Note Sheet 16 - VirusesNote Sheet 16 - Viruses

Swine (H1N1) Swine (H1N1) Flu VirusesFlu Viruses

What is a virus?What is a virus? VirusVirus – a – a particle made of a particle made of a

nucleic acid (DNA or RNA) nucleic acid (DNA or RNA) surrounded by protein coat surrounded by protein coat

CapsidCapsid – the – the outer coat of outer coat of protein that covers a virus protein that covers a virus

Viruses Viruses are extremely small – Millions of are extremely small – Millions of them could fit into one single cell them could fit into one single cell

Viruses Viruses are grouped by the type of are grouped by the type of organisms they infect – There are 3 main organisms they infect – There are 3 main types of viruses: plant viruses, animal types of viruses: plant viruses, animal viruses, and bacterial viruses viruses, and bacterial viruses

Virus TypesVirus Types

Viruses are smallViruses are small

http://learn.genetics.utah.edu/contenhttp://learn.genetics.utah.edu/content/begin/cells/scale/t/begin/cells/scale/

Some viruses cause diseaseSome viruses cause disease

Many human diseases are caused by Many human diseases are caused by virusesviruses

Common coldCommon cold FluFlu AIDSAIDS RabiesRabies

What is the What is the flu?flu?

Influenza (the flu) is a contagious respiratory illness Influenza (the flu) is a contagious respiratory illness caused by influenza virusescaused by influenza viruses

It can cause mild to severe illness, and at times can It can cause mild to severe illness, and at times can lead to death lead to death

Each year in the United States on average, 5% to Each year in the United States on average, 5% to 20% of the population gets the flu; on average, 20% of the population gets the flu; on average, more than 200,000 people are hospitalized from more than 200,000 people are hospitalized from flu-related complications, and; about 36,000 people flu-related complications, and; about 36,000 people die from flu-related causesdie from flu-related causes

There are many different types of flu virus, or There are many different types of flu virus, or “strains” that circulate from year to year and make “strains” that circulate from year to year and make people sick people sick

What is “What is “swine”swine” or “ or “H1N1”H1N1” flu?flu?

Swine flu is a new strain of the flu Swine flu is a new strain of the flu virus that was first identified passing virus that was first identified passing from human to human earlier this yearfrom human to human earlier this year

Because this particular virus has never Because this particular virus has never circulated in human populations circulated in human populations before, nobody has immunitybefore, nobody has immunity

Many more people than usual have Many more people than usual have become, and will become infected become, and will become infected with this particular strain of the viruswith this particular strain of the virus

Percentage of Visits for Influenza-like Illness (ILI) Reported by Percentage of Visits for Influenza-like Illness (ILI) Reported by the U.S. Outpatient Influenza-like Illness Surveillance Network the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet), National Summary 2008-2009 and Previous Two (ILINet), National Summary 2008-2009 and Previous Two Seasons (Week ending 11-14-09)Seasons (Week ending 11-14-09)

Swine Flu VirusSwine Flu Virus

Swine Flu VirusSwine Flu Virus Blue and Red Blue and Red

“spikes” “spikes” represent surface represent surface proteinsproteins

Blue are Blue are hemagglutinin hemagglutinin (HA) proteins(HA) proteins

Red are Red are neuraminidase neuraminidase (NA) proteins(NA) proteins

Flu Virus NamesFlu Virus Names

There are 16 types of HA protein and There are 16 types of HA protein and 9 types of NA protein9 types of NA protein

A flu virus has only one type of HA A flu virus has only one type of HA and one type of NA, so that is how and one type of NA, so that is how they are namedthey are named

Swine flu is grouped as an “H1N1” Swine flu is grouped as an “H1N1” virus because it has type 1 HA virus because it has type 1 HA protein and type 1 NA proteinprotein and type 1 NA protein

Is a virus a living thing?Is a virus a living thing? Viruses do NOT have all the characteristics Viruses do NOT have all the characteristics

of lifeof life Viruses Viruses are NOT made of cells and do not are NOT made of cells and do not have cell partshave cell parts

Viruses Viruses do NOT take in or use energydo NOT take in or use energy Viruses Viruses CANNOT reproduce by themselves CANNOT reproduce by themselves

Although Although there is some argument, most there is some argument, most biologists do not consider viruses to be living biologists do not consider viruses to be living

Where do viruses come Where do viruses come from?from?

