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Origin of viruses

We have several theories for origin of viruses , one theory states

that viruses represent ancient derivatives of degenerate cells or

cell fragments . Some cells undergo degeneration , disintegration& fragmentation , these fragments of cells undergo development

& become viable , they become a separate entity .

Most scientists agree that viruses are non-living entities , they are

not alive outside the cells . Viruses need the machinery of the

host cells in order to replicate themselves .

Bacteriophages

Viruses that infect bacteria are known as bacteriophages orsimply phages . As we have viruses that infect our cells we have

viruses that can infect bacterial cells & they have certain

receptors on certain bacterial cells .

Virulent bacteriophages always cause what is known as the

lytic cycle which ends with the destruction of the bacterial cell .

When the virus enters into a cell ( bacterial , animal or

plant cell ) its DNA or genome , once it gets into the cytoplasm of

the host cell , will either :

(1)integrate with the chromosomes of the bacteria

( become a part of these chromosomes )

OR

(2) use the machienary of the host cell in order to build

the structure or the whole body of the virus . So we will

have a large number of viruses in the cytoplasm of thehost cell , these viruses will secrete enzymes that will

poke a hole from inside of the membrane of the host

cell leading to lysis of the host cell , & finally these

viruses will come out from the cells in large number &

start infecting other neighbouring cells , that's what we

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call lytic cycle .

A partially lysed cell of Vibrio cholerae with attached

virions of phage CP-T1

Human viruses have certain classification , they can be classified

as DNA viruses , RNA viruses , viruses with envelope or naked

viruses . So we have different kinds of classification .

The same thing for the viruses that can infect the bacteria , we

have different families & each has its own members . For example

: Vibrio cholerae has a special phage that can infect the bacteriawhich are called CP-T1 ( it's a bacteriophage ) & under the

electron microscope we will see the bacterial cell with the

bacteriophage infecting it is attached to its surface & it's partially

lysed & in the end it's gonna be destroyed totally .

Question: a virus infect a cell & get out in a large number to

attack neighbouring cells , will only one virus infect this the

neighbouring cell or it will be infected by a group of viruses ?

Answer : infection can be initiated by one virus , it will enter the

cell & start to replicate , when density is enough (they know that

using sensory mechanism ) , they will get out of the cell . The cell

has receptors & can be infected by more than one virus but only

one virus is enough to initiate the infection .

B acteriophage T4

it's an assembly of protein components , it has a head , collar , tail& tail fibers which will be used by the virus to attach the surface

of the bacterial cell , then it will pierce the cell wall to inject the

DNA into the cytoplasm of the cell , so , only the DNA of the virus

will enter the host cell & the other components of the virus will

remanil outside .

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Animal viruses

what happens in animal cells is different from what happen in

bacterial cells .

the steps in multiplication of animal viruses are :* attachment * penetration *uncoating *biosynthesis * assembly

in general , they are the same steps but the details are a little bit

different for the viruses that can infect a human or animal cell

(human & animal cells are the same according to biology books ,

which is not true ).

Inclusion bodies are remnants or collections of viruses , often

seen in infected cells and used as diagnostic tool to identifyparticular virus diseases .

Using electron microscope , we can detect :

- Adsorbtion :attachment of the virus to the surface of

the host cell

- Penetration : enterance of the viral component into the

cytoplasm of the host cell

When bacteria is infected by a virus , only viral DNA will enter the

bacterial cell , while for human viruses , such as Herpes Simplex 1

& 2 , the host cell will be uncoated & the whole virus will enter

into its cytoplasm then DNA will replicate & the structure as a

whole will be built .

Herpes Simplex 1 will cause blisters which will appear around

your mouth when you have a fever , cold , stressful exam &

you can have it also sexually transmitted disease .

Herpes Simplex 2 is also as a result of sexually transmitted

disease .

Replication of animal viruses is different from replication oh

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bacteriophages .

Latent virus infection

Viral infection in which the virus is able to hide from a host's

immune system by entering cells & remaining dormant , such asHerpes virus .

Once you are infected by Herpes Simplex virus , you will have it

for lifetime . you will not be able to get rid of it , there is no cure .

In this case , if you have Herpes Simplex 1 virus , if it's in the oral

cavity , you will carry this virus in the end of the ganglion ( in the

nerve endings in the cheek area ) & when you are exposed to a

hot , fever , cold , stress . It will migrate all the way to theepithelial cells around your lips .

The same things for herps simplex 2 its gonna appear on your

genital and it will be dormant (3adm wgood symptoms) , and

what are the symptoms : vesicles or blisters like Akyas s3ere

feha sa2el . and this liquid will be rich in virus.

Then if you touch the blister and then you touch your eye or nose

you are going to infect other part in your body. So Dont do that !it is going to heal by itself , there is some kinds of inhibitors like

ointments (similar to Vaseline) you can use it (ointment is like a

cream that contain the therapy like antibiotic, steroidit is greasy

preparation that is insoluble in water) so as the dr said you put it

on the blister and it will become dry and hide later on. But the

herpes (type of virus) will be recurrent when you are under

stress like on examination.

