Iridoviridae

• “Iridoviridae” derived from Greek/Roman goddess of the rainbow “Iris”.

• This is due to the iridescence that can be observed in heavily infected insects.

IridoviridaeFirst found in 1954 in the larvae of a crane fly

Most likely found world wide

Large, 120-300 nm in diameterLinear ds DNA150 to 280 kbpCan have an envelope, acquired by budding through the host’s membrane.

Viral Genome and Structure

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

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)

Iridoviridae Diseases

Virus Structure

Virion composed of three concentric domains1. Outer proteinaceous icosahedral capsid(Common feature of all genera, makes up ~45% of total virion protein)

2. Intermediate lipid membrane3. Central core

Viral Replication

1. Virus enters host via endocytosis and uncoating occurs

2. Viral DNA transported to the cell nucleusand transcription is initiated by the host’s RNA polymerase II

3. Parental DNA used to produce genome and greater than genome length DNA that is used as a template4. 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

Iridoviridae Replication

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

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.

Pathogenesis

Virus is very stable and can survive outside the hostIt 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 orbeaks of birds, nets, or through cannibalism.

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

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 PythonIn 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 areservoir host or amplifying host to others in the same environment.

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 an iridovirus infection is the culprit in most of the deaths of U.S. western tiger salamandersmost 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."

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.

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.