Diseases , symptoms / Virus: Origins, size , shape , properties and classification , Viral cycle , capsid , viral envelope

1. By: C. Mahmoud Galal Zidan
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2. Content
 Diseases and Symptoms
 Symptoms Presentation
 Medical Symptoms
 Types of Diseases and Causes
 Introduction of Pathogens
 Introduction of Virology
 Viruses
 Origins
 structure
 Size
 Genes
 Viral life cycle
 Capsid
 Viral Envelope
 Virus classification
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3. What’s Disease ? And How may
the disease be caused ?
A disease is a particular abnormal condition that
negatively affect the structure or function of all or part
of an organism, and that is not due to any immediate
external injury.
 Diseases are often known to be medical
conditions that are associated with
specific symptoms and signs.
A disease may be caused by external factors such
as pathogens or by internal dysfunctions.
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4. What’s Symptoms ? And What’s
the types of symptoms
 A Symptom is a departure from normal function or feeling which is apparent to
a patient, reflecting the presence of an unusual state, or of a disease. A symptom
can be subjective or objective.
 Symptoms may be briefly acute or a more prolonged but acute
or chronic, relapsing or remitting .
 Asymptomatic conditions also exist (e.g. subclinical infections and silent
diseases like sometimes, high blood pressure).
 Constitutional or general symptoms are those related to the systemic effects of a
disease (e.g., fever, malaise, anorexia, and weight loss).
 They affect the entire body rather than a specific organ or location.
 The symptom that ultimately leads to a diagnosis is called a "cardinal symptom".
Non-
Specific
Positive
Negative
Positive
and
Negative
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5. Non- Specific Symptoms
 Non-specific symptoms are self-reported symptoms that do
not indicate a specific disease process or involve an isolated
body system. For example, fatigue is a feature of many acute
and chronic medical conditions, which may or may not be
mental, and may be either a primary or secondary symptom.
Fatigue is also a normal, healthy condition when experienced
after exertion or at the end of a day.
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6. Positive and Negative Symptoms
 Positive symptoms are symptoms that are present in the disorder and are not normally
experienced by most individuals.
 It reflects an excess or distortion of normal functions .
 Examples are hallucinations, delusions, and bizarre behavior.
 For somatic sensory symptoms , the positive ones are tingling, itching and various
sensations described as pricking, bandlike, lightning-like shooting feelings (lancinations),
aching, knifelike, twisting, drawing, pulling, tightening, burning, searing, electrical, or raw
feelings.
 The terms used to describe positive sensory symptoms are paresthesia and dysesthesia.
 Negative symptoms are functions that are normally found in healthy persons, but that
are diminished or not present in affected persons. Thus, it is something that has
disappeared from a person's normal way of functioning.
 Examples are social withdrawal, apathy, inability to experience pleasure and defects in
attention control.
 The negative sensory symptoms are diminished or missing sensations. The most
common one is numbness. The following terms are used for negative symptoms:
 Hypoesthesia (hypesthesia) is a partial loss of sensitivity to moderate stimuli, such as
pressure, touch, warmness, coldness, etc. Anesthesia is the complete loss of sensitivity to
stronger stimuli, such as pinprick. Hypalgesia (analgesia) is loss of sensation to painful stimuli.
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7. Symptoms Presentation ( Can’t and Feeling)
 Breathe normally
 Hear normally: losing hearing , sounds are too
loud ,
ringing or hissing in my ears
 Move one side – arm and/or leg
 Pass a bowel action normally
 Pass urine normally
 Remember normally
 See properly: Blindness , blurred vision,
double vision
 Sleep normally
 Smell things normally
 Speak normally
 Stop passing watery bowel actions
 Stop scratching
 Stop sweating
 Swallow normally
 Taste properly
 Walk normally
 Write normally
 Chills
 Fever
 Paresthesia (numbness, tingling,
electric tweaks)
 Light-headed
 Dizzy
 Dizzy – about to black out
 Dizzy – with the room spinning
around me
 My mouth is dry
 Nauseated
 Sick
 like I have the flu
 like I have to vomit
 Short of breath
 Sleepy
 Sweaty
 Thirsty
 Tired
 Weak
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8. Symptoms Presentations
(Common Pain Expressions )
 abdomen
 back
 chest
 ear
 head
 pelvis
 tooth
 rectum
 skin
 Extremities
 Chronic pain
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9. Types of Medical Symptoms
General
Cardiovascular
Ear, Nose and Throat
Gastrointestinal
Integumentary
Neurological
Obstetric / Gyneacological
Ocular
Psychiatric
Pulmonary
Rheumatologic Urologic
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10. General
Anorexia (R63.0) Fatigue (R53)
Cachexia (R64) Hypothermia (T68)
Chills and shivering Jaundice (P58, P59, R17)
Convulsions (R56) Muscle weakness (M62.8)
Deformity Pyrexia (R50)
Discharge Sweats
Dizziness / Vertigo (R42) swelling
swollen or painful lymph node(s) (I88,
L04, R59.1)
weight gain (R63.5)
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11. Medical Symptoms
Neurological
Abnormal posturing Acalculia Insomnia (F51.0,
G47.0)
Agnosia Anosognosia Lhermitte's sign
Alexia Confusion loss of
consciousness
Amnesia Dysarthria Neck stiffness
Anomia Dysdiadochokinesia Paralysis
and paresis
Aphasia and Apraxia Dysgraphia Paresthesia
(R20.2)
Ataxia Hallucination Prosopagnosia
Cataplexy (G47.4 ) Headache Somnolence
(R40.0)
Hypokinetic
movement disorder
Hyperkinetic movement
disorder
Opisthotonus
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12. Medical Symptoms
Obstetric /
Gyneacological
Ocular Psychiatric
Abnormal vaginal
bleeding
Amaurosis
fugax (G45.3)
and Amaurosis
Amusia Apathy
Amenorrhea Blurred vision Anhedonia Confabulation
Infertility Dalrymple's sign Anxiety Depression
Painful
intercourse (N94.1)
Double vision
(H53.2)
Euphoria Delusion
Pelvic pain Exophthalmos
(H05.2)
Irritability Homicidal
ideation
Vaginal discharge Mydriasis /miosis
(H570)
Mania (F30) Paranoid
ideation
Nystagmus Phobia Suicidal
ideation
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13. Cardiovascular Ear , Nose and
Throat
Gastrointestinal
Arrhythmia Dry mouth (R68.2) Abdominal
pain
Nausea
Bradycardia (R00.1) Epistaxis (R04.0) Bloating Odynophagia
Claudication Halitosis Belching proctalgia
fugax
Chest pain (R07) Hearing loss Bleeding Pyrosis
Palpitations (R00.2) Nasal discharge Constipation Rectal
tenesmus
Tachycardia (R00.0) Otalgia (H92.0) Diarrhea Steatorrhea
Otorrhea (H92.1) Dysphagia Vomiting
Sore throat Dyspepsia Flatulence
Toothache Fecal
incontinence
Heartburn
Tinnitus
Trismus
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14. Medical Symptoms
Urologic Pulmonary Integumentary
Dysuria Apnea and
Hypopnea
Alopecia Rash
Hematospermia Cough Hirsutism Urticaria
Hematuria Dyspnea Hypertrichosis Itching
Retrograde
ejaculation
Hemoptysis Abrasion Nail disease
Impotence Pleuritic chest pain Anasarca Laceration
Polyuria Sputum Blister Edema
Retrograde
ejaculation
Rheumatologic Bleeding into the skin :
Petechia , Purpura ,
ecchymosis
Janeway
lesions and
Osler’s nodeStrangury Arthralgia
Urethral discharge Back pain
Urinary frequency Sciatica
Urinary incontinence
Urinary retention
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15. Main Types and Classification of Diseases
 There are four main types of disease:
 Infectious diseases
 Deficiency diseases
 Hereditary diseases (including both genetic diseases and non-genetic hereditary diseases),
 Physiological diseases.
 Diseases can also be classified in other ways, such as :
 Communicable diseases .
 Non-communicable diseases.
 Diseases may be classified by :
 cause, pathogenesis (mechanism by which the disease is caused),
 symptom(s). Alternatively,
 diseases may be classified according to the organ system involved.
 A chief difficulty in nosology is that diseases often cannot be defined and classified clearly,
especially when cause or pathogenesis are unknown. Thus diagnostic terms often only reflect
a symptom or set of symptoms (syndrome).
 Classical classification of human disease derives from observational correlation between
pathological analysis and clinical syndromes. Today it is preferred to classify them by their
cause if it is known.
 The most known and used classification of diseases is the World Health Organization's ICD.
This is periodically updated. Currently the last publication is the ICD-10 .
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16. Types of Causes
 Airborne
 An airborne disease is any disease that is caused by pathogens and transmitted
through the air.
 Foodborne
 Foodborne illness or food poisoning is any illness resulting from the consumption of
food contaminated with pathogenic bacteria, toxins, viruses, prions or parasites.
 Infectious
