Test #3 Flashcards
Who investigated rabies?
Pasteur
What were the first two viral diseases to be investigated?
Rabies and yellow fever
Who investigated Yellow fever?
Walter Reed
What is the description/definition of a virus?
Viruses are non-living intracellular parasites that cannot be cultivated in cell-free media. Must be grown in tissue culture, frequently grown in embryonated bird eggs
What is the size of a virus?
small in size, largest is about 200nm
What is a single virus particle referred to?
A virion
What is the genome of a virus composed of?
Either DNA or RNA but never both
Nucleic acid is enclosed in protein coat called a?
capsid
nucleic acid + capsid = ?
nucleocapsid
What do some viruses acquire from a host cell?
lipoprotein envelope
If a virus acquires a lipoprotein envelope what does it have and do?
It has glycoprotein spikes for interaction with the host cell
Viruses with a capsid, but no envelope are called?
“naked”
What are the two types of viral symmetry?
1- helical
2- icosahedral
What are the different shapes of viruses?
spherical, bullet shaped, or filamentous
What are prions composed of and what are they possibly related to?
Prions have no detectable nucleic acid and appear to be a self replicating protein, some scientists believe a relationship to viruses exists
What are prions responsible for?
Neurogenerative diseases classified as spongiform encephalopathies (SE). diseases cause holes in tissue, brain appears as a sponge
What are some examples of SE diseases?
mad-cow disease, Creutzfieldt-Jacob, Kuru, scrapie
Where does much of our understanding of how viruses replicate and multiply come from?
From studying bacteriophages (bacterial viruses)
The lytic cycle of bacteriophages has 5 steps what are they?
1- Adsorption 2- Penetration 3- Prefabrication 4- Maturation 5- Viral release
Lytic cycle of bacteriophages step 1 Adsorption is what?
bacteriophage irreversibly absorbs to receptor site using tail fibers
Lytic cycle of bacteriophages adsorption what are the adhering sites?
Lipopolysaccharide of gram (-) cells, pili, and flagella
When is the beginning of the latent period and when does it end?
Lytic cycle of bacteriophages starts in step 1 and continues all the way until the cell lyses
Lytic cycle of bacteriophages Step 2 is?
Penetration
In Lytic cycle of bacteriophages step 2 penetration what happens?
Phage tail penetrates bacterial cell, nucleic acid enters leaving capsid on outside of host cell
Which period begins during Lytic cycle of bacteriophages step 2?
beginning of eclipse period
Lytic cycle of bacteriophages eclipse period is what?
defined as period during which no viral particles can be found either inside or outside cell, viral DNA is taking over machinery of host cell
Lytic cycle of bacteriophages eclipse period what two things happen?
1- mRNA is transcribed to code for a repressor enzyme to prevent entry of other phages
2- additional enzymes are produced to depolymerize host cell DNA
Lytic cycle of bacteriophages What does destruction of host cell DNA lead to?
halt of host cell metabolism, virus assuming control of host cell metabolism, viral nucleic acid being assembled using host nucleotides, use of cell ribosomes for translation
Lytic cycle of bacteriophages step 3?
Prefabrication
Lytic cycle of bacteriophages step 3 prefabrication what is going on?
Viral genome is repllicated many times
necessary viral mNA is synthesized
All viral parts are “prefabricated”
Lytic cycle of bacteriophages step 4 is?
Maturation
Lytic cycle of bacteriophages What period ends at Maturation?
end of the eclipse period
What is going on during Lytic cycle of bacteriophages step 4 Maturation?
New viruses are assembled
Viruses DO NOT grow, cells grow, viruses are assembled
What is Lytic cycle of bacteriophages step 5?
viral release
Lytic cycle of bacteriophages what period ends at step 5?
end of the latent period
What is going on during Lytic cycle of bacteriophages step 5?
New viruses produce lysozyme
Lysozyme causes the bacterial cell wall to rupture
Viruses are released
What are the 5 steps of animal viruses?
1- Adsorption 2- Penetration and uncoating 3- Synthesis (Replication) Different for DNA and RNA viruses 4- Maturation 5- Viral Release
Animal viruses step 1 is? Also what is the difference between a naked virus and an enveloped virus?
