DNA Viruses Flashcards
Describe the structure of Papillomaviruses
-Small circular dsDNA virus, icosahedral and naked
-*It does NOT contain a viral DNA polymerase; it needs to enter the cell cycle to replicate
T/F: A large number of papillomavirus serotypes exist
True!
List the two main types of HPV
Mucosal
Cutaneous
What type of infection is HPV?
-Localized, only on the skin or mucosal surface
Does HPV have a viremic stage?
No
What does Cutaneous HPV form?
Benign warts on the skin that can persist and spread
What is the treatment for the warts formed by Cutaneous HPV?
-Removing the wart with chemicals or ‘burning’ them off the skin
-Tx usually needs to be done more than once
-Most warts will be cleared without tx
Can Cutaneous warts spreads?
Can occasionally spread to the oral or genital mucosa through autoinoculation
Mucosal HPV forms ______ which are the most common sexually transmitted disease in the US
Anogenital warts
What are the most common types of Anogenital warts?
-6 and 11 –> are low risk and are associated with 90% of genital infections
-16 and 18 –> are high risk and are associated with 70% of anogenital cancers
What can HPV 6 and 11 cause?
Recurrent respiratory papillomatosis
How can children acquire oral HPV? Adults?
-Children can acquire oral HPV at birth from their mother
-Adults can acquire it through oral sex
-Warts appear on the larynx, necessitating surgical removal
What is needed in order for HPV to infect the basal cell layer?
A break in the skin/mucosa
What happens once HPV infects the basal cell layer?
-The basal cell will then replicate to repair the wound
-The virus will establish several copies of itself in an episomal form
-Even in apparently cleared infections, sometimes the virus will stay latent in the basal cells
As the HPV virus containing cell moves through the different epithelial layers, it will express ________
different viral proteins
In the upper epithelial layers, how does HPV replicate?
The virus will prod the terminally differentiated cell to replicate so it can makes thousands of copies or viral DNA and lots of capsid protein
What role does the viral E7 protein play in HPV replication?
Binds and inactivates the cellular Rb protein, which causes the cell to go into the cell cycle
How does the HPV virus get released?
The top layer of cells slough off, the cell breaks down, releasing the virus
HPV cancer is caused by dysregulation of the _______ genes of HPV by integrating the viral DNA episome into the basal cells’ cellular DNA
E6 and E7
-Note that genome integration is NOT a normal part of HPV’s replication. This integration of the viral episome turns off a viral protein that controls the levels of E6 and E7 in the cell, leading to high levels of E6 and E7 in the basal cells
In the oncogenic forms of HPV, the E7 protein will bind and degrade the _____ protein causing the cell to go into the cell cycle
Rb
In oncogenic forms of HPV, the E6 protein will cause degradation of _____, allowing the cell to continue to cycle and accumulate mutations
p53
T/F: In most cases, HPV infections spontaneously regress
True
-Problems occur if there is a persistent infection with a high-risk type. Over many years this may result in cancer
T/F: Once the immune system is activated, most people are protected from reinfection from that HPV strain
True
-Some people might have cross-protection between different strains. However, it is possible to be infected with more than one strain, either simultaneously or sequentially
What cancers is HPV known to contribute to?
Cervical, anal, vulvar, vaginal, penile, and oropharyngeal cancers
HPV 16 causes….
-Almost all oropharyngeal cancers caused by HPV
-Having HPV 16 is just a risk factor; many who have infections do not go on to develop cancer
What type of vaccine is the HPV vaccine?
subunit vaccine with just one of the coat proteins of HPV
Which HPV causes most genital warts?
6 and 11
Which HPV causes most cervical cancers?
16 and 18
Why is it recommended that boys and girls ages 9-14 get vaccinated with two doses of the vaccine?
This age is picked because it is best to get vaccinated before any sexual contact, and this age group seems to have the most durable response to the vaccine.
Describe the structure of Polyomavirus
-Small dsDNA circular, naked virus with an icosahedral capsid
-Does NOT have a viral DNA polymerase and need the cell to divide to replicate their viral DNA
JC only causes problems in the ______
Immunocompromised:
-AIDS
-Transplant recipients
-People take some immunosuppressive drugs
-Hematologic malignancies
The JC virus is more active in who?
The immunosuppressed, but even then, most have no problems with the virus.
When does the JC virus become problematic?
When the virus mutates and becomes neurotropic, and the person is immunosuppressed
What does the mutant JC virus infect?
Infects and kills oligodendrocytes causes CNS demyelination and the condition PML (Progressive Multifocal Leukoencephalopathy)
Who is infected with JC?
