Virology Flashcards
What are the components of a Virion?
- Genome: DNA or RNA (Instructions to clone itself)
- Protein coat: Protection, Facilitates attachment, and Antigens
- May contain enzymes needed for transcription (e.g. polymerase)
- No energy source
- No metabolic processes
What are viral spikes or glycoproteins?
- Protein (or protein + glycogen) that are antigens
- Responsible for different viral serotypes (viral subcategories)
What is the difference between a naked and an enveloped virus?
- Enveloped has outer lipid bilayer
- Naked survive better in the environment (i.e. not as sensitive to heat, drying, alcohol, etc)
What is the difference between positive and negative stranded viral RNA?
- Positive stranded can immediately be translated into protein.
- Negative stranded must be transcribed into a positive RNA strand prior to being translated. Virus can have it own enzyme to transcribe negative stranded to positive stranded
What is unique about retroviruses?
Even though they are positive stranded RNA virus they cannot be immediately translated. They use virion reverse transcriptase to copy RNA to DNA, which is then incorporated into the host genome
What are the (+) RNA Naked viruses?
- Calici (Norwalk)
- Hep E
- Reov (Rotavirus) Double Stranded
- Picorna (Polio, Echo, Rhino, Cox, Hep A)
What are the (+) RNA Enveloped viruses?
- Corona (viral pharyngitis)
- Retro (HIV) Reverse- transcribed
- Flavi (Westnile, Hep. C, Dengue, Yellow fever)
- Toga (Rubella, Alpha, Rubi)
What are the (-) RNA enveloped viruses?
- Bunya
- Paramyxo (Mumps and Morbilli –> Measles)
- Orthomyxo (Influenza A, B, C)
- Rhabdo (Rabies)
What are the Naked DNA viruses?
- Parvo (B19 –> Fifths Disease) Single Stranded
- Adeno
- Papilloma
What are the Enveloped DNA viruses?
- Hepadna
- Herpos (Varicella + Herpes Zoster, Herp 6 or 7 –> Roseola)
- Pox (Small pox)
What is unique about DNA viruses?
- DNA must first be transcribed into RNA, then translated into proteins (They make mRNA using host RNA polymerase)
- Positive strand is read and transcribed into mRNA
What is unique about a Prion?
- Composed entirely of protein
- No DNA or RNA
- Disrupts neuron function by converting normal cells into –> B-pleated sheets
Describe Viral Transmission
1-Attachment to host cell: Virion surface proteins attach to receptor proteins on the cell surface
2-Penetration/Entry: Naked viruses engulfed by vesicle
Enveloped viruses undergo fusion
3-Uncoating to release the genome: Low vesicle pH uncoats virion. Rupture or fusion SEE PICTURE
4-Gene expression: Virus specific mRNA synthesis
Synthesis of viral proteins
5-Genome replication: DNA viruses replicate in the nucleus using host cell DNA-dependent RNA polymerase
Exception = poxviruses – cytoplasm
RNA viruses replicate in the cytoplasm
6-Assembly:
Viral nucleic acid packaged within capsid proteins
Rupture of cell membrane releasing assembled virions (usually naked viruses)
OR
Budding process (enveloped viruses)
What happens to host cells when they become infected with a virus?
- Death: Macromolecular synthesis inhibited
- Fusion of cells to form multinucleated cells: Due to cell membrane changes
- Malignant transformation: Unrestrained growth, Prolonged survival, Morphologic changes
- No effect
What are the stages of a viral infection?
- Incubation: Asymptomatic
- Prodromal: Non-specific symptoms
- Specific-illness: Characteristic symptoms and signs
- Recovery: Illness wanes
- Persistence (sometimes): Chronic carrier state, latent infection
List the Viral Infection Diagnostic procedures.
- Cell culture – presumptive diagnosis
- Definitive identification – uses known antibody with various tests
- Microscopic identification
- Serologic procedures
- Viral antigens
- Viral nucleic acids
Define Cell culture diagnosis.
Virus growth produces characteristic cytopathic effect (CPE)
Describe serologic procedures.
Antibody titer in acute-phase and convalescent-phase (10-14 days later) compared (4-fold higher = infected)
What are the different types of vaccination immunity
1) Active immunity
- Attenuated live virus – greater, longer lasting protection
- Killed virus
- Subunit vaccines – contain purified viral proteins
2) Passive immunity
- Preformed antibody administered in immune globulins
3) Herd immunity – “community immunity”
What are some challenges that arise with viral disease control?
- Difficult to obtain selective toxicity against the virus since replication so closely involved with normal synthetic processes of the cell
- Extensive viral replication occurs during the incubation period
- Drug-resistant viral mutants
What are the respiratory illnesses?
