9.1 Orthomyxoviruses and paramyxoviruses

RNA viruses are sneaky shape-shifters. Orthomyxoviruses and paramyxoviruses, two key families, cause widespread infections like flu and measles. They differ in genome structure and replication sites, but both use surface proteins to invade cells.

These viruses spread easily, causing seasonal outbreaks and occasional pandemics. Vaccines are our main defense, but viral mutations pose ongoing challenges. Public health measures and global surveillance are crucial to stay ahead of these evolving threats.

Orthomyxoviruses vs Paramyxoviruses

Structural and Genomic Differences

Top images from around the web for Structural and Genomic Differences

• 

  Measles in the Brain: Fusion Gone Awry - Watching the Watchers View original

  Is this image relevant?

• 

  Frontiers | Control of Plant Viruses by CRISPR/Cas System-Mediated Adaptive Immunity View original

  Is this image relevant?

• 

  Frontiers | The paramyxovirus polymerase complex as a target for next-generation anti ... View original

  Is this image relevant?

• 

  Measles in the Brain: Fusion Gone Awry - Watching the Watchers View original

  Is this image relevant?

• 

  Frontiers | Control of Plant Viruses by CRISPR/Cas System-Mediated Adaptive Immunity View original

  Is this image relevant?

1 of 3

Top images from around the web for Structural and Genomic Differences

• 

  Measles in the Brain: Fusion Gone Awry - Watching the Watchers View original

  Is this image relevant?

• 

  Frontiers | Control of Plant Viruses by CRISPR/Cas System-Mediated Adaptive Immunity View original

  Is this image relevant?

• 

  Frontiers | The paramyxovirus polymerase complex as a target for next-generation anti ... View original

  Is this image relevant?

• 

  Measles in the Brain: Fusion Gone Awry - Watching the Watchers View original

  Is this image relevant?

• 

  Frontiers | Control of Plant Viruses by CRISPR/Cas System-Mediated Adaptive Immunity View original

  Is this image relevant?

1 of 3

• Orthomyxoviruses and paramyxoviruses possess enveloped, negative-sense RNA genomes
  • Orthomyxoviruses feature segmented genomes
  • Paramyxoviruses contain non-segmented genomes
• Viral envelopes of both families display glycoprotein spikes
  • Orthomyxoviruses exhibit hemagglutinin (HA) and neuraminidase (NA) (influenza virus)
  • Paramyxoviruses present fusion (F) and attachment proteins (HN, H, or G) (measles virus)
• Replication sites differ between families
  • Orthomyxoviruses replicate in the host cell nucleus
  • Paramyxoviruses replicate entirely in the host cell cytoplasm

Replication and Pathogenesis Mechanisms

• Orthomyxoviruses employ cap-snatching from host mRNAs during replication
• Paramyxoviruses utilize a stuttering mechanism for mRNA editing
• Both families use surface glycoproteins for host cell attachment and entry
  • Fusion mechanisms vary between the two families
• Pathogenesis targets different body systems
  • Orthomyxoviruses primarily affect the respiratory tract (influenza)
  • Paramyxoviruses cause respiratory, systemic, or neurological infections (measles, mumps)

Epidemiology of Common Viral Infections

Influenza and Measles Characteristics

• Influenza (orthomyxovirus) occurs in seasonal epidemics and occasional pandemics
  • Rapid global spread results from high transmissibility
  • Antigenic changes contribute to virus evolution
• Measles (paramyxovirus) demonstrates high contagiousness
  • Severe complications arise in undernourished children and immunocompromised individuals
  • Outbreaks often occur in densely populated areas (schools, refugee camps)

Mumps and Respiratory Syncytial Virus (RSV) Features

• Mumps (paramyxovirus) typically affects salivary glands
  • Can cause orchitis, oophoritis, and meningitis
  • Outbreaks frequently occur in close-contact settings (dormitories, sports teams)
• RSV (paramyxovirus) leads lower respiratory tract infections in young children
  • Potential for severe bronchiolitis and pneumonia in infants
  • Seasonal patterns vary by geographic location

