Webster's New World Medical Dictionary

viral
Of or pertaining to a virus. For example, if a
person has a viral rash, the rash was caused by a
virus.
viral hepatitis
See 
hepatitis, viral.
viral infection
An infection caused by the pres-
ence of a virus in the body. Depending on the virus
and the person’s state of health, various viruses can
infect almost any type of body tissue, from the brain
to the skin. Viral infections cannot be treated with
antibiotics; in fact, in some cases the use of antibi-
otics makes a viral infection worse. The vast major-
ity of human viral infections can be effectively fought
by the body’s own immune system, with help from
proper diet, hydration, and rest. Treatment of other
viral infections depends on the type and location of
the virus and may include use of antiviral or other
drugs.
viremia
The presence of a virus in the blood.
Viremia is analogous to bacteremia (the presence of
bacteria in the blood) and parasitemia (the pres-
ence of a parasite in the blood). Viremia, bac-
teremia, and parasitemia are all forms of sepsis
(bloodstream infection).
451
viremia
23_189283 ch22.qxp 4/18/08 10:19 PM Page 451
http://www.rashidislamiccenter.com
http://www.allofislam.com/

---

virion
A virus particle.
virology
The study of viruses.
virulence
The ability of an agent of infection to
produce disease. The virulence of a microorganism
is a measure of the severity of the disease it causes.
virulent
Extremely noxious, damaging, deleteri-
ous, and disease causing (pathogenic); marked by
a rapid, severe, and malignant course; poisonous.
virus
A microorganism that is smaller than a bac-
terium that cannot grow or reproduce apart from a
living cell. A virus invades living cells and uses their
chemical machinery to keep itself alive and to repli-
cate itself. It may reproduce with fidelity or with
errors (mutations); this ability to mutate is respon-
sible for the ability of some viruses to change
slightly in each infected person, making treatment
difficult. Viruses cause many common human infec-
tions and are also responsible for a number of rare
diseases. Examples of viral illnesses range from the
common cold, which can be caused by one of the
rhinoviruses, to AIDS, which is caused by HIV.
Viruses may contain either DNA or RNA as their
genetic material. Herpes simplex virus and the hep-
atitis B virus are DNA viruses. RNA viruses have an
enzyme called reverse transcriptase that permits the
usual sequence of DNA-to-RNA to be reversed so
that the virus can make a DNA version of itself. 
RNA viruses include HIV and hepatitis C virus.
Researchers have grouped viruses together into sev-
eral major families, based on their shape, behavior,
and other characteristics. These include the herpes-
viruses, adenoviruses, papovaviruses (including 
the papillomaviruses), hepadnaviruses, poxviruses,
and parvoviruses, among the DNA viruses. On the
RNA virus side, major families include the picorna-
viruses (including the rhinoviruses), calciviruses,
paramyxoviruses, orthomyxoviruses, rhabdoviruses,
filoviruses, and retroviruses. There are dozens 
of smaller virus families within these major classifi-
cations. Many viruses are host specific, capable of
infecting and causing disease in humans or specific
animals only.