Microbiology, pharmacy.
Dr. Amal Bakri.
th
The 12 lecture
Done by: Hadeel Damra.
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Last lecture we started to talk about
virus-like agents ,, in this lecture we will
goes in more details .
Or hepatitis D , defective pathogen that
required coinfection with the hepatitis B
virus in order to replicate. It can be prevented
by vaccinating against HBV (HEPATITES B
VIRUS ), because it cannot infect without its
helper virus.
* Virus-Like Agents :
There are three types of virus-like agents
(Satellites , Viroids and Prions)
HDV lacks a well-defined capsid of its own
and is surrounded by the portion of the HBV
that codes for the surface antigen.
A) Satellites :
Satellites are small, single-stranded RNA
molecules, which lack
genes required for their replication, However,
in the presence
of a helper virus, they can replicate.
WHY they lack genes required 4 their
replication ??
Since they are so small organisms their
genetic material is small too and so it cant
carry all genes needed 4 replication .
There are two types of satellite :
* satellite viruses.
satellite nucleic acids (also known as
virusoids).*
 Satellite viruses are RNA molecules
surrounded by a capsid ( they have the code
required 4 the formation of their own capsid )
but they are defective in being unable to
replicate alone . and so they need a helper
virus to replicate .
B) VIROIDS :
In 1971 the plant pathologist T. O. Diener
described a new type of infectious agent. He
was studying potato tuber spindle disease,
which was thought to be caused by a virus.
However, no virions could be detected.
Rather Diener discovered molecules of RNA
in the nuclei of diseased plant cells.
He proposed the concept of a viroid, an
infectious RNA particle smaller than a
virus without capsid .( capsid is not part of
it).
 Viroids differ from viruses in a six ways :
1. Each viroid consists of a single circular
RNA molecule of low molecular weight,,
while viruses can be either RNA, DNA single
or double stranded.
 Satellite nucleic acids are RNA molecules
only without self-formation capsid
Instead they are covered by a capsid coded
for by their helper virus. ( that’s mean they
lack in their genetic material the code
required 4 capsid formation in contrast to
Satellite viruses ).
2. Viroids exist inside cells, usually inside of
nucleoli, as particles of RNA without capsids
or envelopes,, they cant be found in the
cytoplasm .
3. Viroids don’t require a helper virus and so
it doesn’t consider as virosoid,, it can do its
own replication by itself.
A very common example on Satellite is :
HEPATITES DELTA VIRUS:
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Microbiology, pharmacy.
Dr. Amal Bakri.
th
The 12 lecture
Done by: Hadeel Damra.
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4. Viroid RNA does not produce proteins.
The disease, now called Creutzfeldt–Jakob
disease (CJD), is characterized
by mental degeneration, loss of motor
function, and eventual death.
In other animals, they observe scrapie in
sheep and bovine spongiform encephalopathy
(BSE)—commonly called mad cow disease.
Why it is called spongy ??
Because when organisms infected by , their
brain will be full of pores just like a sponge.
All of these diseases are related to what we
called prions,, so what they are?
prions are normal proteins that become
folded incorrectly, possibly as a result of a
mutation
The harmless, normal proteins are found on
the plasma membrane of many
mammalian cells, especially brain cells.
The prion proteins (PrP) are thought to stick
together inside cells, forming
small fibers, or fibrils. Because the fibrils
cannot be organized in the plasma
membrane correctly, such aggregations
eventually kill the cell.
The effects of prions usually target the CNS .
5. Unlike virus RNA, which may be copied
in the host cell’s cytoplasm or nucleus,
viroid RNA is always copied in the host
cell nucleus.
6. Viroid particles are not apparent in
infected tissues without the use of special
techniques to identify nucleotide sequences
in the RNA. ( in anther way we could say that
it is very difficult to identify viroids when
they cause infections).
