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.
