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Viruses
Virus:
A non-cellular particle composed of genetic
material that can invade living cells.
– Viruses are considered by some to be nonliving since they lack metabolism and are not
made of cells.
• Are extremely small
• Are usually very specific as to what cells they can
invade
Structure of a Virus:
• Contain core of genetic information (either DNA or RNA).
• Genetic material surrounded by a protein coat called a
capsid.
Virus Shapes
Two Virus Cycles
Lytic & Lysogenic Cycles
Life Cycles of viruses
Lytic infection:
Infection: Virus identifies an
attaches itself to a host cell. The
genetic material is then injected
into the host cell.
– Growth: Genetic material of virus
overrides host cell's activities.
Cell is now instructed to replicate
viral genetic material and protein
coats.
– Lysis: Cell is lysed "broken open"
and new viruses are released to
infect other cells. This kills the
host cell
Life Cycles of viruses: Lysogenic infection
• Similar to lytic infection
however important
differences exist
– Instead of immediately
replicating, viral DNA
incorporates itself into the
host cell's DNA.
– Will remain dormant for
significant amounts of time.
– Give certain conditions, the
virus will enter it's lytic phase
similar to a normal lytic
infection
Retroviruses
• A new form of virus has been identified known as a
retrovirus.
– Retroviruses are RNA viruses which can conduct a process
known as Reverse Transcription
• In reverse transcription RNA is used to make DNA (the reverse of
the normal RNA transcription process).
– HIV is a retrovirus.
Viral Immunity
• Viruses are neutralized by special
chemical weapons called antibodies.
• Antibodies are specific to a single virus
strain.
• Once a virus has been encountered your
body can remember that virus and will
quickly produce more antibodies to
prevent a second infection.
• Immunizations/vaccination involves
injecting a killed or weakened virus into
your body. This tricks your body into
producing antibodies to the virus.
Therefore, when you come into contact
with the real virus, your body can prevent
an infection.
Antibodies attacking
a virus
Killer / Dangerous Viruses
HIV
•Human immunodeficiency virus (HIV) is a retrovirus that
can lead to acquired immunodeficiency syndrome (AIDS), a
condition in humans in which the immune system begins to
fail, leading to life-threatening opportunistic infections.
•Infection with HIV occurs by the transfer
of blood, semen, vaginal fluid, pre-ejaculate, or breast milk.
•The most common mode of transmission of HIV is
unprotected heterosexual sex.
HIV Contd.
•HIV infection in humans is now pandemic. As of 2006,
the Joint United Nations Program on HIV/AIDS and
the World Health Organization estimate that AIDS has killed
more than 25 million people since it was first recognized
in December 1, 1981, making it one of the most
destructive pandemics in recorded history
•HIV is believed to infect 90 million people in Africa,
resulting in a minimum estimate of 18 million orphans.
HIV Infection Rates: Global
HIV Infection Rates: Africa
Ebola / Marburg Viruses
Ebola is the common term for a group
of viruses belonging to genus Ebolavirus,
and for the disease which they
cause, Ebola hemorrhagic fever. The
virus is named after the Ebola
River where the first recognized
outbreak of ebola hemorrhagic fever
occurred. The viruses are characterized
by long filaments and have a similar
shape to the Marburg virus.. Since its
discovery, Ebolavirus has been
responsible for thousands of deaths.
Ebola Continued
•The virus is believed to be transmitted
to humans via contact with an infected
animal host. The virus is then
transmitted to other people who come
into contact with infected blood and
bodily fluids of the infected person
•Ebola hemorrhagic fever is potentially
lethal and encompasses a range of
symptoms
including fever, vomiting, diarrhea,
generalized pain or malaise, and
sometimes internal and external
bleeding. Mortality rates are extremely
high, with the human case-fatality rate
ranging from 70–95%, depending on
viral subtype.
Hanta Virus
Hantaviruses belong to
the Bunyaviridae family of viruses..
Viruses in the genus Hantavirus are
unique in that they are transmitted
by aerosolized rodent excreta or
rodent bites
Hantavirus pulmonary syndrome (HPS) is a deadly disease
transmitted by infected rodents through urine, droppings,
or saliva. Humans can contract the disease when they
breathe in aerosolized virus. HPS is potentially deadly.
Rodent control in and around the home remains the
primary strategy for preventing hantavirus infection.
Dengue
Dengue fever is caused by
four closely
related viruses of the
genus Flavivirus.
The geographical spread is
similar to malaria, but
unlike malaria, dengue is
often found in urban
areas. Dengue is
transmitted to humans by
the Tiger mosquito (Aedes
aegypti ).
Tiger Mosquito
Dengue & the Tiger Mosquito
Dengue Symptoms
Dengue is manifested by a sudden onset of with severe
headache, muscle and severe joint pains giving it the
name break-bone fever. There may also be gastritis with
some combination of associated abdominal
pain, nausea, vomiting or diarrhea.
Other symptoms include
•fever;
•chills;
•constant headaches;
•bleeding from nose, mouth or gums;
•severe dizziness; and,
•loss of appetite.