Viroids ( Mechanism of action on their
hosts) :
Viroids must disrupt host cell metabolism in
some way, but because no protein products
are produced, it is not clear how viroids and
their
RNA cause disease ,,
They may interfere with the cell’s ability to
process mRNA molecules
And Without mature mRNA molecules,
proteins cannot be synthesized.
If so, cell metabolism would be so disturbed
that cell death could result
Although some viroids cause no apparent
effect or only mild pathogenic
effects in the host, other viroids are known to
cause several lethal plant
diseases, such as potato spindle tuber
disease.
Prions have the following characteristics:
1. Prions are resistant to inactivation by
heating to 90_C, which will inactivate
viruses.
2. Prion infection is not sensitive to radiation
(ex Gama radiation) treatment that damages
virus genomes.
3. Prions are not destroyed by enzymes that
digest DNA or RNA.
4. Prions are sensitive to protein denaturing
agents, such as phenol and urea.
5. Prions have direct pairing of amino acids.(
since they are proteins and consist of amino
acids too).
C) Prions :
In the 1920s several cases of a slow but
progressive dementing illness in
humans were observed independently by
Hans Gerhard Creutzfeldt and Alfons
Maria Jakob.
Nowadays , as a result of prion's harmless,
any animal derived product or even drug
must has its own -what we called- protein
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Microbiology, pharmacy.
Dr. Amal Bakri.
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The 12 lecture
Done by: Hadeel Damra.
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profile in order to ensure the absence of such
diseases ( that’s mean these products must be
prions free).
So it is recommended in such cases to apply a
Caesarean birth rather than natural.
Rubella and cytomegalovirus (CMV) can
cross the placenta to the fetus and infect him
before birth .
How we achieve prion-free products ??
This requires means of sterilization
(
autoclaving or dry heat method).
It is also recommended by WHO , in order to
obtain a prion free catheter to use chemicals
such as NaOH or NaClO4 .
* VIRUSES AND CANCER :
We can define cancer as an uncontrolled,
invasive growth of abnormal
cells—in other words, cancer cells divide
repeatedly.
In many cases they cannot stop dividing; the
result is a neoplasm
or localized accumulation of cells known as a
tumor.
Let us get back to viruses in order to
focus more on certain points ;
*
VIRUSES
In 1911 by F. Peyton Rous. He showed that
certain sarcomas (neoplasms of connective
tissue) in chickens were caused by a virus ,
named the Rous sarcoma virus (RSV).
Therefore, it was not surprising to discover
that viruses
can be associated with cancer in humans as
well.
AND
TERATOGENESIS:
Teratogenesis is the induction of defects
during embryonic development, Certain
viruses are known to act as teratogens and
can be transmitted across the placenta and
infect the fetus.
Three human viruses—cytomegalovirus
(CMV), herpes simplex virus (HSV) types 1
and 2, and rubella— account for a large
number of teratogenic effects.
HSV infections(more likely type 2 which is
called genetal herpes) usually are acquired at
or shortly after birth, Infections acquired
before birth are rare,, when a pregnant
woman infected by vaginal herpes undergo
natural birth , during delivery the fetus will
get HSV and suffer from disseminated
infections (those that spread through the
body)
some infants die and survivors have
permanent damage to the eyes and central
nervous system.
At least six viruses that are associated with
human cancers.
*The Epstein-Barr virus (EBV) causes
Burkitt’s lymphoma, a malignant
tumor that causes swelling and eventual
destruction of the jaw.
*Human papillomaviruses (HPV) have
shown a strong correlation with some
human cancers. Although some of these
DNA viruses cause only benign
warts, other types (HPV-8 and HPV-16)
lead to a carcinoma
(neoplasm of epithelial tissues) of the uterine
cervix (malignant).
Literally 99.7% of all cases of cervical cancer
are caused by HPV, and are sexually
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Microbiology, pharmacy.
Dr. Amal Bakri.
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The 12 lecture
Done by: Hadeel Damra.
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transmitted (STD) , so nowadays a vaccine in
the USA introduced against it.
