About animals

National Center for Aquaculture and Aquaculture Safety

Pin
Send
Share
Send


1. General Provisions
1.1. Infectious necrosis of hematopoietic tissue (INHT) is a highly contagious viral disease of salmon fish cultivated in artificial conditions, observed in freshwater and sometimes in marine aquaculture. The disease proceeds as an epizootic and is characterized by the development of a septic process, severe damage to the organs of hematopoiesis, hemorrhages in organs and tissues, as well as mass death of fish.

1.2. The disease is common in the United States and Canada (from Alaska to California) adjacent to the Pacific Ocean, in Japan, China, Korea and Taiwan, and since 1987 it has been reported in France, Italy, Germany and Belgium.

1.3. The disease manifests itself in the form of exudative-hemorrhagic syndrome, the development of which is caused by the multiplication of the virus in the connective tissue of organs, hematopoietic tissue and cells of the excretory part of the kidneys, which leads to disruption of the water-mineral balance and the release of plasma and blood cells into the surrounding tissues and body cavities.

2. Etiology
2.1. The disease causes an RNA-containing virus from the genus Lyssavirus. The virus is called Infectious hematopoietic necrosis virus (IHNV). The INHT virus is represented by one serotype, thermolabile: after 15 minutes of heating at 45 °, it is inactivated by more than 99.9% and completely destroyed at 60 ° C.

2.3. Among the field isolates of the virus, both weakly virulent and highly virulent isolates are found.

3. Epizootology
3.1. In freshwater aquaculture, disease outbreaks have been reported in sockeye salmon, chinook salmon, chum salmon, pink salmon, sima, steelhead salmon and rainbow trout. Clark trout and salmon are less likely to get sick.

3.2. Loach and coho salmon are considered resistant to the disease, but can be carriers of the virus.

3.3. Young are most susceptible to the disease in the period from resorption of the yolk tag to 2-6 months of age. Older fish (year-olds and two-year-olds) get sick less often and more easily. For the first time, infected manufacturers may die. Significant individual fluctuations in the susceptibility of fish to INHT were noted.

3.4. The disease develops at a water temperature of 3 to 15 ° C and decays with its further increase. Epizootics of INHT usually have two peaks: spring (end of winter - beginning of summer) and - more rarely, - autumn (end of summer and fall), but at the appropriate temperature they can be observed at any time of the year. The disease is most acute at 10-12 ° C. In this case, up to 80-100% of young people can die. In fish weighing 100-500 g, the disease, as a rule, proceeds in a chronic form, and death does not exceed 10-25%. The smaller the age of the fish, the higher the temperature they can develop a disease. This is due to the imperfection of the immune system in early juvenile fish.

3.5. Even when the virus circulates in a fish population, an outbreak of INHT may not occur. The disease is provoked by stress of the fish during various manipulations with it (transportation, sorting, etc.) or violation of the technological regime of cultivation.

3.6. After an epizootic, part of the diseased or disease-resistant fish become virus carriers.

3.7. Carrier fish form a natural reservoir of infection. In aquaculture, sick and freshly killed fish also serve as a source of infection. Infected fish secrete the virus with urine, intestinal mucous membranes (rarely with feces), with sexual products, through gills, skin and fin tissue.

3.8. The virus is transmitted through water, silt, fish stock. Oral transmission is possible with cannibalism, feeding raw meat or the guts of infected fish. The likelihood of vertical transmission of the virus is negligible. In water at 15 ° C, inactivation of the virus occurs after about a month.

3.9. The mechanical carriers of the virus are blood-sucking parasites of fish (leeches, copepods, etc.), as well as fish-eating birds.

3.10. The gates of infection are the gills, intact skin, fins and the initial section of the digestive tract. Acute infection is systemic. A septic process develops, leading to the defeat of almost all organs and tissues. The most severely affected organs are hematopoiesis - the kidney and spleen. The virus has an increased tropism in relation to connective tissue.

3.11. An ill fish acquires a stable immunity, antibodies appear in the blood.

4. Clinical signs and pathological changes
4.1. The incubation period for natural infections and a water temperature of 10-15 ° C is 1-2 weeks.

4.2. The first signs of the disease are: anorexia and depression of fish, loss of response to external stimuli. Sick fish acquire a dark color, lie on the bottom or rise to the surface of the water and move to the edges of the pool or channel, where the current is weaker.

