RNA Viruses 2

Question 0

Rotavirus life cycle

Answer 0

RDRP in virion transcribes mRNA
After viral proteins translated, new virions and genome segments are synthesized in the cytoplasm
Virions assemble in viroplasm and the bud into rough ER
Egress via exocytosis, cell lysis
Virions mature in gut lumen and then infect more enterocytes or are shed in profuse diarrhea

Question 1

Rotavirus

Answer 1

Reovirus, dsRNA, segmented, naked icosahedron

Causes severe gastroenteritis

Affects infants and children, high incidence during winter

Diagnosis not required, treatment via oral rehydration solutions, prevented by live attenuated vaccines like Rotarix, Rotateq

Question 2

Influenza virus disease

Answer 2

Acute respiratory illness, winter

“Uncomplicated”: upper and lower respiratory tract fever, headache, myalgia, weakness

“Complicated”: primary pneumonia by influenza, secondary pneumonia by bacteria, myositis (pain) and rhabdomyelitis (breakdown)

Reassortment and mutation: different subtypes can have genetic shuffling, antigenic drift to create pandemic flu and different strains

Treatments/preventions: antiviral drugs, vaccines (Fluzone=trivalent inactivated, Flumist=live attenuated)

Question 3

Influenza life cycle

Answer 3

Genome segmented, (-) ssRNA

Genome segments traffic to NUCLEUS for transcription and replication by RDRP

Viral proteins and genome segments accumulate at plasma membrane

Virions assemble and egress by budding, shed in respiratory droplets

Question 4

Human immunodeficiency virus

Answer 4

Retrovirus: RNA to DNA

Stages: exposure (transmission), primary HIV infection (acute phase), seroconversion (when antibodies are detected), latent period, early symptomatic HIV infection, AIDs (CD4 cell count below 200), advanced HIV infection (CD4 cell count below 50)

Only humans infected, virus binds CD4 and chemokine receptors on T cells and macrophages and depletes them, chronic immune inactivation causes immunodeficiency and AIDs (opportunistic infections after loss of T cells)

Question 5

HIV diagnosis, prevention, treatment

Answer 5

Diagnosis:
PCR (serologic assays for antibodies, nucleic acid assays for viral load)
CD4 T cell count

Prevention: avoid risk, awareness, public health measures, antiviral drugs

Treatment: antiretroviral treatment (ART), drugs must be combined to avoid resistance
Goals are to suppress HIV, restore immune function, prevent transmission, prevent drug resistance, improve quality of life

Question 6

HIV life cycle

Answer 6

Virion binds CD4+ and chemokine coreceptors (from immune response) on cell surface
Mediates fusion, uncoating, reverse transcriptase (RT) in virion converts (+)ssRNA into dsDNA
Integrated into host chromosome for life
Host RNA polymerase II transcribes mRNA (also served as genome to be packaged in addition to for protein synthesis)
Viral proteins and genomes bud from plasma membrane
Virion maturation occurs outside cell when viral protease cleaves capsid proteins into final trapezoidal shape