What is Hepatolococcal?
Hepatoborozoans belongs to the family Microsporidium, Enterozoans, and is an obligate intracellular parasite that can infect a variety of eukaryotes. Penaeus vannamei disease is caused by a microsporidium parasitism that is small, 2 to 10 microns long and 1.5 to 4.2 microns wide. Mature spores are oval in shape, 0.75-1 micron in length, with a cavitation at the posterior end, a cell containing a nucleus, 5-6 polar filament rings, an anchor disc connected to the polar filaments, and a layer of electron-dense spore walls.
Penaeus vannamei hepatic enterosporidiosis is one of the most serious diseases affected by global shrimp farming production in recent years. In 2009, it was named after the symptoms that manifested on P. monodon in Thailand. Since 2013, this disease has been found in the main production areas of Penaeus monodon in South America, including the coastal areas of Jiangsu such as East, Qidong, Funing, Dafeng, Sheyang and other places.
Diseases of hepatic enterosporidium
Hepatosporosporium first infects the intestinal epidermis of shrimp, and then infects the liver and pancreas, parasitizing in the epithelial cells of the pancreatic duct of shrimp liver, which is difficult to detect with the naked eye and light microscopy, and can be diagnosed with techniques such as PCR. Infected shrimp do not grow long, occasionally accompanied by white stools, newly infected shrimp intestinal absorption function decreased, severe appearance of enteritis and liver and pancreas atrophy, some infected individuals although the appetite is normal, but thin, thin shell, soft body. Shrimp ponds suffering from this disease vary greatly in size.
The mode of transmission of Hepatosporidium
Penaeus vannamei hepatic enterosporosis is transmitted horizontally, that is, by oral transmission, and the life history of Hepatosporidium is simple and the cycle is short, the whole process is 5 to 11 days, so once infected, the outbreak is fast. Its entire developmental process does not require host switching, and each stage of development is carried out in the nanolarial vacuole formed between the epithelial cell membrane and the cytoplasm of the host small intestine. After maturity, it can be excreted from the body through the digestive tract of the shrimp, forming sporophytes in the aquatic environment, scattered in the water body and attached to the algae, detritus, feed surface, as well as the pond wall and sediment environment, becoming a potential threat to healthy shrimp.
EHP has a wide range of infection routes, which can be transmitted vertically through fertilized eggs and shrimp fry, or horizontally through contaminated cultured water bodies. Cutting off the infection route can effectively prevent infection, through the quarantine of broodstock and shrimp fry, early detection of pathogens, to prevent infection of healthy shrimp fry, so as to protect the fundamental interests of the shrimp farming industry.
Currently, there are no effective treatments for shrimp hepatic enterosporosis (EHP). It can only be predicted by preventing and observing the growth status of shrimp in advance. Using the modified DNA recombinant enzyme to bind to primers to form a protein-DNA complex, looking for homologous sequences in double-stranded DNA and initiating DNA synthesis, exponential amplification of the nucleic acid fragments of template shrimp hepatic enterosporosis (EHP), a large number of amplified products can be combined with DNA dyes and discolored, so as to determine whether EHP virus is contained.
summary
Liver and intestines are a major scourge in the shrimp breeding process, especially in the liver transition period of one month, shrimp feeding normal, normal growth, the appearance can not see any change, will not cause attention, about a month to a month and a half, shrimp feeding will slowly slow down, growth, disease shows differences and changes (there are large and small, individual differences are relatively large), but the intestine, stomach is still full of food, liver and pancreas slightly atrophied, soft, but the color is relatively dark, so from the surface, shrimp has no obvious disease problems, But it is not long, and it is occasionally accompanied by white stools. Although hepatobic and intestinal strima is a chronic disease, due to the mixed infection of the same fungal disease, the pathogenic rate can be as high as 60%, and finally the harvest of the shrimp pond is very low, and even fails, and the economic loss is huge!
So, what precautions can help farmers?
1, the purchase of seedlings to double caution: it is recommended that farmers in the stage of purchasing seedlings do not be too anxious, pay attention to the shop around, try to visit and choose the regular nursery, pay attention to observe whether the shrimp breeding pond of the nursery is clean and thoroughly disinfected; if you determine the purchase of seedlings, you need to do a good job of shrimp fry detection in advance to avoid buying shrimp fry carrying pathogens.
2, thorough disinfection of shrimp ponds: the more organic matter of shrimp ponds, the higher the risk of microsporidia, before the seedlings should be completely cleared and disinfected. Dredging the pond must be thoroughly effective, and then treat the bottom of the pond with strong alkaline disinfectants such as sodium hydroxide, quicklime, etc., so that the pH at the bottom of the pond reaches 12, which can effectively kill most of the microsporidia. Industry recommendation: use more than 400 kg of quicklime per mu of land to treat the bottom of the pond, and then the bottom of the pond should be completely dried. Conditional farmers plough the bottom of the pond about 10 cm, so that the ash and the bottom mud are fully mixed, and then add water to make the quicklime work, so that the PH value of the pond bottom can reach 12, and maintain for a period of time, can effectively kill microsporidia.
3. Strengthen water quality management: try to maintain the health of the water environment, especially to increase the cleaning speed of the bottom of the pond and reduce the chance of metabolites being swallowed by healthy shrimp. In terms of feeding, we should also pay attention to adhering to the principle of "eating less and eating more" and not leaving too much residual bait, which in turn affects the water quality. In addition, we must pay attention to changing the bottom and reducing pathogens.
4, pay attention to liver and intestine care: to completely kill spore worms is not realistic, it is best to use some immune enhancers to improve the resistance of shrimp, enhance immunity, so that you can also control the number of pathogens in the body, so as to achieve sporangia and shrimp can coexist a stable breeding cycle.