Viral Diseases of fish
I. Spring Viraemia of Carp
Spring viraemia of carp is also known as infectious dropsy of carp (IDC).
is a contagious and potentially fatal viral dis. Affecting fish. It occurs in the spring when the
water temperature is raising (13 to 20 C) but it occurs most commonly when the temperature of
the water is 17 centigrade. This disease usually occur in fish which are to one year old, It
spreads fast and the mortality ranges between 80 to 90 % in, 2 to 3 weeks time.
Etiology :
Rhabdovirus carpio , ribonucleic acid (RNA) structure
Signs and Lesions:
The affected fish show darkening of their body, and then tend to assemble at the water inlet.
They exhibit sluggish breathing and finally tilt to one side. In the advanced stage of disease,
symptoms like abdominal distension, protrusion of the eyes, reddening and swelling of the anus,
anemia and hemorrhagic spots in the gills are seen. Various internal organs like intestine,
spleen, kidney, etc, show swelling and degradation.
Transmission:
1-contamenated water with infected fish’s feces, urine or mucus
2- Contaminated equipments
3-Fish parasites
4- birds
5-Infected fish eggs
6- Virus infected carrier fish
Diagnosis:
1- Signs
2- Isolation of the virus
Control:
1- Water supply must free from the dis.
2- Disinfection of eggs by iodophore treatment
3- Regular physical and chemical disinfection of the ponds and equipments
4- Proper disposal of dead fish
5- source of fish known to be free of SVC.
Treatment:
There is no specific treatment ,but it can be used Mathelen blue 3gm/kg of feed /15 times /34 intervals in the mature fish
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2- Viral hemorrhagic Septicemia:
VHS is highly contagious dis. is economically important in rainbow trout, turbot and carp
farming; significant mortality has also been seen in other species.
Etiology:
family: Rhabdoviradae
Clinical signs:
VHS has been divided in to acute, chronic and nervous forms of the dis.
Acute form:
1- Darkening of the body
2- Protrusion of the eyes
3- Hemorrhage may be seen in the eye and gills
4- Hemorrhage it can be seen some times at the base of the pectoral fins and the body
surface
5- High mortality and brief course of acute form
6- Slow movement of the affected fish and may be excitement movement
Chronic form:
1-The infected fish blacken and the gills lose color
2-Protrusion of the eyes
3- Anemia
4- Fluid accumulation in the abdomen are often seen
5- Mortality is usually low
6-Yellow color around the vent
7- Spongy muscle
8- Infected fish are near the pond bank
Nervous form:
1- The body becomes twisted
2- The affected fish swim in circles or on their sides
Post mortem lesions:
*Acute form
1-Scattered hemorrhage may be seen in the skeletal muscles, per visceral adipose tissue in
the abdomen, air bladder, intestine, and other organs
2- The spleen may be enlarged and some times is dark red, the liver usually dark red
3- The kidney is reddened
*Chronic form:
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1- The body cavity may be filled with fluid.
2-The kidney are often grayish swollen and undulating
*Nervous form:
Have no significant gross lesion
Morbidity and Mortality:
VHS can occur at any age, but younger fish appear to be most susceptible.
; this dis. usually develops at temp. between 4-14C
Outbreaks occur most often in the spring, The mortality rate varies from 20%-80%
influenced by environmental conditions, high mortality may be related to age may reach to
100%in the fry.
Transmission :
1-direct contact
2-water
The virus thought to enter the body through the gills or wounds, oral infection probably does
not occur.
Diagnosis:
1- Nervous signs and hemorrhages
2-Lab. Tests
Through the isolation of the virus in cell culture include BF-2 and RTG-2 and EPC cells
Virus identify by
ELISA, and PCR.
3 - Fish Pox
Symptoms :
Fish pox is characterized by white , pink or gray wax , like growths on the skin and fins .
these symptoms seem to progress to a point , then gradually subside, this disease can become
chronic .
Cause:
DNA virus is thought to be Herpes virus, incubation period too long may be one year, i.e.
the dis. Occur more than one year old fish. Viral infection that occurs often in cool and cold
water fish , particularly koi .
Treatment :
There is no known treatment , the illness is no usually fatal and does not appear to be
contagious . the healing process can be speeded up by increasing water quality and the
temperature .
4- Swim bladder inflammation (SBI)
Symptoms :
common disease in the Europe. Usually, young fishes up to two months are infected more and
the mortality could reach 100 per cent. The suitable temperature range for the replication SBI
virus is found to be between 15 –28 C and no growth takes-place above 33°C and below 5°
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Centigrade , In the initial stages the inflammation occurs in the wall tissue of the swim bladder,
especially at the bottom of the swim bladder walls. Gradually, bleeding spots appear and brown
or black spots appear leading to necrosis and the swim ' bladder is destroyed. By this time the
infection would have extended to the other internal organs also.
Cause :
virus belonging to the Rhabdovirus group with Deoxy ribo Nucleic Acid (DNA) ,
Treatment :
Administration of antibiotics either by injection or orally through feed is found to be effective
to control this disease. A dose of 40 mg of chloramphenicol per kilogram weight of the fish
either as abdominal injection or orally through feed is found to be effective. or methylene blue
per individual is reported to be useful. For adult fish administration of food for 3 days in which
3 gm per kg of dry feed followed by feed without drug and the cycle being repeated three times.
5- Lymphocystis disease
The Lymphocystis is caused by virus. Though it is commonly occurring in the wild fish the
cultivated fishes are also affected by it. However it is not reported to be really fatal.
Small blister-like swellings appear or in clusters on the surface of the trunk, head, fins and other
parts of the body. The disease occur in high temperatures (summer months) and automatically
disappear when the temperature becomes less.
Antibiotics may be used at the beginning of the infection. However, proper sanitation and other
prophylactic measures are necessary to control the incidence of the disease.
Proper feeding through the natural and artificial feeds is also a necessary element in the
prevention and control of this disease.
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