Adsorption
Naked virus- capsid proteins bind to host cell receptors
Enveloped virus- glycoprotein spikes bind to host cell receptors
What is animal viruses step 2?
Penetration and uncoating
Animal viruses step 2 what happens to naked viruses?
Naked viruses undergo a major change in capsid structure on adsorption to plasma membrane, so that their nucleic acids are released into the cytoplasm
Animal viruses step 2 what happens to enveloped viruses?what are the two ways that they enter the host?
1- viral envelope may fuse with the host cell cytoplasmic membrane and the nucleocapsid is released into the cytoplasm
2- animal viruses enter by endocytosis whereby the host cell cytoplasmic membrane invaginates and pinches off, placing the virus in an endocytotic vesicle. Lysosomes fuse with vesicle and uncoat releasing nucleic acid
What happens in step 3 of animal DNA viruses?
- Early synthesis = host cell is overtaken- viral DNA is synthesized and transcribed to RNA, inhibit host cell DNA, RNA, and protein synthesis
- Viral DNA replication usually occurs in host nucleus
- DNA viruses usually remain latent in the infected cell
- Early viral genes transcribe DNA binding proteins and enzymes
- late viral genes transcribe structural proteins
Step 3 of animal viruses RNA synthesis what are the 4 groups of RNA viruses?
Positive (sense) strand RNA viruses
Double stranded RNA viruses
Negative (antisense) strand RNA viruses
Retroviruses
Animal viruses step 3 RNA synthesis. what are the 4 things to know about Positive strand virus replication ?
1- (+) strand is used as giant mRNA
2- Host ribosome translates giant mRNA into various viral enzymes
3- RNA polymerase produces a (-) strand RNA
4- The (-) strand is then used to synthesize more (+) strands to be used as mRNA or to be inserted into new viruses
Animal viruses step 3 Double strand RNA. What are the 2 things to know?
- These viruses (retroviruses) have a transcriptase that copies the (-) strand of their genome to generate mRNA
- mRNA is translated into various enzymes to synthesize new viruses
Animal viruses step 3 of RNA synthesis. Negative strand virus replication…3 things to know?
1- A viral transcriptase converts (-) strand RNA to (+) strand RNA
2- The (+) strand acts as mRNA
3- A viral replicase produces double stranded RNA (+/-) that assembles new viruses
What are the 5 things specific to retroviruses which are animal viruses RNA virus synthesis?
1- Possess single stranded (+) RNA genome
2- Synthesize mRNA and replicate RNA genome by converting RNA to DNA
3- Reverse transcriptase converts (+) RNA to (-) DNA
4- The (-) DNA is copied to create a double stranded DNA called proviral DNA
5- Proviral DNA synthesizes (+) RNA genome for new viruses
Animal viruses step 4 is?
Maturation
Animal viruses step 4 maturation what is happening?
Assembly of new viruses
Animal viruses when they are assembling new viruses what are the 2 things that can happen?
There is a capsid formation and other processes as well for enveloped viruses
Animal viruses step 4 capsid formation entails which 3 things?
1- capsid protein synthesis is directed by late genes (structural)
2- spontaneous self assembly- capsid around nucleic acid
3- location of maturation is virus specific
animal viruses step 4 what are the 3 things that go on with an enveloped virus?
1- Late viral mRNA transcribes glycoproteins
2- Glycoproteins are inserted into the host cell membrane
3- Virus particle acquires the glycoprotein envelope during exocytosis
What is step 5 for animal proteins?
Viral release
Animal proteins step 5 what does the Naked virus do?
infected cell usually lyses and the virions are released
Animal viruses step 5 what does the enveloped virus do?
1-the host cell may not be lysed
2- virus obtains its envelope by budding from membrane bound organelles within the cell
3- transport vesicles carry the virus to the cell surface where it is released by exocytosis
What are the 3 effects of viral infection?
Persistence, Transformation, and Immunological escape
What are the persistent effects of a viral infection?
Persistent infections are those in which the virus is not cleared from the host following primary infection, but remains associated with specific cells
What are the transformational effects of a viral infection?
