Micro 615 Principals of Virology: Virus Structure, Classification, Detection

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Micro 615Principals of Virology Virus
Structure, Classification, Detection
PersistenceAlice Telesnitsky
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I. What is a virus? A. A virus is a set of
genes, either DNA or RNA, packaged in a
protein-containing coat B. Viruses are obligate
intracellular parasites capable of directing
their own replication
viruses are small
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II. Examples of how viral infections are
important in many A. Viruses cause diseases
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HIV infection may become a common chronic
condition
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PolioInapparent infection in 90-95Abortive
infection in 4-8Major CNS involvement in 1-2
B. Can replicate in some humans without causing
disease 1. Asymptomatic carriers with inapparent
(subclinical) infection can transmit viral disease
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B. Can replicate in some humans without causing
disease, cont. 2. Viruses serve as co-factors
for some diseasesC. Significant in initiating
disease in aging, immune-deficient (eg
transplant recipients) and other at-risk
populationsD. Virus-related entities such as
endogenous retroelements 1. A significant
portion of the human genome 2. Endogenous
viruses can be mutagens and are a potential
problem in xenograftsE. Emerging viruses
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III. Structural features of human viruses
from the inside outA. GenomesB. CapsidsC. With
or without envelopA virus is a set of genes,
either DNA or RNA, packaged in a
protein-containing coat
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A. Genomes 1. RNA or DNA single- or
double-stranded one or several segments 2.
Small genomes--limited coding capacityB. Capsid
morphologies 1. Helical
Helical rods of a plant virus
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Rabies an enveloped helical virus
Cartoon of rabies Rabies virus
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2. Cubic---Icosahedral20 triangular faces, 12
vertices
adenovirus
3. Other example bullet-shaped capsid of
HIV
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C. Exterior surface 1. Naked or enveloped 2.
Physical properties affect transmission
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IV. Virus classification
influenza
HIV
polio
small
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DNA viruses
large
small
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V. Assay and detection of viruses and their
replicationviruses are obligate intracellular
pathogens A. Virus culture 1. Animals (or
plants, bacteria, etc) 2. Tissue
culture
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B. Assays and detection 1. Plaque assay a. End
point dilution b. Plaque forming units
(PFU) 2. Agglutination 3. Infectivity eg
LD50 4. Cytopathic effect (CPE)
syncytia
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4. Other ways of measuring virus a. Count
particles by electron microscopeViruses differ
in infectious units per biochemical unit
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VI. General types of viral infectionsA. Acute
clinical disease 1. Localized virus
replication at site of infection 2.
Disseminated spread to and replication in
secondary sitesB. Persistent infections on
organism level 1. Chronic infections eg acute
phase disease followed by smoldering infection
sometimes seen for adenovirus 2. Latent
infections eg herpes 3. Others
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C. Viral persistence on cellular level
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VII. Biology of herpes viruses A. Biology 1.
Large enveloped DNA viruses 2. Possess many
genes 3. Replication involves acute and latent
phasesB. Human infection by Herpes simplex
virus I 1. Acute phase disease 2. Latency a.
Physiology of virus and of cell during
latency b. Immune response avoidance 3.
Reactivation
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C. Other human Herpes viruses 1. HSV-II 2.
Varicella-Zoster (VSV) Chicken pox and
shingles 3. Cytomegalovirus (CMV) a.
Epidemiology b. Prenatal infection c.
Transplant mortality
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4. Epstein Barr virus a. Discovery and
association with Burkitt's lymphoma Environmenta
l cofactors? b. Primary infection
(mononucleosis) c. Association with other
malignancies5. HHV-6 (roseola) HHV-76.
Kaposi's Sarcoma Herpes Virus (KSHV)/HHV-8 a.
Epidemiology and prevalence HIV an
environmental co-factor b. Primary disease
unknown