4.2.1.Sharp the outbreak of INHT begins with a sudden mass death, and the first fish can die without external signs of the disease. In patients with fish, exophthalmos, blanching of the gills, point hemorrhages in the periocular connective tissue of the eyes, in the interradiation tissue of the fin bases, less often on the abdomen and behind the head, are noted. Abdomen enlarged (extended). Long strands of a mucus-like consistency with a grayish tinge (sometimes with an admixture of blood) hang from the anus of individual diseased fish. In the larvae there are multiple hemorrhages in the yolk sac and hydrocephalus (swelling on the head in the form of a cap). An autopsy in the body cavity reveals an accumulation of transparent yellowish (sometimes bloody) exudate, multiple petechial hemorrhages in the perivisceral adipose tissue, on the peritoneum, the walls of the intestines and swim bladder, sometimes in the muscles. The liver, kidneys and spleen are pale, swollen. The gastrointestinal tract is free of food, sometimes filled with mucus-like contents of milky white color.

4.2.2. Chronic the form of the course of the disease is characterized by less pronounced signs and moderate, prolonged death of fish over time.

4.2.3. A small fraction of fish - usually at the final stage of an epizootic - develops nervous the form of the disease, manifested in a violation of the behavior of fish (alternating phases of increased excitability and depression) External symptoms of the disease, with the exception of a darker body color, are usually absent in such fish. This form of INHT is caused by damage to the central nervous system, and often the virus in these fish can only be detected in the brain.

4.3. Sick fish usually have some signs of disease from the above complex. Only a few affected individuals during the period of epizootic can meet the whole set of characteristic clinical signs and pathological changes. None of the described symptoms is pathognomonic. In 1-5% of ill fish, curvature of the spine develops (scoliosis, lordosis).

5. The diagnosis
5.1. A preliminary diagnosis of INHT is based on the analysis of epizootological data, detected clinical signs and pathological changes. The final diagnosis is based on the results of virological studies, including the isolation and serological identification of the virus, and, if necessary, staging a bioassay.
Sampling and research is carried out in accordance with the "Methodological guidelines for the identification of viruses and laboratory diagnosis of viral painful fish" from 10.01.97, No. 13-4-2 / ​​1054.

6. Preventive measures
6.1. Prevention of INGT is based on preventing its entry into prosperous farms, strict compliance with fish and veterinary requirements set forth in the Veterinary and Sanitary Rules for Fish Farms and the relevant instructions for combating diseases of salmon fish, ensuring optimal hydrochemical and hydrobiological regimes, and observing density standards fish, the maximum reduction in fish stress during technological manipulations with it.

6.2. The farm carries out regular veterinary control over the state of fish’s health within the time frames specified in the above Rules, paying special attention to the examination of fish in the spring.

6.3. The import of fish and caviar for breeding and rearing purposes is permitted only from fish-breeding farms and fishery reservoirs that are safe for infectious and invasive diseases and are carried out in accordance with the current "Instructions for Veterinary Surveillance for the Transport of Live Fish, Fertilized Caviar, Crayfish and Other Hydrobionts".

6.4. To reduce the possibility of transmission of the virus through ovarian and seminal fluids, the surface of the eggs is disinfected by treating the eggs with solutions of iodinol or chloramine-B in accordance with the current instructions for their use.
Treatments are carried out twice: immediately after fertilization and swelling of the eggs and at the eye stage.

6.5. To protect against fish-eating birds, ponds and pools with fish located in the open air are tightened with a net.

6.6. It is allowed to use wild fish for feeding meat of carcasses (carcasses) of wild fish only after heat treatment (pasteurization for 1 hour at 60 ° C). Feeding raw meat and fish entrails is unacceptable.

6.7. If there is a suspicion of INHT during a fish examination by a veterinarian, farm managers and specialists, under the supervision of local government agencies, organize the delivery of live fish or pathological material (selected in accordance with the Methodological Guidelines for Virus Identification and Laboratory Diagnosis of Fish Viral Diseases) to the laboratory for virological research or call laboratory specialists to select material on site.

Until a final diagnosis is established, the export of fish to other fish farms and fisheries, as well as any fish transplant from suspected ponds and pools, is prohibited.

