Viruses Are they living or not?. Brief History of virus discovery Are agents that can’t be seen...

Viruses Viruses

Are they living or not?Are they living or not?

Brief History of virus discovery

Brief History of virus discovery

Are agents that can’t be seen with an ordinary light microscope

Are agents that pass through filters that can trap even the smallest bacteria

The question that arose was are these agents toxins or poisons?

The Latin word for poisons is viruses

Are agents that can’t be seen with an ordinary light microscope

Are agents that pass through filters that can trap even the smallest bacteria

The question that arose was are these agents toxins or poisons?

The Latin word for poisons is viruses

Basic VirologyBasic Virology

What is a virus? Is it living or nonliving? How are they different from other “living”

organisms? Submicroscopic 18-350 nm in size (10-9 M) Can only be “seen” with an electron microscope Obligate intracellular parasites

Viruses have no genes that encode the proteins that function as the metabolic machinery for energy generation

Viruses have no genes that encode the proteins that function as the metabolic machinery for protein synthesis

Viruses may or may not contain the genes that encode enzymes involved in nucleic acid synthesis

What is a virus? Is it living or nonliving? How are they different from other “living”

organisms? Submicroscopic 18-350 nm in size (10-9 M) Can only be “seen” with an electron microscope Obligate intracellular parasites

Viruses have no genes that encode the proteins that function as the metabolic machinery for energy generation

Viruses have no genes that encode the proteins that function as the metabolic machinery for protein synthesis

Viruses may or may not contain the genes that encode enzymes involved in nucleic acid synthesis


Biochemically Have RNA or DNA, not both Have no small ions or polysaccharides

(sugars) May (enveloped viruses) or may not (naked

viruses) contain lipids

Biochemically Have RNA or DNA, not both Have no small ions or polysaccharides

(sugars) May (enveloped viruses) or may not (naked

viruses) contain lipids


Growth curves of bacteria and viruses are very different

Growth curves of bacteria and viruses are very different

Bacterial growth curve

Viral growth curve

Differences in growth curves:

Virus particles are produced from the assembly of pre-formed components: other organisms grow from an increase in the integrated sum of their components and reproduce by cell division.

Viruses don’t “grow” or undergo division


What is the basic structure of a virus? Nucleic acid of RNA or DNA – is the genetic

information for the virus Single (SS) or double stranded (DS) Linear, circular, or nicked Unsegmented or segmented If SS RNA, may be of the plus (+) or the minus (-)

sense + RNA – genomic RNA can serve as mRNA and be

directly translated into protein - RNA – genomic RNA cannot serve as mRNA and

cannot be translated directly into protein

What is the basic structure of a virus? Nucleic acid of RNA or DNA – is the genetic

information for the virus Single (SS) or double stranded (DS) Linear, circular, or nicked Unsegmented or segmented If SS RNA, may be of the plus (+) or the minus (-)

sense + RNA – genomic RNA can serve as mRNA and be

directly translated into protein - RNA – genomic RNA cannot serve as mRNA and

cannot be translated directly into protein


Protein outer coat – is called the capsid The capsid is composed of individual subunits

called capsomers What is the function of the capsid?

Protects the delicate inner nucleic acid from harsh environmental conditions

May be involved in attachment to host cells There are two basic capsid structures

Icosahedral Helical

Protein outer coat – is called the capsid The capsid is composed of individual subunits

called capsomers What is the function of the capsid?

Protects the delicate inner nucleic acid from harsh environmental conditions

May be involved in attachment to host cells There are two basic capsid structures

Icosahedral Helical


Icosahedral Structure


Helical structure


Viruses that contain only the viral nucleic acid and the capsid are called naked viruses

Some viruses have an outer lipid layer called an envelope The envelope is derived from host cell membranes For viruses that use the plasma membrane as their

envelope, the envelope is acquired as the virus exits the host cell via a process called budding

Virally encoded proteins in the envelope play a major role in the viral life cycle.