 Infectious diseases, also known as transmissible diseases or communicable
diseases, comprise clinically evident illness resulting from the infection, presence
and growth of pathogenic biological agents in an individual host organism.
 Lifestyle
 A lifestyle disease is any disease that appears to increase in frequency as countries
become more industrialized and people live longer, especially if the risk factors
include behavioral choices like a sedentary lifestyle or a diet high in unhealthful
foods
 Non-communicable disease
 is a medical condition or disease that is non-transmissible. Non-communicable
diseases cannot be spread directly from one person to another.
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17. Pathogens
 Pathogens is used to describe an infectious microorganism or agent, such as
 Virus
 Bacterium
 Protozoan
 Prion
 Fungus
 Small animals, such as certain kinds of worms and insect larvae, can also produce disease.
However, these animals are usually, in common parlance, referred to as parasites rather than
pathogens.
 The scientific study of microscopic organisms, including microscopic pathogenic
organisms, is called microbiology, while the study of disease that may include these
pathogens is called pathology.
 There are several pathways through which pathogens can invade a host. The
principal pathways have different episodic time frames, but soil has the longest or
most persistent potential for harboring a pathogen. Diseases in humans that are
caused by infectious agents are known as pathogenic diseases, though not all
diseases are caused by pathogens. Some diseases, such as Huntington's disease,
are caused by inheritance of abnormal genes.
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18. Introduction of Virology
 Virology is the study of viral submicroscopic, parasitic particles of genetic material contained in a
protein coat and virus-like agents. It focuses on the following aspects of viruses: their structure,
classification and evolution, their ways to infect and exploit host cells for reproduction, their interaction
with host organism physiology and immunity, the diseases they cause, the techniques to isolate and
culture them, and their use in research and therapy. Virology is considered to be a subfield of
microbiology or of medicine.
 Viruses are small particles, typically between 20 and 300 nanometers in length, containing RNA or
DNA.
 Viruses require a host cell to replicate. Some of the diseases that are caused by viral pathogens
include smallpox , influenza , mumps , measles , chickenpox , ebola , HIV , and rubella .
 Pathogenic viruses are mainly from the families:
 Adenoviridae
 Picornaviridae
 Herpesviridae
 Hepadnaviridae
 Flaviviridae
 Retroviridae
 Orthomyxoviridae
 Paramyxoviridae
 Papovaviridae
 Polyomavirus
 Rhabdoviridae
 Togaviridae .
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19. Origins
 Viruses co-exist with life wherever it occurs. They have probably existed since living cells first
evolved. The origin of viruses remains unclear because they do not form fossils, so molecular
techniques have been the most useful means of hypothesizing how they arose. These
techniques rely on the availability of ancient viral DNA or RNA but most of the viruses that
have been preserved and stored in laboratories are less than 90 years old. Molecular
methods have only been successful in tracing the ancestry of viruses that evolved in the 20th
century. New groups of viruses might have repeatedly emerged at all stages of the evolution
of life.
 Three main theories speculate on the origins of viruses:
1. Regressive theory
2. Cellular origin theory
3. Coevolution theory
 There are problems with all of these hypotheses: the regressive hypothesis does not explain
why even the smallest of cellular parasites do not resemble viruses in any way. The escape
hypothesis does not explain the structures of virus particles. The coevolution, or virus-first
hypothesis, contravenes the definition of viruses, in that they are dependent on host cells. But
viruses are recognized as ancient and to have origins that pre-date the divergence of life into
the three domains . This discovery has led modern virologists to reconsider and re-evaluate
these three classical hypotheses.
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20. Regressive theory
 Viruses may have once been small cells that parasitised larger cells. Over time, genes
not required by their parasitism were lost. The bacteria rickettsia and chlamydia are
living cells that, like viruses, can reproduce only inside host cells. They lend credence
to this theory, as their dependence on parasitism is likely to have caused the loss of
genes that enabled them to survive outside a cell.
Cellular origin theory
 Some viruses may have evolved from bits of DNA or RNA that "escaped" from the
genes of a larger organism. The escaped DNA could have come from plasmids
pieces of DNA that can move between cells while others may have evolved from
bacteria.
Coevolution theory
 Viruses may have evolved from complex molecules of protein and DNA at the
same time as cells first appeared on earth and would have depended on cellular
life for many millions of years.
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21. Structure
 A virus particle, also known as a virion, consists of genes made from DNA or RNA
which are surrounded by a protective coat of protein called a capsid. The capsid is
made of many smaller, identical protein molecules which are called capsomers.
 The arrangement of the capsomers can either be icosahedral (20-sided), helical or
more complex . There is an inner shell around the DNA or RNA called the
nucleocapsid, which is formed by proteins. Some viruses are surrounded by a bubble
of lipid (fat) called an envelope, which makes them vulnerable to soap and alcohol.
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22. Size
 Viruses are among the smallest infectious agents and are too small
to be seen by light microscopy (in other words, they are sub-
microscopic). Most of them can only be seen by electron
microscopy. Their sizes range from 20 to 300 nanometers; it would
take 30,000 to 750,000 of them, side by side, to stretch to one
centimeter (0.39 in). Bacteria are typically around 1 micrometer
(1000 nm) in diameter, and the cells of higher organisms a few tens
of micrometers. Some viruses such as megaviruses and
pandoraviruses are relatively large. At around 1 micrometer, these
viruses, which infect amoebae, were discovered in 2003 and 2013.
They are around a thousand times larger than influenza viruses and
the discovery of these "giant" viruses astonished scientists.
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23. Genes
 The genes of viruses are made from DNA (deoxyribonucleic acid) and, in
many viruses, RNA (ribonucleic acid). The biological information
contained in an organism is encoded in its DNA or RNA. Most organisms
use DNA, but many viruses have RNA as their genetic material. The DNA
or RNA of viruses consists of either a single strand or a double helix.
 Viruses reproduce rapidly because they have only a few genes compared
to humans who have 20,000–25,000. For example, influenza virus has
only eight genes and rotavirus has eleven. These genes encode structural
proteins that form the virus particle, or non-structural proteins, that are
only found in cells infected by the virus.
 All cells, and many viruses, produce proteins that are enzymes called
DNA polymerase and RNA polymerase which make new copies of DNA
and RNA. A virus's polymerase enzymes are often much more efficient at
making DNA and RNA than the equivalent enzymes of the host cells, but
viral RNA polymerase enzymes are error-prone, and this is one of the
ways why RNA viruses can mutate to form new strains.
 In some species of RNA virus, the genes are not on a continuous
molecule of RNA, but are separated. The influenza virus, for example, has
eight separate genes made of RNA. When two different strains of
influenza virus infect the same cell, these genes can mix and produce
new strains of the virus in a process called reassortment.
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24. Protein synthesis
 Proteins are essential to life. Cells produce new protein molecules
from amino acid building blocks based on information coded in DNA.
Each type of protein is a specialist that usually only performs one
function, so if a cell needs to do something new, it must make a new
protein. Viruses force the cell to make new proteins that the cell does
not need, but are needed for the virus to reproduce. Protein synthesis
consists of two major steps: transcription and translation.
 Transcription is the process where information in DNA, called the
genetic code, is used to produce RNA copies called messenger RNA
(mRNA). These migrate through the cell and carry the code to
ribosomes where it is used to make proteins. This is called translation
because the protein's amino acid structure is determined by the
mRNA's code. Information is hence translated from the language of
nucleic acids to the language of amino acids.
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25.  Transcription is the process where information in DNA, called the
