“Iridoviridae” derived from Greek/Roman goddess of the rainbow “Iris”. • This is due to the iridescence that can be observed in heavily infected insects.
Iridoviridae First found in 1954 in the larvae of a crane fly Most likely found world wide
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 host’s membrane.
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
Iridoviridae Diseases GenusVernacular nameType 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)
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
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 host’s 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
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 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.
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 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.
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 salamandersat 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.