Proteins in the viral envelope are involved in attachment to host cells.

Proteins in the viral envelope mediate fusion of the virus envelope with host cell membrane during the entry of the virus into the host cell.

Viruses that contain only the viral nucleic acid and the capsid are called naked viruses

Some viruses have an outer lipid layer called an envelope The envelope is derived from host cell membranes For viruses that use the plasma membrane as their

envelope, the envelope is acquired as the virus exits the host cell via a process called budding

Virally encoded proteins in the envelope play a major role in the viral life cycle.

Proteins in the viral envelope are involved in attachment to host cells.

Proteins in the viral envelope mediate fusion of the virus envelope with host cell membrane during the entry of the virus into the host cell.


Diagram of an enveloped virus (HIV):

Diagram of an enveloped virus (HIV):

Basic Virology - buddingBasic Virology - budding


What is required for a virus to successfully infect and replicate in a host cell? In order for a virus to successfully infect a host

cell, the cell must contain the receptor that the virus binds to in the process of initiating an infection. The part of the virus that binds to the receptor is

called the ligand. The ligand is on the capsid of naked viruses and on

the envelope of enveloped viruses. gp 120 (the ligand) on HIV binds to CD4 (receptor)

and CXCR4 (co-receptor) on T lymphocytes or CCR5 (co-receptor) on macrophages

What is required for a virus to successfully infect and replicate in a host cell? In order for a virus to successfully infect a host

cell, the cell must contain the receptor that the virus binds to in the process of initiating an infection. The part of the virus that binds to the receptor is

called the ligand. The ligand is on the capsid of naked viruses and on

the envelope of enveloped viruses. gp 120 (the ligand) on HIV binds to CD4 (receptor)

and CXCR4 (co-receptor) on T lymphocytes or CCR5 (co-receptor) on macrophages


In order for a virus to successfully replicate in a host cell, the host cell must not only contain the receptor for the virus, it must also have the cellular machinery that the virus needs for replication.

The host range of a virus is the spectrum of host cells that the virus can successfully infect and replicate in.

If the virus successfully replicates in the host cell, the infection is productive and the host cell is said to be permissive for the virus.

In order for a virus to successfully replicate in a host cell, the host cell must not only contain the receptor for the virus, it must also have the cellular machinery that the virus needs for replication.

The host range of a virus is the spectrum of host cells that the virus can successfully infect and replicate in.

If the virus successfully replicates in the host cell, the infection is productive and the host cell is said to be permissive for the virus.


If the cell lacks something required for viral replication, the infection is abortive or non-productive and the host cell is considered to be non-permissive for the virus.

What are the basic features of the viral life cycle? Attachment or adsorption– ligand on virus binds to

a receptor on a host cell Penetration – virus gets inside the host cell

Penetration of naked viruses usually involves either: Receptor mediated endocytosis or Formation of a pore in the host cell plasma membrane

through which the nucleic acid and possibly associated viral proteins enter the cytoplasm

If the cell lacks something required for viral replication, the infection is abortive or non-productive and the host cell is considered to be non-permissive for the virus.

What are the basic features of the viral life cycle? Attachment or adsorption– ligand on virus binds to

a receptor on a host cell Penetration – virus gets inside the host cell

Penetration of naked viruses usually involves either: Receptor mediated endocytosis or Formation of a pore in the host cell plasma membrane

through which the nucleic acid and possibly associated viral proteins enter the cytoplasm


Penetration of enveloped viruses occurs through a fusion event between the viral envelope and a host cell membrane.

Uncoating – separation of capsid and nucleic acid in preparation of viral transcription and nucleic acid replication (attachment and penetration may occur simultaneously)

Penetration of enveloped viruses occurs through a fusion event between the viral envelope and a host cell membrane.