genetic code, is used to produce RNA copies called messenger RNA
(mRNA). These migrate through the cell and carry the code to
ribosomes where it is used to make proteins. This is called translation
because the protein's amino acid structure is determined by the
mRNA's code. Information is hence translated from the language of
nucleic acids to the language of amino acids.
 Some nucleic acids of RNA viruses function directly as mRNA without
further modification. For this reason, these viruses are called positive-
sense RNA viruses. In other RNA viruses, the RNA is a
complementary copy of mRNA and these viruses rely on the cell's or
their own enzyme to make mRNA. These are called negative-sense
RNA viruses. In viruses made from DNA, the method of mRNA
production is similar to that of the cell. The species of viruses called
retroviruses behave completely differently: they have RNA, but inside
the host cell a DNA copy of their RNA is made with the help of the
enzyme reverse transcriptase. This DNA is then incorporated into the
host's own DNA, and copied into mRNA by the cell's normal
pathways.
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26. Diagram of a typical Eukaryotic cell showing
subcellular components. Organelles:
1. Nucleolus
2. Nucleus
3. Ribosome
4. Vesicle
5. Rough endoplasmic
reticulum (ER)
6. Golgi apparatus
7. Cytoskeleton
8. smooth ER
9. Mitochondria
10.Vacuole
11.Cytoplasm
12.Lysosome
13.Centrioles within
Centrosome
14.Virus particle shown to
approximate scale
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27. Viral Life-cycle
 When a virus infects a cell, the virus forces it to make thousands
more viruses. It does this by making the cell copy the virus's DNA or
RNA, making viral proteins, which all assemble to form new virus
particles.
 There are six basic, overlapping stages in the life cycle of viruses in
living cells:
1. Attachment
2. Penetration
3. Uncoating
4. Replication
5. Assembly
6. Release
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28. Stages in the life cycle of viruses in living cell
1. Attachment is the binding of the virus to specific molecules on the surface of the
cell. This specificity restricts the virus to a very limited type of cell. For example, the
human immunodeficiency virus (HIV) infects only human T cells, because its surface
protein, gp120, can only react with CD4 and other molecules on the T cell's surface.
Plant viruses can only attach to plant cells and cannot infect animals. This
mechanism has evolved to favour those viruses that only infect cells in which they
are capable of reproducing.
2. Penetration follows attachment; viruses penetrate the host cell by endocytosis or by
fusion with the cell.
3. Uncoating happens inside the cell when the viral capsid is removed and destroyed
by viral enzymes or host enzymes, thereby exposing the viral nucleic acid.
4. Replication of virus particles is the stage where a cell uses viral messenger RNA in
its protein synthesis systems to produce viral proteins. The RNA or DNA synthesis
abilities of the cell produce the virus's DNA or RNA.
5. Assembly takes place in the cell when the newly created viral proteins and nucleic
acid combine to form hundreds of new virus particles.
6. Release occurs when the new viruses escape or are released from the cell. Most
viruses achieve this by making the cells burst, a process called lysis. Other viruses
such as HIV are released more gently by a process called budding.
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29. Effects on the host cell
 Viruses have an extensive range of structural and biochemical effects on the host
cell. These are called cytopathic effects. Most virus infections eventually result in
the death of the host cell. The causes of death include cell lysis (bursting),
alterations to the cell's surface membrane and apoptosis (cell "suicide"). Often cell
death is caused by cessation of its normal activity due to proteins produced by the
virus, not all of which are components of the virus particle.
 Some viruses cause no apparent changes to the infected cell. Cells in which the
virus is latent (inactive) show few signs of infection and often function normally.
This causes persistent infections and the virus is often dormant for many months or
years. This is often the case with herpes viruses.
 Some viruses, such as Epstein-Barr virus, often cause cells to proliferate without
causing malignancy; but some other viruses, such as papillomavirus, are an
established cause of cancer. When a cell's DNA is damaged by a virus such that
the cell cannot repair itself, this often triggers apoptosis. One of the results of
apoptosis is destruction of the damaged DNA by the cell itself. Some viruses have
mechanisms to limit apoptosis so that the host cell does not die before progeny
viruses have been produced; HIV, for example, does this.
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30. Viruses and diseases
 There are many ways in which viruses spread from host to host but each species of virus uses
only one or two. Many viruses that infect plants are carried by organisms; such organisms are
called vectors. Some viruses that infect animals, including humans, are also spread by vectors,
usually blood-sucking insects. However, direct transmission is more common. Some virus
infections, such as norovirus and rotavirus , are spread by contaminated food and water, hands
and communal objects and by intimate contact with another infected person, while others are
airborne (influenza virus). Viruses such as HIV, hepatitis B and hepatitis C are often transmitted
by unprotected sex or contaminated hypodermic needles .
 In humans
Common human diseases caused by viruses include the common cold, the flu, chickenpox and
cold sores. Serious diseases such as Ebola and AIDS are also caused by viruses. Many viruses
cause little or no disease and are said to be "benign". The more harmful viruses are described as
virulent. Viruses cause different diseases depending on the types of cell that they infect. Some
viruses can cause lifelong or chronic infections where the viruses continue to reproduce in the body
despite the host's defense mechanisms. This is common in hepatitis B virus and hepatitis C virus
infections. People chronically infected with a virus are known as carriers. They serve as important
reservoirs of the virus.
 Endemic
If there is a high proportion of carriers in a given population, a disease is said to be endemic.
Before the advent of vaccination, infections with viruses were common and outbreaks occurred a
regularly. In countries with a temperate climate viral diseases are usually seasonal. Poliomyelitis,
cause by poliovirus often occurred in the summer months. By contrast colds, influenza and
rotavirus infections are usually a problem during the winter months. Other viruses, such as measles
virus caused outbreaks regularly every third year. In developing countries, viruses that cause
respiratory and enteric infections are common throughout the year. Viruses carried by insects are a
common cause of diseases in these settings. Zika and dengue viruses for example are transmitted
by the female Aedes mosquitoes, which bite humans particularly during their breeding season.
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31. Pandemic and emergent
 Although viral pandemics are rare events, HIV—which evolved from viruses
found in monkeys and chimpanzees—has been pandemic since at least the
1980s. During the 20th century there were four pandemics caused by influenza
virus and those that occurred in 1918, 1957 and 1968 were severe. Before its
eradication, smallpox was a cause of pandemics for more than 3,000 years.
Throughout history, human migration has aided the spread of pandemic
infections; initially by ships and in modern times by air travel.
 With the exception of smallpox, most pandemics are caused by newly-evolved
viruses. These "emergent“ viruses are usually mutants of less harmful viruses
that have circulated previously either in humans or other animals.
 Severe acute respiratory syndrome (SARS) and Middle East respiratory
syndrome (MERS) are caused by new types of coronaviruses. Other
coronaviruses are known to cause mild infections in humans, so the virulence
and rapid spread of SARS infections—that by July 2003 had caused around
8,000 cases and 800 deaths was unexpected and most countries were not
prepared.
 A related coronavirus emerged in Wuhan , China in November 2019 and spread
rapidly around the world. Thought to have originated in bats and subsequently
named severe acute respiratory syndrome coronavirus 2 , infections with the
virus caused a pandemic in 2020. Measures to curtail the impact of the pandemic
have been hampered by fear and prejudice and the stigmatization of infected
people. Unprecedented restrictions in peacetime have been placed on
international travel, and curfews imposed in several major cities worldwide.
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32. Origin and Evolution
All the viruses came from bats as coronavirus-related viruses before
mutating and adapting to intermediate hosts and the to humans and causing
the diseases SARS, MERS and COVID-19.
32

