Quaglio - Viral Diseases

Question 1

What are the common viral diseases affecting fish?

Answer 1

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.

Question 2

What is Viral Hemorrhagic Septicemia (VHS)?

Answer 2

Caused by Novirhabdovirus, affects freshwater and marine fish species, including salmonids. Symptoms: systemic hemorrhages, swollen abdomen, and lethargy.

Question 3

What are the clinical signs of VHS?

Answer 3

• Petechial hemorrhages in muscles and internal organs,
• exophthalmos,
• bloated abdomen due to ascites,
• lethargy
• erratic swimming.

Question 4

What environmental conditions favor VHS outbreaks?

Answer 4

Water temperature range of 4–12°C, higher susceptibility during cold seasons.

Question 5

How is VHS transmitted?

Answer 5

Horizontal transmission through water and infected fish, viral shedding via urine, feces, and gill mucus.

Question 6

What is Spring Viremia of Carp (SVC)?

Answer 6

A viral disease caused by Rhabdovirus carpio, primarily affects carp species. Symptoms: hemorrhages, exophthalmos, swollen abdomen, and lethargy.

Question 7

What are the environmental factors influencing SVC outbreaks?

Answer 7

Water temperatures between 10–18°C, outbreaks often occur in spring as temperatures rise.

Question 8

How is SVC transmitted?

Answer 8

Horizontal transmission via water and fish contact, vertical transmission through infected eggs and ovarian fluids.

Question 9

What are the internal lesions observed in SVC?

Answer 9

Question 10

What is Betanodavirus (Viral Nervous Necrosis – VNN)?

Answer 10

A viral disease affecting more than 40 marine fish species, common in sea bass and groupers. Symptoms: erratic swimming, lethargy, and changes in pigmentation.

Question 11

What are the key symptoms of VNN?

Answer 11

Nervous signs: uncoordinated swimming and corkscrew motion, lethargy and loss of appetite, skin discoloration and exophthalmos.

Question 12

At what water temperatures is VNN most common?

Answer 12

Above 15°C, with peak prevalence in warmer months.

Question 13

How is VNN diagnosed?

Answer 13

Observation of clinical signs, histopathology of brain and retina, PCR for viral detection.

Question 14

What is Epizootic Hematopoietic Necrosis Virus (EHNV)?

Answer 14

A disease caused by Iridovirus, affects rainbow trout and redfin perch. Symptoms: necrosis in hematopoietic tissues, pale gills, and lethargy.

Question 15

What are the clinical signs of EHNV?

Answer 15

Lethargy and loss of appetite, hemorrhages in muscles and internal organs, necrosis of spleen and kidneys.

Question 16

How is EHNV transmitted?

Answer 16

Horizontal transmission via water, contaminated equipment and handling.

Question 17

What diagnostic methods are used for viral diseases in fish?

Answer 17

• Histopathology to identify tissue changes,
• PCR for viral genome detection
• virus isolation in cell cultures.

Question 18

What biosecurity measures help prevent viral diseases?

Answer 18

• Quarantine new fish,
• disinfect equipment and water systems,
• monitor water quality and stress levels.

Question 19

What are the impacts of viral diseases on aquaculture?

Answer 19

• High mortality rates,
• economic losses due to reduced fish production and treatment costs,
• increased susceptibility to secondary infections.

Question 20

What is the role of temperature in viral disease outbreaks?

Answer 20

Cold temperatures favor VHS and EHNV, warm temperatures favor VNN.

Question 21

How does stress influence viral disease susceptibility?

Answer 21

Weakens immune responses, increases the likelihood of infection and mortality.

Question 22

How are fish samples collected for viral disease diagnosis?

Answer 22

• Fresh tissues (brain, kidney, spleen) are sent on ice for PCR and virus isolation
• histopathology samples fixed in 10% buffered formalin.

Question 23

What are the main differences between VHS and SVC?

Answer 23

VHS affects both freshwater and marine fish, peak at 4–12°C; SVC primarily affects carp, outbreaks at 10–18°C.

Question 24

Why are biosecurity measures essential in controlling VNN?

Answer 24

Prevents the spread of the virus to other fish stocks, reduces environmental contamination.

Question 25

What are the histological findings in VNN?

Answer 25

Vacuolation and necrosis in brain and retina tissues, inflammatory cell infiltration.

Question 26

How is SVC managed in aquaculture?

Answer 26

• Quarantine
• culling (killing) infected fish,
• disinfecting ponds and water sources,
• reducing stress through proper management.

Question 27

What are the reservoirs for VHS?

Answer 27

Infected fish and carrier species, viral persistence in water and sediment.

Question 28

What challenges exist in treating viral fish diseases?

Answer 28

• Lack of antiviral treatments,
• reliance on preventive measures and biosecurity.

Question 29

What is the significance of ‘spring’ in SVC?

Answer 29

Refers to seasonal outbreaks during spring as water temperatures increase.

Question 30

What are the main histological findings in EHNV?

Answer 30

Severe necrosis in hematopoietic and splenic tissues, presence of basophilic inclusion bodies.