Flashcards in Virology lecture 1 Deck (40):
structure of simplest virion and more complex structures
nucleic acid (genome) surrounded by a protein shell (capsid) of repeating subunits - capsomers. more complex viruses surrounded by phospholipid membrane (the envelope) acquired from the host. membrane embedded with viral proteins which may be glycosylated.
non structural viral proteins
virus encoded proteins expressed from within the infected host cell
Tobacco mosaic virus
Capsid and envelope
1 - helical capsid, no envelope
1 - icosadhedral capsid, no envelope
2 - +ve ssRNA, monopartite
3 - 7.5kb
1 - helical capsid plus envelope
2 - segmented -ve strand RNA
Herpes simplex virus
1 - icosahedral capsid plus lipid envelope
2 - dsDNA
virus genome structure types
1 - DNA or RNA
2 - linear or circular
3 - monopartite or segmented
4 - double stranded or single stranded
viral RNA subclasses
1 - sense mRNA can be translated into viral protein and is called +ve strand RNA
2 - if complementary then the viral genome is transcribed to produce the mRNA - it's instead called -ve sense
3 - most are monopartite, few are segmented (ie influenza virus)
1 - -ve ssRNA
2 - 15.9kb
3 - monopartite
1 - segmented dsRNA
mechs of increasing coding capacity.
smallest and largest genomes
1 - densely packed genes
2 - small intergenic spaces
3 - few non-coding spaces
4 - overlapping reading frames, one gene for up to 3 different proteins
5 - splicing
6 - smallest = 3kb, largest = 1200kb. v roughly 1kb codes 1 average sized polypeptide
limits on RNA genome size
1 - largest around 30kb (ie coronaviruses), most less than half
2 - limited by error prone nature of RNA polymerases as no proofreading. too large and too many mutations occur which are lethal.
1 - helical capsid plus envelope
2 - segmented -ve strand RNA
3 - 8 segments
4 - 13.6kb
1 - 10kb monopartite but diploid. a retrovirus
2 - +ve ssRNA
virus classification tree
families (viridae), subfamilies (virinae), genera, species and strains
1 - a herpesvirus
what are arboviruses?
1 - a large group of viruses transmitted by biting insects (arthropod bourne viruses)
Describe the Papovaviridae family of viruses
1 - icosahedral capsid, no envelope.
2 - 5-8kbp, dsDNA
3 - includes papillomavirus species which gives rise to warts and cervical carcinoma
Describe the adenoviridae family of viruses
1 - icosahedral capsid, no envelope, 35kbp dsDNA
2 - inc adenovirus species, giving rise to acute respiratory disease
Describe the herpesviridae family of viruses
1 - icosahedral caspid, envelope, around 150kbp (hsv). dsDNA
2 - herpes simplex virus - type 1 gives cold sores, type 2 gives genital herpes.
3 - varicella-zoster virus (VZV) - chicken pox and shingles
4 - epstein-barr virus (EBV) glandular fever and burkitt lymphoma
5 - Human cytomegalovirus (HCMV) - cytomegalic inclusion disease in neonates
6 - Human herpesvirus 8 - Karposi's sarcoma
7 - Marek's disease virus - lymphomas in chickens
8 - pseudorabies virus - aujesky's disease of pigs
Describe the poxviridae family of viruses
1 - complex caspid, envelope, around 200kbp, virion transcriptase. dsDNA
2 - includes species: Variola virus - smallpox
3 - Vaccinia virus - vaccine against smallpox
4 - Myxoma virus - myxomatosis in rabbits
5 - Orf virus - contagious pustular dermatitis in sheep and goats.
Describe the parvovirus family of viruses
1 - icosahedral virion, no envelope, 5kbp, ssDNA.
2 - inc species: canine parvovirus
3 - feline panleucopenia virus - causes cat fever and enteritis
4 - human parvovirus
Describe the Reoviridae family of viruses
1 - icosahedral virion, no envelope, 10-11 fragments, around 20kbp, virion transcriptase. dsRNA.
2 - blue tounge virus - catarrhal fever of sheep
3 - human and animal rotaviruses - acute infantile gastroenteritis.