Uncoating – separation of capsid and nucleic acid in preparation of viral transcription and nucleic acid replication (attachment and penetration may occur simultaneously)


Biosynthesis – viral proteins are made and viral nucleic acid is replicated RNA viruses must bring in their own

enzyme(s) for transcribing their mRNAs and replicating their genome.

This is because neither prokaryotic cells nor eukaryotic cells contain enzymes that can use RNA as a template to make a complementary copy of RNA.

Therefore, most RNA viruses replicate entirely within the cytoplasm.

Biosynthesis – viral proteins are made and viral nucleic acid is replicated RNA viruses must bring in their own

enzyme(s) for transcribing their mRNAs and replicating their genome.

This is because neither prokaryotic cells nor eukaryotic cells contain enzymes that can use RNA as a template to make a complementary copy of RNA.

Therefore, most RNA viruses replicate entirely within the cytoplasm.


DNA containing viruses can either use the host enzymes to transcribe their mRNAs and replicate their genomes, or they may bring in their own enzymes for these processes

Retroviruses are unique RNA viruses in that they bring in an enzyme called reverse transcriptase (RT).

RT makes a double stranded DNA copy of the viral RNA genome.

This DNA then moves to the nucleus where it is incorporated into the DNA of the host cell.

It is only after this occurs that the viral genes are transcribed and translated into protein products.

DNA containing viruses can either use the host enzymes to transcribe their mRNAs and replicate their genomes, or they may bring in their own enzymes for these processes

Retroviruses are unique RNA viruses in that they bring in an enzyme called reverse transcriptase (RT).

RT makes a double stranded DNA copy of the viral RNA genome.

This DNA then moves to the nucleus where it is incorporated into the DNA of the host cell.

It is only after this occurs that the viral genes are transcribed and translated into protein products.


Assembly or maturation – All of the viral components assemble into new viruses. This does not occur until a sufficient

number of viral proteins are made and viral genomes are replicated

Release – newly made viruses exit the host by lysis or budding

Assembly or maturation – All of the viral components assemble into new viruses. This does not occur until a sufficient

number of viral proteins are made and viral genomes are replicated

Release – newly made viruses exit the host by lysis or budding


How are viruses classified? The most commonly used

classification scheme is the Baltimore scheme. This scheme is based on the relationship

between the viral genome and the mRNA used for translation during expression of the viral genome:

How are viruses classified? The most commonly used

classification scheme is the Baltimore scheme. This scheme is based on the relationship

between the viral genome and the mRNA used for translation during expression of the viral genome:

Baltimore Classification of Viruses

Baltimore Classification of Viruses


Effects of the virus on the host cell – even though you can’t see the virus, you can see the effects that the virus has on the host cell Death of the cell – often occurs on release of

the virus Cytopathic effects – are visible effects on the

host cell caused by viral replication Cancer

Requires that the virus integrates all or part of its genome into the host cell DNA

Effects of the virus on the host cell – even though you can’t see the virus, you can see the effects that the virus has on the host cell Death of the cell – often occurs on release of

the virus Cytopathic effects – are visible effects on the

host cell caused by viral replication Cancer

Requires that the virus integrates all or part of its genome into the host cell DNA

Overview of viral infections


Viral diseases of the skin Warts

Caused by human papilloma virus (double stranded DNA)

Spread by direct contact Treated with acids or cryotherapy

Smallpox (variola) Caused by variola major (mortality >20%) and minor

(mortality < 1%) (double stranded DNA) Transmitted by respiratory route Virus moves from respiratory tract to the

bloodstream to the skin to cause a pustular rash Leaves disfiguring scars

Viral diseases of the skin Warts

Caused by human papilloma virus (double stranded DNA)

Spread by direct contact Treated with acids or cryotherapy

Smallpox (variola) Caused by variola major (mortality >20%) and minor

(mortality < 1%) (double stranded DNA) Transmitted by respiratory route Virus moves from respiratory tract to the

bloodstream to the skin to cause a pustular rash Leaves disfiguring scars

Smallpox lesionsSmallpox lesions



Other symptoms include fever, malaise, severe backache and abdominal pain

Vaccination has successfully eradicated this disease Problem – use in bioterrorism

