Aquaculture Viruses What a Virus IsnвЂ™t вЂў Not a bacterium... вЂў Not independent... вЂў Cannot survive in absence of a living cell within which to replicate... вЂў Antibiotics generally donвЂ™t work on them... What Viruses Are... вЂў Infectious agents composed mainly of nucleic acid with a protein coat (capsid) вЂў Visible with electron microscope (10-200 nM) вЂў Carry on normal cell-like function (unless free, then infectious) вЂў In infectious form: no growth; no respiration??? вЂў Can enter living plant, animal or bacterial cell Virus Appearence? вЂў 1. Capsid вЂў 2. Core and genetic material (DNA/RNA) вЂў Capsid: outer shell of the virus which encloses genetic material (link: chemical structure of capsid helps determine immune response to virus) вЂў capsid is made of many identical individual proteins вЂў protein core under capsid protecting genetic material вЂў sometimes an additional covering (lipid bilayer w/embedded proteins) on outside known as an envelope ( like a baseball) вЂў various forms: rods, filaments, spheres, cubes, crystals Capsid capsomere: unit/molecule associated with capsid structure Typical Virus Shapes SPHERES RODS CUBES More Virus Shapes Composition of T-Even Bacteriophage вЂў Capsid: brains of virus, tightly-wound protein protecting nucleic acids вЂў Body: attached to capsid head, rod-like structure w/retractible sheath, hollow core вЂў Tail: at end of core is a spiked plate carrying 6 slender tail fibers, anchor virus to its host How do viruses work? вЂў Viruses make use of the host cellвЂ™s chemical energy, protein and nucleic acid synthesizing ability to replicate themselves... вЂў each virus attacks a specific type of cell вЂ“ cold viruses attack cells of the lung вЂ“ the AIDS virus attacks T4 cells of the immune system вЂ“ fish viruses are just as specific Bacteriophage Attack Virusal Mechanism вЂў Viruses contain single- or double- stranded DNA or RNA вЂў Often, the virus alters the intracellular environment enough to damage or kill the cell (oops!!) вЂў If enough cells are destroyed, disease results! Role of RNA/DNA вЂў Supplies the codes for building the protein coat (capsid) and for producing enzymes needed to replicate more viruses вЂў Information given so newly-built viruses can lyse cells (e.g., bacteriophage) вЂў Result: cell destroyed. Bottom Line... вЂў All viruses only exist to make more viruses вЂў Most are harmful вЂў Replication = host cell death. The Virus Invasion: Step by step вЂў Phase 1: Attachment of virus to bacteria, etc. вЂў Phase 2: injection of DNA or RNA вЂў Phase 3: DNA (RNA) enters the host cell вЂў Phase 4:DNA incorporated (10 minutes) hundreds of virions appear causing the cell to rupture, releasing hundreds of small viral replicates вЂў This is how it can replicate so quickly! The Virus Invasion WhatвЂ™s Infected by a Virus? вЂў All living things have some susceptibility to a particular virus вЂў Virus is specific for the organism вЂў Within a species, there may be a 100 or more different viruses which can affect that species alone вЂў Specific: for example, a virus that only affects one organism (humans and smallpox) вЂў Influenza can infect humans and two animals Different Types of Viruses вЂў Major classifications: animal, plant, bacterial вЂў Sub-classified by arrangement and type of nucleic acid вЂў Animal virus group: double-stranded DNA, singlestranded DNA, double-stranded RNA, singlestranded RNA, retrovirus вЂў Influenza: SS-RNA Do Viruses ever Change? вЂў Mutations do occur. вЂў If the mutation is harmful, the new virus particle might no longer be functional (infectious) вЂў However, because a given virus can generate many, many copies, a small number of non-functional viruses is not important вЂў Mutation is not necessarily damaging to the virus -it can lead to a functional but new strain of virus Defense Against Viruses вЂў First Line: skin and mucous membrane, which