April 2010, tilapia streptococcus disease in Hainan Province, which was dotted occurred, indicating the occurrence of streptococcal disease in the extended season, also means streptococcus may be widespread in 2010.
□ Text / Figure Freshwater Fisheries Research Institute of Fujian Province, Hai-Ping Fan
1, Streptococcus Overview
Worldwide death of fish caused by streptococcal infection in the twentieth century has been sporadic seventies and eighties reported nineties the rise, now has become a major streptococcal pathogens of fish. Primary infection of Streptococcus fish head, fish brain damage, then damage the blood circulation through the liver, kidney, spleen and other organs caused systemic hemorrhage, is a bacterial disease, contagious, high mortality, treatment difficulties and the higher the temperature the more severe disease.
Streptococcus cultured species have a certain selectivity, occur mainly in salmonids, tilapia, catfish, carp and freshwater pomfret, and grass carp, carp, silver carp and bighead carp have not been reported. Streptococcus infection reported in literature tilapia strains are mainly dolphins Streptococcus (S.iniae) and Streptococcus agalactiae (S.agalaciate), the domestic strains of Streptococcus isolated from Streptococcus mostly dolphins, Fujian Institute of Freshwater Fisheries S. agalactiae was first reported outbreak of deaths caused by tilapia. Robinson and Meyer in 1966, first reported in U.S. freshwater fish golden bream (Notemigonus crysoleucas) an isolated group B Streptococcus.
Subsequently, Plumb and Baya isolated from fish such as multiple strains of non-hemolytic streptococcus group B, but not sure is right. 1994, Eldar, etc. to be called Streptococcus difficile. Wilkinson, Elliott, and Vandamme, etc. to isolation and identification of streptococci, mostly assigned to group B Streptococcus agalactiae. 2002, Evans and other re-reported hemolytic Streptococcus agalactiae is the major pathogen of fish. In 2005, Kawamura and other proposed re-division of S difficilis attribution, identified as Streptococcus agalactiae synonyms. 2006, Evans and other marine mammals from isolated Streptococcus agalactiae. Streptococcus agalactiae is considered the sole owner of group B Streptococcus-specific antigen.
Second, an overview of Tilapia Streptococcus
Streptococcus disease occurs mainly in poor water quality, breeding density of water, low-cost long-term use of low-quality feed is also contributory factors. In addition, there is a lot of streptococcal bacteria in water also has a direct link. Sometimes in the natural incidence of ovarian broodstock can be detected in the presence of pathogens, so there may be pathogens in tilapia in the possibility of vertical transmission. Streptococcal disease of fish disease control are mainly drugs control, ecological control and immune control.
Chemical drugs and Chinese herbal medicine the most direct and simple control yes De Kongzhishouduan, However prolonged use of chemicals inevitably Shi resistant pathogens Chan Sheng Xing, Daozhifangzhi failure, Tong Shi Ye Keneng lead to products of the drug residue Yinqizhiliang health safety Wen Ti. Therefore, the ecological control and immune control as an important means of control. Streptococcus agalactiae is a major pathogen of fish, but also one of zoonotic pathogens in aquaculture should place no pathogen carrying seed, maintain good water quality, full fed high-quality feed, the tracing of pathogens source of infection, cut off the route of transmission is the important work of ecological control. Streptococcus disease in the event, both the brain infection, brain damage, but also damage the liver, kidneys and other organs, affect the fish's own immune function, vaccines and immune activator control the research and development is caused by Streptococcus agalactiae non-Luo Fish of the Epidemic mainstream.
3, tilapia streptococcus epidemic Overview
Tilapia streptococcus often long-term high temperature, oxygen, or breeding density is too large outbreaks such circumstances, in the spring, summer and autumn, is the peak was from May to September, popular water temperature 25-37 ℃, in particular water temperature higher than 30 ℃, easily lead to disease outbreaks; main hazards broodstock and 100g or more juvenile and adult fish. Contagious, the incidence rate is 20-30%, the incidence of fish mortality rate of 80%, and duration of long duration, mortality continued to peak 2-3 weeks; In winter, the mortality rate is relatively low, but longer duration . China's major farming areas such as tilapia Hainan, Guangdong, Guangxi, Fujian and other areas in recent years, outbreaks of different degrees, resulting in a more serious losses.
IV symptoms and pathological changes
Tilapia streptococcus main symptoms: prevalence disease fish losing balance, some tumbling in the water, some sideways movement to do a circle; serious condition, the dying disease fish in channeling the water around on tour or intermittent; abdominal surface with a point-like or plaque bleeding or ulcers, jaw and two lower edge of gill cover diffuse bleeding, liver, gallbladder, spleen swelling, bleeding, severe erosion; intestine and the stomach or the product water yellow mucus, anal outstanding; eye congestion, swelling, prominent, serious corneal opacity white, or even eye loss. Pathology revealed a small piece gill congestion, edema, necrosis, respiratory epithelial hyperplasia, fusion, capillary swelling, congestion, congestive enlargement of the end of the gill filaments, lymphocyte infiltration; epicardial rupture, muscle fiber breakage, disorder, loose myocarditis edema, lymphocyte infiltration; granular degeneration and fatty degeneration of the liver, arterial pipe and liver cell separation, wall accumulation of blood cells and liver cell nuclei and blood iron flavin calm, hepatocellular cloudy swelling, necrosis; intestinal epithelial necrosis, loss, natural meningitis leukocyte infiltration; spleen hemorrhage, edema, lymphocytes decreased, the organization has a large number of hemosiderin deposition; purulent foci within the kidney, there are a large number of neutrophils infiltration, renal swelling and kidney central capillary blood sedimentation capsule lacunar increased renal tubular cells increased, irregular, hyaline degeneration of small arterial wall, formation of micro vascular thrombosis, necrosis of epithelial cells; periosteum choroidal and orbital inflammatory injury occurs, the lens fiber fracture and separated from the capsule and the lens was severe necrosis, corneal ulceration occurs, retina damage.
