Can RNA (ribonucleic acid) viruses be enveloped?

RNA Viruses and Envelope Structure

Yes, RNA viruses can be enveloped, as evidenced by numerous examples including coronaviruses, influenza viruses, and flaviviruses. 1, 2

Types of Enveloped RNA Viruses

RNA viruses can be classified based on their genomic structure and the presence or absence of an envelope:

• Positive-sense single-stranded RNA (ssRNA+) enveloped viruses:

  • Coronaviruses (including SARS-CoV-2) 1, 2
  • Flaviviruses (including Yellow fever virus) 1
  • Togaviruses (including Sindbis virus) 1

• Negative-sense single-stranded RNA (ssRNA-) enveloped viruses:

  • Rhabdoviruses (including Vesicular stomatitis virus) 1
  • Respirovirus 1
  • Influenza viruses 3

• Double-stranded RNA (dsRNA) enveloped viruses:

  • Cystoviridae (including bacteriophage φ6) 1

Structure of Enveloped RNA Viruses

Enveloped RNA viruses possess distinctive structural characteristics:

• The viral envelope consists of a lipid bilayer derived from the host cell membrane 1
• Surface glycoproteins embedded in the envelope facilitate attachment to host cells 4
• The envelope surrounds the nucleocapsid, which contains the RNA genome 1
• In coronaviruses, the envelope contains spike (S) proteins, membrane (M) proteins, and envelope (E) proteins 1

Examples of Enveloped RNA Viruses

Several well-studied RNA viruses possess envelopes:

• SARS-CoV-2: An enveloped, positive-sense single-stranded RNA virus with a genome of approximately 30,000 nucleotides 1
• Vesicular stomatitis virus: An enveloped, negative-sense RNA virus with a bullet-shaped morphology, 180 nm long and 75 nm wide 1
• Yellow fever virus: An enveloped, positive-sense RNA virus with a spherical structure, approximately 50 nm in diameter 1
• Human Immunodeficiency Virus (HIV): An enveloped, positive-sense RNA virus 1

Non-Enveloped RNA Viruses

Not all RNA viruses possess envelopes. Examples of non-enveloped RNA viruses include:

• Picornaviridae (including Theilers' Murine encephalomyelitis virus) 1
• Caliciviridae (including Tulane virus) 1

Significance of the Envelope in Viral Pathogenesis

The envelope plays crucial roles in viral infectivity and susceptibility to environmental factors:

• Enveloped viruses typically use their surface proteins to bind to specific receptors on host cells 1
• The envelope facilitates viral entry through membrane fusion between the viral envelope and host cell membrane 4
• Enveloped viruses are generally more susceptible to disinfectants and environmental conditions than non-enveloped viruses 1
• The lipid envelope of RNA viruses like SARS-CoV-2 makes them vulnerable to oxidizing agents like ozone, which can damage the lipid membrane and associated proteins 1

Viral Budding and Envelope Acquisition

Enveloped RNA viruses acquire their lipid envelope through a budding process:

• During viral replication, viral components assemble at the host cell membrane 5
• The viral nucleocapsid pushes against the membrane, causing it to bulge outward 5
• As the virus buds from the cell, it becomes wrapped in a portion of the host cell membrane, which becomes the viral envelope 5
• Viral glycoproteins are incorporated into this envelope during the budding process 5

In summary, RNA viruses can indeed be enveloped, with numerous examples across different viral families. The envelope provides these viruses with specific mechanisms for host cell entry but also makes them more vulnerable to certain environmental conditions and disinfection methods 1.