7. Control measures
7.1. When a diagnosis is made, the farm is declared unsuccessful for infectious necrosis of the hematopoietic tissue of salmon fish and quarantined. Regardless of the form of the disease — carriage of a virus or a clinically occurring disease — the fact that the virus is isolated from fish is sufficient to quarantine.
The veterinarian of the farm must:
- immediately inform the immediate manager of the departmental line about the trouble of the farm, as well as notify the fish farms into which the fish were exported for rearing and rearing,
- at the same time inform the chief veterinarian of the district (city) and the higher veterinary authority about the occurrence of the disease and the area of ​​its spread,
- specify the time of occurrence of the disease and the number of dead fish of all age groups separately,
- take measures to identify the source of infection in the household.
- take measures to speedy stop and eliminate the disease.

7.2. Given the well-being of Russia according to INHT, and in order to prevent the occurrence of foci of infection, the health of quarantined farms is carried out by radical disinfection and flying.

7.3. Work on improving the economy is carried out in accordance with a plan developed by the local authority of the state veterinary service, approved by the district administration.

7.4. Elimination of the disease:

7.4.1. Commodity fish, producers and a repair group of fish that do not have signs of disease are allowed to be exported directly to the distribution network without overexposure it in cages of live-fishing bases, the water in which the fish was transported is chlorinated and then poured into the sewer network, and poured into the countryside to fields at a distance no closer than 500 m from water bodies, the container after transportation, the fish are washed and disinfected with a 2% formalin solution.

7.4.2. All other fish, caviar and dead fish are collected and buried away from water bodies to a depth of at least 1.5 m with preliminary disinfection with a solution of bleach or quicklime. According to the conclusion of the veterinarian, technical disposal of this fish (except for corpses) and caviar (boiling and feeding to birds, pigs or fur animals) is allowed.

7.4.3. Ponds, pools and canals are drained, cleaned of sludge and garbage and disinfected with quicklime at the rate of 0.5 kg per 1 m2 of area.

7.4.4. The rooms of the incubation workshops, pools, locks, grates and other equipment in them, storage rooms and rooms for preparing feed are thoroughly cleaned and disinfected with a hot 2% sodium hydroxide solution using brushes or sprayers. Disinfection with a 2% formalin solution is also allowed.

7.4.5. Live-transport, tanks, flasks, containers are subjected to mechanical cleaning using a 0.2% solution of bicarbonate of soda, and then disinfected with a 2% solution of formalin. Low-value inventory is burned.

7.4.6. If possible, transfer the farm to an infection-free water source (artesian well, spring, stream free of wild fish), or establish ozonation or treatment with ultraviolet radiation of the water supplied to the farm.

7.4.7. After these measures, the farm (fish factory) has not been operated for at least one more month, and then caviar is imported from a source safe for infectious diseases.

7.4.8. For 12 months after stocking, farms carry out veterinary monitoring of fish grown in it. During this period, a virological study of juveniles is carried out at least twice (in spring and autumn at a water temperature of 10-12 ° C). The work is carried out in accordance with the provisions of the "Guidelines for the identification of viruses and laboratory diagnosis of viral diseases of fish" and these Instructions. Virologically examined 150 fish with the calculation of detection of virus carriers. In addition to parenchymal organs, samples of mucus, gills, skin, fins and brain

7.5. If several farms unsuccessful by INGT are identified in the river basin or in the reservoir, all of them are rehabilitated simultaneously, using the above method of complete disinfection for flying.

7.6. In the event that a persistent outbreak of INGT infection is found in the zone of location of the dysfunctional economy and the presence of a pathogen in the water source, a complex method of eliminating the disease is designed for the gradual improvement of the economy. In accordance with it, measures are being taken to identify and destroy sources of infection, rupture pathogens, improve the physiological condition of fish and increase their resistance to disease.

7.6.1. Under quarantine conditions in a fish farm that is healed by the integrated method, the following is prohibited:
- import and export of caviar, fish and feed aquatic organisms,
- mixed planting of fish of different age groups,
- the use of fish-breeding equipment used in a dysfunctional pond (pool) in other ponds (pools).

