Download PowerPoint Presentation - Introduction to viruses

Virus Tissue Tropism
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Targeting of the virus to specific tissue
and cell types
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Receptor Recognition
 CD4+ cells infected by HIV
 CD155 acts as the receptor for
poliovirus
DNA Viruses
• Herpesviridae
• Poxviridae
Herpesviridae
• Causes diseases in animals
• The family name is derived from the
Greek word herpein ("to creep"),
referring to the latent, recurring
infections typical of this group of
viruses. (Can cause lytic or latent
infections)
• Causes diseases in animals
• The family name is derived from the
Greek word herpein ("to creep"),
referring to the latent, recurring
infections typical of this group of
viruses. (Can cause lytic or latent
infections)
• More than 90% of adults have been
infected with at least one of these, and a
latent form of the virus remains in most
people.
• All herpesviruses are enveloped viruses
composed of relatively large doublestranded, linear DNA encoding 100-200
genes encased within an icosahedral
capsid.
Poxviridae
• Causes diseases in vertebrates and
invertebrates
• Causes diseases in vertebrates and
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invertebrates
Five species of Herpesviridae –
 HSV-1 and HSV-2 (both of which can
cause orolabial herpes and genital
herpes),
 Varicella zoster virus (which causes
chicken-pox and shingles),
 Epstein-Barr virus (which causes
mononucleosis)
 Cytomegalovirus
Smallpox
• Variola is a large brick-shaped virus
measuring approximately 302 to 350 nm
by 244 to 270 nm, with a single linear ds
DNA of 186 (kbp) in size.
• The life cycle of poxviruses is
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complicated by having multiple
infectious forms, with differing
mechanisms of cell entry.
Poxviruses are unique among DNA
viruses in that they replicate in the
cytoplasm of the cell rather than in the
nucleus.
• In order to replicate, poxviruses produce
a variety of specialized proteins not
produced by other DNA viruses, the
most important of which is a viralassociated DNA-dependent RNA
polymerase.
Smallpox in the New World
• In the early 16th century smallpox began
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to imported into the western
hemisphere.
The Spanish inadvertently owe success
in conquering the Aztec and Incas in
Mexico to smallpox.
Smallpox arrived in North America via
Canada, and Mexico.
• The disease killed an estimated 400,000
Europeans annually during the closing
years of the 18th century (including five
reigning monarchs), and was responsible
for a third of all blindness.
• Of all those infected, 20–60%—and over
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80% of infected children—died from the
disease. Smallpox was responsible for an
estimated 300–500 million deaths during
the 20th century.
As recently as 1967, the WHO estimated
that 15 million people contracted the
disease and that two million died in that
year.
Smallpox as Biological Warfare
• Lord Jeffrey Amherst, Commanding
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General of British Forces in North
America during the French and Indian
War. (1754-1763)
Used blankets (smallpox blankets)
coated with smallpox dust as germ
warfare to wipe out the Native American
population.
RNA viruses
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Poliovirus
Rhinovirus
Norovirus
Influenza
Rotavirus
Hantavirus
Ebola
• RNA viruses can be further classified
according to the sense or polarity of
their RNA into negative-sense and
positive-sense, or ambisense RNA
viruses.
• Positive-sense viral RNA is similar to
mRNA and thus can be immediately
translated by the host cell
• Negative-sense viral RNA is
complementary to mRNA and thus must
be converted to positive-sense RNA by
an RNA polymerase before translation.
• Purified RNA of a positive-sense virus
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can directly cause infection though it
may be less infectious than the whole
virus particle
Purified RNA of a negative-sense virus is
not infectious by itself as it needs to be
transcribed into positive-sense RNA;
each virion can be transcribed to several
positive-sense RNAs.
• Ambisense RNA viruses resemble
negative-sense RNA viruses, except they
also translate genes from the positive
strand.
Poliovirus
Properties of the virus
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Enterovirus.
+ stranded RNA virus
Transmitted by the
faecal oral route.
Cause of
gastrointestinal illness
and poliomyelitis.
Poliovirus
Poliovirus Infection
Virus
Infection
Gut
Non-neuronal
tissues
Viremia
Neuronal
tissues
Virus excretion
in the feces
Paralysis
Incidence of Poliomyelitis
A
B
Number of cases (in thousands)
40
Poliovirus vaccines
A: Salk – killed inactivated
vaccine.
B: Sabin – live attenuated
vaccine
30
20
10
0
1950
1960
1970
1980
Influenza A virus
Properties of the virus
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Myxovirus
Enveloped RNA virus
Infects a wide range of
animals other than
humans
Undergoes extensive
antigenic variation
Major cause of
respiratory infections
Weekly consultation rates for influenza and influenza-like illness: Weekly
Returns Service of the Royal College of General Practitioners, 1988 to
1999
Rate per 100 000 population
600
500
Epidemic activity
400
300
200
Higher than expected
seasonal activity
Baseline activity
Normal seasonal activity
100
0
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
Year
CDR Weekly Report: 5th November 1999
Norovirus
• Genus of genetically diverse single•
stranded RNA, non-enveloped viruses in
the Caliciviridae family
The known viruses in the genus are all
considered to be the variant strains of a
single species called Norwalk virus.