5, tilapia streptococcus disease diagnosis
Anatomical disease fish sterile equipment, were taken gill, liver, kidney, spleen, gonad, eye and other organs of the small piece of tissue or fluid membrane inside the gill cover, smear on clean glass slides and dried, Gram stain, microscopic examination in the oil, can be found in the chain of Gram-positive bacteria, found more bacteria for in pairs, in a serious condition may find the typical chain of bacteria, symptoms can be combined with the basic diagnosis of fish. Types of pathogens can be identified by bacterial pathogens isolated or immunological detection methods confirmed.
6, and the outbreak of factor analysis
Culture environment, breeding patterns and breeding species and is closely related to the incidence of Streptococcus, breeding density, breeding water pollution by livestock to maintain high levels of feeding whole high incidence of artificial feed; high temperature and disease outbreaks and lead to high closely related mortality, and once the temperature dropped, the death rate decreased significantly; cultured species has a relationship with the incidence rate, which may be fish food consumption with high, fast growth, the; and specifications related to fish, 100g or more of the fish disease high, which may also related to food consumption and rapid growth; onset of segregation is not the fish, diseases and breeding ponds in different areas of horizontal transmission; Also, in some natural disease of broodstock gonads can sometimes detect pathogens, the existence of vertical transmission also need further research. As for the zoonotic pathogen Streptococcus one, livestock pollution is the source of infection is also worth exploring.
7, tilapia streptococcus disease prevention and control measures
Since the pathogen was Gram-positive bacteria, the prevention and treatment than Gram-negative bacteria more difficult. Prevention and control of Streptococcus main measures:
1, strengthen the culture water environmental control of microbial and sediment quality improver, regulate water quality, maintain good water quality environment. Disease outbreaks in the warm seasons, lower stocking density, increase the oxygen machine to open the time, maintain good water quality, particularly water contaminated by livestock and poultry breeding areas, should be strictly controlled the flow of contaminated water, and reduce the amount of baits, in the case of conditions can reduce the water temperature.
2, to enhance disease management, dead fish promptly remove, as harmless, and to strengthen the disease in isolation incidence pool and health pool of water, tools and personnel.
3, in season and easy to outbreaks of epidemics season, strengthening the control of the number of pathogens, such as the environment and control the number of fish pathogens. Breeding environment using disinfectants such as chlorine preparations, antioxidants, such as hydantoin, disinfecting water, reducing the number of environmental pathogens and the infection rate; fish carrying the pathogen commonly used oral medication to control sensitivity, but the use of oral medication, you should pay attention to medication the type, dose and administration period, to choose the type of drug-sensitive drugs or compounded preparations, such as the use of penicillin, ampicillin, and more West tetracycline, minocycline, sulfonamides and other drugs on the G + bacteria sensitive; drug dose to ensure Drug use is able to effectively kill and inhibit the reproduction of the dose of pathogen, the general dose of 50mg/kg to achieve more than the fish; drug use cycle, generally up to 7-10 days.
4, to improve fish's body, strengthen the improvement of non-specific immune function. Such as dietary vitamin C and immune polysaccharides, enzymes and other immune enhancer, improve fish function, effective against pathogens harmful to the body.
5, in the treatment of disease, they should pay attention to environmental conditions and body function improvement, while in the application of these drugs, fish liver and other organs function improved, such as the use of 654-2 (trade name), Glucurolactone ( trade name), etc. Oral, auxiliary control the disease have significant effects.
6, immunization prevention and treatment of Di research techniques are being carried out, in order to be truly effective in controlling the disease's Chuanbo, immune prevention and treatment always the most important resort in Xianjie Duan Guo Nei Guangxi Fisheries Yanjiu Suo, Zhongshan University, Pearl River Fisheries Research Institute, Freshwater Fisheries Research Institute of Fujian Province were carried out streptococcal vaccines.
8, Problems
Because tilapia streptococcus study also is not deep enough, as it exists vertical transmission? Whether livestock pollution is unknown. Breeding species are sensitive pathogen-related issues and needs further confirmation.
In 2010, Hainan Province in April that spotty occurrence, indicating the occurrence of streptococcal disease in the extended season, also means streptococcus may be widespread in 2010, therefore, need competent trade authorities, scientists and aquaculture industry mutual coordination and efforts to strengthen the epidemiological investigation and surveillance, strengthen the collection and analysis of pathogenic strains can the immune control techniques of research, development and provide necessary basic materials. Although the disease can not confirm whether vertical transmission, seed quarantine will not only support the existence of vertical transmission, but also effectively control the spread of the disease, therefore, I propose that the unit should carry out seed quarantine.
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