Vibriosis is an infectious disease of salmon, eels and other fish species when grown in cages and pools with sea and brackish water.
The pathogens include several different bacteria of the genus Vibrio. The most studied agent is V. anguillarum . Vibrios of this species are found in water, silt, intestinal tract and on the surface of the body of marine aquatic organisms. These are small, slightly curved sticks with one polar flagellum, gram-negative, oxide-positive. They are halophilic bacteria, facultative anaerobes, possess proteolytic and hemolytic enzymes, and are sensitive to the pteridine agent (0/129). For their normal growth, a sufficient NaCl content and low concentrations of Mg ++, Ca ++, Na + cations are necessary. The optimal concentration of sodium chloride is 1.5-3.3%. In fresh water, vibrios die. Pathogenic for fish are also V. parahaemolyticus, V. alginolyticus and V. ordalii.
The disease occurs in many countries of the world in cultivated salmon, eels and other brackish water species of fish. In cases of vibriosis in rainbow trout in fresh water, the pathogen was transmitted by feeding minced meat from raw sea fish. The occurrence of the disease is promoted by high water temperature (above 15 ° C), pH above 8.0, low oxygen content, water pollution by organic substances (MIC above 2 mg / l) and nitrogen compounds (nitrogen content above 1 mg / l), handling. In our country, vibriosis is noted in trout cage farms located in the Gulf of Finland in the Baltic Sea. Trout yearlings are more likely to be affected. With age, the resistance of fish to vibriosis increases. When grown in marine cages, fish losses from the disease reach 70-100%, in fresh water they are much lower than 4-50%. The main transmission route of infection is horizontal: feed (minced meat from raw fish infected with vibrios), water, direct contact of sick fish with healthy ones.
The clinical picture and pathogenesis
Once in the body of the fish, the pathogen with a blood stream spreads to all organs and causes septicemia. At the same time, serous hemorrhagic inflammation and degenerative necrotic changes develop in the organs. The incubation period, depending on the temperature of the water, can be from 3-5 to 14 days. Vibriosis is acute, with high mortality (sometimes in the absence of external signs) or chronically. Under the influence of hemolysin produced by vibrios, fish develop anemia. The clinical picture of vibriosis varies in different fish species, but there are some common symptoms (hemorrhages, necrosis, and ulcers on the surface of the body). In acne, hemorrhages and inflamed areas of the skin, hyperemia of the fins and anus, and the formation of ulcers on the surface of the body are observed. Rainbow trout at the beginning of the outbreak dies without pronounced clinical signs. She refuses to feed, inactive. Later, focal ruffling of scales develops in diseased fish, hyperemic areas and swelling appear 2.5-3.0 cm in size and about 0.5 cm high, and then ulcers of a dark red color appear. The edges of the dorsal fin are necrotic. In some fish, an increase in the abdomen is noted. Extensive hemorrhages in internal organs and muscles are recorded in Atlantic salmon ("cunning disease", or cold-water vibriosis) The causative agent of this disease is Vibrio salmonicida. The disease occurs at low water temperatures. Vibriosis in the yellowtail occurs with hemorrhages and necrosis of the skin and muscles, destruction of the fins, opacification and hyperemia of the eyes. In sea bream, septic phenomena are noted, in flatfish, ulcers and anemia appear, in Pollock - necrotic skin lesions, intestinal hemorrhages. In cod, bright spots are observed behind the head on the surface of the body, developing into ulcerative lesions of various sizes and depths. The affected area is surrounded by a hemorrhage zone and is covered with a gray-yellow necrotic mass. There is an accumulation of granular tissue or its necrotic decay. Some foci are deep and similar to pustules. Peritonitis is not observed, although perforation of the peritoneal cavity sometimes occurs. In some individuals ulceration of the intestinal mucosa is noted. The internal organs look normal. In chum, pink salmon, chinook salmon, pike, there are redness at the base of the fins and on the lateral surfaces of the body, necrotic areas in the musculature, small petechiae on the gill covers and in the oral cavity, hemorrhages on the body surface that turn into bloody abscesses, cardiac muscle thrombosis, gills, peritoneum, inflammation of the lower intestine. In pike, inflammation manifests itself in the hypodermis, and sometimes in the muscles and serous membrane. The liver is sometimes hyperemic, with foci of coagulating necrosis.