Norovirus
• The viruses are transmitted by fecally
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contaminated food or water, by personto-person contact, and via aerosolization
of the virus and contamination of
surfaces.
Noroviruses are the most common cause
of viral gastroenteritis in humans, and
affect people of all ages.
Rotovirus
• Genus of dsRNA virus in the family
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Reoviridae.
11 unique double helix molecules of
RNA which are 18,555 nucleotides in
total. Each helix codes for a protein.
The RNA is surrounded by a threelayered icosahedral protein capsid. Viral
particles are up to 76.5 nm in diameter
and are not enveloped.
Rotovirus
• Nearly every child in the world has been
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infected with rotavirus at least once by
the age of five.
There are five species of this virus,
referred to as A, B, C, D, and E.
Rotavirus A, the most common species,
causes more than 90% of rotavirus
infections in humans.
Rotovirus
• Transmitted by the fecal-oral route. It
infects and damages the cells that line
the small intestine and causes
gastroenteritis.
HIV
• HIV is a member of the genus Lentivirus
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part of the family Retroviridae.
ss positive-sense, enveloped virus
HIV is different in structure from other
retroviruses. It is roughly spherical[ with
a diameter of about 120 nm, around
60 times smaller than a RBC yet large
for a virus.
• Infection with HIV occurs by the
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transfer of blood, semen, vaginal fluid,
pre-ejaculate, or breast milk.
Within these bodily fluids, HIV is
present as both free virus particles and
virus within infected immune cells.
• HIV infects vital cells in the human
immune system such as helper T cells
(specifically CD4+ T cells), macrophages,
and dendritic cells.
Ebola
• Ebolavirions are filamentous particles
of ssRNA that may appear in the shape
of a shepherd's crook or in the shape of
a "U" or a "6", and they may be coiled,
toroid, or branched.
• The current outbreak in west Africa,
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(first cases notified in March 2014), is
the largest and most complex Ebola
outbreak since the Ebola virus was first
discovered in 1976. There have been
more cases and deaths in this outbreak
than all others combined.
As of Oct 8, 2014:
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Total Cases: 8400
Laboratory-Confirmed Cases: 4656
Total Deaths: 4033
Ebola
• Cells lining the inside of blood vessels
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(endothelial cells), macrophages,
monocytes and liver cells are the main
targets of infection.
After infection, a secreted glycoprotein,
known as small soluble glycoprotein
(sGP) or as the Ebola virus glycoprotein
(GP), is synthesized
• Human-to-human transmission occurs
only via direct contact with blood or
body fluid from an infected person
(including embalming of an infected
dead body), or by contact with objects
contaminated by the virus, particularly
needles and syringes.
• Other body fluids that may transmit
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ebolaviruses include saliva, mucus,
vomit, feces, sweat, tears, breast milk,
urine, and semen.
The dried virus can live on doorknobs
and countertops for several hours
Entry points include the nose, mouth,
eyes, or open wounds, cuts and abrasions
• Humans are not infectious until they
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develop symptoms.
Symptoms usually begin suddenly with
an influenza-like stage characterized by
fatigue, fever, headaches, and pain in the
joints, muscles, and abdomen.
Vomiting, diarrhea, and loss of appetite
are also common.
• Less common symptoms include sore
throat, chest pain, hiccups, shortness of
breath, and trouble swallowing.
• The average time between contracting
the infection and the start of symptoms
(incubation period) is 8 to 10 days, but it
can vary between 2 and 21 days
• In the bleeding phase, which typically
begins five to seven days after first
symptoms,internal and subcutaneous
bleeding may present itself in the form
of reddened eyes and bloody vomit
and/or stools.
• People remain infectious as long as their
blood and body fluids, including semen
and breast milk, contain the virus. Men
who have recovered from the disease can
still transmit the virus through their
semen for up to 7 weeks after recovery
from illness
• The disease is only spread by direct
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contact with the secretions from
someone who is showing signs of
infection
A person's ability to spread the disease is
often limited as the individual is often
too sick to travel during the infectious
stages of the disease.
• As transmission via air is generally ruled
out, the possibility of transmission
between non-seat-mate airline
passengers is generally ruled out
What about pets?
• In the 2001-2002 outbreak in Gabon,
scientists found signs of the virus in 25%
of the dogs living near the outbreak. The
animals were not symptomatic, nor did
they die during the time the scientists
were studying them.
Pets?
• So..the animals came in contact with
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Ebola virus and their immune systems
responded.
Whether or not dogs shed Ebola once
their immune systems encounter it
remains to be seen.
Scientists are studying the pets of the
infected humans currently.
Cats have not found to contract virus.
• At this time, there have been no reports
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of dogs or cats becoming sick with Ebola
or of being able to spread Ebola to
people or other animals.
Even in areas in Africa where Ebola is
present, there have been no reports of
dogs and cats becoming sick with Ebola.
• Why did hospital workers contract
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virus?
There are only 5 hospitals that really are
equipped to handle Ebola patients. The
Dallas hospital is not one of them.
Decontamination procedures and the
“buddy-system” were not used...