Morphology and Biology of Viruses Flashcards
What are the 3 criteria used for virus classification?
1) TYPE and ORGANISATION of genome:
- DNA/RNA
- Single or double stranded
- Genome relatedness
2) VIRAL REPLICATION strategy:
- eg does it go through reverse transcription?
3) STRUCTURE and SIZE of the virion:
- envelope?
- Viral structure - most sre icosahedral
Describe 6 further criteria for viral classification
Host range
Tissue tropism
Pathogenicity
Mode of transmission
Physiochemical properties
Antigenic properties of the virion
Describe the 5 human hepatitis viruses
A = enteric transmission - vaccine
B = non-enteric, persistent - vaccine
C = non-enteric, persistent - trial of vaccines
D = non-enteric, persistent - hep B vaccines
E = enteric transmission - vaccine
Describe hepatitis A (structure, incubation, onset, transmission)
- Most common viral hepatitis
- Picornaviridae family
- Naked (no envelope), icosahedral
- Single stranded RNA (+ve sense)
- Incubation (days): 15-45, mean 25
- Onset: Acute, mainly infects children, young adults
- Transmission: Foecal-oral
- Sexual: possible but less likely
Describe the structure and 5 features of hepititis B
- Hepadnaviridae family, enveloped (42nm)
- Icosahedral nucleocapsid
- Circular DNA partially double stranded
- Tubular filaments & spherical particles composed of envelope proteins – hep B surface antigen
- Incubation (days): 30-150, mean 75
- Onset: Insidious or acute
- Age preference: Young adults, babies, toddlers
- Transmission: Faecal-oral, Percutaneous, Perinatal, Sexual
- Can cause chronic and acute infection (most fully recover in few months)
Describe the structure and transmission of hepatitis D
What is required for its replication?
- Single stranded, negative sense, circular RNA
- Viral envelope is made of HBAg
- The virus requires Hep B virus to be present in the cell for its replication.
- Infection can occur simultaneously or after hep B infection.
- Transmission: contact with blood or other body fluids. Mother to child transmission at birth can also occur.
Describe hepatitis C (structure, incubation, onset, transmission)
What are some risk factors for hep C?
- Flaviviridae family, enveloped, icosahedral
- Single stranded RNA
- NS1 non structural protein 1
- E proteins are major envelope proteins of the virus
- Incubation (days): 15-120, mean 50
- Onset: Insidious, more common in adults
- Transmission: Fecal-oral, though can also be Percutaneous, Perinatal, Sexual (though less likely)
Risk factors: blood transfusion, IV drug abuse, body piercing, tattoos, needle stick injury,
What are 3 structural features of hepatitis E?
- Non enveloped
- Icosahedral nucleocapsid
- RNA - single stranded - positive sense
Compare the structural differences between norovirus and rotavirus (GI infections)
What are symptoms of rotavirus infection?
NORAVIRUS (27 nm)
- Calicviridae
- Icosahedral, Non-enveloped, Single stranded RNA
ROTAVIRUS (75nm) :
- Reovirdae
- Icosahedral, Non-enveloped, Double stranded RNA (11 segments)
Symptoms:
- Fever
- Vomiting
- Diarrhoea
- Abdo pain
No antivirals but vaccine available (live oral)
What are the viral proteins for rotavirus and how does it replicate?
- Structural proteins: VP1-VP7
- Non structural: NSP1-NSP6
- Infects and replicates in intestinal epithelial cells
- Outmost layer has VP7 and VP4 = important in virus attachment and entry
Describe the replication cycle for rotavirus.
- Virus binds to receptors, enters cell by endocytosis, losing its outer layer
- Within virus, structure dsRNA can replicate
because virus has a protein VP6, acts as a channel, allowing movement of RNA - Inside virus core there are VP1, VP2 and VP3, involved in transcription
- Viral proteins are made in infected cell cytoplasm
- Core assembly of single and double shelled particles in cytoplasm –> enters ER
Describe the structure of measles virus, its symptoms and how it’s spread?
- Enveloped, RNA single stranded, Negative sense, Paramyxoviridae family (100-300nm), Pleomorphic (occurs in many forms)
- Fever, cough, runny nose, red eyes, sore throat
- 2 days later small white (Koplik’s) spots may appear in the mouth.
