Viruses are infectious intracellular obligate parasites consisting of nucleic acid (RNA or DNA) enclosed in a protein coat called capsid
In some cases, a membranous envelope may be present outer to the capsid
Viruses are classified based on the presence or absence of this envelope around the protein coat
1. Enveloped viruses eg: Herpes simplex, Chickenpox virus, Influenza virus etc
2. Non-enveloped viruses eg: Adeno virus, parvovirus etc
Characteristics of viral envelope
Made of lipid and proteins rarely glycoprotein
May be modified host plasma membrane or internal membranes
Projections from the envelope are known as spikes or peplomers
Function: attachment of the virus to the host cell.
HIV virus uses its spikes for this purpose.
Non enveloped viruses:
Non enveloped viruses - Adeno virus
1. The outermost covering is the capsid made up of proteins
2. Non enveloped viruses are more virulent and causes host cell lysis
3. These viruses are resistant to heat, acids, and drying
4. It can survive inside gastrointestinal tract
5. It can retain its infectivity even after drying
6. It will induce antibody production in the host
7. Mode of transmission is through fecal or oral matter, formites and dust
Enveloped viruses
Enveloped viruses - Influenza virus
1. The outermost envelope is made up of phospholipids, proteins or glycoprotein which surround the capsid
2. Enveloped viruses are less virulent often released by budding and rarely cause host cell lysis
3. Are sensitive to heat, acids, and drying
4. Generally it cannot survive inside gastrointestinal tract
5. It lose its infectivity on drying
6. It will induce both cell mediated and antibody mediated immune response in the host
7. Mode of transmission is through blood or organ transplants or through secretions