The same thing for herps simplex 2 which will appear in the

genital area.

If there is no symptoms like no blister it doesnt mean that there

is no virus ; still you have it. It is infectious and contagious

(mo3dde) .

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Herpes virus infections are acquired (you get it from

other people), we call it cold sore (Al7amo).

Genital Herpes

Chickenpox .and Shingles

Now chickenpox is most children infected by it. Almostall of us we had chickenpox , nowdays there is vaccine for it.

When you are infected by chickenpox virus it can be mild like

no symptoms, and it can present as blisters (similar to the

Herpes virus).

Note: Chekenpox virus belong to the same family of Herpes

viruses which is called Human Herpes Virus type 3 , and the

virus that cause chickenpox called Varicella zoster virus again

which type 3 in the group.

Now Chickenpox virus might come back in the forties (at age

40, 50 or even 60). It is going to be stimulated and comeback

to appear on you, when your immune system is down, and it

will appear in a different form and we call it Shingles. (in other

ward to have Shingles you have to be infected by the

virus for the first time during childhood, and later on at

age 40 for example when your immune system is weak

Virus will be stimulated and the second appearance we

call it Shingles).

Shingles :

Very painful , and the blisters will not be limited to the oral

cavity, it also will appear on your skin at your back and neck ,

like a girdle hens its name .

Mainly as we said it appear in old people.

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Again the same virus that cause Chickenpox in childhood, it

cause Shingles in middle-age or older, when we are

immunosuppressed.

Antiviral agent: medication to treat the virus.For example you go to the pharmacy asking for drug to relief

the sore throat

It is important for you as a dentist to know these information

because you are the one who is dealing in patients mouth and

you should know how to discover that this patients is infected

(if he didnt tell you) because sometimes you are not allowed to

treat him for your safety because as we said viruses is

contagious).

Viruses can cause Septicemia (blood toxicity) , or affect the

heart casing Infective Endocarditis by the blood that circulate in

your body when it reach the heart.

Going back to the Sore throat, when the patient open his mouth

you can see inflamed tonsils (enlarged and red) , if you see pus

then it is bacterial infection. If you see enlarged, red inflamed

tonsils without pus then it is Viral infection.

Bacterial infection can be treated by Antibiotic for

example: Amoxicillin

Now all of us do the same mistake that when we have Viral throat

infection we take Antibiotic which is wrong, it will not help us. The

antibiotic that we take is a broad spectrum it means will work ongram negative and gram positive bacteria . By taking the

Antibiotic when there is no need we will encourage bacteria to be

Resistant

For viral infection we take Antiviral agents and usually we dont

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treat Virus, they are not curable. We can inhibit the development

of the virus but we cant get rid of it.

Steps for viral attacking the body :

1. Absorption or Attachment

3. Penetration

4. Replication and then they are going to come out

Now the drugs that are design to treat viruses will target one of

these steps either it inhibit the attachment of the virus onto the

body cell surface or it will be targeted to inhibit penetration intothe cytoplasm in human cells or its not going to allow the coating

process , or transcription , translation process.

Again one of the previous steps will be inhibited by the antiviral

(depend on the manufacture) . and to be honest the treatment is

not really effective especially because it is Virus infection.

Some of the viruses are Oncogenic which mean can cause Cancer

they are carcinogenic (causing cancer) we have also chemicals,

radiation.

Examples of oncogenic viruses that are

carcinogenic:

Epstein Bar virus

Human papilloma virus

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Thats why HIV very bad disease because in one hand we are

infected by the virus and in the other hand we will be

infected by bacteria and Fungi.

Aswe know that DNA will transcript to messenger RNA(it is thenormal function,) but in retroviruses will happened something else

or the opposite , because in the viruses we have an enzymecalled reveres transcripts , that able to reverse the process ,which mean from RNA to a copy DNA (CDNA) , then DNA willreplicate ,and will integrate it self to chromosome of the host cellwhich human cell , and will look for a receptor on T cells whichpart of cellular defense ( T CELLS MORE SPICEFIC AND POWRFULL

THAN HUMRALL IMUNO DEFENS ) ,and because they are morespecific so when the HIV attack T CELLS which we can find on it

( CD4+) on the surface , so it will find this receptor (CD4+) andthen destroy these important cells of the immune system , as theresult the immune system will reduced down , in this caseeverything will attack us like fungi , Bactria lets see a picture forHIV

As you can see its an envelope layer which its lipid layer , and wehave glycol-protein 120 , GP 41 , AND THE enzymes that we canfind them like reverse transcriptase , integrase ,protease and this3 enzymes very important to get in the host cell in order toreplicate and integrate

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VIRIODS AND PRIONS:Viruses are very small nonliving infectious agent , viroids andprions are even smaller and less complex infectious agent .

