Virology Quiz: COVID-19 and Norovirus

COVID-19

• COVID-19 is caused by SARS-CoV-2, a severe acute respiratory syndrome coronavirus 2.
• Its genome is single-stranded RNA, enveloped.
• Origins are unknown but likely not the seafood market, possibly animals like bats.
• It's genetically similar to other coronaviruses (SARS-CoV and MERS-CoV).
• The virus infects non-human primates and other animals.
• Genome encodes large proteins that are cleaved into non-structural proteins, crucial for transcription and replication.
• Transmission methods include airborne, transplacental (in some cases), ocular, fecal, and direct contact via fomites.
• Diagnosis involves repeated nucleic acid amplification tests (swabs), chest CT scans, and serologic antibody detection.

COVID-19 Components

• S protein is the viral spike protein of COVID-19.
• TMPRSS2 is a transmembrane protease serine protease 2, found in many tissues, often with ACE2.
• RdRp is the RNA-dependent RNA polymerase of COVID-19.
• 3CLpro is a 3C-like protease, a cysteine protease of COVID-19.
• Endosomes facilitate viral entry and release into host cells (other viruses sometimes enter this way).

COVID-19 Pathogenicity

• SARS-CoV-2 binds the angiotensin-converting enzyme 2 (ACE2) receptor in humans, pigs, ferrets, rhesus monkeys, civets, cats, and others.
• The 211-amino acid region RBD binds ACE2, facilitating virus entry.
• Viral replication in the respiratory tract epithelial cells triggers immune response (cytokine storm), leading to respiratory distress, failure, and eventually death if severe.
• Histopathology shows bilateral alveolar damage, desquamation of pneumocytes, fibrin deposits, and exudative inflammation.

COVID-19 Clinical Features

• Age is a major risk factor for severity of COVID-19.
• Most cases start with asymptomatic or mild disease (81%).
• Fever, fatigue and dry cough are typical symptoms.
• Ground-glass opacities and pneumonia can occur.
• Severe cases (14%) involve dyspnea, coexisting illnesses, and intensive care unit (ICU) need.
• Critical disease and death (5%) happen in cases with ARDS (acute respiratory distress syndrome), acute cardiac injury, and multi-organ failure. Incubation period is ~5 days. Typical symptom onset is ~8 days and critical/fatal cases will occur at ~16 days

COVID-19 Treatment

• Remdesivir inhibits the COVID-19 RdRp, preventing viral polypeptide proteolysis.
• Nirmatrelvir, in combination with ritonavir (Paxlovid), inhibits SARS-CoV-2 3CLpro cysteine protease and inhibits nirmatrelvir metabolism.

COVID-19 Prevention

• mRNA vaccines (Pfizer-BioNTech, mRNA-1273, Moderna) are available, using mRNA technology to encode COVID spike protein.
• mRNA vaccines are lipid nanoparticle-based and modified mRNA.
• Vaccines are devoid of preservatives, eggs, and latex.

Childhood Viruses

• Measles: Single-stranded, negative-sense RNA, enveloped, helical nucleocapsid, one serotype, spread by respiratory droplets. Symptoms include maculopapular rash and Koplik spots. Complications include encephalitis, deafness, and mental retardation, and increased risk of stillbirth in pregnancy. Live, attenuated vaccine available.
• Mumps: Single-stranded, negative-sense RNA, enveloped, helical nucleocapsid, single serotype, spread by respiratory droplets. Symptoms include salivary gland swelling (parotid gland). Complications include orchitis (in males), and typically benign meningitis, potentially leading to sterility if bilateral orchitis is severe. Live, attenuated vaccine available.
• Rubella: Single-stranded, positive-sense RNA, lipoprotein envelope, icosahedral nucleocapsid, spread by respiratory droplets and transplacentally. Features include maculopapular rash. Complications include intrauterine growth retardation, hepatosplenomegaly, congenital heart defects (patent ductus arteriosis, pulmonary stenosis), cataracts, sensorineural hearing loss, thrombocytopenic purpura, and mental retardation. Live, attenuated vaccine available.
• Parvovirus B19: Small, nonenveloped, single-stranded DNA, negative-strand, icosahedral nucleocapsid, one serotype, respiratory route or transplacental. Features include erythema infectiosum ("fifth disease"), slapped cheek syndrome, and aplastic anemia. Symptoms can vary in severity from asymptomatic to potentially serious outcomes like hydrops fetalis (severe fetal edema). No antiviral treatment.
• Human Herpesvirus 6: High fever and rapid-onset rash. Infection of B & T cells, often latent, potential for complicated in immunocompromised patients (pneumonia, hepatitis, encephalitis). May be transmitted via saliva, nasal secretions, or sexual contact. No antiviral treatment for immunocompetent patients.

Enteric Tract Viruses

• Norovirus: Nonenveloped, single-stranded RNA, fecal-oral transmission, watery diarrhea, vomiting, headaches, typically mild, not entirely understood mechanism, resistant to desiccation, chlorination.
• Rotavirus: Double-stranded RNA, usually causing severe diarrhea in infants and young children. Fecal-oral transmission. Vaccination available (Rotarix, RotaTeq).
• Poliovirus: Single-stranded RNA, causing paralysis and death in cases of poliomyelitis. Fecal-oral transmission. Vaccination available.
• Coxsackievirus: Single-stranded RNA, causing hand-foot-and-mouth disease, hemorrhagic conjunctivitis, meningitis (multiple serotypes). Fecal-oral transmission. No specific antiviral treatment.
• Echovirus: Single-stranded RNA, often causing meningitis, aseptic meningitis. Fecal-oral transmission. No specific antiviral treatment.