33. Host Resistance
 Innate immunity of animals
 Animals, including humans, have many natural defences against viruses.
Some are non-specific and protect against many viruses regardless of the
type. This innate immunity is not improved by repeated exposure to viruses
and does not retain a "memory" of the infection. The skin of animals,
particularly its surface, which is made from dead cells, prevents many types
of viruses from infecting the host. The acidity of the contents of the stomach
destroys many viruses that have been swallowed. When a virus overcomes
these barriers and enters the host, other innate defences prevent the spread
of infection in the body. A special hormone called interferon is produced by
the body when viruses are present, and this stops the viruses from
reproducing by killing the infected cells and their close neighbours. Inside
cells, there are enzymes that destroy the RNA of viruses. This is called RNA
interference. Some blood cells engulf and destroy other virus-infected cells.
 Adaptive immunity of animals
 Two rotavirus particles: the one on the right is coated with antibodies which
stop its attaching to cells and infecting them
 Specific immunity to viruses develops over time and white blood cells called
lymphocytes play a central role. Lymphocytes retain a "memory" of virus
infections and produce many special molecules called antibodies. These
antibodies attach to viruses and stop the virus from infecting cells. Antibodies
are highly selective and attack only one type of virus. The body makes many
different antibodies, especially during the initial infection. After the infection
subsides, some antibodies remain and continue to be produced, usually
giving the host lifelong immunity to the virus.
33