Some DNA viruses and retroviruses establish persistant infections that stimulate uncontrolled cell growth causing transformation or immortalization of the cell(cancer cell)
What is meant by the immunological escape effects of viral infections?
Many viruses have evolved systems of immunological escape to evade detection
i.e. herpes viruses escape detection by integration into host cell DNA
The big section of the notes… DNA viruses… what are the 5 major categories? (bolded font)
1- Poxviruses 2- Herpes viruses 3- Adenoviruses 4- Papovaviridae 5- Parvoviruses
What are the 5 types of poxviruses?
1-Molluscum contagiosum 2-Smallpox 3-Cow pox 4-Monkey pox 5-Orf
What is the basic description of a Poxvirus? Size, shape, virions…
Large brick shaped viruses- largest of all viruses, 200nm
Virions contain one molecule of liner double stranded DNA
3 things to know about Molluscum contagiosum?
Small pearly or flesh-colored bumps, contagious but is not harmful, in people with suppressed immune systems bumps can by extensive and disfiguring
What are the 2 forms of small pox?
Variola major- the more severe form
Variola minor- more mild form
What is the specific virus that causes small pox?
Variola virus
Is smallpox contagious and what are the symptoms?
Highly contagious, respiratory secretions and dirct conact transmission, fever, chills, nausea, severe muscle aches
How does smallpox begin and progress?
Rash begins as flat lesions, progress to papules-eruptive sage
papules become pustules, scab, and leave a scar
What are the important dates to know for smallpox?
1967- WHO undertook global program of smallpox vaccination. At that time 10-15 million new cases a year and 2 million deaths
1977- last case of endemic smallpox was reported in somalia
1980- considered eradicated
How do people get cow pox?
causes human disease through zoonosis
What is the specific virus for cow pox?
Vaccinia virus
What is known about Vaccinia virus?
not much and remains a big mystery in virology. May be a product of genetic recombination or a representative of a now extinct virus
Cow pox- Vaccinia virus what was it used for in the past?
smallpox vaccination
How common is monkey pox and where is it found?
It is a rare viral disease found mostly in the rain forest in west africa
Where did monkey pox get its name?
1958- it was first discovered on laboratory monkeys
What type of DNA virus is monkey pox?
poxvirus
What is Orf? infection of and what do we get it from?
it is a viral pox infection of the skin contracted from sheep and goats?
How common is Herpes?
A leading cause of human viral disease, second only to influenza and cold viruses. Once a patient has become infected by herpes virus, the infection remains for life
Basic descriptors of a herpes virus?
icosahedral, enveloped, single molecule of double stranded DNA, attracted to neurons
What are the 7 categories of herpes virus?
1- Cytomegalovirus 2- Varicella-Zoster virus (VZV) 3- Herpes Simplex viruses 4- Epstein Barr (EBV) 5- Human Herpes virus 6 6- Human Herpes virus 7 7- Human Herpes virus 8
Infection rate of cytomegalovirus?
15% by college and 50% by age 35 in US
What is the abbreviation for cytomegalovirus?
CMV
How is CMV spread?
in most bodily secretions
How is CMV transmitted?
Sexually
CMV can be spread sexually and by?
Transplacental infection- spread to a fetus in a pregnant woman
What is the most common viral cause of congenital disease(mental retardation)?
CMV
How many new borns in the US are infected with CMV?
1 in 40
What are the symptoms of CMV?
no symptoms in children and at most mild disease in adults
Who can CMV be a problem for?
Those who are immunosuppressed
What does CMV cause in immunosuppressed patients?
Retinitis in the eye which occurs in up to 15% of all AIDS patients
Varicella- Zoster Virus (VZV) is also known as what?
human herpes virus 3
VZV causes what 2 diseases?
Chicken pox in childhood and shingles later in life
How is chicken pox transmitted?
Respiratory droplet or with direct contact of vesicles
Is chicken pox easily transmitted?
Yes, 90% infection rate in households
How does the VZV virus of chicken pox spread in the body?
spreads from the lungs by entering the blood stream, from blood vessels first infects sub-epithelial sites and then epithelial sites forming papula, papulae become fluid filled vesicles. Fluid filled vesicles become pustules and then scab.
