Intro to Virology

Question 1

What are the general features of viruses?

Answer 1

obligate parasite, smaller in size than bacteria and cells, RNA or DNA genomes, packaged in protein and sometimes in lipid envelope as well

Question 2

Why are viruses obligate parasites?

Answer 2

lack ribosomes and must use the hosts to produce proteins

Question 3

What are the symptoms often seen with viral disease?

Answer 3

rash, fever, conjunctivitis, pharyngitis, gastroenteritis, hepatitis, pneumonia, bronchiolitis, adneopathy, parotitis, meningoencephalitis, arthritis, congenital or perinatal disorders

Question 4

What is the difference between (+) or (-) RNA?

Answer 4

(+) -> encodes the proteins, readable by our ribosomes; (-) -> have to carry replication enzymes, to make a single copy = mRNA

Question 5

How are viruses classified? Why do we care?

Answer 5

disease produced, physical characteristics (structures and envelopes), Genome sequence used primarily (PCR amplification to ID and quantify); diagnosis, determine treatment or outcome, best method of disinfection or prevention

Question 6

What are the different kinds of viral genomes?

Answer 6

RNA or DNA, segmented or monopartite, packaged often as a nucleoprotein.

Question 7

what are viral envelopes made of?

Answer 7

viral transmembrane proteins (often glycoproteins), some interact with receptors, often have matrix and tegument proteins that interact with envelope and core proteins

Question 8

What is the process of budding?

Answer 8

when a virus pushes through a membrane structure of the cell allowing acquisition of an envelope

Question 9

What are the general features of viruses with RNA genomes?

Answer 9

evolve rapidly because of high error rate of RNA-dependent RNA polymerase

Question 10

What are the general features of viruses with DNA genomes?

Answer 10

use host enzymes to replicate and transcribe mRNA, low error rate, allows for larger genomes, more coding capacity

Question 11

What is the function of nucleoprotein?

Answer 11

protein for packaging and replication, allows for coiling the complex of genome and protein,

Question 12

What is the core or capsid of a virus?

Answer 12

protein structure encasing the nucleoprotein, some virion are just capsid and genome (can increase stability of the virion)

Question 13

What are some characteristic shapes of viruses?

Answer 13

helical, icosahedral, or complex (many different forms)

Question 14

How do viruses infect?

Answer 14

fomites (susceptible to drying out with envelope, longer if just capsid), droplets (cough or sneeze on to fomites or inhaled), body fluids (blood, semen, urine, slaiva, breast milk), vectors (mosquitos or ticks, virus replicates to increase concentration in saliva)

Question 15

What are the various modes of Transmission of viruses?

Answer 15

respiratory, fecal-oral, sexual transmission, direct contact, urine-associated transmission, parenteral transmission, vertical (mom to child), arthropod-borne transmission (ticks, mosquitos, sandflies), zoonotic infections (from animals, rodents, even breathing in their urine)

Question 16

How do viruses get into cells?

Answer 16

receptors= host encoded proteins on cell surface, often between cells and only available during mitosis, bind envelope glycoproteins cause fusion of viral envelope with cell membranes; non-enveloped via endosomes

Question 17

How is the distribution of effects of a virus determined?

Answer 17

based on the distribution of receptor variants that the virus can bind with= tropisms

Question 18

What are some antiviral targets?

Answer 18

polymerases- reverse transcriptase or RNA dependent RNA polymerase; viral proteases- cleave viral proproteins to generate infectious virus; components of viral capsid involved in receptor binding; immune activators- interferon B, trx with IgG

Question 19

How do positive RNA viruses replicate?

Answer 19

bind receptor, conformational change to release RNA, translate to produce viral proteins processed by viral proteases, virion RNA copied by viral RNA-dependent RNA polymerase (cytoplasm), lysis to release virus

Question 20

How do DNA viruses replicate?

Answer 20

attachment of virus to receptors, entry and fusion with cell membrane, DNA release from core released into nucleus, transcription of viral RNA-> expression of viral proteins including DNA replication proteins and capsid. replicated DNA assembled in cores in nucleus and bud through nuclear membrane

Question 21

How do retroviruses replicate?

Answer 21

attach virus to CD4 allows entry and fusion with plasma membrane, viral RNA is copied as DNA by reverse transcriptase in nucleocapsid, transport to nucleus, viral cDNA integrated into host genome, viral RNA exported from nucleus, translated, and packaged, viral particles assembled and matured by viral protease

Question 22

What is the pathway and replication pattern from ingestion of virus to secondary infection?

Answer 22

virus ingested, primary site of infection GI (first replication), primary viremia (circulates through blood stream), replication in second sites (spleen, lymph nodes, meninges, etc), pathogenic virus replication in secondary organs (necrosis, inflammation, etc), virus excreted from primary site and secondary sites (fecal), virus cleared from system by adaptive immune response or becomes persistent

Question 23

When in the phase of disease is the virus excreted?

Answer 23

prior to symptomatic disease

Question 24

What can be detected during acute phase of viral infection?

Answer 24

virus cant be detected, but antiviral IgG lasts for years.

Question 25

What is a persistent infection?

Answer 25

a virus not cleared after acute period, leading to chronic infection (ex: Hep C, herpes simplex, etc), some virus infections can be cleared if a sufficient immune response is generated and/or antiviral therapy is effective

Question 26

What is a latent virus reactivation?

Answer 26

regulated to prevent virus replication except during short periods of virus activation (herpes, cytomegalovirus, Epstein-Barr), not same as clinical latency (no symptoms of disease)

Question 27

What is perinatal disease?

Answer 27

infection before birth from mother at birth or via breast milk after birth; HIV, Parvovirus (miscarriage, hydrops fetalis), Rubella (congenital infection, hearing loss, miscarriage, teratogenic), CMV infection (fetal infection, hearing loss, neurologic comp.), Herpes, HBV, Hepatitis E (moratlity of pregnant women), enterovirus (systemic multi-organ disease of neonates) and influenza

Question 28

What viruses are known to cause cancer?

Answer 28

HBV and HCV- persistent infections-> HCC, HPV: strains associated with cervical cancer and oropharyngeal cancer, Epstein-Barr virus (lymphoma, gastric carcinoma, nasopharyngeal carcinoma), HHV8 (Karposi’s sarcoma, lymphoma), HTLV1 (T-cell lymphoma)

Question 29

What are the various vaccine-preventable viral diseases?

Answer 29

Hep B and A, influenza, measles, mumps, polio, rubella, rotavirus, HPV, shingles and chickenpox, rabies, yellow fever, Japanese encephalitis, small pox, adenovirus

Question 30

What are some remerging viral disease?

Answer 30

influenza, sin-nombre hanta virus, SARS, Ebolavirus

Question 31

what viruses are new to humans?

Answer 31

new influenza serogroups, SIV-like primate virus became HIV 1 and 2, Ebola

Question 32

How are new medical, cultural, agricultural practice results in new transmissions of virus?

Answer 32

west nile virus via birds to New York, global warning increased mosquito populations in temperate region of globe-> inc. dengue and chikungunya infections, and human transport via airplanes