Summary
Summary - VIR-20803 (VIR-20803)
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Summary of human infectious diseases
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Human Infectious DiseasesViruses changes the course of history viruses been brought
through travelling (Malaria is not a virus parasite)
For example Poxvirus, influenzavirus, HIV and COVID
Spanish Flu
The Spanish flu in 1918 is caused by the Influenzavirus especially young people getting sick,
because their immune system reacts heavily
Eventually after the third wave the virus died out people were immune or have died
The Spanish flu caused a dip in life expectancy but this increased very fast
Smallpox virus
Brought to the Americans
Due to vaccination programs it is not here anymore
o Same for Poliovirus
Measles
Virus with the biggest R-score (like 30)
o Because it travels through the air
Recurring measles outbreaks due to poor
vaccination (Bible belt)
Herpes Simplex virus (HSV)
Once infected you will carry it in your
body for the rest of your life especially
when you have a lower resistance
Chicken pox and shingles (gurdle herpes) caused by varicella zoster virus (a herpesvirus)
o Sometimes the chicken pox virus is reactivated in later life cause gordelroos
which is central nervous system related
HPV, genital warts
Mostly a benign virus
Sexually transmitted
Some variants however cause (cervical) cancer
Starting 2009, HPV vaccine against cervical cancer is included in national vaccination program
HIV-infection can lead to AIDS
Acquired ImmunoDeficiency Syndrome: virus targets the immune system (to low levels of T-cells)
Breaks down the immune system: opportunistic infections such as by Candida lead to 100% mortality
Foot-and-Mouth disease virus (FMDV): FMDV is an extremely infectious picornavirus
Virus infections often dictate population dynamics:
Phocine distemper virus
2002 epidemic killed 21700 seals
Every decade in the Dutch Wadden Sea
Relative of measles
,Zika Virus
Almost gone because of natural immunity
Brain is under developed
Virus
Viruses are the smallest genetic entities which are only visible by a electron microscopy
Their presence often causes infectious diseases
Virus can’t do anything until it enters an host cell
The surface proteins on the protein coat can recognize the cells they want to effect when
the particle enters the cell, the protein coat falls apart nucleic acid is released RNA starts to
replicate which goes very quickly
Characteristics of viruses:
1. Infectivity (property to penetrate a cell, to multiply
within this cell, and to leave the cell spread to other
cells)
2. Obligate, intracellular parasitism (virus can’t multiply
without entering a living host cell)
-No protein synthesizing machinery
-No energy producing machinery
3. Property to survive outside a living cell (in an inert
state or via carrier)
Functions of the protein coat
Protection of the genetic material
Recognition and penetration of the host cell
Escape from the immune/defense system
Therefore: pursuing maximal symmetry (
minimal energy)
Viral coat
Viral coat is built up by smaller subunits
Saving space on the genome
Genetic stability
Possibility to self-assembly
Structural requirement: assembly symmetric
particle from asymmetric proteins
,All spherical viruses have an icosahedrical
building plan, but some viruses are bigger than
others further ‘’triangulation’’
E-Module
Viruses are at the boundary of the living world: when in rest they are inert, "dead" particles, as soon
as they infect a host cell they might start to multiply rapidly, a process paralleled by pathological
effects (diseases).
Tetanus, whooping cough, diphtheria and the pest are examples of diseases caused by bacteria.
Bacterial diseases may be controlled by antibiotics (or prevented through vaccination) and therefore
they appear less prominent these days compared to the past. A recent example of an emerging
bacterial disease in the Netherlands is Q-fever, a disease that primarily infects goats but occasionally
also infects people (zoonotic disease). Of course there are also infectious diseases caused by
parasites and these include malaria, trypanosomiasis, and elephantiasis.
Viruses possess genetic material surrounded by a protecting protein coat/ lipid envelope. Viruses are
the only living entities on earth that may have a genome composed of RNA viruses can be divided
in RNA and DNA viruses
Viruses and viroid’s higher mutation rate than cellular organisms
Mutation rate: number of nucleotide positions per 1000nt of genome length that mutate per year
nature of genetic material and the number of generations per year affects the mutation
rate
Viruses with a RNA genome mutate quicker than viruses with a DNA genome DNA polymerases
have proofreading ability, which means that they check their work by comparing it to the template.
RNA polymerases don’t have this ability and make more mistakes this explains why most
emerging viruses that threaten human health are RNA viruses
Some viruses carry all their genetic information on a single RNA or DNA molecule, while others have
a genome divided over several molecules of RNA or DNA, in which case their genome is segmented.
Viral DNA genomes may be linear or circular. All viral RNA genomes are linear, except the genomes of
viriods, which consist of circular, single-stranded RNA with no coding capacity (i.e. viroid genomes do
not encode proteins). Viroids are the ultimate “selfish genes”.
The exact properties of the viral genetic material depend on
the family to which the virus belongs.
, Most negative-stranded RNA viruses lack a clear protein coat, although a nucleoprotein protects the
RNA. These viruses also have a viral envelope that surrounds and protects the genome.
The viral-encoded proteins that are present in the virus particle (virion) are called structural
proteins (e.g. coat proteins, nucleoprotein, glycoproteins). Non-structural proteins, on the other
hand, are not present in the virus particle, but are produced after the virus has entered a host cell.
Non-structural (Ns) proteins have crucial roles in the virus replication cycle. These may have essential
enzymatic activities (e.g. viral polymerase, protease, helicase, etc.) or affect the host's immune
response, such as interferon antagonists or anti-apoptotic proteins. The NS proteins are also encoded
by the viral genome, but are not integrated in the virions. The RdRP is normally seen as a non-
structural protein, but this is not entirely correct for negative-stranded RNA viruses, since a small
amount is needed in the virion to initiate the viral replication.
When the outermost layer of a virus particle is a lipid membrane, then this envelope contains one or
more glycoproteins. These are proteins with complex sugar groups (glycans) attached. This is for
instance the case for influenza virus, which carries two glycoproteins: haemagglutinin (HA or H)
and neuraminidase (NA or N).
The outer layer of a virus (either the protein coat or the viral envelope containing the glycoproteins)
forms the interface between the virus particle and the host cell
surface. This outer layer executes specific functions in terms of
recognizing and binding to suitable host cells and assisting the viral
genome to enter these cells.
The surrounding protein coat and/or lipid envelope needed
for protection of the viral genome during the extracellular state of
the virus. A special functional requirement in the extracellular
stage is avoiding recognition and inactivation by the immune
system of the host. This is achieved by having a protein coat or
lipid envelope with maximal symmetry and with minimal variation
at the surface the number of antigenic determinants is kept to a minimum. The more antigenic
determinants the higher the risk of recognition by appropriate B cell receptors and antibodies.
Viral coat is built from individual protein subunits coat proteins their tertiary structure is never
symmetrical
The required symmetry of a virus particle to avoid immune attack is realized by regular
arrangement of smaller, non-symmetric components. Viral coat proteins encoded by relatively
small open reading frames to achieve this these small units serve as building blocks
Small genes increase genetic stability of the virus, because the risk of lethal mutations
with an open reading frame is smaller
Genetic space reduction: composing a virion from small but identical blocks, limits the length of the
coding sequence in the genome and limits the space needed inside the virus particle to package the
genome
Different shaped viruses
Rod shaped virus: built up by a growing spiral (helical symmetry) in which all subunits are
placed in equivalent positions relative to each other, except for the first and the last coat
protein molecules
o Viral genome encapsidated as a spiral or helix
o Size of the resulting rod-shaped particles can freely vary with the size of the genome
to be encapsidated
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