Quaglio - Viral Diseases Flashcards
What are the common viral diseases affecting fish?
Viral Hemorrhagic Septicemia (VHS), Spring Viremia of Carp (SVC), Betanodavirus (Viral Nervous Necrosis – VNN), Epizootic Hematopoietic Necrosis Virus (EHNV)
These diseases impact various fish species and present with different symptoms.
What is Viral Hemorrhagic Septicemia (VHS)?
Caused by Novirhabdovirus, affects freshwater and marine fish species, including salmonids. Symptoms: systemic hemorrhages, swollen abdomen, and lethargy.
What are the clinical signs of VHS?
- Petechial hemorrhages in muscles and internal organs,
- exophthalmos,
- bloated abdomen due to ascites,
- lethargy
- erratic swimming.
What environmental conditions favor VHS outbreaks?
Water temperature range of 4–12°C, higher susceptibility during cold seasons.
How is VHS transmitted?
Horizontal transmission through water and infected fish, viral shedding via urine, feces, and gill mucus.
What is Spring Viremia of Carp (SVC)?
A viral disease caused by Rhabdovirus carpio, primarily affects carp species. Symptoms: hemorrhages, exophthalmos, swollen abdomen, and lethargy.
What are the environmental factors influencing SVC outbreaks?
Water temperatures between 10–18°C, outbreaks often occur in spring as temperatures rise.
How is SVC transmitted?
Horizontal transmission via water and fish contact, vertical transmission through infected eggs and ovarian fluids.
What are the internal lesions observed in SVC?
What is Betanodavirus (Viral Nervous Necrosis – VNN)?
A viral disease affecting more than 40 marine fish species, common in sea bass and groupers. Symptoms: erratic swimming, lethargy, and changes in pigmentation.
What are the key symptoms of VNN?
Nervous signs: uncoordinated swimming and corkscrew motion, lethargy and loss of appetite, skin discoloration and exophthalmos.
At what water temperatures is VNN most common?
Above 15°C, with peak prevalence in warmer months.
How is VNN diagnosed?
Observation of clinical signs, histopathology of brain and retina, PCR for viral detection.
What is Epizootic Hematopoietic Necrosis Virus (EHNV)?
A disease caused by Iridovirus, affects rainbow trout and redfin perch. Symptoms: necrosis in hematopoietic tissues, pale gills, and lethargy.
What are the clinical signs of EHNV?
Lethargy and loss of appetite, hemorrhages in muscles and internal organs, necrosis of spleen and kidneys.
How is EHNV transmitted?
Horizontal transmission via water, contaminated equipment and handling.
What diagnostic methods are used for viral diseases in fish?
- Histopathology to identify tissue changes,
- PCR for viral genome detection
- virus isolation in cell cultures.
What biosecurity measures help prevent viral diseases?
- Quarantine new fish,
- disinfect equipment and water systems,
- monitor water quality and stress levels.
What are the impacts of viral diseases on aquaculture?
- High mortality rates,
- economic losses due to reduced fish production and treatment costs,
- increased susceptibility to secondary infections.
What is the role of temperature in viral disease outbreaks?
Cold temperatures favor VHS and EHNV, warm temperatures favor VNN.
How does stress influence viral disease susceptibility?
Weakens immune responses, increases the likelihood of infection and mortality.
How are fish samples collected for viral disease diagnosis?
- Fresh tissues (brain, kidney, spleen) are sent on ice for PCR and virus isolation
- histopathology samples fixed in 10% buffered formalin.
What are the main differences between VHS and SVC?
VHS affects both freshwater and marine fish, peak at 4–12°C; SVC primarily affects carp, outbreaks at 10–18°C.
Why are biosecurity measures essential in controlling VNN?
Prevents the spread of the virus to other fish stocks, reduces environmental contamination.
What are the histological findings in VNN?
Vacuolation and necrosis in brain and retina tissues, inflammatory cell infiltration.
How is SVC managed in aquaculture?
- Quarantine
- culling (killing) infected fish,
- disinfecting ponds and water sources,
- reducing stress through proper management.
What are the reservoirs for VHS?
Infected fish and carrier species, viral persistence in water and sediment.
What challenges exist in treating viral fish diseases?
- Lack of antiviral treatments,
- reliance on preventive measures and biosecurity.
What is the significance of ‘spring’ in SVC?
Refers to seasonal outbreaks during spring as water temperatures increase.
What are the main histological findings in EHNV?
Severe necrosis in hematopoietic and splenic tissues, presence of basophilic inclusion bodies.
