Section I. VIROLOGY
STRUCTURE OF A VIRUS
A virus is an intracellular parasite that will develop both acute and chronic
infections that may or may not lead to host cell transformation and malignancy. The
structure of a virus consists of a core, a capsid, and an envelope. The core consists
mainly of a nucleic acid, either DNA or RNA, never both together. The capsid is a
protective protein coat around the core. It is constructed of individual subunits termed
capsomers. The envelope is a lipid outer covering; it may or may not be present
depending on the virus.
CLASSIFICATION OF VIRUSES
Viruses are classified by the following properties: morphology, structure, and
cytopathic effects in cell cultures.
Section II. HUMAN IMMUNODEFICIENCY VIRUS
HISTORY OF HUMAN IMMUNODEFICIENCY VIRUS
Acquired Human Immunodeficiency Virus (HIV) [immunodeficiency syndrome (AIDS)] is
a new disease entity that was first recognized in the late 1970's. The origin of the virus is unclear.
Epidemiological data and serological data suggest that the viral infection began in Central Africa.
The virus that causes AIDS belongs to a unique class of viruses distinguished by
the presence of an enzyme that catalyzes the formation of DNA from RNA. The
catalyzing enzyme is a reverse transcriptase; viruses that contain it are called
retroviruses. Human Immunodeficiency Virus (HIV) is a cytopathic retrovirus that appears to
be genetically related to some of the other cytopathic retroviruses, such as visna virus, which
causes a dementing disease in sheep.