Viruses are not cells. They do not have a nucleus or other organelles that
are associated with cells. They have no metabolism and are considered
genetic parasites in that they use the host cell for but one purpose—to
replicate their genetic material and produce progeny virions (infectious
viral particles). The effect on the host cell, which can range from no
effect, to a disruption in cellular function, to killing of the host cell,
is related to the disease state caused by the infecting virus.

The structural organization and morphology of viruses vary. Basically they
are composed of a protein, called the capsid, that surrounds their genetic
material—nucleic acid of either DNA or RNA. Together this structure is
called the nucleocapsid. In addition, some viruses have an outermost
covering called the envelop that is added to the virus as the virus buds
from the host cell. Thus, this structure is of host cell origin. The lipid
composition of this envelop is identical to the host cell membrane; it may
carry some of the host cell membrane proteins as well. The virus can add
its’ own proteins to this envelop. An example of such an enveloped virus is
HIV.

The size of animal viruses range from a diameter of approximately 20
nanometers (nm = 10- 9 meters) for Parvoviruses to approximately 200nm for
Poxviruses. The diameter of animal cell is approximately 0.01mm (millimeter=
10 – 3 meters).

The highest taxonomic grouping for viruses is the Family with subdivision
into subfamilies, genera, species, and strains or serotypes.

In humans, viruses can cause a variety of diseases and have been associated
with some cancers; cervical cancer, some lymphomas, and T-cell leukemias.
Some viruses can be introduced into human population from other animals
resulting in serious and sometimes fatal disease; the flu virus from birds
and pigs, HIV from some primates and the West Nile Virus from birds via the
mosquito for example. In the case of the West Nile, the virus is responsible
for the recent outbreaks of a sometimes lethal encephalitis along the east
coast, from Massachusetts to Maryland; introduced into Queens New York from
Israel.

An otherwise benign virus, in its’ particular host species, when introduced
into another species can be carcinogenic or result in a disease previously
not found in the new host. This reservoir of potentially infectious and
deadly pathogens represents a serious health threat in an era when every
household has its’ “pet”…from the traditional cat or dog to exotic “pet”
primates, birds, and pigs…etc. These animals are moving into this country
without the proper enforcement of health and regulatory standards
representing a threat to the health of susceptible Americans.

A virus is either benign or pathogenic..none have been found, to date, to be
beneficial…excepting those used as vectors in Gene Therapy.