Viral envelopes

• No defined shape• Derived from host cell

membranes– Intracellular membranes

(nuclear, ER)– Plasma membrane

• Contain viral glycoproteins (peplomers) necessary for entry into cells– Attachment proteins– Fusion proteins– Enzymes (Flu neuraminidase)– Host proteins (Mumps)

Examples of viral envelopes

EBV

RabiesCourtesy S.K. Vernon

WHRI, Wyeth-Ayerst Research, Radnor, Pa.

Influenza Courtesy Dr. L StannardUniv of Cape Town

HIV-1

PROPERTY NONENVELOPED VIRUSES ENVELOPED VIRUSES

Components Proteins Phospholipids, proteins, glycoproteins

Sensitivity to heat, acid, detergent, drying

Resistant (stable) Sensitive (labile)

Release from host cell Cell lysis Budding (cell survives) and lysis

Transmission Fomites, dust, fecal-oral, droplets

Droplets, secretions, organ or blood transplant

Effect of drying Retains infectivity Loses infectivity

Survival within GI tract Yes No ( except for rotavirus & enterovirus)

Host immune response Antibody response Antibody and cell-mediated responses (latter contributes to pathogenesis)

Adapted from Rapid Reviews Microbiology and Immunology, Table 18-1

(Naked viruses)