Viruses
Viruses
• Viruses are very simple forms of life.
• There is open debate over whether they are
alive at all, since they do not feed, respire or
excrete waste.
• Remember MRS GREN
• Viruses are extremely efficient at
reproduction, multiplying rapidly in the right
conditions.
Virus Structure
• Viruses are extremely tiny, hundreds of times
smaller than a bacterium.
• They can only be seen using a powerful
electron microscope.
• Viruses come in many shapes:
– Rod
– Sphere
– Threads
– More complex forms
TMV – tobacco mosaic
virus
Spherical Virus
e.g. Influenza
Complex Viruses
e.g. T4 and HIV
Virus Structure
• Viruses are made of 2 parts:
– A piece of genetic material (DNA or RNA)
– A protein case
A Generalised Virus
Extensions – for
attachment to
cells
Protein Coat
Genetic Material
Reproduction
• Viruses use living cells from other organisms
such as plants and animals to reproduce.
• The genetic material from the virus enters a
living cell and makes copies of the virus.
• See diag.
Viral Diseases
• The organism / cell that the virus infects is
called the host.
• Because the host cells are always damaged by
viruses, all viruses are pathogenic.
Viral Diseases
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HIV - Human immunodeficiency virus
The common cold - rhinovirus
Measles - Rubeola
German Measles – Rubella virus
Polio - poliovirus
Flu – Influenza virus
Chicken pox - varicella
Mumps – mumps virus
Viral Diseases
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Hepatitis B – Hepatitis B Virus
Herpes – herpes virus
Ebola Hemorrhagic Fever - ebolavirus
Cervical cancer – Human Papilloma Virus
Gastroenteritis – norovirus
Rabies - rabdovirus
Ebola
• one of the most virulent viral diseases known
to humankind.
• Ebola virus was first identified in the western
equatorial province of Sudan and in a nearby
region of Zaire (now Democratic Republic of
the Congo) in 1976
• The Ebola virus is transmitted by direct
contact with the blood, body fluids and tissues
of infected persons.
Ebola
• Transmission of the Ebola virus has also
occurred by handling sick or dead infected
wild animals (chimpanzees, gorillas, monkeys,
forest antelope and fruit.
Ebola
• When a person becomes infected, the virus
begins to multiply within the body.
• After four to six days on average, Ebola
symptoms can begin.
• The period between infection with the virus
and the start of Ebola symptoms is called the
incubation period.
• The Ebola incubation period can be as short as
2 days or as long as 21 days.
Common Ebola Symptoms
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Fever
Sore Throat
Weakness
Severe headache
Joint and muscle aches
Diarrhea
Vomiting
Dehydration
Dry, hacking cough
Stomach pain.
Ebola
• A rash, red eyes, hiccups, and internal and
external bleeding may be seen in some patients.
When the rash develops on dark skin, it is often
not recognized until the rash begins to peel.
• In pregnant women, abortion (miscarriage) and
heavy vaginal bleeding are common Ebola
symptoms.
• Death usually occurs during the second week of
Ebola symptoms. Death in Ebola victims is usually
from massive blood loss.
HIV/ AIDS
• The first documented cases were in 1981,
when homosexual men with symptoms of a
disease that now are considered typical of
AIDS were first described in Los Angeles and
New York.
• The men had an unusual type of lung infection
called pneumonia (PCP) and rare skin tumors
called Kaposi's sarcomas.
HIV/ AIDS
• The patients were noted to have a severe
reduction in a type of cell in the blood that is an
important part of the immune system. These
cells, often referred to as T cells, help the body
fight infections.
• The time from HIV infection to the development
of AIDS varies. Rarely, some individuals develop
complications of HIV that define AIDS within one
year, while others remain completely
asymptomatic after as many as 20 years from the
time of infection.
HIV/ AIDS
• Within weeks of infection, many people will
develop the varied symptoms of primary
infection which typically have been described
as an "influenza" like illness but can range
from minimal fever, aches, and pains to very
severe symptoms. The most common
symptoms of primary HIV infection are:
– fever,
– aching muscles and joints,
– sore throat,
– and swollen glands (lymph nodes) in the neck.
HIV/ AIDS
• Shortly after primary infection, most
individuals enter a period of where they have
no symptoms at all. During this time, T cells
may gradually decline, and with this decline in
the immune system, patients may develop the
mild symptoms of HIV such as thrush (a fungal
infection), fungal infections of the nails, a
white brush-like border on the sides of tongue
called hairy leukoplakia, chronic rashes,
diarrhea, fatigue, and weight loss.
HIV/ AIDS
• This weakening of the immune system means
that the patient is prone to secondary
infections such as TB, Chronic diarrhea etc.
Viruses
• Viruses are not affected by antibiotics.
• Viruses can change their form rapidly, this is
why new diseases caused by viruses have
arisen.
– HIV in the early 1980s
– Ebola in the late 1980s
– influenza
Viruses
• Our immune system eventually fights off most
diseases caused by viruses.
Culturing Viruses
• Viruses can only be cultured inside living cells.
• Fertilised hen’s eggs are a suitable culture
medium.