7.6.2. Fish is grown in isolation by species and age groups, for the maintenance of which separate personnel are fixed, the necessary work clothing and equipment (scrapers, brushes, nets, etc.). Sorting and replanting fish is carried out only within these groups.

7.6.3. Establish thorough veterinary monitoring of all fish grown on the farm. When a disease occurs in individual ponds or pools, they destroy (disinfect and bury) all the fish contained in them and clean and disinfect them.

7.6.4.They provide enhanced flow of water, take measures to enrich it with oxygen, cut the density of fish landing and the loading density of hatching eggs with caviar as much as possible (for sockeye salmon - not more than 100 thousand eggs per m 2).

7.6.5. Antiparasitic treatments are carried out in a timely manner, paying special attention to the fight against blood-sucking parasites.

7.6.6. The open-air ponds and pools with fish are pulled by a net to protect against fish-eating birds.

7.6.7. Strictly observe the regime of fish rearing, reducing the influence of technogenic stresses.

7.6.8. Provide fish feeding with full, balanced feed. In the spring - at the time of the highest risk of the disease, - feed is enriched with ascorbic acid (vitamin C) or its derivative is used - ascorbate monophosphate or polyphosphate. Ascorbic acid is introduced into the feed at the rate of 1-2 g / kg, acid phosphates - 50 mg / kg. This food feeds fish for 2-4 months.

If possible, increase the water temperature in yearlings and older fish to 15-16 ° and up to 18-20 ° C in fry and yearlings.

7.6.9. The herd of repairs and producers is formed from fish that were not sick during the period of epizootic and have increased resistance to the disease. It is advisable to switch to the cultivation of fish of more resistant species to INHT (coho salmon, char, Clark salmon, trout). Their import into the economy is carried out in agreement with the bodies of the state veterinary service.

7.6.10. It is recommended to conduct individual testing of manufacturers for virus carriers by selecting sex products during their spawning campaign and their virological research. Caviar of fish, from the reproductive products of which the virus was isolated, and the producers themselves are discarded and destroyed.

7.7. Regardless of the method of recovery, quarantine is removed from the farm and it is declared safe if, within 12 months of observation, the fish did not show any clinical signs and pathological changes characteristic of INHT, and two-time virological studies (see clause 7.4.8.) Gave a negative result.

With the approval of this Instruction, the “Interim Instruction on measures for the prevention and control of infectious necrosis of the hematopoietic tissue of salmon fish”, approved by the GUV of the Ministry of Agriculture of the USSR on March 20, 81, No. 115-6a, is no longer valid.

Epizootology

In freshwater aquaculture, disease outbreaks have been reported in sockeye salmon, chinook salmon, chum salmon, pink salmon, sima, steelhead salmon and rainbow trout. Clark trout and salmon are less likely to get sick. Loach and coho salmon are considered resistant to the disease, but can be carriers of the virus. Young are most susceptible to the disease in the period from resorption of the yolk sac to 2-6 months of age. The incubation period of infection at a water temperature of 10-15 ° C is 1-2 weeks. Older fish (year-olds and two-year-olds) get sick less often and more easily. For the first time, infected manufacturers may die. Significant individual fluctuations in the susceptibility of fish to INHT were noted. The disease proceeds as an epizootic and is characterized by the development of a septic process, severe damage to the organs of hematopoiesis, hemorrhages in organs and tissues, as well as mass death of fish. The disease is common in the United States and Canada (from Alaska to California) adjacent to the Pacific Ocean, in Japan, China, South Korea and Taiwan. It is found in France, Italy, Germany, Belgium and Russia. The disease develops at a water temperature of 3-15 ° C and decays with its further increase. Epizootics of INHT usually have two peaks: spring (end of winter - beginning of summer) and less often - autumn (end of summer and fall), but at the appropriate temperature they can be observed at any time of the year. The disease is most acute at 10-12 ° C. In this case, up to 80-100% of juveniles can die. In fish weighing 100-500 g, the disease, as a rule, proceeds in a chronic form and death does not exceed 10-25%. This is due to the imperfection of the immune system in early juveniles. The virus can circulate in a fish population without causing an outbreak of INHT. The disease is provoked by stressing the fish during various manipulations with it (transportation, sorting, etc.) or violation of the technological regime of rearing. After an epizootic, part of the diseased or disease-resistant fish become virus carriers. Virus-carrying fish form a natural reservoir of infection. In aquaculture, sick and freshly killed fish also serve as a source of infection. Infected fish secrete the virus with urine, intestinal mucous membranes (rarely with feces), with sexual products, through gills, skin and fin tissue. The virus is transmitted through water, silt, fish stock. Oral transmission is possible with cannibalism, feeding raw meat or the guts of infected fish. The likelihood of vertical transmission of the virus is negligible. In water at 15 ° C, inactivation of the virus occurs after about 1 month. The mechanical carriers of the virus are blood-sucking parasites of fish (leeches, copepods, etc.), as well as fish-eating birds. The gates of infection are the gills, skin, fins and the initial section of the digestive tract. An acute infection is systemic. A septic process develops, leading to the defeat of almost all organs and tissues. The organs of hematopoiesis - the kidneys and spleen - are most severely affected. The virus has an increased tropism in relation to connective tissue. An ill fish acquires a stable immunity, antibodies appear in the blood.

