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2 genera
o Aviadenovirus (avian)
o Mastadenovirus
Frequent cause of URT infections (colds)
o 5-10% URT in children
First isolated in human adenoids
Widespread in nature
Can undergo latent infection in lymphoid tissue, becoming
reactivated sometime later
Medium-sized (60-90nm)
Non-enveloped, icosahedral
Non-segmented, linear, dsDNA (26-45 Kbp)
o Carries 22-40 genes
Largest non-enveloped virus
o They are the maximum size able to be transported through
the endosome
o Membrane bound compartment inside eukaryotic cells
o Compartment of the endocytic membrane transport
pathway from the plasma membrane to the lysosome
Oncogenic potential
Can be vectors to carry and express foreign genes for
therapeutic purposes
o Easily manipulated in vitro
Most infects vertebrae
Enveloped, RNA
Replicated via a DNA intermediate
Stores its nucleic acid in the form of a (+) mRNA genome
o Serves as means of delivery of that genome into cells it
targets as an obligate parasite
Relies on the enzyme reverse transcriptase to perform the
reverse transcription of its genome from RNA to DNA
o Can be integrated into the host’s genome with an integrase
Once in the host’s cell, the RNA strands undergo reverse
transcription in the cytosol and are integrated into the host’s
genome, at which point the retroviral DNA is referred to as a
Difficult to detect the virus until it has infected the host
Retrovirus enters a host cell – provokes RNA strands inside of the
normally-functioning cell – reverse transcription (violates central
o DNA – RNA – Protein
Retrovirus inside of a cell = first two steps of the process will be
o Host cell becomes provirus
When retroviruses have integrated their genome into the germ
line – their genome is passed on to a following generation
Endogenous retroviruses
o Makes up a large portion of the human genome
o Most insertions have no known function and is often
referred to as “junk DNA”
o Play important roles in host biology
Gene transcription
Cell fusion during placental development in the course
of the germination of an embryo
Resistance to exogenous retroviral infection
Greek: Herpein: to creep = chronic, latent, recurrent infections
Composed of relatively large dsDNA, linear
Encodes 100-200 genes encased within an icosahedral protein
~100 herpesviruses have been isolated
8 known human herpesviruses
o Infects humans
Ubiquitous and contagious
o Watery blisters in the skin or mucus membranes of the
mouth, lips, genitals
Heals with a scab characteristic of herpetic disease
As neurotropic and neuroinvasive viruses
o HSV 1 and 2 – persists in the body for the life of the carrier
by becoming latent and hiding from the immune system in
the cell bodies of nerves
After initial infection, some experience sporadic episodes of
viral reactivation or outbreaks
o In an outbreak, the virus in a nerve cell becomes active and
is transported via the nerve’s axon to the skin, where virus
replication and shedding occurs and causes new sores
No known cure for HSV infection
o Treatments can reduce likelihood of viral shedding
Viruses that infects bacteria
Among the most common biological entities on earth
Some named as a member of a T series
Sea water
o One of the densest natural sources for phages and other
o Up to 9x108 virions/ml in microbial mats at the surface
o Up to 70% of marine bacteria may be infected by phages
Used over 60 years as an alternative to antibiotics in the former
Soviet Union and Eastern Europe
Seen as possible therapy against multi-drug resistant strains of
many bacteria
First reported in the US (1981)
33 million worldwide are infected
Infection cycle
o Virus hones in on CD4 T cells, infecting and killing them
Without T cells, body cannot defend against invading
bacteria or viruses
Each HIV particle possesses glycoprotein (gp120) on
its surface
Precisely fits a cell-surface marker protein (CD4)
on surfaces and T cells
o After docking onto the macrophage CD4 receptor, HIV
requires a second macrophage receptor (CCR5) to cross
the cell membrane
Once inside the macrophage, the HIV particle sheds
its protective coat
RNA and reverse transcriptase left floating in the
Double strand of DNA, complementary to RNA
Viruses released via exocytosis
Future of HIV treatment
o Combination drug treatment
AZT and protease inhibitors
Keeps disease in check
o Vaccine therapy
May reduce reproductive capability of HIV
o Blocking replication
Chemokines bind to and block receptors
CAF: prevents viral replication
o Disabling receptors
Animal retroviruses distinguished by their capsid
Types A, B, C
Subtypes differ in protein spikes
Association between Hep B and liver cancer
HPV and cervical cancer
15% of all cancers worldwide
Viral genes are readily re-assorted by genetic recombination
Novel combinations of H and N spikes unrecognizable by
human antibodies
Inability to make perfect vaccines
Flu pandemics
Ebola: 90% lethality
o 2003
o From civets in china eaten as delicacies
o UK variant B.1.1.7,20I/501Y.V1
More transmissible
70% more contagious
Proteinaceous infectious particle
Nobel prize 1997
Responsible for transmissible spongiform encephalopathies
Scrapie: sheep
Mad cow disease: cattle
o Kuru: fore people in new guinea
Tiny, naked molecules of RNA
Important infectious disease agent in plants
o Recent outbreak killed 10 M coconut palms in PH
Resembles sequences of introns within ribosomal RNA genes
o Capable of catalyzing destruction of chromosome integrity