- 3-5 days after symptoms start: rash on face and spreads to neck, trunk, arms, legs, and feet.
- When rash appears, fever may spike then both reduce after a few days
- Very contagious, spread by droplet infection
Describe the structure of mumps virus, its symptoms and its transmission?
- Paramyxovirus, Pleomorphic, Enveloped, Helical nucleocapsid, ss RNA linear genome
- Fever, headache, muscle aches, tiredness, loss of appetite, swollen salivary glands (16-18 days after infection)
- Transmission = droplets
Describe the structure of rubella virus, its symptoms and its transmission?
What is congenital rubella?
- Togavirus family, Enveloped, Single stranded RNA, Icosahedral
- An acute viral disease causes fever and rash
mild disease in children and young adults
Rash/fever for 2-3 days - Spread by coughing and sneezing
- Birth defects if acquired by a pregnant woman, esp early pregnancy: Deafness, Cataracts, heart, liver and spleen defects, Damage to foetal brain
Describe the structure and symptoms of adenoviruses
- Adenovirdae, No envelope, icosahedral, DNA double stranded, linear
- Different serotypes exist, most cause resp illness
- May also cause gastroenteritis, conjunctivitis, cystitis, rash.
What is the structure of papillomavirus and 2 things it can cause?
- No envelope, icosahedral, Circular, double stranded DNA, Papovaviridae family
- Different serotypes
- Some cause infections in the genital tract or cervical cancer
What is the structure, incubation period and virology of parvovirus?
- Non-enveloped, single stranded DNA,
small (22nm), Nucleocapsid icosohedral - Incubation period between 10-21 days
- The virus has a receptor which allows it to attach to erythrocyte progenitor cells
- Parvovirus B19 inhibits erythropoiesis
- Shortened life span of RBCs <120 days, viraemia present (virus in blood)
Describe the clinical manifestations of parovirus and how its is transmitted?
- “slapped-cheek” rash, red rash on trunk and limbs.
- May have a low-grade fever, malaise a few days before the rash breaks out. Rash may itch (Resolves in 7-10 days)
- Gloves and socks syndrome
- Arthropathy
- Transient aplastic crisis
- Chronic red cell aplasia
- Neutropenia, thrombocytopenia and pancytopenia
- Respiratory route, mother to the foetus transmission (first trimester + mother having no IgG antibodies against virus)
No specific drug to treat Parvovirus B19 infection.
Describe influenza
- Orthomixoviridae (family)
- lipid envelope derived from host cell membrane
- Subtypes A, B and C
- Airborne virus producing feverish illness
- Causes serious illness in immunocompromised
Describe the influenza subtypes
TYPE A - Most serious, affects mammals and birds
- Genetic cross-over between strains can lead to pandemic
- Subtyped according to its surface Ags- (HA) and (NA)
TYPE B: affects humans, minor outbreaks
TYPE C: affects humans, endemic, similar to common cold
Describe the 7 stages in replication cycle of influenza
- Uses haemagglutinin to attach to sialic acid, enters by endocytosis
- Virus envelope fuses w endosome, triggering uncoating
- Viral nucleocapsid released into cytoplasm
- Copies of viral RNA and mRNA made, mRNA translated in cytoplasm
- Early viral proteins required for replication/transcription are transported back to the nucleus.
- Late in infection cycle, M1 and NS2 proteins facilitate nuclear export of newly made viral ribo nuclear proteins.
- RNA segments assembled within nucleocapsid and bud at plasma membrane
How does the influenza virus mutate?
Surface Ags of Influenza A mutate rapidly bc:
Viral RNA polymerase involved in replication has low selectivity and no proof reading mechanism
Therefore mutants are generated and spread rapidly.
Two patterns of mutation: antigenic drift and antigenic shift
Describe antigenic shift associated with influenza
Type A only
Genetic reassortment: mixing genetic material between strains, when they infect the same host
Creates novel strains ppl dont have immunity to.
Rapid spread - pandemic
Mixed strains from diff species= mas virulent/fuera control
What is the current strategy in dealing with the different strains of influenza?
What are its limitations?
Global Influenza Network estimate the strain of virus before the following season and recommend vaccines
Limitations: errors in the estimate
manufacturing difficulties
time constraints, lack of resources
antigenic drift continues (vaccine mismatch)