Clinical signs and pathological changes

The disease manifests itself in the form of exudative-hemorrhagic syndrome, the development of which is due to the multiplication of the virus in the connective tissue of organs, hematopoietic tissue and cells of the excretory part of the kidneys, which leads to disruption of the water-mineral balance and the release of plasma and blood cells into the surrounding tissues and body cavities. The first signs of the disease are: anorexia and depression of fish, loss of response to external stimuli. Sick fish acquire a dark color, lie on the bottom or rise to the surface of the water and move to the edges of the pool or channel, where the current is weaker. An acute outbreak of INHT begins with a sudden mass death, and the first fish can die without external signs of the disease. In patients with fish, exophthalmos, blanching of the gills, point hemorrhages in the periocular connective tissue of the eyes, in the interradiation tissue of the fin bases, less often on the abdomen and behind the head, are noted. Abdomen enlarged (extended). Long strands of mucus-like consistency with a grayish tinge (sometimes with an admixture of blood) hang from the anus of individual sick fish. In the larvae there are multiple hemorrhages in the yolk sac and hydrocephalus (swelling on the head in the form of a cap). An autopsy in the body cavity reveals an accumulation of transparent yellowish (sometimes bloody) exudate, multiple petechial hemorrhages in the perivisceral adipose tissue, on the peritoneum, the walls of the intestines and swim bladder, sometimes in the muscles. The liver, kidneys and spleen are pale, swollen. The gastrointestinal tract is free of food, sometimes filled with mucus-like contents of milky white color. The chronic form of the course of the disease is characterized by less pronounced clinical signs and moderate, long-term death of fish. In a small part of the fish, usually at the final stage of the epizootic, a nervous form of the disease develops, manifested in a violation of the behavior of the fish (alternating phases of increased excitability and depression). External symptoms of the disease, with the exception of a darker body color, are usually absent in such fish. This form of INHT is caused by damage to the central nervous system, and often the virus in these fish can only be detected in the brain. Sick fish usually have some signs of disease from the above complex. Only a few affected individuals during the period of epizootic can meet the whole set of characteristic clinical signs and pathological and anatomical changes. None of the described features is pathognomonic. In 1-5% of ill fish, curvature of the spine develops.

A preliminary diagnosis of INHT is made on the basis of an analysis of epizootological data, detected clinical signs, and pathological and anatomical changes. The final diagnosis is based on the results of virological studies, including the isolation and serological identification of the virus, and, if necessary, staging a bioassay.