also lines the gastrointestinal and respiratory passageways вЂў skin is tough and stomach acidity acts as a disinfectant вЂў Second Line: after the virus enters the blood and other tissues, white blood cells and related cells (phagocytes) consume them вЂў accumulation of phagocytes in area of infection is known as вЂњpussвЂќ Defense Against Viruses Antibodies attacking chickenpox virus Defense Against Viruses вЂў вЂў вЂў вЂў Antibodies are the best defense against viruses unfortunately, they are specific in their action chickenpox antibody will only attack a chickenpox virus a particular virus stimulates the production of a particular antibody Defense Against Viral Infection вЂў Animals are protected in several ways: вЂў 1) intracellular: if a particular virus attacks cells, our bodies produce interferons вЂў interferons (alpha, beta or gamma) are proteins which interact with adjacent cells and cause them to become more resistant to infection by the virus вЂў if the resistance is not quite good enough, we become sick Defense Against Viral Infection вЂў 2) immune system (extracellular): kills the virus outside the cell вЂў also kills the infected cells вЂў virus cannot spread вЂў eventually the virus is completely removed and we get better вЂў exception: HIV because it infects cells of the immune system, itself вЂў chemicals/drugs: acyclovir, AZT, HIV protease inhibitor, several fish vaccines available. Major Fish Viruses Major Viral Infections in Fish вЂў Infectious pancreatic necrosis (IPN) вЂў Viral hemorrhagic septicemia (VHS) вЂў Infectious hematopoetic necrosis (IHN) вЂў Channel catfish virus disease (CCVD) (1) Infectious Pancreatic Necrosis (IPN) вЂў What?: viral infection of salmonids (trout and char) вЂў Time: Acute вЂў Result: high mortality (fry and fingerlings) вЂў Rare in larger fish (good thing!) вЂў History: Isolated in Pacific NW in 1960вЂ™s, wiped out brook trout in Oregon in 1971-73 вЂў Size: Only 65 nM in diam., smallest of fish viruses IPN: general notes вЂў Single capsid shell, icosohedral symmetry, no envelope вЂў Contains two segments of DS-RNA вЂў Fairly stable and resistant to chemicals (acid, ether, etc.), variable resistance to freezing вЂў Remains infectious for 3 months in water (uh oh!) вЂў Targets pancreas and hematopoietic tissues of kidney and spleen IPN: epizootiology (disease process) вЂў Who?: All salmonids, brook trout most susceptible, marine fish (flounder?) вЂў Reservoirs (where)?: carriers, once a carrier always a carrier, virus particles shed in feces/urine вЂў Transmission (how?): horizontal, by waters via carriers or infected fry; vertical from adults to progeny; experimentally by feeding infected material, IP injection вЂў Pathogenesis: entry via gills, digestive tract вЂў Environmental factors: mortality reduced at lower temps (why?); however, carriers not reduced IPN: pathology (what do we see?) IPN: detection, diagnosis and control вЂў Isolation: whole fry, kidney, spleen, pyloric cecae, sex fluids are all good sources, .i.e. check these!!! вЂў Presumptive tests: epizootiological evidence and/or typical PCR in infected cells вЂў Definitive tests: serology (fluorescent antibody test (FAT)) вЂў Control: avoid virus in water, virus-free stock, destruction of infected stock, vaccine exists now! How Bad Can It Be?? Fish severely affected by IPNV: вЂў Atlantic salmon* (Salmo salar) brook trout* (Salvelinus fontinalis) brown trout* (Salmo trutta) danio zebrafish* (Brachydanio rerio) rainbow trout* (Oncorhynchus mykiss) yellowtail* (Seriola lalandi) Other species known to be susceptibleвЂ¦ вЂў amago salmon (Oncorhynchus rhodurus) Arctic char (Salvelinus alpinus) Atlantic menhadden (Brevoortia tyrannus) carangids (Carangidae) chinook salmon (Oncorhynchus tshawytscha) chum salmon (Oncorhynchus keta) cichlids (Cichlidae) coho salmon (Oncorhynchus kisutch) common scallop (Pecten maximus) cutthroat trout (Salmo clarki) cyprinids (Cyprinidae) Danube salmon (Salmo hucho) drums/croakers (Sciaenidae) eels (Anguilla spp) grayling (Thymallus thymallus) MoreвЂ¦ вЂў halibut (Hippoglossus stenolepis) Jap. amberjack (Seriola quinqueradiata) lampreys (Petromyzontyidae) loach (Misgurnus anguillicaudatus) masou salmon (Oncorhynchus masou) perches (Percidae) silversides (Atherinidae) soles (Soleidae) striped snakehead (Channa striatus) summer flounder (Paralichthys dentatus) white seabass (Moronidae) carp (Cyprinus carpio) redfin perch (Perca fluviatilis) yellowfin bream (Acanthopagrus australis) herrings/sardines (Clupidae) lake trout (Salvelinus namaycush) left-eye flounders (Bothidae) loaches (Cobitidae) Pacific salmon (Oncorhynchus spp) pikes (Esocidae) sockeye salmon (Oncorhynchus nerka) Southwest European nase (C. toxostoma) suckers (Cotostomidae) turbot (Psetta maxima) whitefish (Coregonidae) goldfish (Carassius auratus) southern flounder (P. lethostigma) Asymptomatic carriers... вЂў coalfish (Pollachius virens) common carp (Cyprinus carpio) discus fish (Symphysodon discus) goldfish (Carrasius auratus) heron (Ardea cinerea) loach (Cobitidae) minnow (Phoxinus phoxinus) noble crayfish (Astacus astacus) Infectious pancreatic necrosis in Atlantic salmon. pike (Esox lucius) Note swollen stomach and 'pop eye' river lamprey (Lampetra fluviatalis) Source: Australian Animal Health Laboratory shore crab (Carcinus maenas) Spanish barbel (Barbus graellsi) white suckers (Catostomas commersoni) ...what now??? (2) Viral Hemorrhagic Septicemia (VHS) (2) Viral Hemorrhagic Septicemia (VHS) вЂў What?: Viral disease of European salmonids вЂў When?: Recognized in Denmark in 1949, isolated from Pacific Coast in 1989 вЂў Size: rhabdovirus, bullet-shaped (one rounded end), 185 x 65 nM, lipoprotein envelope вЂў non-segmented SS-RNA вЂў Constitution: sensitive to ether and chloroform, heat, acid, resistant to freeze-drying Viral Hemorrhagic Septicemia вЂў Produces a general viremia, tissue and organ damage, liver necrosis, spleen, kidney вЂў Epizootiology: cultured rainbow trout, also brown trout, steelhead, chinook, coho (most cases in WA state) вЂў Reservoirs: again...survivors are life-long carriers, usually rainbow trout, brown in Europe вЂў Transmission: horizontal through water, virus can occur on eggs spawned by carriers, IP injection, birds, hatchery equipment Viral Hemorrhagic Septicemia (VHS) вЂў Pathogenesis: infection results in viremia, disrupts many organ systems, 200-300g fish most affected вЂў Environmental factors: low temp (< 8oC, 46oF) вЂў External pathology: lethargy, hanging downward in water (dropsy), swimming in circles, exopthalmia, dark discoloration, hemorrhages in roof of mouth, pale gills w/focal hemorrhages Viral Hemorrhagic Septicemia (VHS) вЂў Internal pathology: gut devoid of food, liver pale, hemorrhages in connective tissue, kidney gray and swollen (chronic), red and thin (acute) вЂў Histopathology: necrosis of liver, kidney nephrons, spleen, pancreas, melanin in kidneys and spleen (OUCH!) вЂў Isolation/tests: isolated from kidney/spleen, epizootiological evidence, definitive test is serum neutralization, or FAT. Viral Hemorrhagic Septicemia (VHS) External hemorrhages Liver red in acute stage Viral haemorrhagic septicaemia in rainbow trout. Note pale color of stomach region, pinpoint haemorrhages in fatty tissue, and pale gills Source: T HГҐstein Viral haemorrhagic septicaemia in rainbow trout. Note swollen stomach and вЂњpop eyeвЂќ Type Prevalent host type and location I-a Farmed rainbow trout and a few other freshwater fish in continental Europe I-b Marine fish of the Baltic Sea, Skagerrak, Kattegat, North Sea, Japan I-c Farmed rainbow trout Denmark I-d Farmed rainbow trout in Norway, Finland, Gulf of Bothnia I-e Rainbow trout in Georgia, farmed and wild turbot in the Black Sea II Marine fish of the Baltic Sea III Marine fish of the