Chickenpox and shingles Caused by varicella-zoster (a herpes virus - double

stranded DNA) Infection is through the respiratory route Incubation is ~ 2 weeks, but the infected individual is

contagious at this stage Virus localizes in the skin to cause a vesicular rash with

vesicles that fill with pus, rupture, and form scabs After chickenpox the virus remains latent in nerve cells

and can be reactivated later in life to cause shingles

Other symptoms include fever, malaise, severe backache and abdominal pain

Vaccination has successfully eradicated this disease Problem – use in bioterrorism

Chickenpox and shingles Caused by varicella-zoster (a herpes virus - double

stranded DNA) Infection is through the respiratory route Incubation is ~ 2 weeks, but the infected individual is

contagious at this stage Virus localizes in the skin to cause a vesicular rash with

vesicles that fill with pus, rupture, and form scabs After chickenpox the virus remains latent in nerve cells

and can be reactivated later in life to cause shingles



Shingles is characterized by severe pain due to inflammation of the nerve branches of the cutaneous sensory nerves around one side of the trunk.

A vaccine to prevent chickenpox is now available

Shingles is characterized by severe pain due to inflammation of the nerve branches of the cutaneous sensory nerves around one side of the trunk.

A vaccine to prevent chickenpox is now available

Chicken pox and shinglesChicken pox and shingles



Measles (rubeola) Caused by a paramyxovirus (single stranded –

sense RNA) Is highly contagious Spread by the respiratory route Incubation 10-12 days Symptoms are similar to the common cold plus a

papular rash (small, raised spots) Koplik spots (red patches with central white

specks) in the oral cavity are diagnostic

Measles (rubeola) Caused by a paramyxovirus (single stranded –

sense RNA) Is highly contagious Spread by the respiratory route Incubation 10-12 days Symptoms are similar to the common cold plus a

papular rash (small, raised spots) Koplik spots (red patches with central white

specks) in the oral cavity are diagnostic



Severe complications include encephalitis, pneumonia, ear infections, and even death

May later cause subacute sclerosing panencephalitis with progressive nerve destruction and death

A vaccine is available (part of the MMR – Measles, Mumps, and Rubella)

We should be able to eradicate this virus since man is the only known host

Severe complications include encephalitis, pneumonia, ear infections, and even death

May later cause subacute sclerosing panencephalitis with progressive nerve destruction and death

A vaccine is available (part of the MMR – Measles, Mumps, and Rubella)

We should be able to eradicate this virus since man is the only known host

Measles (rubeola)Measles (rubeola)



German measles (rubella) Caused by a togavirus (single stranded +

sense RNA) Transmitted via the respiratory route Symptoms include a slight fever and a

rash of small red spots. Infection during the first trimester of

pregnancy can lead to birth defects (deafness, eye cataracts, heart defects, mental retardation) or death of the fetus

Vaccination via MMR

German measles (rubella) Caused by a togavirus (single stranded +

sense RNA) Transmitted via the respiratory route Symptoms include a slight fever and a

rash of small red spots. Infection during the first trimester of

pregnancy can lead to birth defects (deafness, eye cataracts, heart defects, mental retardation) or death of the fetus

Vaccination via MMR

German measles (rubella)German measles (rubella)



Cold sores Caused by herpes simplex virus (HSV), type I

(double stranded DNA) Characterized by lesions of the oral mucous

membranes Following the initial infection, the virus may

remain latent in the nerves Physical or emotional stress may cause a

reactivation of the latent infection

Viral diseases of the eye Corneal lesions caused by HSV, type I can

lead to blindness or CNS invasion

Cold sores Caused by herpes simplex virus (HSV), type I

(double stranded DNA) Characterized by lesions of the oral mucous

membranes Following the initial infection, the virus may

remain latent in the nerves Physical or emotional stress may cause a

reactivation of the latent infection

Viral diseases of the eye Corneal lesions caused by HSV, type I can

lead to blindness or CNS invasion

HSV I infectionsHSV I infections



Viral diseases of the respiratory tract The common cold

Caused mainly by rhinoviruses (single stranded + sense RNA) and coronaviruses (single stranded + sense RNA)

>200 different types of viruses can cause the common cold!