Control measures

Prevention of INGT is based on the prevention of its entry into prosperous farms, the strict implementation of fish-reclamation and veterinary-sanitary requirements. When a diagnosis is made, the farm is declared dysfunctional and quarantined. Regardless of the form of the disease — carriage of a virus or a clinically occurring disease — the fact that the virus is isolated from fish is sufficient to quarantine. Work on improving the economy is carried out in accordance with a plan developed by the local authority of the state veterinary service, approved by the district administration. The elimination of foci of infection is carried out by the method of disinfection and flying. It is also recommended that individual manufacturers test for virus carriers by selecting sex products during their spawning campaign and their virological research. Caviar of fish, from the reproductive products of which the virus was isolated, and the producers themselves are discarded and destroyed. After quarantine measures, the farm has not been operated for at least 1 month, and then caviar is imported from a source that is safe for infectious diseases. For 12 months after stocking the farm, veterinary monitoring of fish grown in it is carried out. During this period, a virological study of juveniles is carried out at least twice (in spring and autumn at a water temperature of 10-12 ° C). When the fish farm is located in the natural center of INGT, the herd of repair and producers are formed from fish that were not sick during the period of epizootic and have increased resistance to the disease. It is advisable to switch to the cultivation of fish species that are more resistant to INHT (coho salmon, char, Clark salmon, trout). Their import into the economy is carried out in agreement with the bodies of the state veterinary service. Regardless of the method of rehabilitation, quarantine is removed from the farm and it is declared safe if, within 12 months of observation, the fish did not notice clinical signs characteristic of INHT and pathological and anatomical changes, and two-time virological studies gave a negative result. To prevent INHT in the United States, Germany and Canada, work is underway to create genetically engineered (recombinant) vaccines.

Infectious necrosis of hematopoietic tissue of salmon fish

Infectious hematopoietic necrosis, IHN (Infectious hematopoietic tissue necrosis) is a highly contagious viral disease of salmonids observed in freshwater and marine aquaculture.

Etiology. The disease causes an RNA-containing virus from the genus Novirhabdovirus. The INHT virus is represented by one serotype, thermolabile: after 15 minutes of heating at 45 ° C, it is inactivated by more than 99.9% and completely destroyed at 60 0 C. Among the field isolates of the virus, both weakly and highly virulent are found.

Epizootology. In freshwater aquaculture, disease outbreaks have been reported in sockeye salmon, chinook salmon, chum salmon, pink salmon, steel-headed salmon and rainbow trout. Clark trout and salmon are less likely to get sick. Loach and coho salmon are considered resistant to the disease, but can be carriers of the virus.

Young are most susceptible to the disease in the period from resorption of the yolk sac to 2-6 months of age. The incubation period of infection at a water temperature of 10-15 ° C is 1-2 weeks. Older fish (year-olds and two-year-olds) get sick less often and more easily. For the first time, infected manufacturers may die. Significant individual fluctuations in the susceptibility of fish to INHT were noted. The disease proceeds as an epizootic and is characterized by the development of a septic process, severe damage to the organs of hematopoiesis, hemorrhages in organs and tissues, as well as mass death of fish.

The disease is common in the United States and Canada (from Alaska to California) adjacent to the Pacific Ocean, in Japan, China, South Korea and Taiwan. It is found in France, Italy, Germany, Belgium and Russia.

The disease develops at a water temperature of 3-15 ° C and decays with its further increase. Epizootics of INHT usually have two peaks: spring (end of winter - beginning of summer) and less often - autumn (end of summer and fall), but at the appropriate temperature they can be observed at any time of the year. The disease is most acute at 10-12 ° C. In this case, up to 80-100% of juveniles can die. In fish weighing 100-500 g, the disease, as a rule, proceeds in a chronic form and death does not exceed 10-25%. This is due to the imperfection of the immune system in early juveniles.

The virus can circulate in a fish population without causing an outbreak of INHT. The disease is provoked by stressing the fish during various manipulations (transportation, sorting, etc.) or a violation of the technological regime of cultivation.

After an epizootic, part of the diseased or disease-resistant fish become virus carriers. Carrier fish form a natural reservoir of infection. In aquaculture, sick and freshly killed fish also serve as a source of infection. Infected fish secrete the virus with urine, intestinal mucous membranes (rarely with feces), with sexual products, through gills, skin and fin tissue.

The virus is transmitted through water, silt, fish stock. Oral transmission is possible with cannibalism, feeding raw meat or the guts of infected fish. The likelihood of vertical transmission of the virus is negligible. In water at 15 ° C, inactivation of the virus occurs after about 1 month.

The mechanical carriers of the virus are blood-sucking parasites of fish (leeches, copepods, etc.), as well as fish-eating birds.

The gates of infection are the gills, skin, fins and the initial section of the digestive tract. An acute infection is systemic. A septic process develops, leading to the defeat of almost all organs and tissues. The most severely affected organs are hematopoiesis - the kidney and spleen. The virus has an increased tropism in relation to connective tissue.

An ill fish acquires a stable immunity, antibodies appear in the blood.

