative stranded RNA.

Influenza viruses are typed based on the antigenic properties of the nucleoprotein and membrane proteins.

Influenza A viruses are further subtyped into different groups based on pathogenicity.

The HA protein must be cleaved for the virus to infect cells, which differs between low and high pathogenicity strains.

Influenza A viruses like seasonal H1N1 and H3N2 occur annually, with H3N2 being a major cause in recent years.

The 2009 H1N1 pandemic virus spread worldwide causing a large number of infections.

Antivirals for influenza include ion channel blockers and neuraminidase inhibitors.

Amantadine and rimantadine are ion channel blockers, but resistance develops quickly.

Neuraminidase inhibitors, such as oseltamivir and zanamivir, prevent virus release from cells.

Experimental compounds like DAS181 and T-705 are being investigated for influenza treatment.

Current influenza vaccines include inactivated vaccines and live attenuated vaccines.

Vaccines are designed to induce antibodies to the type-specific hemmagglutinin antigen.

Vaccine effectiveness can vary, with the 2015 vaccine being only 20-30% effective.

New vaccine technologies, such as recombinant plasmids, have improved vaccine safety and efficacy.

Broadly reacting antibodies have been identified and are being studied for universal vaccine development.

Transcripts

[Music]

this first lecture will be on influenza

viruses presented by James Macari

professor emeritus of a medical college

Albany New York influenza viruses are

negative sense envelope RNA viruses that

contains segmented genomes they infect

waterfowl birds ducks ease things like

that occasionally influenza viruses

spread from waterfowl or other animals

including people causing mild to very

serious and often deadly disease current

influenza viruses that are circulating

through the world right now are h5 n2

and h5n8 this this particular slide

shows what happened in 2014 and the Oh

most simultaneous detection of closely

related viruses in Asia Europe and North

America

so just linkage with a bird migration

via large rate region in Russia now back

in 1997 h5n1 appeared in in China and

that spread throughout the world

now those h5n1 has mutated to become the

h5 h5 n2 and h5 n H which are causing

major problems in poultry throughout the

world today influenza virus is this is a

model of influenza virus on the exterior

there are two lipoproteins the

hemagglutinin or H a which is the blue

knob

is this this DHA attaches the virus to

salic acid containing receptors on the

surface of the cell the n na is the norm

in today's this is a tetra mer this is

the orange colored glycoprotein on the

outside of the virus particle and this

protein actually functions as the virus

is released from the cell inside the

first one is the matrix protein the m1

protein this is one major proteins of

the virus particle coached to complete

inside of the lipid envelope of the

green proteins or the m2 protein is an

ion channel which is involved in

encoding the virus inside the cell as we

enter the virus particle the interior

you see there are eight

ribonucleoproteins

labeled PD - PD one PAH a and T na and

NS these ribonucleoproteins

contain negative stranded RNA and

multiple copies of the na protein the

nucleic acid protein the influenza

viruses are designated they are typed on

the base of the antigenic properties of

the nucleic acid protein and the

membrane proteins and they are type a B

and C a and B because these and people

see is a minor entity in terms of human

infection but it is involved in other

infections swine influenza viruses is

type a influenza viruses are sub

a the energetic properties of the H a

and M a proteins there are 16 H a and 9n

a swine influenza virus is type a

subtype h1n1 the avian influenza viruses

um into two different groupings in terms

of their pathogenicity the in order for

the virus to infect the cell the H a has

to be clean so and it's cleaved the

trypsin trypsin like segments in low

pathogenic avian influenza viruses the

protease level is just four amino acids

and it's very slowly cleaved or its

markets not completing Germans but the

cleavage occurs in the respiratory tract

and in the gut only or is the highly

pathogenic avian influenza virus is

susceptible to numerous proteases so

cleavage occurs footage of the HEA

occurs throughout the animal and virus

infection can occur throughout the

animal and that is why it is much more

deadly influenza virus influenza viruses

influenza A viruses like seasonal h1n1

and h3n2 viruses these occur every year

and particularly recently we have more

h1n1 this past season 19 - or 2015-2016

h3n2 was the major cause of disease 2009

a new influenza virus appeared and was

pandemic h1n1 and this virus spread

throughout the world and caused very

very large numbers of infections it

wasn't quite as big as bad as people

worried

about what people thought maybe similar

to the 1918 pandemic which killed

approximately 50 million people this

h1n1 probably killed a much much smaller

number of people there's also an

influenza B viruses those are the humans

now the avian influenza viruses h5n1 h5

n2 h5 n 8 8 7 n 7 and h9 and to

occasionally spread from verged people

human infection with these avian

influenza viruses occurs rarely but can

be deadly

what it does occur all avian influenza A

viruses separate potential was influenza

pandemics pandemic is a worldwide

epidemic this is a replication cycle for

influenza viruses the first step is

attachment the virus attaches to cyclic

acid containing glycoproteins and

glycolipids on the plasma membrane of a

susceptible cell next step is put the

virus to get taken into the cytoplasm

through placing coated pits this is in

the pit the pH of the medium inside the

the endosome is reduced to about 6 under

which circumstances they even gloat the

hemagglutinin undergoes a conformational

change which allows the viral envelope

to fuse with the endosomal membrane

releasing the ribonucleoprotein so for

each of the eight ribonucleoproteins in

the virus they will get released into

the cytoplasm

now these proteins have nuclear

localization signals on them so they are

transported to the nucleus where two

kinds of transcription occur one is to

make

messenger rnas and this is a rather

