Iridoviridae

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Iridoviridae
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• Iridoviridae derived from Greek/Roman goddess
  of the rainbow Iris.
• This is due to the iridescence that can be
  observed in heavily infected insects.

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Iridoviridae
First found in 1954 in the larvae of a crane fly
Most likely found world wide
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Viral Genome and Structure
Large, 120-300 nm in diameter Linear ds DNA 150
to 280 kbp Can have an envelope, acquired by
budding through the hosts membrane.
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Iridoviridae

• Found in invertebrate and non-mamalian vertebrate
  hosts.
• 4 genera
• Ranavirus----amphibians reptiles
• Lymphocystivirus------fresh and marine fish
• Iridovirus----invertebrates (including
  barnacles)
• Choloridovirus----insects

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Iridoviridae Diseases
Genus Vernacular name Type
species Iridovirus Small
iridescent insect virus Chilo iridescent
virus (IV6) Chloriridovirus Large
iridescent insect viruses Mosquito
iridescent virus (IV3) Lymphocystivirus
Lymphocystis disease virus Lymphocystivirus
type 1 (LCDV-1) Ranavirus Frog
virus Frog Virus 3 (FV3)
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Virus Structure
Virion composed of three concentric domains 1.
Outer proteinaceous icosahedral capsid (Common
feature of all genera, makes up 45 of total
virion protein) 2. Intermediate lipid membrane 3.
Central core
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Viral Replication
1. Virus enters host via endocytosis and
uncoating occurs 2. Viral DNA transported to the
cell nucleus and transcription is initiated by
the hosts RNA polymerase II 3. Parental DNA
used to produce genome and greater than genome
length DNA that is used as a template 4. Progeny
DNA transported to the cytoplasm where large
concatamers are formed 5.Concatemers then
packaged into virions and exit host by budding
or cell lysis
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Iridoviridae Replication
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Disease Presentation
Chronic or benign skin infections (lesions,
ulcers), enlarged cells of organs. Problematic
aesthetically.
In insects iridescent patches In fish swim
bladder expands, loss of equilibrium In
amphibians has been implicated in mass die offs
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Pathogenesis
Little is known about the pathogenesis of
iridoviruses. The pathogenesis is, however,
temperature dependent and iridoviruses are thus
confined to cold-blooded hosts. In a lethal
infection by insect iridoviruses the fat bodies
and haemocytes are the initial sites of
replication, this leading to a systemic
infection. Insects become flaccid and iridescent
7-10 days post-infection although death may take
3 weeks or longer.
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Pathogenesis
Virus is very stable and can survive outside the
host It can tolerate a wide range of pH (4-12)
and is able to overwinter in the bottom of ponds.
Could be transmitted through water, on feathers
or beaks of birds, nets, or through cannibalism.
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Possible Implications
Insects Apiculture, Biocontrol
In insects, virus has been isolated from black
flies, Japanese beetles, corn earworms, rice stem
borers, locusts, mosquitoes, and honey bees
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Possible Implications
Vertebrates Aquaculture, Animal Husbandry, Zoos,
Ecological
In fish systemic disease found in Gouramis (pet
fish), salmonids (salmon trout), catfish,
Large Mouth Bass In reptiles Box turtles, Gopher
Tortoise, Green Tree Python In amphibians
Bullfrog, Edible Frog, Leopard Frog, Tiger
Salamander, Red Spotted Newt Eft.
Because of similar characteristics in disease
among fish, amphibians, and reptiles, one of
these species may act as a reservoir host or
amplifying host to others in the same
environment.
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ReleaseAugust 8, 2000 USGS Diagnoses Causes of
Many U.S. Amphibian Die-Offs U. S. Geological
Survey (USGS) scientists are making headway in
unraveling clues to the causes of massive
die-offs of frogs and other amphibians. The
agency announced today that a little-understood,
emerging iridovirus disease associated with large
die-offs of frogs and salamanders in the Midwest
and the East has caused another recent die-off,
in North Dakota. USGS wildlife pathologist D.
Earl Green said an iridovirus infection is the
culprit in most of the deaths of U.S. western
tiger salamanders at the U.S. Fish and Wildlife
Service's Cottonwood Lake Study Area near
Jamestown, North Dakota. "The U.S. Geological
Survey is leading the government's efforts to
help determine why amphibians are disappearing,"
said Interior Secretary Bruce Babbitt. "This is a
crisis that has attracted worldwide concern. It
requires timely, aggressive research. It is no
exaggeration to say that USGS research on these
die-offs has global implications."
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Amphibian Decline

• Ranavirus
• World wide decline of frogs, salamanders and
  other amphibians
• Amphibians hypothesized to be sentinels of
  environmental degradation because of
  characteristics of their biology and physiology,
  such as permeable eggs, skin and gills and
  complex life-cycles, which make them more
  susceptible to these effects.
• North American species under threat is the Tiger
  Salamander Ambystoma tigrinum.

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African Swine Fever

• Originally grouped as an Iridovirus now has its
  own Family Asfarviridae from African Swine Fever
  And Related Viruses
• Spread mechanically and with a tick (Ornithodoros
  spp.) vector
• In severe disease can cause up to 100 mortality
  in pigs.