Spread by respiratory secretions on the hands Symptoms include sneezing, nasal discharge, and

congestion Influenza

Caused by orthomyxoviruses (segmented, single stranded – sense RNA viruses)

Viral diseases of the respiratory tract The common cold

Caused mainly by rhinoviruses (single stranded + sense RNA) and coronaviruses (single stranded + sense RNA)

>200 different types of viruses can cause the common cold!

Spread by respiratory secretions on the hands Symptoms include sneezing, nasal discharge, and

congestion Influenza

Caused by orthomyxoviruses (segmented, single stranded – sense RNA viruses)



Transmitted via respiratory secretions Symptoms include fever, chills, headache, and

general muscle aches These organisms are continually changing their

antigenic structure by shift and drift making it difficult to develop effective vaccines

Shift occurs with genetic recombination or gene reassortment

Drift occurs by mutations

Viral diseases of the central nervous system Meningitis or encephalitis

Transmitted via respiratory secretions Symptoms include fever, chills, headache, and

general muscle aches These organisms are continually changing their

antigenic structure by shift and drift making it difficult to develop effective vaccines

Shift occurs with genetic recombination or gene reassortment

Drift occurs by mutations

Viral diseases of the central nervous system Meningitis or encephalitis



These are infections of the membranes that cover the brain and spinal cord or of the brain itself

Many different viruses can cause meningitis and encephalitis

Organisms that enter through the blood need to cross the blood-brain barrier to cause disease.

Other organisms move along peripheral nerves to the CNS

Viral meningitis is often called aseptic meningitis because no bacteria or fungi can be cultivated from the CSF

These are infections of the membranes that cover the brain and spinal cord or of the brain itself

Many different viruses can cause meningitis and encephalitis

Organisms that enter through the blood need to cross the blood-brain barrier to cause disease.

Other organisms move along peripheral nerves to the CNS

Viral meningitis is often called aseptic meningitis because no bacteria or fungi can be cultivated from the CSF



Poliomyelitis (polio) Caused by a picornavirus (small single stranded+

sense RNA) There are three different serotypes of poliovirus Transmission occurs via the gastrointestinal tract

after ingestion of fecal contaminated water Symptoms include fever, sore throat, and headache In 1-2% of the cases (mainly in adults) the virus

penetrates the capillary walls and enters the CNS where it it multiplies in the motor nerve cells eventually killing them and causing paralysis

Two vaccines have been used Salk – virus inactivated by formalin

Poliomyelitis (polio) Caused by a picornavirus (small single stranded+

sense RNA) There are three different serotypes of poliovirus Transmission occurs via the gastrointestinal tract

after ingestion of fecal contaminated water Symptoms include fever, sore throat, and headache In 1-2% of the cases (mainly in adults) the virus

penetrates the capillary walls and enters the CNS where it it multiplies in the motor nerve cells eventually killing them and causing paralysis

Two vaccines have been used Salk – virus inactivated by formalin



Sabin – live, attenuated virus ( recently reactivation problems have resulted in the discontinuation of the use of this vaccine)

Rabies Caused by a bullet-shaped rhabdovirus (single

stranded – sense RNA) Transmission is via the saliva of a rabid (rabies

infected) animal Virus travels along the peripheral nerves to the CNS

where it causes encephalitis Symptoms include painful spasms of the muscles of

the mouth and pharynx when swallowing liquids (hydrophobia)