British Isles and northern France, farmed turbot in the UK and Ireland, and Greenland halibut (Reinhardtius hippoglossoides) in Greenland IV-a Marine fish of the Northwest Pacific (North America), North American north Atlantic coast, Japan, and Korea IV-b Freshwater fish in North American Great Lakes region Virus presence spread through much of the Great Lakes from 2003-2007. Viral Hemorrhagic Septicemia вЂў Prevention: clean broodstock and water = clean fish, avoid infected broodstock, test and slaughter вЂў Can spread very quickly from farm to farm: avoid close proximity to other farms вЂў Vaccines are under development. вЂў One EPA-approved disinfectant: VirkonВ® AQUATIC (made by Dupont). Bleach kills the VHS virus. (3 ) Infectious Hematopoietic Necrosis (IHN) вЂў Who: sockeye, chinook, rainbows; cohos resistant вЂў When?: 1950вЂ™s in Oregon hatcheries. 100 million mortalities between 1970-1980, if infected, 70% mortality likely, esp. in young fish (fry: 90-95% mort. possible) вЂў What?: bullet shaped rhabdovirus, non- segmented SS-RNA, sensitive to heat and pH, glycoprotein is spiked on surface of virus Infectious Hematopoietic Necrosis (IHN) вЂў Reservoirs: survivors life-long carriers, adults shed virus at spawning вЂў Transmission: horizontal, primary mode is vertical via ovarian fluid (virus hitches ride on sperm into egg); however, feces, urine, and external mucus possible. Also, feeding and inoculation have worked experimentally вЂў Pathogenesis: gills suspected; incubation period depends on temp, route, dose, age; extensive hemorrhaging, necrosis of many tissues; death usually due to kidney failure Infectious Hematopoietic Necrosis (IHN) вЂў Environmental factors: temp. very important, slows below 10в—¦C, holding in tanks/handling increase severity (doesnвЂ™t occur naturally >15 в—¦C) вЂў External pathology: lethargy, whirling, dropsy, exopthalmia, anemia, hemorrhaging of musculature/fins, scoliosis вЂў Internal pathology: liver, kidney, spleen pale; stomach/intestines filled with milky fluid; petechial hemorrhaging вЂў Histopathology: extensive necrosis of hematopoetic tissue of kidney/spleen Infectious Hematopoietic Necrosis (IHN) вЂў Definitive diagnosis: serum neutralization, FAT, ELISA вЂў Prevention: avoidance, quarantine, clean water with UV, ozone, virus-free stock; test, slaughter, disinfect; disinfect eggs; vaccines under development; elevated water temp вЂў No vaccines as of June 2007. (4) Channel Catfish Virus Disease (CCVD) вЂў Contagious herpes virus affecting only channel catfish less than four months old вЂў Occurs in SE United States, California, Honduras вЂў Acute hemorrhagia, high mortality, discovered in 1968 вЂў Agent: enveloped capsid, icosohedral nucleocapsid with 162 capsomeres вЂў Physio/chemical properties: easy to kill, sensitive to freeze-thaw, acid, ether, etc. Channel Catfish Virus Disease (CCVD) вЂў Environmental factors: optimal temperature 28-30в—¦C, common during warmer months, cooler water = big difference вЂў epizootiology: horizontal, vertical suspected вЂў external pathology: spiral swimming; float with head at surface; hemorrhagic fins, abdomen; ascites; pale or hemorrhagic gills; exophthalmia Channel Catfish Virus Disease (CCVD) вЂў Internal pathology: hemorrhages of liver, kidney, spleen, gut, musculature; congestion of mesenteries and adipose вЂў Histopathology: necrosis of kidney, other organs; macrophages in sinusoids of liver, etc.; degeneration of brain вЂў Presumptive diagnosis: clinical signs, epizootiological evidence вЂў Definitive diagnosis: SN or FAT. Channel Catfish Virus Disease (CCVD) вЂў Prevention: avoid potential carriers (survivors) or infected fry, keep temperature below 27oC (will still produce carriers), attenuated vaccine shows some promise вЂў Therapy: none available... Channel Catfish Virus Disease Channel Catfish Virus Disease However, you can always take precautions!