Viruses Viruses enter living enter living cells and use the cells and use the cell parts of the cell parts of the infected cell to build infected cell to build more viruses more viruses

Host cellHost cell – a – a cell cell that has been that has been infected by a virus infected by a virus

What happens when a virus infects a What happens when a virus infects a cell?cell? Lytic CycleLytic Cycle – process – process where a virus enters where a virus enters

a cell, makes copies of itself, and causes a cell, makes copies of itself, and causes the cell to burst, releasing the new virusesthe cell to burst, releasing the new viruses

What happens when a virus infects a What happens when a virus infects a cell?cell? Lytic CycleLytic Cycle – process – process where a virus enters where a virus enters

a cell, makes copies of itself, and causes a cell, makes copies of itself, and causes the cell to burst, releasing the new virusesthe cell to burst, releasing the new viruses

What happens when a virus infects a What happens when a virus infects a cell?cell? Lytic CycleLytic Cycle – process – process where a virus enters where a virus enters

a cell, makes copies of itself, and causes a cell, makes copies of itself, and causes the cell to burst, releasing the new virusesthe cell to burst, releasing the new viruses

What happens when a virus infects a What happens when a virus infects a cell?cell? Lytic CycleLytic Cycle – process – process where a virus enters where a virus enters

a cell, makes copies of itself, and causes a cell, makes copies of itself, and causes the cell to burst, releasing the new virusesthe cell to burst, releasing the new viruses

Flu Attack! How A Virus Flu Attack! How A Virus Invades Your BodyInvades Your Body

http://www.xvivo.net/zirus-antivirotichttp://www.xvivo.net/zirus-antivirotics/s/

What happens when a virus infects a What happens when a virus infects a cell?cell?

Lysogenic CycleLysogenic Cycle – process – process where the where the virus injects its DNA into the DNA of virus injects its DNA into the DNA of the host cell which is then replicated the host cell which is then replicated along with the host cell’s DNA along with the host cell’s DNA Eventually, Eventually, the virus DNA will begin the virus DNA will begin

making more viruses (lytic cycle)making more viruses (lytic cycle) Viruses Viruses either make more viruses either make more viruses

immediately (lytic cycle) or “hide out” immediately (lytic cycle) or “hide out” for a while (lysogenic cycle) for a while (lysogenic cycle)

The Common The Common Cold – What is Cold – What is

it?it?

The common cold is a group of symptoms in the The common cold is a group of symptoms in the upper respiratory tract caused by a large number upper respiratory tract caused by a large number of different virusesof different viruses

Although more than 200 viruses can cause the Although more than 200 viruses can cause the common cold, the perpetrator is usually the common cold, the perpetrator is usually the rhinovirus, which is to blame for causing 10% to rhinovirus, which is to blame for causing 10% to 40% of colds40% of colds

Also, the coronaviruses cause about 20% of colds Also, the coronaviruses cause about 20% of colds

Corona VirusCorona Virus

Rabies VirusRabies Virus

HIV (Human Immunodeficiency HIV (Human Immunodeficiency Virus)Virus)

How do we defend against How do we defend against viruses?viruses? Viruses Viruses attack and attack and

destroy specific types destroy specific types of cells, causing the of cells, causing the symptoms of particular symptoms of particular diseases (flu, common diseases (flu, common cold, AIDS, rabies) cold, AIDS, rabies)

VaccineVaccine – a – a weakened or killed virus that is weakened or killed virus that is injected into the body so the immune system can injected into the body so the immune system can recognize the virus and destroy it recognize the virus and destroy it

Vaccines Vaccines only work if they are given before an only work if they are given before an infection – once a viral disease is contracted, it is infection – once a viral disease is contracted, it is often too late to control it often too late to control it