-A large majority of people have been infected with the JC virus by adulthood.
-Many people are latently infected and sporadically shed the virus in their urine
What is the treatment against the JC virus?
-The treatment is to stop the immunosuppressive agent or start HIV therapy to make the immune system more active in fighting the infection
-Unfortunately, there can be lasting damage from the PML
Describe the structure of Parvovirus
-Small ssDNA linear, naked virus with an icosahedral capsid
-It has NO DNA polymerase and cannot stimulate the cell to grow (like polyomavirus or papillomavirus).
-To replicate, the virus needs to infect actively dividing cells
____ causes Erythema infectiosum-fifth disease, a generalized infection
B19
What characterizes B19 infections?
The “slapped cheek rash”
What do Parvovirus B19 symptoms start as?
Fever, runny nose and headache. This is when the infection spreads by respiratory secretions
When is a person with parvovirus B19 no longer contagious?
A rash develops because of the immune response and the person is no longer contagious
What is the problem with parvovirus B19?
The virus needs to infect actively dividing cells and preferentially infects erythroid precursor cells, killing those cells. This can cause transient anemia if infected
For people who already have an increase in RBC turnover due to hemoglobin disorders like sickle cells or chemotherapy, B19 infection can cause ________
a transient aplastic crisis
-This can cause a severe drop in RBC
What happens when infected with B19 during pregnancy?
-If infected during the first trimester, there’s a chance of miscarriage
-B19 infection anytime during pregnancy has a chance of causing hydrops fetalis
Describe the structure of Poxvirus
complex DNA virus with an envelop and ds linear DNA
Where do Poxviruses replicate?
-Solely in the cytoplasm
-The virus brings into the cell a DNA-dependent RNA polymerase so that it can make messenger RNA. This way, it doesn’t have to enter the nucleus
What is Molluscum contagiosum? How is it spread?
A local skin infection and is spread by close personal contact or autoinoculation
What are the symptoms of Molluscum contagiosum?
Raised lesions on the skin that appear smooth with a dimple in the middle (these lesions are secreting virus)
What type of infection is Molluscum contagiosum?
Local infection of the skin (no viremic stage)
How long does Molluscum contagiosum last?
Usually disappears without intervention by 2 to 12 months without scarring and affects children more than adults
List the Orthopoxviruses
Variola
Cowpox
Mpox
Vaccinia
Orthopoxviruses are similar enough that there is _________
cross-protection
This means that infection with one orthopox protects against infection with other orthopoxviruses
The _____ route transmitted smallpox, but lesions were also contagious
respiratory
A person with smallpox is still contagious until when?
All scabs fall off the body. Scabs contain infectious virus
Smallpox is ______
eradicated
______ vaccination within 3 days of exposure to smallpox can prevent or substantially lessen disease
Prophylactic
If smallpox is spread from germ warfare, the CDC favors what kind of treatment?
Ring vaccination over mass vaccination and isolation of the infected.
This is the virus contained in the vaccine for smallpox. It is an attenuated virus in humans.
Vaccinia virus
Is the virus in the vaccine now, vaccinia virus, cowpox?
No
Although the vaccine started with cowpox, the virus in the vaccine now, vaccinia virus, is not cowpox.
Are there risks with the vaccinia vaccination?
Yes, there are some risks
What does the more inactivated for of the vaccine (vaccinia virus) require?
Two shots 4 weeks apart and is protective after the 6th week
______ looks very much like smallpox
Mypox
Where is Mpox found?
-Is endemic in some African countries with spodic outbreaks
What is the animal reservoir for mpox?
It is unknown
-Monkeys are not the natural reservoir, but it can be found in several rodents
What was the 2003 mpox outbreak in the US caused by?
Imported rodents from Africa
What vaccine is effective at preventing mpox?
-Live vaccinia virus
-Non-replicating attenuated vaccina virus vaccine
-An antiviral can also be used to treat mpox
There is currently an outbreak of mpox. How is this strain appearing to be spread?
-Appears to be efficiently spread through sex/close personal contact as well as respiratory and has spread to at least 104 non-endemic countries.
-It can present non-traditionally with lesions at the site of contact before systemic symptoms or without systemic symptoms
What type of infections are smallpox and mpox?
Generalized infections
_____, if given on the arm, can be a local infections
Vaccinia
However, vaccinia can, in some cases, become generalized; there is where the adverse effects of the vaccine are seen
Remember, vaccinia is the name of the virus in the ________
smallpox/mpox vaccine