*Hepatitis B virus (HBV) causes 80% of
liver cancers .
*Human herpesvirus 8 which cause
Kaposi’s sarcoma, a cancer of the
endothelial cells of the blood vessels or
lymphatic system,this disease usually
associated with the latest stages of AIDS
patients ( small explanation : HIV virus
infects vital cells in the human immune
system
such
as helper
T
cells (specifically CD4+ T cells) which mount
immunological response and so their number
will decline rapidly and the situation getting
worst in this stage herpes virus 8 causes
Kaposi’s sarcoma which result in dark skin
Many other insert all or part of their DNA at
random sites into the host DNA.
Exact mechanism :
segments of DNA called oncogenes in DNA
tumor-causing viruses, cause a neoplasm and
contain the information for synthesizing viral
proteins needed for viral replication. The
oncogenes in RNA tumor viruses are quite
different,, some RNA tumor viruses pick up
‘‘extra’’ genes from normal host cells during
viral replication. These genes, which are
similar to oncogenes, are called protooncogenes. A proto-oncogene is a normal
gene that, when under the control of a virus,
can cause uncontrolled cell division; that is, it
can act as an oncogene.
The major human cancer viruses discovered
so far are dsDNA viruses ( all viruses
mentioned above are DNA viruses).
However, some (+) sense RNA viruses,
specifically the retroviruses (by the effect of
reverse transcriptase enzyme which convert
the RNA into DNA) , are also associated with
cancers; for example, HTLV-I (Human T
cell Lymphoma viruse) causes adult T cell
leukemia/lymphoma.
*
HOW
CANCER
Anyway these oncogenes lead to
production of certain proteins that cause
uncontrolled host cell division.
This figure For demonstration purposes.
VIRUSES
CAUSE CANCER :
In the case of DNA tumor viruses, which can
exist as proviruses (a virus genome that is
integrated into the DNA of a host cell.),
The major CPE (cytophathic effect) of
existing as proviruses is the uncontrollable
division of the infected cells. This process,
called neoplastic transformation, is typical
of DNA tumor viruses.
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the
Microbiology, pharmacy.
Dr. Amal Bakri.
th
The 12 lecture
Done by: Hadeel Damra.
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Chapter 11…… .
(Eukaryotic
Microorganisms and Parasites)
Most parasites are obligate parasites:
They must spend at least some of their life
cycle in or on a host. For example, the
protozoan that causes malaria invades red
blood cells. A few parasites are facultative
parasites:
They normally are free-living, such as some
soil fungi, but they can obtain nutrients from
a host, as many fungi do when they cause
skin infections.
*Principles of parasitology :
A parasite is an organism that lives at the
expense of another organism, called the host.
Parasitology : is the study of parasites (
usually consider the harmful effect rather
than the beneficial one ).
Parasites that cause disease are called
pathogens.
Parasites are also categorized according to
the duration of their association
with their hosts :
* Permanent parasites, such as
tapeworms, remain in or on a host once they
have invaded it.
*Temporary parasites, such asmany
biting insects, feed on and then leave their
hosts
ex : mosquito .
Historically, parasitology came to refer to
the study of protozoa,
helminths, and arthropods that live at the
expense of
other organisms. But logically bacteria also
considered as a parasite ,, in spite of this fact
parasitology include only Eukaryotic
parasites.
* Accidental, parasites invade an
organism other than their normal
host. Ticks that ordinarily attach to dogs or to
wild animals
sometimes attach to humans in case of direct
contact, the ticks are then accidental
parasites.
* PARASITES IN RELATION TO
THEIR HOSTS:
Parasites can be divided into:
* ectoparasites, such as ticks and lice,
which live on the surface of other organisms.
*endoparasites, such as some protozoa
and worms, which live within the bodies of
other organisms. Ex : Entameba Histolytica
)type of protozoa causes Amoebic
dysentery).
