10 Viruses (2) Flashcards
What’re viruses?
Non-cellular agents that cannot reproduce independently
Very general structure of a virus?
Nucleic acid surrounded by a protein (capsid) coat
4 types of viral outcomes/infections?
- Lytic (acute) infection
- Persistent (chronic) infection
- Latent infection
- Oncogenic infection (“Host Cell Transformation”)
Life cycle of all viruses involves…
- Adsorption
- Penetration/uncoating
- Gene expression
- Assembly
- Release
List three ways a virus can cause damage to the host tissue.
- Viral replication can cause host cell LYSIS
- Cell metabolism is altered by virus infection > impaired fn
- Viral proteins get inserted into host cell membrane > cell appears foreign to immune sys > cell gets attacked
T or F: Tissue damage that’s caused by viruses often make the host less susceptible to infections by other microbes.
F
Tissue damage that’s caused by viruses often make the host MORE susceptible to infections by other microbes
T or F: Diff classes of viruses often infect the SAME organ or tissue.
T
T or F: Almost every body system is susceptible to viral infection
T
T or F: Viruses infect the site at which they first make contact with the host.
F
Not necessarily true. Infection can occur at sites distant from site of first contact.
How can viruses be spread throughout the body? (2)
- Blood
2. Lymph
What must be present for viruses to initially infect cells?
Suitable cell receptors
T or F: The site of virus entry does not always equate to the site of disease symptoms.
T
Why is it important to identify the specific virus causing an infection? (3)
- Rules out other microbes
- Help with patient management
- Infection ctrl (inds w/ the same infection can be kept in the same place)
Diagnostic challenges w/ viral infections? (3)
- Viral infection symptoms sometimes similar to those caused by other microbes
- Diff viruses often produce the SAME symptoms OR a single virus can cause a range of diff symptoms
- Virus diagnostic methods are v. diff from those of bacteria and fungi (need a living cell; agar plates, etc., aren’t appropriate for viruses)
Three steps to diagnosing viral infections?
- Assess clinical picture (i.e. are the pt’s symptoms and history consistent w/ a viral infection?)
- Collect appropriate specimen
- Lab testing
What’re the two types of lab tests for viruses?
- Direct tests
2. Indirect tests
If I’m testing for the presence of the virus itself, then I’m using a(n) ____ laboratory test.
direct
If I’m testing for the body’s immune response to the virus, then I’m using a(n) ____ laboratory test.
indirect
Name the two specific direct lab tests used in viral diagnosis.
- Nucleic Acid Amplification tests (NAATs)
2. Direct Fluorescent Antibody (DFA) tests
What does one look for during a NAAT (Nucleic Acid Amplification test)?
One looks for the virus’s DNA or RNA in the clinical specimen
NAATs (Nucleic Acid Amplification tests) utilize what kind of technology?
Polymerase Chain Reaction (PCR) technology
What does one look for in a Direct Fluorescent Antibody (DFA) test?
One looks for virus-infected cells by seeing if any of them (the infected cell, not the virus) are bound by antibodies that have been tagged w/ a fluorescent dye
What is the advantage of using NAATs over DFA tests?
Nucleic Acid Amplification tests are much more sensitive than Direct Fluorescent Antibody tests (i.e. We need LOTS of infected cells for DFA to be feasible)
In NAATs, you’re looking for…
In DFA tests, you’re looking for…
Viral DNA/RNA
Virus-infected cells
What indirect test is used in lab viral diagnosis?
Serology tests
What does one look for in serology tests?
One looks for anti-viral antibodies in the pt’s blood
What specific test is used to detect anti-viral antibodies in serology testing?
ELISA tests
Enzyme-Linked Immunosorbent Assay
Why are you not automatically considered to be currently infected if you’re found to have antibodies for a specific virus?
Because antibodies can persist for a long time, even after the virus is long gone
T or F: Serology tests are useful at any time to indicate the presence of an infection
F
Serology tests aren’t useful in the early stages of an infection since your body hasn’t had enough time to make antibodies against the virus
What types of skin lesions are commonly caused by viruses that infect the skin?
- Rashes
- Fluid-filled blisters
- Warts
2 routes of transmission for viruses that infect the skin:
- Direct contact (e.g. w/ a blister)
2. Inhalation of respiratory secretion (it migrates to epithelial surfaces)
What are some skin viruses able to do?
Migrate further and enter the CNS
Name two viruses that’re able to migrate from skin epithelia cells into nerves.
- Herpes
2. Varicella
HSV is a(n) _____ virus
a. enveloped
b. naked
c. DNA
d. RNA
e. both a and c
f. both a and d
g. both b and c
h. both b and d
e.
HSV = enveloped, DNA virus
How does one acquire HSV?
DIRECT contact w/ someone who has an active HSV lesion
Initially, HSV is THIS type of viral infection when it enters epithelial cells.
Lytic (acute) infection
What kind of skin lesions are caused by HSV?
Fluid-filled blisters
To where can HSV spread?
Nearby sensory nerves
What does the HSV virus do when it reaches the nerve cell? What kind of infection results?
It enters the nucleus > its viral DNA gets inserted into the cell’s chromosome > it becomes a LATENT infection
What’s the hypothesized purpose of HSV latency?
Protection from the immune system
T or F: HSV genes can be reactivated by external stimuli, such as stress, trauma, fever, and sunlight.
T
T or F: HSV eventually gets cleared by the immune system.
F
HSV persists for LIFE, switching b/w lytic and latent states
HSV-1 usually causes three types of herpes infections:
- Oral herpes (“cold sores”)
- Herpes Keratitis
- Herpetic Whitlow
Herpes keratitis is an HSV infection of the _____.
