Viruses lecture Flashcards
Herpes viruses (4)
1) Herpes simplex type 1 and 2 Varicella zoster virus
2) Cytomegalovirus (CMV)
3) Epstein Barr virus
4) Herpes virus 8 – Kaposi’s sarcoma
Eicosahedrical core surrounded by lipid envelope
After initial infection, virus replicates in neurons in non-infectious state. Virus activated to produce?
New disease symptoms
Herpes viruses cause?
Latent infection:
Acute infection – Quiescent – Acute infection
Acute infection ____ cycle. Latent infection _______ cycle
Acute infection – lytic cycle Latent infection – lysogenic cycle
Herpes Simplex Viruses (HSV) Diseases & host
1) HSV-1 – Herpes labialis- Cold sore
2) HSV-2 – Herpes genitalis
Humans are natural hosts of HSV1 and 2
Herpes viruses Transmission fore HSV-1 & HSV-2
Transmission:
HSV-1 – Saliva
HSV-2 – Sexual Contact
Herpes viruses Epidemiology
- 10- 20% cases can result in HSV-1 in the genitals and HSV-2 in the oral cavity.
- 80% Americans are infected with HSV-1 and 40% have recurrent reactivations
- Infection with HSV-1 is stable in numbers, HSV-2 is on the rise
Herpes viruses Mechanism of Disease
- Lytic cycle – Skin – Vesicular rash
- Lysogenic cycle – ganglia (trigeminal – HSV-1 and sacral for HSV-2)
- Cell mediated immunity – CD4+ cells are essential to avoid reactivation.
Clinical findings for herpes viruses
Clinical findings – painful vesicular rash (lips and nose – HSV-1, genital area- HSV-2)
Herpes viruses HSV-1 and HSV-2 complications
Corneal ulcers – HSV-1
Encephalitis – HSV-1
Neonatal Herpes – HSV-1 and HSV-2
Prevention and treatment for herpes viruses
Prevention – Avoid contact with lesions Treatment – Antiviral (Acyclovir – Zovirax)
Varicella-Zoster Virus Chickenpox (Primary disease) Shingles (Zoster):
1) Hosts
2) Cycle
3) Transmission
4) Mechanism of disease
5) Clinical findings
1) Humans are the natural hosts
2) Cycle – Same as herpes
3) Transmission – Respiratory droplets
4) Mechanism of disease – same as herpes
5) Clinical findings: Varicella and zoster
Varicella-Zoster Virus:
1) Treatment
2) Prevention
Treatment – No drugs are necessary for immunocompetent individuals
Prevention – Vaccine (Varivax, Zostavax) – Live attenuated virus. Recommended to 1- 12yo.
* Avoid contact with vesicular lesions.
Cytomegalovirus (CMV)
1) Causes
2) Cycle
3) Transmission
1) Most common cause of congenital abnormalities in US.
2) Cycle – same of HSV
3) Transmission:
* Early – Placenta
* Children – Saliva
* Adults – Sexual activity
~ 80% adults had contact with CMV
Cytomegalovirus (CMV)
1) Congenital abnormalities includes
2) Immunocompetent there is?
3) Immunosuppressed there is?
4) Treatment
5) Prevention – There is no Vaccine, isolation of individuals shedding virus.
1) Congenital abnormalities – infection during the 1st trimester.
2) Immunocompetent – fever, lethargy
3) Immunosuppressed- pneumonia, hepatitis, retinitis.
4) Treatment required for immuno suppressed
5) Prevention – There is no Vaccine, isolation of individuals shedding virus.
“Blueberry muffin” lesions
Congenital Cytomegalovirus
Infectious Mononucleosis (Epstein-Barr Virus) causes and transmission
Causes lymphomas (Leukemia) and Cancer
Transmission:
* Saliva – Kissing disease
* Virus infect white blood cells ( B lymphocytes) No symptoms in most cases
* Fever, sore throat, anorexia and lethargy – spontaneous recovery in 2-3 weeks.
Human Papillomaviruses (HPV):
1) Causes?
2) Types of papillomaviruses
3) Transmission
1) Causes papillomas – Benign tumor of skin (warts) and cancer of cervix and penis.
2) 100 types of papillomaviruses – 30 HPV infect genital tract.