Epidemiological Patterns and Clinical Manifestations

• Incubation periods vary among viruses
  • Influenza: 1-4 days
  • Measles: 7-14 days
  • Mumps: 16-18 days
  • RSV: 2-8 days
• Modes of transmission differ
  • Respiratory droplets (all four viruses)
  • Direct contact with infected secretions (RSV)
• Duration of infectivity impacts control strategies
  • Influenza: 1 day before symptoms to 5-7 days after onset
  • Measles: 4 days before rash to 4 days after rash onset
• Clinical manifestations range from mild to severe
  • Influenza and RSV: mild respiratory symptoms to pneumonia
  • Measles: characteristic rash, fever, cough
  • Mumps: swollen salivary glands, fever, headache

Prevention and Control Strategies

Vaccination and Antiviral Treatments

• Vaccination serves as primary prevention strategy
  • Annual influenza vaccines target predicted strains
  • Combination MMR (measles, mumps, rubella) vaccine provides long-term immunity
  • RSV vaccines under development for various age groups
• Antiviral drugs play dual roles in treatment and prophylaxis
  • Neuraminidase inhibitors (oseltamivir) for influenza
  • No specific antivirals for measles, mumps, or RSV
• Passive immunization with monoclonal antibodies prevents RSV in high-risk infants (palivizumab)

Public Health Measures and Surveillance

• Implement isolation of infected individuals to prevent transmission
• Conduct contact tracing to identify potential cases
• Promote hygiene practices (hand washing, respiratory etiquette)
• Utilize global surveillance networks
  • WHO Global Influenza Surveillance and Response System monitors virus evolution
  • Guides vaccine development and strain selection
• Aim for herd immunity through vaccination
  • Particularly important for measles and mumps prevention
  • Requires high vaccination coverage (95% for measles)

Challenges in Prevention and Control

• Viral mutation rates challenge vaccine effectiveness
  • Influenza requires annual vaccine updates
  • Potential for vaccine mismatch with circulating strains
• Vaccine hesitancy impacts population-level protection
  • Misinformation and distrust in medical authorities
  • Resurgence of measles outbreaks in areas with low vaccination rates
• Emergence of new viral strains poses ongoing threats
  • Zoonotic spillover events (influenza from avian or swine sources)
  • Need for rapid response and vaccine development capabilities

Antigenic Drift and Shift in Influenza

Mechanisms of Antigenic Change

• Antigenic drift involves gradual accumulation of point mutations
  • Affects hemagglutinin (HA) and neuraminidase (NA) genes
  • Results in seasonal influenza epidemics
  • Necessitates annual vaccine updates
• Antigenic shift occurs through genetic reassortment
  • Different influenza A subtypes exchange genome segments
  • Produces novel strains with pandemic potential
  • Facilitated by segmented genome structure

Pandemic Potential and Surveillance

• Pandemic influenza strains arise from antigenic shift events
  • Introduce viral subtypes with little human population immunity
  • Historical examples: 1918 Spanish flu (H1N1), 2009 swine flu (H1N1pdm09)
• Animal reservoirs play crucial roles in new strain emergence
  • Birds and swine serve as mixing vessels for influenza viruses
  • Interspecies transmission leads to novel human-infecting strains
• Global surveillance monitors antigenic changes
  • Predicts vaccine effectiveness for upcoming seasons
  • Identifies potential pandemic threats
  • Informs public health preparedness and response strategies

Implications for Vaccine Development and Control

• Rapid evolution challenges vaccine development timelines
  • 6-8 month lead time for current egg-based production
  • Efforts to develop universal influenza vaccines targeting conserved viral regions
• Antiviral drug efficacy affected by viral mutations
  • Emergence of resistant strains necessitates new drug development
  • Combination therapies may reduce resistance development
• Continuous research and adaptation of control strategies required
  • Improved surveillance techniques (next-generation sequencing)
  • Development of platform technologies for rapid vaccine production
  • Enhancement of global coordination for pandemic preparedness