Treatment is with rabies immune globulin followed by active immunization

Sabin – live, attenuated virus ( recently reactivation problems have resulted in the discontinuation of the use of this vaccine)

Rabies Caused by a bullet-shaped rhabdovirus (single

stranded – sense RNA) Transmission is via the saliva of a rabid (rabies

infected) animal Virus travels along the peripheral nerves to the CNS

where it causes encephalitis Symptoms include painful spasms of the muscles of

the mouth and pharynx when swallowing liquids (hydrophobia)

Treatment is with rabies immune globulin followed by active immunization

RabiesRabies



Viral diseases of the cardiovascular system Myocarditis – inflammation of the heart

muscle Caused by many different organisms, but is

commonly caused by Coxsackieviruses (single stranded + sense RNA)

Infection occurs via the respiratory route or via the gastrointestinal tract

The organism gains access to the heart via the bloodstream or the lymphatics

Viral diseases of the cardiovascular system Myocarditis – inflammation of the heart

muscle Caused by many different organisms, but is

commonly caused by Coxsackieviruses (single stranded + sense RNA)

Infection occurs via the respiratory route or via the gastrointestinal tract

The organism gains access to the heart via the bloodstream or the lymphatics



Infectious mononucleosis Caused by Epstein-Barr virus (a herpes virus

– double stranded DNA) Transmission is via saliva and hence the

disease is often called the kissing disease Symptoms include fever, sore throat,

swollen lymph nodes, and general weakness Like all herpes virus infections, after the

primary infection the virus remains latent, this time in B lymphocytes

Infectious mononucleosis Caused by Epstein-Barr virus (a herpes virus

– double stranded DNA) Transmission is via saliva and hence the

disease is often called the kissing disease Symptoms include fever, sore throat,

swollen lymph nodes, and general weakness Like all herpes virus infections, after the

primary infection the virus remains latent, this time in B lymphocytes



The virus has been linked to three human cancers

Hodgkins disease Burkit’s lymphoma Nasopharyngeal carcinoma

The virus has been linked to three human cancers

Hodgkins disease Burkit’s lymphoma Nasopharyngeal carcinoma

Burkitt’s lymphomaBurkitt’s lymphoma



Viral hemorrhagic fevers Caused by several different types of virus Ebola virus causes this type of disease Are transmitted from human to human Have a high mortality rate from

hemorrhaging and shock

Viral hemorrhagic fevers Caused by several different types of virus Ebola virus causes this type of disease Are transmitted from human to human Have a high mortality rate from

hemorrhaging and shock

Ebola hemorrhagic feverEbola hemorrhagic fever



Viral disease of the digestive system Mumps

Caused by a paramyxovirus (single stranded – sense RNA)

Transmission is via salivary secretions and portal of entry is the respiratory tract

Incubation is 16-18 days – during this time the virus moves from the respiratory tract to the bloodstream to the parotid (salivary) glands and testes in males

Symptoms include swelling, fever, painful swallowing and occasionally sterility.

Vaccination is via the MMR

Viral disease of the digestive system Mumps

Caused by a paramyxovirus (single stranded – sense RNA)

Transmission is via salivary secretions and portal of entry is the respiratory tract

Incubation is 16-18 days – during this time the virus moves from the respiratory tract to the bloodstream to the parotid (salivary) glands and testes in males

Symptoms include swelling, fever, painful swallowing and occasionally sterility.