Describe the picornaviridae family of viruses
1 - icosahedral capsid, no envelope, no envelope, around 7.5kbp. +ve ssRNA
2 - poliovirus - poliomyelitis
3 - hepatitis A virus - acute hepatitis
4 - rhinovirus - common cold
5 - foot and mouth disease virus (FMDV) - foot and mouth disease
Describe the caliciviridae family of viruses
1 - icosahedral caspid, no envelope, 8kb.+ve ssRNA
2 - norovirus - winter vomiting disease
3 - feline calicivirus - respiratory disease
Describe the togaviridae and flaviviridae families of viruses
1 - icosahedral capsid, envelope, 11kbp. +ve ssRNA
2 - rubella virus - congenital abnormality (german measles)-toga
3 - Hepatitis C virus - acute and chronic hepatitis- flavi
4 - yellow fever virus - yellow fever -flavi
5 - classical swine fever virus - swine fever -flavi
6 - west nile virus - encephalitis -flavi
Describe the coronaviridae family of viruses
1 - helical nucleocapsid and envelope. approx 30kbp. +ve ssRNA
2 - infectious bronchitis virus - avian bronchitis
3 - SARS-coronavirus - severe acute respiratory syndrome (SARS)
Describe the orthomyxoviridae family of viruses
1 - helical capsid and envelope, 8 segments, 12kb, virion transcriptase. -ve ssRNA
2 - influenza A virus - influenza epidemics and pandemics, avian and equine influenza
Describe the paramyxoviridae family of viruses
1 - helical capsid and envelope, pleomorphic, 15kb, virion transcriptase. -ve ssRNA
2 - measles virus - measles
3 - distemper virus (CDV) - canine distemper
4 - mumps virus - mumps
5 - respiratory syncytial vius - bronchitis
6 - newcastle disease virus (NDV) - fowl pest
Describe the rhabdoviridae family of viruses
1 - helical capsid and envelope, bullet shape, 10kb, virion transcriptase, -ve ssRNA
2 - vesicular stomatitis virus (VSV) - visicular stomatitis in cattle and horses
3 - rabies virus - rabies in mammals
Describe the retroviridae family of viruses
1 - capsid with envelope, 8-10kb, virion transcriptase, +ve ssRNA with DNA intermediate.
2 - rous sarcoma virus (RSV) - sarcomas in fowl
3 - feline leukaemia virus - leukaemia in cats
4 - human immuno-deficiency virus (HIV) - acquired immuno-deficiency syndrome (AIDS)
Describe the hepadnaviridae family of viruses
1 - icosahedral capsid and envelope, 3.2kbp, dsDNA with RNA intermediate
2 - hepatitis B virus - acute and chronic hepatitis, primary liver cancer.
methods of measuring viruses?
1 - electron microscopy - mix viral solution with small beads of known conc, measure relative conc and deduce viral. gives total no of virions, not no of infectious.
2 - polymerase chain reaction (PCR) - genome sequences of many viruses known so PCR with specific primers to identify and quantify. v. sensitive but like em doesnt give infectious level.
3 - immunological evidence of infection - detect presence/increase in antibodies/T cells for pathogen antigens. slow but good for retrospective epidemiology.
4 - plaque assay - preferred method to deduce infectivity. add series of dilutions to lawns of susceptible cells, cells destroyed and plaques form. each plaque derives from one initial infectious virus particle, so the conc of infectious virions can be calculated. expressed as plaque forming units (PFU) per ml. (em value vs PA value = particle/pfu ratio and can be over 1000 to 1.
virus life cycle phases?
1 - adsorption and penetration
2 - eclipse phase
3 - assembly and release
shortly after infection the cell viral titre drops close to zero, rising again at the end of the eclipse phase. final titre being much higher than the input titre due to replication.
viral latent period?
the time taken to start producing new particles - this varies greatly
mean burst size?
average yield of viral particles per cell. varies greatly with specific virus-host combination and host metabolic activity.
describe virus binding (HIV,influenza, EBV)
1 - virus binds specific cell surface molecules, the receptor may determine tissue trophism. HIV uses its gp120 to bind CD4 and a chemokine co-receptor. CD4 limited to T cells and macrophages/dendritic cells
2 - influenza uses its haemagglutinin (HA) to bind sialic acid (terminal sugar on most glycoproteins). as it binds essentially all cell types this doesnt determine its tissue trophism. (will agglutinate RBCs in vitro)
3 - EBV uses its glycoprotein 340 (GP340) to bind CD21
neutralising antibodies can be used to block this process
describe virus penetration
1 - viral envelope fises with surface membrane or endosome after endocytosis. non enveloped virus process is porrly understood - may disrupt host cell membrane integrity.
many will membrane fuse via a receptor-target conformational change (ie HIV), but influenza is endocytosed, the vesicle acidified and this causes the conformational change in the HA.
why quantative and temporal regulation of viral synthesis?
temporal - some proteins needed early in assembly ie nucleic acid polymerases and as enzymes, in low amounts. vs capsid proteins needed late and in higher amounts to build the virions.