Lesions itch and can cause bacterial super infection
How long does chick pox usually last?
2 weeks
When can chicken pox cause major problems?
infection in utero during the first trimester
What is shingles?
recurrence of a latent varicella infection
How does shingles travel in the body?
Moves down nerves to epidermis
What can trigger shingles?
Reactivation of virus due to stress, injury, disease
What is shingles pain like?
Severe radicular pain in discrete areas, those innervated by the nerve in which latent infection has occurred
Where do shingles lesions occur?
They are chicken pox like lesions that occur in restricted areas that are innervated by a single ganglion(dermatome)
How do you diagnose chicken pox and shingles?
definitive diagnosis can be made by culture of the virus from the lesions, search for giant cells with inclusions
What are two ways that treatment is done for chicken pox and shingles?
vaccination or chemotherapy
Herpes simplex viruses-what are the 2 types?
HSV-1 and HSV-2
How do you get herpes simplex virus?
they firest infect cells of the mucoepithelia or enter through wounds. Then frequently set up latent infections in neuronal cells
What is an often noted difference between HSV-1 and HSV-2?
HSV-1 causes infections above the waist. HSV-2 below the waist. However, this is more due to the modes of transmission and not ability of the virus to cause disease
What are the 3 diseases primarily caused by HSV-1?
1- Herpes labialis
2- Eczema hereticum
3- Keratoconjunctivitis
What is Herpes labialis?
Fever blisters and cold sores on lips
What is Eczema herpeticum?
Widespread cutaneous HSV in patients with pre-existing eczema
What is keratoconjunctivitis?
Infection of the cornea-leading cause of corneal blindness in industrialized nations
What are the 3 diseases caused by HSV-2?
Genital herpes
Herpetic Whitlow
Herpes Gladiatorum
Describe the various stages of genital herpes
- Prodrome(early symptoms indicate the onset of the disease) 1-2 days of burning sensation in the area that is about to erupt
- primary infection is characterized by viremia, fever, swollen lymph nodes, pain on urination
- Secondary episodes result from reactivation of th virus and are usually less severe-triggered by fever, menstruation, stress, UV light
- Where this is an apparent active disease or not, an infected patient remains infectious without overt symptoms
Describe Herpetic Whitlow
herpes infection of fingers and hands
Describe Herpes gladiatorum
skin lesions contracted by wrestlers spread by direct contact
What are the treatment options for Herpes infections?
- patient counseling
- drug treatment- Acyclovir
Herpes virus type 4 of 7 is?
Epstein Barr(EBV)
What are the 4 diseases caused by Epstein Barr virus?
1-Infectious mononucleosis
2-African-Burkitts lymphoma
3-Nasopharyngeal cancer
4-Hairy oral leukoplakia
Describe the etiology of Infectious mononucleosis
Infection with EBV occurs worldwide usually during childhood
it is contracted through contact with infected cervical or oral secretions
Most infections in children are asymptomatic, symptoms are more pronounced in previously uninfected adults
T-cell response results in enlarged lymph glands, liver, spleen and disease resolves in 8-10 days
Describe African-Burkitts lymphoma
Tumor of the jaw and face found in children
Tumor cells show evidence of EBV DNA and tumor antigens
Also patients have a lot more Anti-EBV antibodies
Describe Nasopharyngeal cancer
Tumor of the epithelium of the upper respiratory tract
Tumor cells contain EBV DNA
There may be genetic or environmental cofactors that play into ones predisposition
Describe Hairy oral leukoplakia
EBV- associated disease results in lesions in the mouth and has increased in frequency ecently as it is an opportunistic infection of HIV-infected patients
What are the factors of diagnosis with EBV?
Elevated white count
Atypical white blood cells-Downey cells
Human herpes virus 6 causes what?
Causes roseola infantum(sudden rash, 3 day fever, rose rash)
Human herpes virus 7 causes what?
HHV 7 has no known causes
What was human herpes virus 8 formerly known as?
Kaposi’s sarcoma
Where is human herpes virus 8 found and describe the lesions
Found in the saliva of many aids patients
Lesions are nodules or blotches that may be red, purple, brown, or black, usually painless but sometimes painful and swollen