34. Two rotavirus particles: the one on the right is coated with
antibodies which stop its attaching to cells and infecting them
34

35. Prevention and treatment of viral disease
 Vaccination is a way of preventing diseases caused by viruses. Vaccines simulate a natural infection
and its associated immune response, but do not cause the disease. Their use has resulted in the
eradication of smallpox and a dramatic decline in illness and death caused by infections such as polio,
measles, mumps and rubella. Vaccines are available to prevent over fourteen viral infections of
humans and more are used to prevent viral infections of animals. Vaccines may consist of either live or
killed viruses. Live vaccines contain weakened forms of the virus, but these vaccines can be
dangerous when given to people with weak immunity. In these people, the weakened virus can cause
the original disease.[Biotechnology and genetic engineering techniques are used to produce
"designer" vaccines that only have the capsid proteins of the virus. Hepatitis B vaccine is an example
of this type of vaccine . These vaccines are safer because they can never cause the disease.
 Antiviral drugs
 Since the mid 1980s, the development of antiviral drugs has increased rapidly, mainly driven by the AIDS
pandemic. Antiviral drugs are often nucleoside analogues, which are molecules very similar, but not
identical to DNA building blocks. When the replication of virus DNA begins, some of these fake building
blocks are incorporated. As soon as that happens, replication stops prematurely the fake building blocks
lack the essential features that allow the addition of further building blocks. Thus, DNA production is
halted, and the virus can no longer reproduce. Examples of nucleoside analogues are acyclovir for herpes
virus infections and lamivudine for HIV and hepatitis B virus infections. Aciclovir is one of the oldest and
most frequently prescribed antiviral drugs.
 Other antiviral drugs target different stages of the viral life cycle. HIV is dependent on an enzyme called
the HIV-1 protease for the virus to become infectious. There is a class of drugs called protease inhibitors,
which bind to this enzyme and stop it from functioning.
 Hepatitis C is caused by an RNA virus. In 80% of people infected, the disease becomes chronic, and they
remain infectious for the rest of their lives unless they are treated. There is an effective treatment that
uses the nucleoside analogue drug ribavirin. Treatments for chronic carriers of the hepatitis B virus have
been developed by a similar strategy, using lamivudine and other anti-viral drugs. In both diseases, the
drugs stop the virus from reproducing and the interferon kills any remaining infected cells.
 HIV infections are usually treated with a combination of antiviral drugs, each targeting a different stage in
the virus's life-cycle. There are drugs that prevent the virus from attaching to cells, others that are
nucleoside analogues and some poison the virus's enzymes that it needs to reproduce. The success of
these drugs is proof of the importance of knowing how viruses reproduce.
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35