* Concept of Hyperparasitism :
Hyperparasitism refers to a parasite itself
having parasites. Some mosquitoes, which
are temporary parasites, harbor the malaria
parasite or other parasites.
Parasites also can be either obligate or
facultative ,,
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Microbiology, pharmacy.
Dr. Amal Bakri.
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The 12 lecture
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Such insects serve as vectors, or agents of
transmission, of
many human parasitic diseases.
parasitic diseases typically are wild or
domestic animals.
Many parasites have one or more of the
following mechanisms for evading host
defense mechanisms:
What is a vector ??
An organism that transfers a parasite to a new
host.
1. Encystment, the formation of an outer
covering that protects against unfavorable
environmental conditions. These resistant
cyst stages also sometimes provide a site for
internal reorganization of the organism and
cell division, help attach a parasite to a host,
or serve to transmit a parasite from one host
to another.
Ex : in case of being infected with amoeba ,
patient start to taka a medication sometimes
after a period of being healed they infected
back , this related to the formation of such
encyctment which is more resistant than the
vegative form of amoeba.
Vectors divided into 2 types :
biological vector : A vector in which the
parasite goes through part of its life cycle. Ex
: The malaria mosquito is both a host and a
biological vector.
in this case if we could treat Malaria we can
either treat the infected individuals or get rid
of malaria mosquito.
A mechanical vector : is a vector in which
the parasite does not go through any part of
its life cycle during transit. Ex Flies that
carry parasite eggs, bacteria, or viruses from
feces to human food are mechanical vectors.
Such as in case of Leishmaniasis ( a disease
caused by protozoan parasites)
Which transmitted by a fly ,, here the fly
doesn't involve the parasite in its life cycle.
And if we ger rid of these flies we won't stop
the disease , we only reduce the proability of
being infected by.
2. Changing the parasite’s surfaCe
antigens (molecules that elicit immunity)
faster than the host can make new antibodies
(molecules that recognize
and attack antigens)and so the immune
system wont be capable to recognize them as
fast as they change.
Hosts are classified as:
* Definitive hosts if they harbor a parasite
while it reproduces sexually;
Ex ;The mosquito is the definitive host for
the malaria parasite because inside it sexual
reproduction of Plasmodium occurs.
3. Causing the host’s immune system
to make antibodies that cannot
reaCt
with
the
parasite’s
antigens.
4. Invading host cells, where the
parasites are out of reach of host defense
mechanisms ( intracellular) When parasites
successfully evade host defenses, they can
cause several kinds of damage.
* Intermediate hosts if they harbor the
parasite during some other developmental
stages. Ex : the human is an intermediate host
related to Plasmodium .
We have also what we called Reservoir
hosts : are infected organisms that make
parasites available for transmission to other
hosts. Ex : Reservoir hosts for human
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Microbiology, pharmacy.
Dr. Amal Bakri.
th
The 12 lecture
Done by: Hadeel Damra.
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* PROTISTS :
- Mastigophorans ; they have flagella , a few
species are free-living in either fresh or salt
water, but most live in symbiotic
relationships with plants or animals.
Mastigophorans that parasitize humans
include
members
of
the
genera
Trypanosoma, Leishmania,
Giardia, and Trichomonas. Trypanosomes
cause African sleeping sickness which is
transmitted via (Tsetse fly). Leishmanias
cause leishmaniasis ( ‫ ( حبة الرمان‬which is a
disease causes skin lesions or systemic
disease with fever ( common in Syria and AlGhor ) . Giardias cause diarrhea.
Trichomonads cause vaginal inflammation
which is a sexual transmitted disease , it is
one of the predominant protozoal vaginal
infections in females and it is largely spread
in the world and may cause infertility , if the
female affected was pregnant then the born
baby might be affected too .
- amebozoa (sarcodines ): free living ,
move by means of pseudopodia , an example
on them is Entamoeba histolytica which
causes Dysentery .
- Ciliates : The largest group of protozoans .