It is put according to the results of bacteriological analysis, taking into account epizootological data, clinical signs and pathological changes. The causative agent in almost pure form is secreted from the blood, liver, kidneys, spleen and abscesses. The virulence of the pathogen is determined by the results of a biological test with intraperitoneal infection of healthy fish of susceptible species. For the rapid diagnosis of vibriosis, a red blood cell antigen has been developed. In this case, to detect antibodies, the blood serum of fish is examined in an agglutination reaction with a red blood cell antigen.
Control Measures and Prevention
In farms unsuccessful in terms of vibriosis, restrictions are introduced and a set of health-improving, veterinary-sanitary and organizational-economic measures are carried out. To prevent disease, improve the living environment and fish farming. They carry out breeding and breeding work on the selection of producers and fish that are resistant to vibriosis of the repair group. Over 25 commercial vaccines are produced abroad, which are used to treat fish by injection, bath or feed. In Russia, a domestic anti-vibration vaccine has been created, which has passed successful tests in cage trout farms. For the treatment of fish, furazolidone, oxytetracycline, tetracycline or chloramphenicol are used. The choice of the drug, its dosage and duration of treatment are determined depending on the sensitivity of the pathogen to it, the form of the course of the disease, the age and condition of the fish, water temperature and other factors.
VIBRIOSIS OF ACEAS
VIBRIOSIS OF ACEAS (brackish-water rubella, plague, or vibrio acne disease) is an acutely infectious infectious disease characterized by damage to the skin of fish, manifested in redness and inflammation of the skin, as well as in the subsequent formation of small bumps or cones on the front of the body and head of the acne, and then open bleeding ulcers. Bergmann (1909) first described this disease as rubella or bubonic disease. In the USSR, acne vibriosis is recorded in the waters of the Baltic Sea.
Etiology. The causative agent is the bacterium Vibrio anguillarum Bergmann, bean-shaped, its length is 1.5 microns, width is 0.5 microns, at one end there is a flagellum. Vibrios move quickly, do not form capsules and spores, are gram-negative. On agar, the bacterium gives a mucous, almost colorless coating, dilutes gelatin, ferments glucose, lactose and maltose with the formation of acid, sucrose and mannitol for the most part does not change, does not release hydrogen sulfide, sometimes forms indole, neutralrot and litmus does not reduce, gives hemolysis, grows well in environments containing 1.5 - 3.3% sodium chloride. At a salt concentration of 0.05%, as well as in clean running water, vibrios die quickly. V. anguillarum - facultative anaerobic.
Epizootological data. Mostly acne of older age groups migrating to the place of spawning. Sometimes the disease was noted in younger age groups, as well as in cod and flatfish. The source of the infectious beginning is sick fish, their excretion and the corpses of dead fish. Ways of infection of fish and the spread of the disease in natural waters have not been studied. Viriosis can be artificially reproduced by intramuscular or subcutaneous administration of a pure pathogen culture. From unsuccessful water bodies to safe pathogens, it is transferred during the migration of rubella-infected eels or during the transport and cage maintenance of infected fish in coastal marine areas and estuaries. The disease is promoted by high temperature, and when the temperature drops and the water temperature drops, the strength of the epizootic decreases sharply.
Symptoms The disease is super-constructive, acute, subacute and chronically. In a super-acute course, sick acne floats sluggishly in the surface layer of water and dies after several hours with the effects of convulsive muscle contraction. In the acute course, redness and inflammation of certain areas of the skin near the dorsal fin, around the anus and abdomen are noted, and in the subacute, in addition, inflamed swelling or bumps (usually on the head) appear, from which further abscesses form. When opening in their places, ulcers arise, surrounded by a vitreous rim. The chronic course of the disease is characterized by the appearance of individual abscesses and ulcers and the absence of inflammation and redness of the skin. Acne dies mainly in the case of an overexposure and acute course of the disease.
Pathogenesis has not been studied.
The diagnosis is made on the basis of epizootological data, symptoms of the disease and the results of a bacteriological study - the allocation of the pathogen. In difficult cases, a bioassay is carried out on fish susceptible to vibriosis by injecting them subcutaneously or intramuscularly with 0.25 - 0.5 ml of an I - 2-day-old broth culture of the pathogen.
The treatment has not been developed.
Prevention and control measures. To prevent the occurrence and spread of acne vibriosis, carry out veterinary control of fishery ponds and transportation of fish. In the coastal zones of the seas, bays and estuaries, where sick fish appeared, they organize intensive fishing not only for eels, but also for fish of other species susceptible to this disease.
Fish Diseases: A Guide. - M. G.V. Vasilkov, L.I. Grishchenko, V.G. Engashev et al., Ed. V.S. Osetrova. . 1989.