Download An overview to virology! - University of the Witwatersrand

An overview to virology!
U luv ‘em
They
make
you sick
They make
you work
U hate ‘em
They make you scared
U fight
‘em
Objectives
•
•
•
•
•
To describe the classification of viruses.
To understand the spectrum of disease
caused by viruses.
To understand the public health
implications of viral infections.
To describe the pathogenesis of viral
infections.
To discuss the transmission of viral
infections.
What is a virus?
• Genetic material inside a protein coat.
• Very small 20 - 300nm.
Pox virus 300nm
Parvovirus 20nm
E.coli 1000nm
What else makes up a virus?
• A virus is an obligate intracellular parasite.
It is completely dependent on living cells
for replication and survival.
• Unlike other larger organisms, it contains
either RNA or DNA. Never both forms of
nucleic acid.
Viral structure.
• There are two basic shapes found in
viruses:
• Icosahedral structure:
• Helical structure:
Viruses consist of the following
components:
The matrix
protein
The genome. RNA
or DNA.
The capsid
The envelope
Various non-structural
proteins
Glycoprotein
spikes
Viral classification.
• Type of nucleic acid:
– RNA or DNA
• Number of strands of nucleic acid.
• Polarity of the genome.
– Positive sense or Negative sense
• Shape of the capsid / nucleocapsid
– Icosahedral or Helical
• Presence of an envelope
Non Enveloped
DS
Enveloped
DNA
SS
Virus
Adeno
Papova
Herpes
Pox
Hepadna
Non Enveloped
Parvo
Enveloped
Retro
Arena
DS
Non Enveloped
RNA
Enveloped
SS
Non Enveloped
Reo
Para,
Ortho etc
Picorna
Calici
Nomenclature conventions:
• Family: ---viridae e.g. Herpesviridae
• Subfamily:---virinae e.g.
alphaherpesvirinae
• Genus: ---virus e.g. Herpesvirus
• Species: --- e.g. Herpes Simplex virus
• Type: --- e.g. Herpes simplex virus type 1
Pathogenesis of viral infections:
• Localized:
– Portal of entry is where the virus replicates
and causes disease.
– There is seldom spread of the virus beyond
the localized area of infection
– Short incubation period of 1-5 days.
– Symptoms may be caused by the viral
replication or by the immune response to the
virus.
Generalized infections
Portal of entry
Incubation
period
Migration to local lymph nodes
14-21 days
Primary viraemia
RES
Prodrome
2-3 days
Sick
Secondary viraemia
Target organs
How transmission happens:
• Inhalation
• Ingestion
• Direct contact with skin or mucous
membranes
• Indirect contact - fomites
• Transplacental
• Organ transplant or blood transfusion.
Conclusion
• Small BUT:
– Virulent
– Dangerous
– Major public health threats
– Major public health disasters.