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In today's discussion, we will step into the second part to know more about AHPND in shrimp. In the last blog, we saw the overview of AHPND including its occurrence and disease occurrence in shrimp. In this section, we will study about the role of toxins in causing AHPND in shrimp.
Have you ever heard about the toxins before? Yes there is a lot of possibility to know about that but not that much deep, right?
No worry, stick to each line of the blog to understand the effect and role of toxins in disease.
What are toxins in bacteria?
There are different types of toxins that can be secreted by the pathogen to cause infection to the host organism. Toxins are a biological substance that may be a peptide or protein which is produced from a bacteria and leads to infection to the host. Just imagine, toxins are the primary substances that cause damage to the cells which leads to rupture and more on. In that row, AHPND causes V.parahemolyticus bacteria producing toxins called PirA and PirB which is responsible for causing AHPND.
Does all V.parahemolyticus cause AHPND?
NO. It depends on the strain. In many cases most of the V.parahemolyticus did not show infection like AHPND upon challenge studies.
PirAB toxin role in AHPND:
Macrophages and neutrophils are the major cells in mediating the innate immune system at the early stage of the infection. The target organ of these toxins is hepatopancreas and stomach but most primarily affect hepatopancreas of the shrimp. The toxins are secreted extracellularly and it's very similar to the toxins secreted by the insects. Experimental challenge with PirAB toxins showed the occurrence of AHPND in shrimp but it depends on the amount of toxins secreted. In some cases researchers isolated two strains of V.parahaemolyticus from the same shrimp,on which one strain possessed PirAB toxins but another strain didn't possess PirAB toxins.
It is advisable to the farmers to check the presence of major toxin genes in their culture system. When you are doing PCR for WSSV or EHP or any other pathogen, it is better to do gene tests for mostly presented bacteria colonies in your culture system.
Image source: (Ramya et.al 2020) https://onlinelibrary.wiley.com/authored-by/Kumar/Ramya
The above mentioned image shows how environmental stress leads to disease in shrimp pond.
Transmission of plasmid from one generation to generation:
Apart from all the above, one of the important characteristics acquired by the plasmid pVA1 is natural genetic transformation. It is really serious threat and silently affecting our culture system. Molting is the commonly occurring phenomenon in the shrimp pond, the moulted shells undergo different cycles. For more about molting shells kindly read this Molting shells in shrimp pond. Chitin is the compound present in the shells of the shrimp. Studies found that some Vibrio sp can undergo Natural genetic transformation in the presence of chitin.
Management is the key factor to keep these things under control. Improper management indirectly leads to the occurrence of various bacterial or other pathogens and in some cases it may lead to mutation or other dangerous phenomenon.
Treatments and alternatives for AHPND:
1. Plant extracts
2. Immunostimulations, antioxidants
3. Better feed better environment
4. Pathogen screening and sampling
5. Use of probiotics isolated from the gut and tissues of healthy shrimp
6. Production of improved genetics and need adopt improved broodstock development
7. Development in immunology related to shrimp
Conclusion:
I hope this blog gives some useful information on the toxins and their effect on shrimp. There is a lot of research available to give wide exposure on this topic. Unity is the only key to success in shrimp farming.
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For more information on technical support,
Kindly E-mail : dhivagarfcri2000@gmail.com
References:
1. https://onlinelibrary.wiley.com/doi/10.1111/raq.12414
2. https://pubmed.ncbi.nlm.nih.gov/31777397/
3. https://pmc.ncbi.nlm.nih.gov/articles/PMC8041169/#sec001
4. https://www.sciencedirect.com/topics/medicine-and-dentistry/bacterial-toxin
5. https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2016.00042/full
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