36. The structure of the
DNA base guanosine
and the antiviral drug
Aciclovir
36

37. Role in Ecology
 Viruses are the most abundant biological entity in aquatic environments there
are about ten million of them in a teaspoon of seawater and they are essential to
the regulation of saltwater and freshwater ecosystems. Most of these viruses are
bacteriophages, which are harmless to plants and animals. They infect and
destroy the bacteria in aquatic microbial communities and this is the most
important mechanism of recycling carbon in the marine environment. The
organic molecules released from the bacterial cells by the viruses stimulate fresh
bacterial and algal growth.
 Microorganisms constitute more than 90% of the biomass in the sea. It is
estimated that viruses kill approximately 20% of this biomass each day and that
there are fifteen times as many viruses in the oceans as there are bacteria and
archaea. Viruses are mainly responsible for the rapid destruction of harmful algal
blooms, which often kill other marine life. The number of viruses in the oceans
decreases further offshore and deeper into the water, where there are fewer
host organisms.
 Their effects are far-reaching; by increasing the amount of respiration in the
oceans, viruses are indirectly responsible for reducing the amount of carbon
dioxide in the atmosphere by approximately 3 gigatonnes of carbon per year.
 Marine mammals are also susceptible to viral infections. In 1988 and 2002,
thousands of harbour seals were killed in Europe by phocine distemper virus.
Many other viruses, including caliciviruses, herpesviruses, adenoviruses and
parvoviruses, circulate in marine mammal populations.
37

38. Capsid
 A capsid is the protein shell of a virus. It consists of several oligomeric structural
subunits made of protein called protomers. The observable 3-dimensional
morphological subunits, which may or may not correspond to individual proteins,
are called capsomeres. The capsid encloses the genetic material of the virus.
 Capsids are broadly classified according to their structure. The majority of viruses
have capsids with either helical or icosahedral structure.
 Some viruses are enveloped, meaning that the capsid is coated with a lipid
membrane known as the viral envelope. The envelope is acquired by the capsid
from an intracellular membrane in the virus' host; examples include the inner
nuclear membrane, the Golgi membrane, and the cell's outer membrane.
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38

39. Illustration of geometric model changing between two possible capsids.
A similar change of size has been observed as the result of a single amino-acid mutation
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39

