9.2 Picornaviruses and coronaviruses

Picornaviruses and coronaviruses are two important families of RNA viruses that cause a range of human diseases. From the common cold to global pandemics, these viruses have significant impacts on public health and society.

Their distinct structures and replication mechanisms lead to diverse clinical outcomes. Understanding their biology, epidemiology, and management strategies is crucial for effective disease control and future pandemic preparedness.

Picornavirus and Coronavirus Structure

Structural Characteristics

Top images from around the web for Structural Characteristics

• 

  Frontiers | Toward Understanding Molecular Bases for Biological Diversification of Human ... View original

  Is this image relevant?

• 

  Frontiers | Evolutionary and Structural Overview of Human Picornavirus Capsid Antibody Evasion View original

  Is this image relevant?

• 

  Frontiers | Scrutinizing Coronaviruses Using Publicly Available Bioinformatic Tools: The Viral ... View original

  Is this image relevant?

• 

  Frontiers | Toward Understanding Molecular Bases for Biological Diversification of Human ... View original

  Is this image relevant?

• 

  Frontiers | Evolutionary and Structural Overview of Human Picornavirus Capsid Antibody Evasion View original

  Is this image relevant?

1 of 3

Top images from around the web for Structural Characteristics

• 

  Frontiers | Toward Understanding Molecular Bases for Biological Diversification of Human ... View original

  Is this image relevant?

• 

  Frontiers | Evolutionary and Structural Overview of Human Picornavirus Capsid Antibody Evasion View original

  Is this image relevant?

• 

  Frontiers | Scrutinizing Coronaviruses Using Publicly Available Bioinformatic Tools: The Viral ... View original

  Is this image relevant?

• 

  Frontiers | Toward Understanding Molecular Bases for Biological Diversification of Human ... View original

  Is this image relevant?

• 

  Frontiers | Evolutionary and Structural Overview of Human Picornavirus Capsid Antibody Evasion View original

  Is this image relevant?

1 of 3

• Picornaviruses consist of small, non-enveloped viruses with positive-sense, single-stranded RNA genome
  • Size ranges from 22-30 nm in diameter
  • Genome length approximately 7.2-8.4 kb
• Coronaviruses comprise larger, enveloped viruses with positive-sense, single-stranded RNA genome
  • Size ranges from 80-120 nm in diameter
  • Genome length approximately 26-32 kb (largest among RNA viruses)
• Picornavirus capsid exhibits icosahedral symmetry composed of four structural proteins (VP1-VP4)
  • VP1, VP2, and VP3 form the outer surface
  • VP4 located internally, interacts with the RNA genome
• Coronavirus envelope contains spike (S), envelope (E), and membrane (M) proteins
  • S protein forms distinctive crown-like appearance (corona)
  • Helical nucleocapsid encases the RNA genome

Replication Mechanisms

• Picornavirus replication occurs entirely in the cytoplasm
  • Involves formation of a single polyprotein cleaved into functional proteins
  • Utilizes internal ribosome entry site (IRES) for cap-independent translation initiation
• Coronavirus replication produces nested sets of subgenomic mRNAs
  • Employs cap-independent translational enhancer (CITE) for translation initiation
  • Replication complex associates with double-membrane vesicles

Pathogenesis and Infection Outcomes

• Picornaviruses typically cause lytic infections leading to cell death
  • Enter host cells through specific receptors (ICAM-1 for rhinoviruses)
  • Rapid replication cycle (6-8 hours) results in cell lysis and virus release
• Coronaviruses induce both lytic and persistent infections
  • Entry mediated by S protein binding to host cell receptors (ACE2 for SARS-CoV-2)
  • Can establish persistent infections in certain cell types (neurons, kidney cells)
• Picornavirus pathogenesis often involves entry through gastrointestinal or respiratory tract
  • Local replication followed by potential systemic spread (enteroviruses)
  • Neurotropic strains (poliovirus) can invade the central nervous system
• Coronavirus pathogenesis frequently involves respiratory tract infection
  • Can lead to severe inflammatory responses (cytokine storm in COVID-19)
  • Some strains (SARS-CoV-2) can affect multiple organ systems

Picornavirus Infections: Clinical Manifestations and Epidemiology

Poliovirus Infection

• Infection ranges from asymptomatic to severe, potentially causing acute flaccid paralysis
  • Approximately 72% of infections asymptomatic
  • 24% result in minor illness (fever, sore throat, malaise)
  • Less than 1% develop paralytic poliomyelitis
• Global eradication effort significantly reduced incidence
  • Wild poliovirus remains endemic in only a few countries (Afghanistan, Pakistan)
  • Vaccine-derived poliovirus outbreaks occur in areas with low vaccination coverage