- Common cold (Rhinoviruses)
- Viral pharyngitis
- Influenza
Common Cold Infectious agent…
- Rhinoviruses (30-50% case): Picornavirus family
- Naked (+) RNA
Common Cold transmission…
- Hosts: humans and chimps
- Entry point: URT
- Droplets (direct & indirect)
- Peaks: early fall or spring
Common Cold Signs/symptoms…
- Incubation: 2-4 days
- Duration: 1 week
- sneezing, nasal discharge, sore throat, cough, headache
Viral pharyngitis infectious agents…
Multiple!!… Coronavirus
Viral pharyngitis signs and symptoms…
- Headache, malaise, +/- fever, sore throat
- Nasal congestion, coryza, hoarseness, sinus discomfort/tenderness, ear pain, cough
Influenza infectious agents…
- Influenza A, B, C: Orthomyxovirus family
- Enveloped (–) RNA
- 2 glycoproteins
- Hemagglutinin (H1, H2, H3)
- Neuraminidase (N1, N2)
Describe antigenic shift vs drift
Drift: mutations
Shift: animal –> human… causes re-assortment of genome segments (big change!!) (H1N1)
Influenza transmission…
- Host: Humans
- Influenza A: mammals and birds
- Influenza B: seals
- Influenza C: pigs, dogs
- Entry point: respiratory tract
- Direct droplet spread
- Peak: winter months
Influenza signs and symptoms…
- Incubation: 2 days
- Duration: acute phase 3-5 days. Normal in 2-6 weeks
- Abrupt onset: FACTS
- F - fever
- A - aches (aka myalgias)
- C - chills
- T - tiredness
- S - sudden onset
- 6-12 hrs later respiratory signs (dry, nonproductive cough)
Influenza prevention…
Antivirals
- Neuraminidase inhibitors: block the enzyme so it can’t release/spread/infect
- Viral protein M2 inhibitor: block uncoating/assembly
Vaccines
- Killed (inactivated): virions/split subunits made of hemagglutinin antigens
- Live attenuated: antibodies form 2 weeks after vaccination
Influenza complications…
- Pneumonia
- Bacterial superinfection
- Reye’s syndrome
What are the Exanthem viruses?
- Varicella (Chickenpox)
- Herpes zoster (Shingles)
- Measles
- Roseola
- Rubella
- Fifth disease
Varicella (Chickenpox) infectious agents…
- Varicella zoster virus: Herpesvirus family
- Enveloped DNA
- Single serotype
Varicella (Chickenpox) transmission…
- Host: humans
- Respiratory droplets and direct contact w/lesions
- Mucosa of URT
- blood –> skin
- Sensory neurons: travels to dorsal root ganglia then becomes latent
Varicella (Chickenpox) signs and symptoms…
- Incubation: 14-21 days
- Prodrome: fever & malaise
- Papulovesicular rash in trunk and spreads to head/extremities
- Pruritis (itchy skin): Papule, Blister, Ulser
Varicella (Chickenpox) Prevent/Control…
- Diagnosed with Tzanck smear
- Antivirals: acyclovir, Foscarnet, Famciclovir, Valacyclovir
- Live, attenuated vaccines
- Varicella
- Zoster (14x more virus)
- varicella-zoster immune globulin
Varicella (Chickenpox) complications…
- Varicella pneumonia
- Encephalitis
- Reye’s syndrome
- Postherpetic neuralgia(Shigls)
Herpes Zoster (Shingles) signs and symptoms…
-Painful vesicles along course of sensory nerve of the head or trunk
Measles Infectious agents
- Morbillivirus: paramyxovirus fam.
- Enveloped (–) RNA
- 2 envelope spikes
- Hemagglutinin
- Cell fusing & hemolytic activity
- single serotype
Measles Transmission
- Host: humans
- Person-to-person contact through respiratory droplets
- URT –> Mucosal epithelium
- Epidemics: winter & spring as well as unimmunized/ partially immunized
Measles Signs and symptoms
Incubat: 7-18 days (usually 9-11)
- Fever, cough, coryza, conjunctivis
- 1-3 days later: KOPLIK SPOTS lasting 1-2 days
- 1 day later: rash (head trunk/extremities) lasting 3-5 days
Measles prevention/control
- Live attenuated vaccine
- Immune serum globulin
Measles complications
- Varicella pneumonia
- Encephalitis
- Reye’s syndrome
Roseola infectious agents
- Hum. herpesvirus 6 or 7: Herpesvirus family
- Enveloped DNA
Roseola transmission
-Mainly through saliva