Download Microbiology: A Systems Approach, 2nd ed.

An Introduction to the Viruses
Non-Living Etiologies
Cytopathic effect (CPE) (or
Cytopathogenic effect) refers to
degenerative changes in cells,
associated with the multiplication of
certain viruses.
Thus identification of a viral
infection can be made by
examining the characteristic
cytopathic effect produced on
different cell sheets.
Influenza, commonly referred to
as the flu, is an infectious
disease caused by RNA viruses
of the family Orthomyxoviridae
(the influenza viruses), that
affects birds and mammals.
The name influenza is Italian and
means "influence" (Latin: influentia).
The most common symptoms of the
disease are chills, fever, sore throat,
muscle pains, severe headache,
coughing, weakness and general
Discomfort.
The 2009 flu pandemic is a global
outbreak of a new strain of influenza
A virus subtype H1N1, first identified
in April 2009, which is officially
termed novel H1N1 and commonly
called swine flu.
The virus is a mixing of four known
strains of influenza A virus: one
endemic in humans, one endemic in
birds, and two endemic in pigs
(swine).
Transmission of the new strain is
typically human-to-human; eating
cooked pork products will not
transmit the virus.
The reported mortality rate of
highly pathogenic H5N1 avian
influenza in a human is high;
WHO data indicates that 60% of
cases classified as H5N1 resulted
in death.
However, there is some evidence that
the actual mortality rate of avian flu
could be much lower, as there may
be many people with milder
symptoms who do not seek
treatment and are not counted.
Arbovirus is a shortened name given to
viruses that are transmitted by arthropods,
or arthropod-borne viruses.
Arthropods are able to transmit the virus
upon biting allowing the virus to enter the
bloodstream which can cause viraemia.
The majority of the Arboviruses are RNA
viruses.
Symptoms consist of a mild infection such
as a fever or a rash.
Others however are epidemic and can
cause serious infections such as meningitis
and encephalitis that can be fatal
WEE
EEE
VEE
St. Louis
West Nile
Dengue Fever
Dengue fever is an acute febrile
diseases, found in the tropics, and
caused by four closely related virus
serotypes of the genus Flavivirus,
family Flaviviridae.
Herpes simplex is a viral disease
caused by both herpes simplex virus
1 (HSV-1) and herpes simplex virus 2
HSV-2). Herpes viral disease caused by
varicella zoster virus.
Infection with the herpes virus is
categorized into one of several distinct
disorders based on the site of infection.
Oral Herpes, the visible symptoms of
which are colloquially called cold sores,
infects the face and mouth. Oral herpes is
the most common form of infection.
Genital herpes, commonly known simply as
Herpes, is the second most common form
of herpes
Common infection of the skin or
mucosa may affect the face and
mouth (orofacial herpes), genitalia
(genital herpes), or hands (herpes
whitlow).
More serious disorders occur when
the virus infects and damages the eye
(herpes keratitis), or invades the
central nervous system, damaging
the brain (herpes encephalitis).
The central nervous system is made
up of the brain and spinal cord. The
brain functions to receive nerve impulses
from the spinal cord and cranial nerves.
The spinal cord contains the nerves that
carry messages between the brain and the
body.
The rabies virus spreads through the
nerves of the brain and spinal cord first
causing flu-like symptoms such as fever
and malaise.
As the disease advances it causes anxiety,
confusion, brain dysfunction, progressing
to hallucinations, delirium, and insomnia.
If left untreated, rabies is nearly always
fatal.
The incubation period for Ebola Hemorrhagic
Fever ranges from 2 to 21 days.
The onset of illness is abrupt and is
characterized by fever, headache, joint and
muscle aches, sore throat, and weakness,
followed by diarrhea, vomiting, and
stomach pain.
A rash, red eyes, hiccups and internal and
external bleeding may be seen in some
patients.
Researchers do not understand why some
people are able to recover from Ebola HF
and others are not.
However, it is known that patients who die
usually have not developed a significant
immune response to the virus at the time of
death.
Smallpox is an infectious disease
unique to humans, caused by either
of two virus variants, Variola major
and Variola minor.
Smallpox localizes in small blood
vessels of the skin and in the mouth
and throat.
In the skin, this results in a
characteristic maculopapular rash, and
later, raised fluid-filled blisters. V.
major produces a more serious disease
and has an overall mortality rate of 30–
35%.
Acquired immune deficiency
Syndrome (AIDS) is a disease of the
human immune system caused by the
Human Immunodeficiency Virus (HIV).
HIV causes AIDS by depleting CD4+ T
helper lymphocytes. This weakens the
immune system and allows
opportunistic infections to manifest.
T lymphocytes are essential to the
immune response and without them, the
body cannot fight infections or kill
cancerous cells.
AIDS Diagnosis:
HIV positive
ARC (AIDS Relate Complex)
CD4+ T cell count below 200 per µL
In 1993, the CDC expanded their definition
of AIDS to include all HIV positive people
with a CD4+ T cell count below 200 per µL
of blood or 14% of all lymphocytes.
The AIDS diagnosis still stands even if,
after treatment, the CD4+ T cell count rises
to above 200 per µL of blood or other
AIDS-defining illnesses are cured.
Current treatment for HIV infection
consists of highly active antiretroviral
therapy, or HAART.
This has been highly beneficial to
many HIV-infected individuals since
its introduction in 1996 when the
protease inhibitor-based HAART
initially became available.
Current optimal HAART options
consist of combinations (or
"cocktails") consisting of at least
three drugs belonging to at least two
types, or "classes," of antiretroviral
agents.
Standard goals of HAART include
improvement in the patient’s quality
of life, reduction in complications,
and reduction of HIV viremia below
the limit of detection, but it does not
cure the patient of HIV nor does it
prevent the return, once treatment is
stopped, of high blood levels of HIV,
often HAART resistant.
Moreover, it would take more than
the lifetime of an individual to be
cleared of HIV infection using
HAART.
Despite this, many HIV-infected individuals
have experienced remarkable
improvements in their general health and
quality of life, which has led to the
plummeting of HIV-associated morbidity
and mortality.
A prion is an infectious agent that is
composed primarily of protein.
The protein itself does not self-replicate
and the process is dependent on the
presence of the polypeptide in the host
organism.
The prion protein has been implicated in a
number of diseases in a variety of
mammals, including bovine spongiform
Encephalopathy (BSE, also known as "mad
cow disease") in cattle and CreutzfeldtJakob disease (CJD) in humans.
All known prion diseases affect the
structure of the brain or other neural
tissue, and all are currently untreatable
and are always fatal.