Rhinovirus and Enterovirus Infections

• Rhinoviruses serve as primary cause of the common cold
  • Result in upper respiratory tract symptoms (nasal congestion, sore throat, cough)
  • Highly contagious with seasonal patterns, peaking in spring and fall in temperate climates
• Enteroviruses cause wide range of clinical manifestations
  • Hand, foot, and mouth disease common in young children
  • Myocarditis affects heart muscle, leading to inflammation and potential heart failure
  • Aseptic meningitis presents with fever, headache, and neck stiffness
• Coxsackieviruses, a subgroup of enteroviruses, induce various syndromes
  • Herpangina characterized by painful mouth ulcers and fever
  • Pleurodynia (Bornholm disease) causes sharp chest pain and fever
  • Exhibit seasonal pattern with increased incidence in summer and early fall

Epidemiological Factors and Surveillance

• Picornavirus infection epidemiology influenced by multiple factors
  • Population density affects transmission rates (higher in urban areas)
  • Hygiene practices impact spread (hand washing reduces transmission)
  • Environmental conditions affect virus survival (enteroviruses stable in water)
• Higher prevalence observed in children and immunocompromised individuals
  • Developing immune systems more susceptible to infection
  • Immunosuppression increases risk of severe or prolonged infections
• Molecular epidemiology techniques crucial for tracking spread and evolution
  • Genomic sequencing allows identification of specific strains and lineages
  • Phylogenetic analysis reveals transmission patterns and emerging variants
  • Informs public health interventions and vaccine development strategies

Coronavirus Infections: Global Impact

SARS and MERS Outbreaks

• Severe Acute Respiratory Syndrome (SARS) emerged in 2002-2003
  • Caused global outbreak with over 8,000 cases and 774 deaths
  • Demonstrated potential for rapid international spread of novel coronaviruses
  • Originated in bats, with civet cats as intermediate hosts
• Middle East Respiratory Syndrome (MERS) first identified in 2012
  • Continues to cause sporadic outbreaks, primarily in Arabian Peninsula
  • High case fatality rate (approximately 35%) but limited human-to-human transmission
  • Dromedary camels serve as primary reservoir

COVID-19 Pandemic

• SARS-CoV-2 infection resulted in millions of infections and deaths worldwide
  • Over 500 million confirmed cases and 6 million deaths as of 2022
  • Led to unprecedented global health, economic, and social disruptions
  • Rapid development and deployment of vaccines (mRNA, viral vector)
• Highlighted importance of zoonotic disease surveillance and rapid response systems
  • Enhanced global disease monitoring networks
  • Accelerated development of diagnostic technologies (rapid antigen tests)
• Economic impact includes direct healthcare costs and productivity losses
  • Global GDP contracted by 3.1% in 2020 due to pandemic
  • Disruptions to global trade and travel (airline industry losses exceeded $370 billion in 2020)

Research and Social Impact

• Accelerated research in virology, immunology, and vaccine development
  • mRNA vaccine technology advanced rapidly
  • Improved viral detection methods (RT-LAMP, CRISPR-based diagnostics)
• Social impact includes changes in public health practices and societal behaviors
  • Increased awareness of infectious diseases and prevention measures
  • Shifts in work patterns (remote work, hybrid models)
  • Changes in social interactions and norms (mask-wearing, social distancing)

Picornavirus and Coronavirus Management

Diagnostic Approaches

• Molecular techniques include RT-PCR and antigen detection assays
  • RT-PCR detects viral RNA with high sensitivity and specificity
  • Rapid antigen tests provide quick results for point-of-care testing
• Serological tests measure antibody responses to infection
  • IgM antibodies indicate recent or current infection
  • IgG antibodies suggest past infection or vaccination
• Rapid diagnostic tests crucial for timely identification and containment
  • Multiplex PCR panels detect multiple respiratory pathogens simultaneously
  • Loop-mediated isothermal amplification (LAMP) offers faster results than traditional PCR

Treatment Strategies

• Picornavirus infections primarily managed with supportive care
  • Hydration, antipyretics, and analgesics alleviate symptoms
  • Limited antiviral options available (pleconaril for enterovirus infections)
• Coronavirus infections treated with antivirals and immunomodulatory therapies
  • Remdesivir inhibits viral RNA-dependent RNA polymerase
  • Dexamethasone reduces inflammation in severe COVID-19 cases
• Ongoing research focuses on identifying new therapeutic targets
  • Protease inhibitors (nirmatrelvir) show promise for SARS-CoV-2
  • Monoclonal antibodies provide passive immunity for high-risk patients

Prevention and Control Measures

• Vaccination serves as key preventive strategy for both virus families
  • Inactivated and live-attenuated poliovirus vaccines crucial in global eradication effort
  • Multiple COVID-19 vaccine platforms developed (mRNA, viral vector, protein subunit)
• Non-pharmaceutical interventions play significant role in preventing spread
  • Hand hygiene reduces transmission of both picornaviruses and coronaviruses
  • Respiratory etiquette and social distancing limit airborne spread
• Surveillance systems and early warning networks essential for outbreak detection
  • Integrate clinical, laboratory, and epidemiological data
  • Guide public health actions and resource allocation
• Research into broad-spectrum antivirals and universal vaccines ongoing
  • Aim to improve preparedness for future outbreaks and pandemics
  • Focus on conserved viral targets to provide protection against multiple strains