40. Specific shapes
Icosahedral Prolate Helical
40

41. Functions and Origin and evolution
 The functions of the capsid are to:
 protect the genome,
 deliver the genome, and
 interact with the host.
 The virus must assemble a stable, protective protein shell to protect the
genome from lethal chemical and physical agents. These include forms of
natural radiation, extremes of pH or temperature and proteolytic and
nucleolytic enzymes. For non-enveloped viruses, the capsid itself may be
involved in interaction with receptors on the host cell, leading to penetration of
the host cell membrane and internalization of the capsid. Delivery of the
genome occurs by subsequent uncoating or disassembly of the capsid and
release of the genome into the cytoplasm, or by ejection of the genome
through a specialized portal structure directly into the host cell nucleus.
 It has been suggested that many viral capsid proteins have evolved on
multiple occasions from functionally diverse cellular proteins. The recruitment
of cellular proteins appears to have occurred at different stages of evolution,
so that some cellular proteins were captured and refunctionalized prior to the
divergence of cellular organisms into the three contemporary domains of life,
whereas others were hijacked relatively recently. As a result, some capsid
proteins are widespread in viruses infecting distantly related organisms (e.g.,
capsid proteins with the jelly-roll fold), whereas others are restricted to a
particular group of viruses (e.g., capsid proteins of alphaviruses).
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42. Viral envelope
 Some viruses (e.g. HIV and many animal viruses) have viral
envelopes as their outer layer at the stage of their life-cycle when they
are between host cells. Some enveloped viruses also have a protein
layer called a capsid between the envelope and their genome . The
envelopes are typically derived from portions of the host cell
membranes (phospholipids and proteins), but include some viral
glycoproteins. They may help viruses avoid the host immune system.
Glycoproteins on the surface of the envelope serve to identify and bind
to receptor sites on the host's membrane. The viral envelope then
fuses with the host's membrane, allowing the capsid and viral genome
to enter and infect the host.
 The cell from which the virus itself buds will often die or be weakened
and shed more viral particles for an extended period. The lipid bilayer
envelope of these viruses is relatively sensitive to desiccation, heat,
and detergents, therefore these viruses are easier to sterilize than
non-enveloped viruses, have limited survival outside host
environments, and typically must transfer directly from host to host.
Enveloped viruses possess great adaptability and can change in a
short time in order to evade the immune system. Enveloped viruses
can cause persistent infections.
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43. Classes of Enveloped and Nonenveloped Viruses
1. Enveloped Viruses
i. DNA viruses
ii. RNA viruses
iii.Retroviruses
2. Nonenveloped Viruses
i. DNA viruses
ii. RNA viruses
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44. Enveloped Viruses Examples
Herpesviruses
Poxviruses
Hepadnaviruses
Asfarviridae
DNA viruses
Flavivirus
Alphavirus
Togavirus
Coronavirus
Hepatitis D
Orthomyxovirus
Paramyxovirus
Rhabdovirus
Bunyavirus
Filovirus
RNA viruses
Retroviruses
Retroviruses
Adenoviridae
Papillomaviridae
DNA viruses
Picornaviridae
Caliciviridae
RNA viruses
Nonenveloped Viruses Examples
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45. Virus classification
1. ICTV classification
2. Structure-based virus classification
3. Baltimore classification
I. DNA viruses : ( dsDNA , ssDNA )
II. RNA viruses : ( dsRNA , +ssRNA , -SSRNA )
III. Reverse transcribing viruses ( ssRNA-RT , dsDNA-RT )
4. Holmes classification
5. LHT System of Virus Classification
6. Subviral agents
I. Viroids
II. Satellites
III. Prions
IV. Defective interfering particles
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46. Realm (-viria)
Subrealm (-vira)
Kingdom (-viriae)
Subkingdom (-virites)
Phylum (-viricota)
Subphylum -viricotina
Class-viricetes
Subclass (-viricetidae)
Order (-virales)
Suborder (-virineae)
Family (-viridae)
Subfamily (-virinae)
Genus (-virus)
Species
International Committee
on Taxonomy of Viruses
Classification (ICTV)
Viral classification starts at the
level of realm and continues as
follows, with the taxon suffixes
given in italics
46

47. 47

48. Baltimore Classification 48

49. DNA Viruses
Virus family Examples (common names)
Virion
naked/enveloped
Capsid
symmetry
Nucleic acid
type
Group
1. Adenoviridae
Adenovirus, infectious canine
hepatitis virus
Naked Icosahedral ds I
2. Papovaviridae
Papillomavirus, polyomaviridae,
simian vacuolating virus
Naked Icosahedral ds circular I
3. Parvoviridae
Parvovirus B19, canine
parvovirus
Naked Icosahedral ss II
4. Herpesviridae
Herpes simplex virus, varicella-
zoster virus, cytomegalovirus,
Epstein–Barr virus
Enveloped Icosahedral ds I
5. Poxviridae
Smallpox virus, cow pox virus,
sheep pox virus, orf virus,
monkey pox virus, vaccinia
virus
Complex coats Complex ds I
6. Anelloviridae Torque teno virus Naked Icosahedral ss circular II
7. Pleolipoviridae HHPV1, HRPV1, HGPV1, His2V Enveloped
ss/ds
linear/circula
r
I/II
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49