It occurs due to _____.
eyes (corneas, specifically)
autoinoculation
Herpetic whitlow is an HSV infection of the ______.
fingers
What percentage of adults have antibodies to HSV-1?
~65%
THIS type of herpes infection is commonly contracted in contact sports.
Herpes gladiatorum
What strain of herpes virus is most commonly associated w/ genital herpes?
HSV-2
Genital herpes manifests itself as what?
Vesicular lesions in the genital area
About 15% of HSV infections cause _____
encephalitis
Adult encephalitis is mostly caused by THIS strain of HSV, while neonatal encephalitis is usually caused by THIS strain of HSV.
HSV-1 (adults)
HSV-2 (neonates)
How does adult encephalitis develop from an HSV infection?
Latent HSV gets reactivated > instead of migrating to epithelial cells, it migrates backwards towards the brain
HSV-induced encephalitis in adults is usually seen in these two pops:
- Elderly
2. Immunocompromised
How do babies get infected initially?
A newborn can contract it from his mother if she has active genital HSV lesions during birth.
How does the primary infection of HSV-2 manifest itself in newborns? How is neonatal encephalitis caused?
Widespread skin lesions.
The herpesvirus makes its way into the CNS > encephalitis results
T or F: Neonatal encephalitis due to HSV-2 causes PERMANENT neurological damage or death.
T
What should mothers who have active HSV lesions consider if they’re expecting to give birth?
C-section
What type of test can rapidly test for HSV-1 or HSV-2?
NAATs (Nucleic acid amplification tests)
HSV should be tested for in THIS if neurological symptoms are present.
CSF
HSV should be tested for in THIS if vesicular lesions are present.
Fluid from the blisters
What cures are available for HSV?
None
What drugs are available for treating HSV?
- Acyclovir (and other “-cyclovir” drugs in general)
- Abreva (10% docosanol topical cream)
- Topical anesthetics
How does acyclovir help with HSV outbreaks?
Shortens duration of lesions
What drug is effective for HSV-induced encephalitis?
Acyclovir
How does Abreva work?
Blocks entry of HSV into host cells
How do topical anesthetics help w/ HSV outbreaks?
They reduce discomfort ONLY
Why can HSV be destroyed by soap and water?
It’s an enveloped virus, so its lipid envelope can be disrupted by detergents
Avoiding active HSV lesions is a good way to avoid spreading it and autoinoculation. However, this isn’t always feasible. Why?
Some active lesions are small, and thus not obvious.
HPV is a(n) _____ virus
a. enveloped
b. naked
c. DNA
d. RNA
e. both a and c
f. both a and d
g. both b and c
h. both b and d
b. and c.
HPV comprises over ____ “genotypes”
100
Most common HPV infections manifest themselves as what?
warts (abnormal skin growths that project outward)
Rarely, serious HPV infections can cause what? Where do they usually occur in men and women (if they occur at all)?
Cancer
In men: Oropharynx (throat)
In women: Cervix
How is HPV transmitted?
Direct skin-to-skin contact
Where amongst the skin layers does HPV specifically enter?
The basal layer (stratum basale) of the epidermis
How does HPV work?
It causes the basal cells to divide more rapidly, and to continue dividing after they normally should have stopped
What triggers the production and assembly of new HPV?
The MIGRATION of infected basal cells upward to skin surface
About how many HPV particles per cell are present by the time the basal cell reaches the skin surface?
1000s
HPV-infected epithelial cells form characteristic warts/papillomas. Why?
They divide more rapidly than non-infected cells
HPV is an example of a(n) “______” virus bc it causes unctrled host cell growth.
“oncogenic”
What occurs when HPV-infected epithelial cells die?
They release HPV onto the skin surface > new rounds of infection are initiated
What effective anti-viral agents are there for HPV?
None
Name 4 ways HPV-infected epithelial tissue can be killed?
- Caustic chemicals
- Cryogenic treatment (liquid nitrogen)
- Laser treatment
- Surgical removal
Approximately ___% of skin warts spontaneously disappear within 6-18 months w/o treatment due the body’s immune sys response.
50%
List the 4 HPV types that have a preference for infecting epithelial cells of the genital area:
- 6
- 11
- 16
- 18
What HPV types are considered “low-risk” i.e. cause genital warts only
6, 11
What HPV types are considered “high-risk” i.e. can cause cancer, in addition to genital warts
16, 18
Why are high-risk HPV infections more likely to lead to cancer? (2)
- They cause far more rapid epidermal basal cell replication
- They interfere more w/ the host cell’s proteins that regulate cell growth and repair mutated DNA
T or F: Presence of high-risk HPV is sufficient to cause cancer.
F
Other factors must be present
How can HPV and cervical cancer be diagnosed?
- Pap test (looks for cervical cancer, not HPV specifically)
- “HPV PCR” test (looks for HPV specifically)
–>Ideally, both are done together
About ___% of sexually-active men and women will acquire a genital HPV infection before the age of 50.
85%
What three factors determine whether s.o. w/ genital warts caused by HPV will go on to develop cancer?
- HPV type (high- vs low-risk)
- DURATION of infection
- Presence of other poorly-defined FACTORS
The vaccine against HPV is made by using what part of the HPV virus?
The CAPSID proteins = “Virus-like particles”
Gardasil contains virus-like particles from which HPV types?
6, 11, 16, and 18
Gardasil is approved for use in males and females b/w the ages of…
9-26 years
Gardasil should be given BEFORE what?
The onset of sexual activity
If the vaccine is almost 100% effective in preventing infection by high-risk HPV types, why is your protection vs. cervical cancer only 90%?
Because 10% of cervical cancers are caused by OTHER non-HPV stuff.