Vaccine Success Story - Vaccine Success Story - SmallpoxSmallpox

Smallpox is a highly Smallpox is a highly infectious, devastating, infectious, devastating, and disfiguring disease and disfiguring disease that is caused by variola that is caused by variola virus virus

Smallpox is characterized Smallpox is characterized by numerous pustules by numerous pustules containing infectious containing infectious virus all over the body virus all over the body

The fatality rate is more The fatality rate is more than one quarter of than one quarter of infected patients infected infected patients infected by the most serious form by the most serious form caused by caused by Variola majorVariola major

Vaccine Success Story - Vaccine Success Story - SmallpoxSmallpox

The disease killed an estimated 400,000 The disease killed an estimated 400,000 Europeans each year during the 18th century Europeans each year during the 18th century

Of all those infected, 20–60% — and over 80% of Of all those infected, 20–60% — and over 80% of infected children — died from the disease infected children — died from the disease

In the United States, from 1843 to 1855 first In the United States, from 1843 to 1855 first Massachusetts, and then other states required Massachusetts, and then other states required smallpox vaccination smallpox vaccination

By 1897, smallpox had largely been eliminated By 1897, smallpox had largely been eliminated from the United States from the United States

In the early 1950s an estimated 50 million cases In the early 1950s an estimated 50 million cases of smallpox occurred in the world each year of smallpox occurred in the world each year

After successful vaccination campaigns After successful vaccination campaigns throughout the 19th and 20th centuries, the WHO throughout the 19th and 20th centuries, the WHO certified the eradication of smallpox in December certified the eradication of smallpox in December 1979 1979

The last cases of smallpox in the world occurred The last cases of smallpox in the world occurred in an outbreak of two cases (one of which was in an outbreak of two cases (one of which was fatal) in Birmingham, England in 1978 fatal) in Birmingham, England in 1978

Vaccine Success Story - Vaccine Success Story - PolioPolio

Polio is a viral disease, usually affecting Polio is a viral disease, usually affecting children and young adults, caused by any children and young adults, caused by any of three poliovirusesof three polioviruses

Polio virus causes inflammation of the Polio virus causes inflammation of the motor neurons of the brain stem and motor neurons of the brain stem and spinal cord spinal cord

Symptoms include motor paralysis, Symptoms include motor paralysis, followed by muscular atrophy and often followed by muscular atrophy and often permanent deformitiespermanent deformities

Polio was one of the most dreaded Polio was one of the most dreaded childhood diseases of the 20th century childhood diseases of the 20th century

Polio epidemics have crippled thousands Polio epidemics have crippled thousands of people, mostly young children; the of people, mostly young children; the disease has caused paralysis and death for disease has caused paralysis and death for much of human historymuch of human history

Vaccine Success Story - Vaccine Success Story - PolioPolio

By 1910, much of the By 1910, much of the world experienced a world experienced a dramatic increase in dramatic increase in polio cases and polio cases and frequent epidemics frequent epidemics became regular became regular events, primarily in events, primarily in cities during the cities during the summer monthssummer months

These epidemics left These epidemics left thousands of children thousands of children and adults paralyzed and adults paralyzed

The polio vaccines developed by Jonas Salk in 1952 The polio vaccines developed by Jonas Salk in 1952 and Albert Sabin in 1962 are credited with reducing and Albert Sabin in 1962 are credited with reducing the global number of polio cases per year from many the global number of polio cases per year from many hundreds of thousands to around a thousandhundreds of thousands to around a thousand

Why don’t we have vaccines Why don’t we have vaccines for all viral diseases?for all viral diseases?

There are many problems inherent in There are many problems inherent in developing a good protective anti-viral vaccine developing a good protective anti-viral vaccine

Different types of virus may cause similar Different types of virus may cause similar diseases -- e.g. the common cold. As a result, a diseases -- e.g. the common cold. As a result, a single vaccine will not be possible against such single vaccine will not be possible against such a disease a disease

Viruses can change as they circulate (mutation)Viruses can change as they circulate (mutation) Large animal reservoirs. If these occur, re-Large animal reservoirs. If these occur, re-

infection after elimination from the human infection after elimination from the human population may occur. population may occur.