* Genital warts are the most common sexually transmitted disease.
3) Transmission – Skin-to-skin contact and genital contact.
Human Papillomaviruses (HPV):
1) Most genital warts are?
2) HPV16/18
3) Immunosuppressed individuals have?
4) Treatment
5) Prevention
Human Papillomaviruses (HPV)
1) Most genital warts are benign and do not evolve to cancer (genital area and anus).
2) HPV16/18 – inactivate tumor suppressor genes in human cells (p53 and Rb genes).
3) Immunosuppressed individuals have more extensive warts and cervix, anal cancer.
4) Treatment – antiviral drugs and liq Nitrogen
5) Prevention – Vaccine (Gardasil) 9-26 yo female.
Influenza Virus Disease
1) Pandemics – last pandemic was?
2) Most common?
3) 1918 pandemic of flu (Spanish flu) killed?
1) Pandemics – last pandemic happened in 1968.
2) Most common respiratory infection that leads to physician and Emergency Room visits.
3) 1918 pandemic of flu (Spanish flu) killed more Americans than WW I, WW II, Korean and Vietnam wars combined.
Is Influenza Virus RNA or DNA enveloped or non-enveloped?
RNA enveloped
Influenza Virus Important features
– Segmented genome
– 2 major molecules in the envelope
* Hemagglutinin (H) – 16 variants
* Neuraminidase (N) – 9 variants
– Combination of H genes and N genes gives the identity of the virus isolate.Influenza Virus
1) Transmission
2) Mechanism of Disease
3) Treatment
4) Prevention
1) Transmission – Airborne droplets
2) Mechanism of Disease – Lytic cycle in the lungs.
3) Treatment – Tamiflu (Swine flu was resistant)
4) Prevention – Vaccine (2 isolates of A and 1 B)
Is Rhinovirus an RNA or DNA enveloped or non-enveloped?
RNA non-enveloped virus
Rhinovirus:
1) Cause of the common cold
2) Important features
3) Transmission
1) Cause of the common cold
2) Important features
– More than 100 types
– Grows better at 33C
– Mildly resistant to detergents and alkali but susceptible to acid
3) Transmission – Worldwide
– Aerosol droplets and HANDS
Rhinovirus:
1) Mechanism of Disease
2) Prevention
3) Treatment
1) Mechanism of Disease– Lytic cycle in the lungs
2) Prevention– Wash hands, avoid exposure. There is no Vaccine
3) Treatment– Symptomatic
– Vitamin C and Zinc–unproved efficacy.
– no proven treatment to control virus
1) Norwak Virus (Norovirus) is?
2) Rotavirus is?
3) Transmission
4) Mechanism of Disease
1) Norwak Virus (Norovirus)– Most common viral gastroenteritis in adults
2) Rotavirus– Most common viral gastroenteritis in Children
3) Transmission– Oral fecal contamination
4) Mechanism of Disease– Lytic cycle in the intestinal tissue
Norwak Virus (Norovirus) & Rotavirus Prevention
- Vaccine for Rotavirus
- There is no vaccine for Norovirus
- Personal hygiene, proper sewage and water treatment and hand washing
A virus consists of: RNA or DNA and a cell membrane RNA or DNA and a protein coat RNA and DNA and a protein coat proteins, cell membrane and RNA
RNA or DNA and a protein coat
How do viruses reproduce?
a) they divide by mitosis
b) sexually, by external fertilization
c) replication outside the host
d) inserting DNA into the host cell
inserting DNA into the host cell
Which of the following is smallest?
a) eukaryote cell
b) bacteria
c) bacteriophage
d) cell membrane protein
c) bacteriophage
Retroviruses are different from viruses in that:
a) they have RNA instead of DNA
b) they can become dormant
c) they are symmetrical
d) all of these
a) they have RNA instead of DNA
Vaccines can be used to prevent viral infection by:
a) creating an immune response in the host
b) destroying any viruses that enter the host
c) creating a blocking protein on the cell
d) preventing replication of the virus
a) creating an immune response in the host
Antiviral drugs that are used after infection often prevent:
a) cell division
b) immune system degradation
c) reinfection by other viruses
d) uptake of the virus
d) uptake of the virus
Why do some viruses seem to go away and then return later, like a cold sore?