Vaccination is via the MMR

MumpsMumps



Hepatitis – an inflammation of the liver Hepatitis A (single stranded + sense RNA)

Causes infectious hepatitis Is transmitted via the fecal-oral route Symptoms include anorexia, malaise, nausea,

diarrhea, abdominal discomfort, fever and chills for 2-21 days

2/3 of infected individuals have jaundice which is indicative of liver damage

Hepatitis – an inflammation of the liver Hepatitis A (single stranded + sense RNA)

Causes infectious hepatitis Is transmitted via the fecal-oral route Symptoms include anorexia, malaise, nausea,

diarrhea, abdominal discomfort, fever and chills for 2-21 days

2/3 of infected individuals have jaundice which is indicative of liver damage



Hepatitis B (double stranded DNA virus) Causes serum hepatitis Is transmitted through the blood Incubation is 4-26 weeks Symptoms range from subclinical to severe fever

and headache with jaundice 90% recover completely and 10% become chronic

carriers and have a high incidence of liver disease including hepatoma

A vaccine is available Hepatitis C (single stranded RNA virus)

Causes serum hepatitis Is transmitted through blood The disease is clinically similar to that of hepatitis B

Hepatitis B (double stranded DNA virus) Causes serum hepatitis Is transmitted through the blood Incubation is 4-26 weeks Symptoms range from subclinical to severe fever

and headache with jaundice 90% recover completely and 10% become chronic

carriers and have a high incidence of liver disease including hepatoma

A vaccine is available Hepatitis C (single stranded RNA virus)

Causes serum hepatitis Is transmitted through blood The disease is clinically similar to that of hepatitis B



Viral gastroenteritis In children is most commonly caused by

rotavirus (double stranded RNA) or adenoviruses (double stranded DNA)

Symptoms include fever, diarrhea, and vomiting

Viral diseases of the reproductive system Genital herpes

Viral gastroenteritis In children is most commonly caused by

rotavirus (double stranded RNA) or adenoviruses (double stranded DNA)

Symptoms include fever, diarrhea, and vomiting

Viral diseases of the reproductive system Genital herpes



Caused by herpes simplex virus (HSV), type II (double stranded DNA)

Incubation is ~ 1 week Symptoms include painful vesicular lesions

containing infectious fluid. This virus also becomes latent in nerve cells and

can be reactivated to cause the same type of lesions found in the primary infection

This virus can cross the placenta to infect the fetus leading to mental retardation and defective sight and hearing

The fetus can also be infected during the delivery, therefore all women positive for this virus routinely deliver their babies by a C- section

Caused by herpes simplex virus (HSV), type II (double stranded DNA)

Incubation is ~ 1 week Symptoms include painful vesicular lesions

containing infectious fluid. This virus also becomes latent in nerve cells and

can be reactivated to cause the same type of lesions found in the primary infection

This virus can cross the placenta to infect the fetus leading to mental retardation and defective sight and hearing

The fetus can also be infected during the delivery, therefore all women positive for this virus routinely deliver their babies by a C- section

HSV II infectionHSV II infection



Genital warts Caused by human papilloma viruses

(double stranded DNA viruses) Some strains of these viruses can cause

cervical cancer There is now a vaccine for the strains

associated with cervical cancer.

Genital warts Caused by human papilloma viruses

(double stranded DNA viruses) Some strains of these viruses can cause

cervical cancer There is now a vaccine for the strains

associated with cervical cancer.

Genital wartsGenital warts



Prions Cause diseases that were formerly called slow

viral infections Prions are not viruses; they have no nucleic

acid associated with them Prions are infectious proteins They cause a misfolding of a normal cellular

protein counterpart They cause neurological diseases

characterized by a spongiform encephalopathy that results in eventual death

Examples include:

Prions Cause diseases that were formerly called slow

viral infections Prions are not viruses; they have no nucleic

acid associated with them Prions are infectious proteins They cause a misfolding of a normal cellular

protein counterpart They cause neurological diseases

characterized by a spongiform encephalopathy that results in eventual death

Examples include:



Kuru Creutzfeldt-Jakob disease Mad cow disease

Kuru Creutzfeldt-Jakob disease Mad cow disease

Prion diseasesPrion diseases

Viruses Are they living or not?. Brief History of virus discovery Are agents that can’t be seen...

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Transcript of Viruses Are they living or not?. Brief History of virus discovery Are agents that can’t be seen...