The viroids consist of short naked fragments of single strand RNA

that can interfere with plant cells but not our cells, they aretransmitted between plants in the same manner as viruses.

Plant diseases caused by viroids :- ,

1. potato spindle2. citrus exocorits

Prions: are the dangerous one for us, they are small infectiousprotein particles abnormal in shape that apparently cause fatal

neurologic diseases in animals (sheep, deer, cow). Such as1. Scarpie2. Bovine spongiform encephalopathy

(mad cow disease)Note : mad cow disease happened becausepeople was fed cows bones from another diedanimals.

3. Creutzfeldt Jakob disease

What Happened?

When prions face normal proteins especially in brain tissue, they

convert the normal protein particles to prions, This will formed a

chain of infictions. That means when the normal proteins

converted into prions (abnormal proteins ) they will infect the

normal one again and again and again, so all the brain tissue will

be completely dissolved.

- Of all pathogens, prions are believed to be the most

resistant to disinfectant : prions can't be killed ( even

by radiation).

- The mechanisms by which prions cause disease

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remains a mystery. Although it is thought that prions

convert normal protein molecules into nonfunctional

ones by causing the normal molecules to change their

shape.

'Now lets back to the bacteria'

Bacteria divided into three categories:

1- Gram Negative and have cell wall.

2- Gram Positive and have cell wall.

3- Lack a cell wall.

The differences between the three categories:

1- Gram Negative :- they have additional outer

membrane beside the cell wall. Their cell wall formed

from a thin peptidoglycan layer ( 22 layers)

2- Gram- Positive :- they don't have additional outer

membrane. Their cell wall formed from a thick

peptidoglycan layer.

3- Lack a cell wall :- they are bacteria that lost their cell

wall. So how they can live without it ( without

protection) ? the answer is that they have a different

structure that give rigidity and protection.

Many characteristics of bacteria are examined to provide data

for identification and classification, these characteristics

include:

1)Cell morphology (shape) :-

There are three basic shapes of bacteria :

a- Round or spherical :- The cocci

b- Rectangular or rod :- The bacilli

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c- Curved or spiral :- The spirilla

The cocci :

a- May seen in pairs :- Diplococci.

Example: neisseria gonorrhoeae that causes gonorrhea

disease

b- May seen in chains :- Streptococci.

Example: streptococcus pyogenes that causes strep throat

( pharyngitis)

c- May seen in clusters :- Staphylococci.

Example: staphylococcus aureus that causes boils (acne)-

d- May seen in pucket of 4:- Tetrad

Example: micrococcus luteus ( normally on our skin) and

their colonies in the plate are yellow they are rarely

pathogenic.

e- May seen in packet of 8 :- Octad.

Example: sarcina ventriculi, they are rarely pathogenic.

1)Staining reaction :

a- They may be Gram- Positive (red in color) or Gram-

Negative (violet in color), it depends on the wall

structure.

b- They may be Acid- Basic stain for special kind of

microorganisms, such as: Mycobacterium. Gram stain

will not be benefit to the Mycobacterium because

their cell wall structure is different , they have thick

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lipid layer because of that layer it's hard to the stains

to penetrate the cell wall. But this Acid-Basic stain

has special procedure that let the stain to enter the

cell and don't let it get out.

1)Motility :

Some of these microorganisms have structures that enable

them to move, these structures called Flagella, but if they

don't have flagella, they will move by the media that they

exist in it.

2)Colony morphology :

Colony means : when you cultured the bacteria in the agarand put it in the incubator and give it all the things that is

similar to our body (37c , O2 , CO2), then we wait 24 hours

or more ( it depends on the type of the bacteria). Then we

check if there is growth on the surface of the agar or not, if

there is a growth, this growth will be in different forms ( it

may be large colonies with different colors or it may be flat

colonies. )

3)Atmosphere requirement :

We classify it on the basis of their relationship to O2:-

a- An aerobic microorganisms that can't live without O2.

b- An anaerobic microorganisms that can live without

O2.

c- Some of them in between that can live with small

amount of O2

Also if it needs CO2, N2, H2 we must give it what it needs.

1)Biochemical and metabolic activities :

As bacteria grow, they produce many waste products and

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secretions, some of which are enzymes that enable them to

invade their host and cause disease.

This biochemicals added to the bacterial nutrition, they

includes different reagents, if the reagent shift from onecolor to another this will indicate that this bacteria producing

specific kind of enzyme, which means using a substrate in

the presence of the reagent will change the substrate into

another one, this substrate has an enzyme that able to use

the substrate in the tube of the product according to the

color changing.

2)Pathogenic and genetic composition :

The most modern and fastest identification of bacteria using

some types of test procedure which referred as molecular

diagnostic procedure.

DoNe By :

Wala Hamada

MoNa Simon Obeid

Nihad Bishara

Suzan Elmansour

http://www.facebook.com/suzan.elmansourhttp://www.facebook.com/suzan.elmansour