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Questions and Answers
What is the shape of Ranaviruses virions?
What is the size of the double-stranded DNA genome of Ranaviruses?
Where do Ranaviruses replicate?
How long can EHNV survive in frozen fish tissues?
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What is effective in inactivating EHNV?
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At what temperature can EHNV be inactivated?
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How can EHNV be shed into water?
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What cell types can be infected by EHNV?
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How can EHNV survive outside the host?
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What is the route of infection of EHNV?
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Study Notes
Life Cycle of Aphanomyces invadans
- The primary zoospore transforms into the secondary zoospore, which is reniform with laterally biflagellate cells and can swim freely in the water.
- The secondary zoospore remains motile for a period dependent on environmental conditions and the presence of the fish host or substratum.
- The zoospore encysts and germinates to produce new hyphae, although further tertiary generations of zoospores may be released from cysts (polyplanetism).
Disease Information: Host Factors
- EUS causes disease and mortality in farmed and wild fish, worldwide, with around 76 species of fish confirmed to be naturally affected by histological diagnosis.
- Susceptible host species include yellowfish sea bream, straightfin barb, striped snakehead, and many others.
- Some fish, such as common carp, Nile tilapia, and milkfish, are considered to be resistant to EUS.
- Juvenile and young adults are usually susceptible stages of the host.
- EUS can be readily detected in diseased fish specimens collected from EUS-infected areas using histological techniques.
Disease Information: Disease Pattern
- EUS is transmitted horizontally, with Aphanomyces zoospores capable of attaching to the damaged skin of fish and germinating into hyphae.
- The pathogen migrates towards the central nervous system, producing proteolytic enzymes that destroy muscle and other tissues.
- Hyphae invade widely into the surrounding skin and deeply into underlying muscle tissues, resulting in extensive, bloody ulceration and destruction of tissues.
- The prevalence of EUS in the wild and in aquaculture farms is high in endemic areas that share the same water way or system.
Disease Information: Disease Pattern (continued)
- Geographical distribution: First reported in Oita Prefecture, Kyushu Island, Japan in 1971, and later reported in estuarine fish in eastern Australia in 1972.
- EUS has been detected in many fish species and has a high prevalence in endemic areas.
Disease Information: Sampling
- Scoop net, cast net, or seine net are the best choices for catching EUS-infected fish in natural waters or in fish ponds.
- Fish specimens should be transported to the laboratory live or in ice-cooled boxes for further diagnosis.
- Fixed specimens are transferred to double-layer plastic bags with formalin-moistened tissue paper for semi-dry conditions.
Disease Information: Diagnostic Methods
- Diagnosis of EUS is based on clinical signs and confirmed by histopathology.
- Diagnosis of EUS in clinically affected fish may be achieved by histopathology or by oomycete isolation.
- Positive diagnosis of EUS is made by demonstrating the presence of mycotic granulomas in histological sections or isolation of A. invadans from internal tissues.
Disease Information: Agent Factors
- EHNV has large (150–180 nm), icosahedral virions, a double-stranded DNA genome, and replicates in both the nucleus and cytoplasm with cytoplasmic assembly.
- EHNV is extremely resistant to drying and can survive for months in water, persisting in frozen fish tissues for more than 2 years and frozen fish carcasses for at least a year.
- EHNV is susceptible to 70% ethanol, 200 mg/liter sodium hypochlorite, or heating to 60°C for 15 minutes.
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Description
Learn about the life cycle of Aphanomyces invadans, a parasitic fungus, including the transformation of zoospores and their motility, encystment, and germination. Understand the environmental and host-dependent factors influencing its life cycle.