a) host has been infected with a different strain
b) the immune system forgot the virus
c) the virus had entered the lysogenic cycle
d) the virus mutated
c) the virus had entered the lysogenic cycle
Why is it difficult to develop vaccines for retroviruses?
a) their small size evades the immune system
b) RNA mutates more frequently than DNA
c) the capsid of retroviruses is resistant
d) vaccines can only target blood-borne pathogens
b) RNA mutates more frequently than DNA
Viruses are often named by:
a) where they were first discovered
b) the scientist who discovered it
c) the animal that carries it
d) all of these
all of the above
What happens after the virus has been taken up by the cell?
a) it begins making protein
b) it divides
c) it inserts into the host DNA
d) it switches to infectious mode
c) it inserts into the host DNA
American Continent Colonization
600 Spaniards conquered 8 million Native Americans
- Smallpox and lack of immunity
Spanish flu – 1918 to 1920
3% of the world population died – up to 100 million people
Main Features of Viruses, Viroids and Prions
• Not living agents
• Require host intracellular environment
• Much smaller than bacteria
• Nanometer scale
For viruses:
• Carrier or normal host: Harbor the virus without symptoms
• Accidental Host: Not usual carrier, may develop disease
Enveloped Viruses
Nucleocapsid is covered by a lipid membrane
Naked Viruses
Nucleocapsid is the virus
Nucleocapsid
Protein coat + genetic material
Viral proteins
- Provide Protection
- Mediate adhesion
- Give host and organ specificity Some are enzymes
- Some can act like toxins
Viral envelope
- Lipids and proteins
- Hybrid structure (contains host and viral molecules)
- Envelope gives instability to virus
– Susceptibility to soaps and lipid solvents (alcohol)
– Enveloped virus rely on direct transmission (HIV, Herpes, Hepatitis B and C)
– Non enveloped viruses can survive environment for limited period of time (Hepatitis A, Norovirus, Rotavirus)
Genome replication and expression
- First step for replication – Production of viral mRNA
- DNA viruses replicate in the nucleous
- RNA viruses replicate in the cytoplasm
- RNA viruses can be divides in:
– Positive RNA strand virus (genome is the mRNA)
– Negative RNA strand virus (need RNA polymerase to make mRNA
– Ambisense – double strand RNA
– Reverse transcription – RNA produces DNA
Genome of replication and expression
- Protein production
- Positive strand of RNA is translated into a polyprotein (more than one protein translated together).
- Proteins are separated by Virus Protease
Lytic cycle
1) Virus enters the cell, hijacks the host machinery and immediately initiates replication
2) The host cell ruptures after a few cycles of replication.
3) Viral particles are released and infect new cells
Lysogenic cycle
1) Virus enters the cell, integrates to the host genome and stays latent
2) Latency is broken and the virus switches to the lytic mode. The host cell ruptures after a few cycles of replication.
3) Viral particles are released and infect new cells
Groupings based on?
route of transmission
Disease-causing viruses often grouped by route of transmission
1) Enteric viruses:
- Generally transmitted via fecal-oral route
- Often cause gastroenteritis
- Some can cause systemic disease
2) Respiratory viruses
- Usually inhaled via infected respiratory droplets
- Generally remain localized in respiratory tract
3) Zoonotic viruses
- Transmitted from animal to human via animal vector
4) Sexually transmitted viruses
- Can cause lesions on genitalia or cause systemic infection
Normal hosts
– No obvious disease or damage is caused to host
– State of balanced pathogenicity
– Lassa fever carried by rodents
Accidental hosts
- Outcome of infection of eukaryotic cells depends on factors independent of cell (Defense mechanisms of host)
- Relationships divided into two categories
– Acute
– Persistent
Acute infections
– Usually short in duration
– Host may develop long-lasting immunity
– Result in productive infections
– Produce large number of viruses during replication
– Disease symptoms result from tissue damage and infection of new cells
Acute infections animal virus replication

- Attachment
- Entry
- Targeting
- Uncoating
• Exposing nucleic acid - Replication & Synthesis
- Maturation
- Cell lysis
- Spreading - within host
- Shedding & Transmission