interesting way to make messenger RNAs

the tack the 5-prime cat of cellular

newly made messenger RNA is cleaved off

and that's used as a primer to make

messenger rna's for each of the eight or

ten proteins of the virus and those are

all made in in the in the nucleus in

addition the ribonucleoprotein is copied

into a positive sense and then back into

a negative sense which is used to make

progeny viruses these viruses accumulate

and are released into the cytoplasm the

messenger RNAs for the H a and the

neuraminidase

associate with ribosomes and roughened

mm particular where they become bike

oscillated and exported to the plasma

membrane the other messenger RNAs are

made into proteins and those proteins go

back into the nucleus to form new nucleo

capsid and in this way the virus

replicates itself and and many many many

viruses are made now the there are a

number of antivirals that are used for

to complete patients who are exactly

with influenza originally they were ion

channel blockers remember to go back to

the model for the virus and there were

those green ion channels amantadine and

Romancing are very similar compounds

and they block that ion channel show you

a picture shortly they are only good for

type a influenza virus and currently

they are not recommended because they

generate resistant viruses very quickly

in addition to the ion channel blockers

there are enormous inhibitors these have

come about in the last couple of years

one is awful County our carboxylate also

known as Tamiflu it's good for both type

A and type B viruses and banana beer or

Belen for lens ax

also good for type A and type B these

two inhibitors block the ability of

influenza viruses to remove the salad

gases from the virus and hence the virus

tends to stay inside the cell and

doesn't get released

now for the amantadine that has blocked

the ion channels again Anthony just

sticks into the channel and blocked it

prevents the ions from flowing and hence

the pH doesn't change in the zone and

the virus doesn't understand code for

the norman ace inhibitors they block the

ability of the millah days to clean off

the terminal ayala gasses on these

lipoproteins and that again prevents the

release of the virus from itself in

addition to those licensed antiviral

drugs there are a number of experimental

compounds of treatment of influenza one

is called - das 181 this compound

removes alig acid from services of

glycoproteins and glycolipids of

themselves at the upper respiratory

tract just enough to control the

infection for not so much to cause harm

another

newly developed method well is T 7:05

this inhibits the RNA dependent RNA

polymerase

there are several novel compounds under

investigation for the inhibition of

influenza daughter

so it's a very active area of research

and another active area of research is

combination chemotherapy where more than

one drug is used at the same time you

probably ones the amantadine is plus

norm in today's inhibitors something

like that and that's an active field for

research current influenza vaccination I

rolled have vaccines the current

influenza vaccines are an inactivated

vaccine containing type a seasonal and

pandemic h1n1 viruses and fight a

seasonal h3n2 virus and type the

influenza virus oh so this has three or

four different viruses that are

inactivated and put into a solution

which is injected intramuscularly we

also have what's called a pole adapted

live attenuated influenza virus vaccine

which contains the same four strains

viruses inactivated vaccine and it's

delivered intranasally so there's no

needles kid-friendly but it is kind of

expensive this is a slide of somebody

giving the live attenuated vaccine to a

patient current flu vaccines type a and

type D viruses are designed to induce

antibodies to the type specific DJ Huen

antigen like attachment virus to the

cell presenting infections when they

work currently on a good day you get

about eighty percent protection close to

the fine sometimes it doesn't work at

all the current - 2015 vaccine is only

20 to 30 percent effective as an example

now the way the vaccines are made this

is fairly new this is 2004 paper from

dr. Peter Polizzi and what they did in

the past

I think the first influenza vaccines

were dissolved in 1940s and they just

threw the virus today and activated it

and all the vaccines but you have all

kinds of problems with that with the

authority to use recombinant technology

what they've done now is to make

plasmids of each of the eight genes for

the virus the H a and the NA and the P D

1 PB 2 PA and PM and NS and those are

all those plasmids are put into a cell

to make a new virus which is a

combination of the backbone the only the

AJ and the na are specific for the

parent vaccine the backbone comes from a

photo Rico which is well tolerated in

people and once they started using this

vaccine all of the programs that

compared with vaccines in the past or

most of the problems have gone away

problems with current employees acting

type A viruses random mutations of the

hae lead to different AJ antigens

each year therefore need a new vaccine

each year it's very expensive to make

and also is kind of hit or miss when you

get it correct as I said in 2015 the

vaccine didn't match very well about 30

percent effective and a few years ago

they had a vaccine that didn't work at

all so that's a problem

type D virus's does not change much from

year to year so that's not a problem

now they had

found that there are broadly reacting

antibodies and people so they have

figured out ways to make vaccines from

that and and on this slide uses a slide

of the H a it's a trimer and the the red

is the globular head this is where

individual mutations occur every time

the virus replicates basically and this

is why you have to make a new vaccine

each year because those antibodies are

directed against the head of the virus

now recently it's been discovered that

broadly reacting antibodies are also

generated in people over time and

they're directed toward the central

region of the evil group and a number of

these broadly acting antibodies have

been analyzed and and they are now being

studied and to be used as at the vaccine

which will work against all of the

influenza viruses all these in Taipei

and to inspire

[Music]