Cilia allow the organisms to move .
Paramecium is an example on ciliates , cilia
in paramecium assist in food gathering .
Balantidium coli, the only ciliate that
parasitizes humans, causes dysentery (which
results in severe diarrhea ).
CHARACTERISTICS
OF
PROTISTS:
The protists, members of the kingdom
Protista, are a diverse assortment of
organisms that share certain common
characteristics. Protists are unicellular
(though sometimes colonial), eukaryotic
organisms with cells that have true nuclei
and
membrane-enclosed
organelles.
Although most protists are microscopic, they
vary in diameter from5 mm to 5 mm.
CLASSIFICATION OF PROTISTS
1. Fungus like protists .
2. Plantlike protists .
3. Animal-like protists
protozoa .
which
include
protozoa ; are heterotrophic , mostly
unicellular organisms . Most of them are free
living such as : Paramecium and Amoeba
which are free living in water . Some of them
are commensals which live in or on other
organisms without harming them .
2. Immotile protozoans such as ;
Apicomplexans
(sporozoans
).
Apicomplexans contain enzymes present in
groups (complexes) in the region of mouth (
apices) , giving the
group the name Apicomplexans .
Apicomplexans are parasitic and immobile .
An example on them is Plasmodium with
different species like Vivax ; Plasmodium
vivax causes malaria ,
These parasites
usually have complex life cycles and they
NOTE : the relationship between the
parasites and the host is either mutualism ,
commensalism , parasitism .If it was
Commensalism then the parasi and the host
will live with each other and the host will not
be harmed .
Classification of Protozoa :
Most of the protozoa are motile , so they are
classified into :
1. Motile protozoa which includes :
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Microbiology, pharmacy.
Dr. Amal Bakri.
th
The 12 lecture
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enter different stages which are : sporozoites,
merozoites, trophozoites, gametocytes . An
important example is the life
cycle of the malaria parasite, Plasmodium,
which requires both a human and a mosquito
host .
5. Some merozoites enter the sexual
reproductive phase and become gametocytes,
or male and female sex cells.
6. When a mosquito takes a blood meal from
an infected human, it also takes in
gametocytes, most of which mature and unite
to form zygotes ( sexual reproduction ) in the
lining of the mosquito’s stomach.
Zygotes pass through the stomach wall and
produce sporozoites, which eventually make
their way to the salivary glands. These can
then infect other people.
The life cycle of the malaria parasite
Plasmodium
NOTE >>> When we want to treat malaria
using antimalarial agents , we must have
drugs acting on red blood cells and others
acting on the liver to clear the parasites from
the two sides .
* FUNGI:
Now we will talk about another
microorganism which is the Fungi ; Fungi
Can be in the form of mold or in the form of
yeast . The field which is concerned in the
studying of fungi is called Mycology . The
diseases caused by the fungi are called
Mycosis . Many of the
fungi are
decomposers ( saprophytes ) which digest the
organic matter and waste , and some of them
can cause infections . Decomposers need
enzymes in order to be able to make
digestion for human being , so they have
lysosomes which are similar to the
macrophages enzymes .
The growth of the fungus is like the filaments
and it is similar in shape to certain bacteria
that have thread like shape (filamentous
shape) such as
: actinomycin and
streptomycin .
1.
Female infected mosquito transmits
sporozoites from its salivary glands when it
bites a human. The sporozoites travel in
human blood to the liver.
2. In the liver, the sporozoites multiply and
become merozoites. After 10 days , they are
shed into the bloodstream when liver cells
rupture .
3. The merozoites enter red blood cells and
become trophozoites.
4. Trophozoites reproduce asexually,
producing many more merozoites, then
merozoits are released by the rupture of the
red blood cells, accompanied by chills, high
fever (40 C degree) ( Fever increases and
decreases ), and sweating. They can then
infect other red blood cells. Multiplication
and release of merozoites is repeated several
times during a bout of malaria .
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