50. RNA Viruses
Virus Family Examples (common names)
Capsid
naked/enveloped
Capsid
Symmetry
NA type Group
Reoviridae Reovirus, rotavirus Naked Icosahedral ds III
Picornaviridae
Enterovirus, rhinovirus, hepatovirus, cardiovirus,
aphthovirus, poliovirus, parechovirus, erbovirus
kobuvirus, teschovirus, coxsackie
Naked Icosahedral ss IV
Caliciviridae Norwalk virus Naked Icosahedral ss IV
Togaviridae Rubella virus, Eastern equine encephalitis Enveloped Icosahedral ss IV
Arenaviridae Lymphocytic choriomeningitis virus, Lassa fever Enveloped Complex ss(-) V
Flaviviridae
Dengue virus, hepatitis C virus, yellow fever virus,
Zika virus
Enveloped Icosahedral ss IV
Orthomyxoviridae
Influenzavirus A, influenzavirus B, influenzavirus C,
isavirus, thogotovirus
Enveloped Helical ss(-) V
Paramyxoviridae
Measles virus, mumps virus, respiratory syncytial
virus, Rinderpest virus, canine distemper virus
Enveloped Helical ss(-) V
Bunyaviridae California encephalitis virus, Sin nombre virus Enveloped Helical ss(-) V
Rhabdoviridae Rabies virus, Vesicular stomatitis Enveloped Helical ss(-) V
Filoviridae Ebola virus, Marburg virus Enveloped Helical ss(-) V
Coronaviridae SARS-CoV-2 Enveloped Helical ss IV
Astroviridae Astrovirus Naked Icosahedral ss IV
Bornaviridae Borna disease virus Enveloped Helical ss(-) V
Arteriviridae Arterivirus, equine arteritis virus Enveloped Icosahedral ss IV
Hepeviridae Hepatitis E virus Naked Icosahedral ss IV
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51. Reverse Transcribing Viruses
Virus Family
Examples
(common names)
Capsid
naked/enveloped
Capsid
Symmetry
Nucleic acid
type
Group
Retroviridae HIV Enveloped dimer RNA VI
Caulimoviridae
Caulimovirus,
Cacao swollen-
shoot virus
(CSSV)
Naked VII
Hepadnaviridae Hepatitis B virus Enveloped Icosahedral
circular,
Partially ds
VII
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51

52. Holmes classification
 Group I: Phaginae (attacks bacteria)
 Group II: Phytophaginae (attacks plants)
 Group III: Zoophaginae (attacks animals)
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53. LHT System of Virus Classification
Phylum Vira (divided into 2 subphyla)
 Subphylum Deoxyvira (DNA viruses)
 Class Deoxybinala (dual symmetry)
 Order Urovirales
 Family Phagoviridae
 Class Deoxyhelica (helical symmetry)
 Order Chitovirales
 Family Poxviridae
 Class Deoxycubica (cubical symmetry)
 Order Peplovirales
 Family Herpesviridae (162
capsomeres)
 Order Haplovirales (no envelope)
 Family Iridoviridae (812 capsomeres)
 Family Adenoviridae (252 capsomeres)
 Family Papiloviridae (72 capsomeres)
 Family Paroviridae (32 capsomeres)
 Family Microviridae (12 capsomeres)
 Subphylum Ribovira (RNA viruses)
 Class Ribocubica
 Order Togovirales
 Family Arboviridae
 Order Tymovirales
 Family Napoviridae
 Family Reoviridae
 Class Ribohelica
 Order Sagovirales
 Family Stomataviridae
 Family Paramyxoviridae
 Family Myxoviridae
 Order Rhabdovirales
 Suborder Flexiviridales
 Family Mesoviridae
 Family Peptoviridae
 Suborder Rigidovirales
 Family Pachyviridae
 Family Protoviridae
 Family Polichoviridae
53

54. Subviral agents
 Viroids
 Family Avsunviroidae
 Genus Avsunviroid; type species: Avocado
sunblotch viroid
 Genus Pelamoviroid; type species: Peach
latent mosaic viroid
 Genus Elaviroid; type species: Eggplant
latent viroid
 Family Pospiviroidae
 Genus Pospiviroid; type species: Potato
spindle tuber viroid
 Genus Hostuviroid; type species: Hop stunt
viroid
 Genus Cocadviroid; type species: Coconut
cadang-cadang viroid
 Genus Apscaviroid; type species: Apple scar
skin viroid
 Genus Coleviroid; type species: Coleus
blumei viroid 1
 Satellite viruses
 Single-stranded RNA satellite viruses
 Subgroup 1: Chronic bee-paralysis satellite
virus
 Subgroup 2: Tobacco necrosis satellite
virus
 Double-stranded DNA satellite viruses
(virophages)
 Satellite nucleic acids
 Single-stranded satellite DNAs
 Double-stranded satellite RNAs
 Single-stranded satellite RNAs
 Subgroup 1: Large satellite RNAs
 Subgroup 2: Small linear satellite RNAs
 Subgroup 3: Circular satellite RNAs
(virusoids)
54

55. Subviral agents
 Prions
 Mammalian prions:
 Agents of spongiform
encephalopathies
 Fungal prions:
 PSI+ prion of Saccharomyces
cerevisiae
 URE3 prion of Saccharomyces
cerevisiae
 RNQ/PIN+ prion of Saccharomyces
cerevisiae
 Het-s prion of Podospora anserina
 Defective interfering particles
 Defective interfering RNA
 Defective interfering DNA
55

56.  I am an academic who believes the role of a researcher is not only to better understand the world
but also to improve it and I devote my time equally to both goals. I work as a medical
representative then a research chemist .
 My primary position is at FLI as Researcher Chemist My studies about the role of biochemistry
and biotechnology in Virology Science . Current projects studding the mechanism of action of
COVID-19 in Human and capsid structure and the prevention of diseases by providing the
background for modern control strategies for animal diseases and zoonoses .
 Mobile : +201272122218
 E-Mail : m7moud.zidan@fli.de
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