Clinical signs and pathological changes. The disease manifests itself in the form of exudative-hemorrhagic syndrome, the development of which is due to the multiplication of the virus in the connective tissue of organs, hematopoietic tissue and cells of the excretory part of the kidneys, which leads to disruption of the water-mineral balance and the release of plasma and blood cells into the surrounding tissues and body cavities.

The first signs of the disease are: anorexia and depression of fish, loss of response to external stimuli. Sick fish acquire a dark color, lie on the bottom or rise to the surface of the water and move to the edges of the pool or channel, where the current is weaker.

An acute outbreak of INHT begins with a sudden mass death, and the first fish can die without external signs of the disease. In patients with fish, exophthalmos, blanching of the gills, point hemorrhages in the periocular connective tissue of the eyes, in the interradiation tissue of the fin bases, less often on the abdomen and behind the head, are noted. Abdomen enlarged (extended).Long strands of mucus-like consistency with a grayish tinge (sometimes with an admixture of blood) hang from the anus of individual sick fish. In the larvae there are multiple hemorrhages in the yolk sac and hydrocephalus (swelling on the head in the form of a cap). When opening in the body cavity, an accumulation of transparent yellowish (sometimes bloody) exudate, multiple petechial hemorrhages in the perivisceral adipose tissue, on the peritoneum, the walls of the intestine and swim bladder, sometimes in the musculature, are found. The liver, kidneys and spleen are pale, swollen. The gastrointestinal tract is free of food, sometimes filled with mucus-like contents of milky white color.

The chronic form of the course of the disease is characterized by less pronounced clinical signs and moderate, long-term death of fish.

In a small part of the fish, usually at the final stage of the epizootic, a nervous form of the disease develops, manifested in a violation of the behavior of the fish (alternating phases of increased excitability and depression). External symptoms of the disease, with the exception of a darker body color, are usually absent in such fish. This form of INHT is caused by damage to the central nervous system, and often the virus in these fish can only be detected in the brain.

Sick fish usually have some signs of disease from the above complex. Only a few affected individuals during the period of epizootic can meet the whole set of characteristic clinical signs and pathological changes. None of the described symptoms is pathognomonic. In 1-5% of ill fish, curvature of the spine develops.

Diagnosis. A preliminary diagnosis of INHT is based on the analysis of epizootological data, detected clinical signs and pathological changes. The final diagnosis is based on the results of virological studies, including the isolation and serological identification of the virus, and, if necessary, staging a bioassay.

Control measures. Prevention of INGT is based on the prevention of its entry into prosperous farms, the strict implementation of fish-reclamation and veterinary-sanitary requirements.

When a diagnosis is made, the farm is declared dysfunctional and quarantined. Regardless of the form of the disease — carriage of a virus or a clinically occurring disease — the fact that the virus is isolated from fish is sufficient to quarantine.

Work on improving the economy is carried out in accordance with a plan developed by the local authority of the state veterinary service. The elimination of foci of infection is carried out by the method of disinfection and flying.

It is also recommended that individual manufacturers test for virus carriers by selecting sex products during their spawning campaign and their virological research. Caviar of fish, from the reproductive products of which the virus was isolated, and the producers themselves are discarded and destroyed.

After quarantine measures, the farm has not been exploited for at least 1 month, and then caviar is imported from a source safe for infectious diseases.

For 12 months after stocking, farms carry out veterinary monitoring of fish grown in it. During this period, a virological study of juveniles is carried out at least twice (in spring and autumn at a water temperature of 10-12 ° C).

When the fish farm is located in the natural center of INGT, the herd of repair and producers are formed from fish that were not sick during the period of epizootic and have increased resistance to the disease. It is advisable to switch to the cultivation of fish species that are more resistant to INHT (coho salmon, char, Clark salmon, trout). Their import into the economy is carried out in agreement with the bodies of the state veterinary service.

Regardless of the method of rehabilitation, quarantine is removed from the farm and it is declared safe if, within 12 months of observation, the fish did not notice clinical signs and pathological changes characteristic of INHT, and two-time virological studies gave a negative result.

In order to prevent INHT in the USA, Germany and Canada, work is underway to create genetically engineered (recombinant) vaccines.

Pin
Send
Share
Send