2-11 RNA Viruses II

Question 1

What are the clinical features of rotavirus?

Answer 1

• Reovirus, dsRNA, segmented, naked icosahedron
• Causes severe gastroenteritis: profuse watery diarrhea, dehydration, maladsorption
• Infants and children (adults usu. asymptomatic)
• >600,000 deaths/yr, mostly in developing world
• Peak incidence during winter

Question 2

What is the life cycle of rotavirus?

Answer 2

• Genome is segmented, one gene each
• RDRP in the virion first transcribes mRNA
• Viral proteins are translated
• New virions and genome segments are synthesized in cytoplasm
• Virions assemble, bud into the rough ER
• Egress via exocytosis/cell lysis
• Virions mature in gut lumen, then infect more enterocytes or are shed in profuse diarrhea

Question 3

What are the clinical features of influenza virus?

Answer 3

• Orthomyxovirus, (-) ssRNA, segmented, enveloped
• Acute respiratory illness; mainly wintertime
• “Uncomplicated”: upper and/or lower respiratory tract involvement, fever, headache, myalgia, weakness
• “Complicated”: 1° pneumonia caused by influenza, 2° bacterial pneumonia, mixed viral and bacterial pneumonia, muscle pain (myositis) and breakdown (rhabdomyelitis)

Question 4

What is the life cycle of influenza virus?

Answer 4

• Genome is segmented, (-) ssRNA
• Genome segments traffic to nucleus for transcription and replication by RDRP
• Viral proteins and genome segments accumulate at the plasma membrane
• Virions assemble and egress by budding
• Neuraminidase (N antigen) releases virions from sialic acid on cell surface
• Virions are shed in respiratory droplets (coughs and sneezes)

Question 5

What are the clinical features of HIV?

Answer 5

• Retrovirus, (+) ssRNA, 2 copies, enveloped
• Only humans infected
• Virus binds to CD4 and chemokine receptors on T cells and macrophages
• Depletion of these cells + chronic immune activation → immunodeficiency
• Symptoms include: fever, weight loss, headache, oral sores and thrust, lymphadenopathy, myalgia, rash, hepatosplenomegaly, nausea/vomiting

Question 6

What are the stages of HIV disease?

Answer 6

• Exposure to virus (transmission)
• Primary HIV infection (acute phase)
• Seroconversion
• Latent period
• Early symptomatic HIV infection
• AIDS (CD4 cell count below 200/mm³)
• Advanced HIV infection (CD4 cell count below 50/mm³)

Question 7

What is the life cycle of HIV?

Answer 7

• Virion fuses with the plasma membrane
• Reverse Transcriptase enzyme (RT, included in the virion): (+) ssRNA genomes → dsDNA
• dsDNA genomes integrate into the host chromosome for life
• Host RNA Pol II transcribes mRNA from the integrated genome, which also serves as the genome that is packaged into new virions
• Viral proteins + 2 genomes bud from the plasma membrane
• Viral protease cleaves the capsid proteins, forming the final trapezoidal shape
• Virion maturation occurs outside the cell

Question 8

What are the main symptoms of AIDS?

Answer 8

Question 9

What types of HIV drugs are there?

Answer 9

• Nucleoside reverse transcriptase inhibitors (NRTIs)
• Non-nucleoside reverse transcriptase inhibitors (NNRTIs)
• Protease inhibitors (PIs)
• Integrase strand transfer inhibitors (INSTIs)
• CCR5 antagonists

Question 10

What are the goals of HIV treatment?

Answer 10

• Durable suppression of HIV viral load
• Restoration of immune function
• Prevention of HIV transmission
• Prevention of drug resistance
• Improvement in quality of life