Early disease mitigation and management

During the end of the 1970s and throughout the 80s and 90s, shrimp farming experienced increasing production intensity. All over the world, new management methods, new hatcheries, and integrated enterprises were blooming. From Asia to The Americas, shrimp farming was gaining momentum, increasing production, intensity, technification, and investment.

In 1974 Couch described the very first shrimp pathogenic virus observed in aquaculture, baculovirus penaei. In his paper, Couch stated that “… crowding and chemical stress of shrimp in aquaria may enhance and increase the virus infection and prevalence.” This phrase turned out to be accurate and highly significant for future shrimp aquaculture.

Since the intensification of shrimp aquaculture rose, so did disease outbreaks and new pathogen descriptions, achieving an average of one new pathogenic virus per year described in the scientific literature from 1974 to 2004, some more damaging than others. In most extreme cases, a pathogen can wipe out the entire production in a few days, bankrupting farms worldwide.

As a response to increased disease outbreaks, especially in Asia, where until 2003 the predominant cultured species was Penaeus monodon or the giant tiger prawn, producers started looking into a new, more resistant, and resilient species, Litopenaeus vannamei. This led to a shift in the selection of species produced, transforming L. vannamei into the most farmed crustacean species worldwide, achieving 4.9 million tons produced in 2018, representing almost 50% of all the crustacean aquaculture production worldwide, and maintaining an average annual growth of nearly double the aquaculture industry average.

The fact that L. vannamei is an easier to manage species led farmers to increase production densities, productivity, and profitability, but also raised the probability and impacts of disease outbreaks. Being more resilient doesn’t necessarily mean they will not get pathogens and subsequent disease under stressful high-density culture conditions and so the same problem that had P. monodon appeared in the new reared species. Furthermore, world trade ha increased significantly by 2004 compared to 1970, speeding the spread of these diseases worldwide. This panorama, added to the lack of disease control in the production of larvae, led to a series of shrimp epidemics that destabilized the industry, being the most known ones the WSSD pandemic from the mid-90s to the beginning of the 00s, and the EMS (AHPND) pandemic during the 2009-2015 period.

To face these problems, farmers harden their biosecurity measures, accounting for the different transmission vectors, reducing the pond’s area, disinfecting equipment, improving infrastructure, reducing interaction with pond water, and training personnel. Despite these measures, diseases kept appearing with severe tolls.

To better understand why disease management in shrimp farming is so tricky, one must know that, as opposed to fish, symptoms are rarely observable by behavior in the farm due to the nature of the average shrimp pond system, where turbidity is high and farming areas are large. Instead, they tend to be detected and identified once the pathogen presents physical manifestations, and once there are physical manifestations, that means the disease is heavily present. There is not much to do in terms of therapeutic responses (particularly when talking about viral diseases), so the farmer must look into cutting the losses and, when possible, harvest.

As a result of the damages caused by all the diverse diseases presented in shrimp aquaculture and the lack of a profitable response, diseases became the main constraining factor in shrimp aquaculture investment, increasing risk premiums significantly, making it impossible to create solid insurance schemes, which scared investment capital, reducing the capacity of the industry to grow sustainably.

And so, enters early disease mitigation and management. In Shrimpstar, we had the opportunity of talking with Dr. Melony Sellars, a leading expert in early disease management, founder and CEO of Genics Pty Ltd, and the scientist responsible for the development of Shrimp MultiPath™.  A revolutionary next-generation technology that allows testing for a long list of disease-causing pathogens in a single assay. It is both simple and affordable, while opening a wide new panorama for disease management and reporting. Not least, improvement of biosecurity protocols, investment opportunities, significantly reducing risk and improving both in-farm management and industry-wide opportunities.

Q: What is early disease management?

MS: Early disease management focuses on detecting the presence and prevalence of a pathogen that causes a disease weeks before you see clinical signs of sickness. Through well-designed sample plans that are statistically significant and taking the correct tissue types (in combination with the cost-effective highly sensitive and accurate platform Shrimp MultiPath^TM), farmers can detect pathogens weeks before they have sick animals. This early warning system gives farmers time to make time-critical data-driven management choices which can range from increased biosecurity through reducing stress and adjusting feeds.

Q: In a brief statement, what is the most significant advantage of this management strategy?

MS: In the case of a pathogen like WSSV or EMS/AHPND, it can be the difference between harvesting or not harvesting at all.

The strategy allows farmers to maximize profits by better managing inputs in the event of a pathogen being present and prevalent.

Q: Do you test all species of shrimps and prawns produced in aquaculture or only some?

MS: All Penaeid shrimp species, polychaetes, environment (water) samples – anything that carries shrimp pathogens, Genics can test on Shrimp MultiPath^TM.

Q: Do you only test on adult shrimp, or is it possible to get information for PL as well?

MS: At Genics we test all life-history stages and have different protocols for sampling of different ages, in addition to protocols for destructive and non-destructive sampling.

Q: Do I need special equipment and/or a laboratory to send specific samples?

MS: You will need a flame to sterilize sample equipment, scissors, tubes, and 70% laboratory-grade ethanol for preserving the samples. We have many educational videos on our website (www.genics.com.au) to help out with training for sterilization and sampling.

Q: Which organs do you sample and why?

MS: This depends on the goals of the testing and whether animals need to be kept alive or can be killed. We take the suitable organs to meet the farm’s objectives, whether that be early pathogen detection in PL before stocking, or during pond culture. The typical target organs for destructive sampling are the gill, lymphoid organs, stomach, hepatopancreas, epithelium, and muscle.

Q: How long does a farmer have to wait before getting their results? Are they easy to read?

MS: 48 hours, and yes, they are presented in a table or profile image.

Q: If a farmer sends a sample and is positive for a significantly dangerous disease, say EMS, what can they do?

MS: Again this is on a case-by-case basis, depending on the life stage, farm set up, etc. With a severe pathogen the farmer can immediately increase biosecurity (not share nets between ponds, tell neighbors, be cautious of birds and other animal vectors like crabs), adjust feed rates as they will drop intake and water quality will reduce and cause increased stress, etc. They also have time to plan an early harvest if shrimp are going to reach a suitable size, or may choose to stop the crop, dry out and start again if the animals are still very young and not too much investment has gone into the crop at that point in time.

Q: Do you have a general action protocol for disease detection, or is its management entirely up to the farmer?

MS: We discuss options with farmers before they engage with us. The farmer is then in a position to make choices based on their data. We also have Veterinary Experts in the Genics Team and farmers can access through our Genics360 Consultancy Services.

Q: What auditable standards do you operate under?

MS: We operate in ISO17025 Accredited Services Laboratories. As part of the quality standards of an accredited laboratory, independent audits occur of equipment servicing, standard operating procedures etc. This ensures that customers can be 100% confident in their data and its quality, meaning if they get a positive result, they can be confident this is a true positive, if they get a negative result, they can be confident this is a true negative.

Q: Which diseases are you testing for right now?

MS: All shrimp pathogens of commercial importance. Shrimp MultiPath™ has 13, and MultiPath Xtra has 14. We have additional assays for all other shrimp pathogens up and running at Genics.

Q: Are you planning on expanding your range of diseases detected, or are you sticking to the ones you are already testing?

MS: We are always expanding our range of pathogens detected based on customer and industry needs. We welcome industry feedback and input at all times on their challenges and requirements so we can develop solutions that are scientifically proven.

Q: In very simple words, how do you test the sample? How accurate is it?

MS: Our technology has unrivaled performance compared to industry standards, and OIE (the World Organization for Animal Health) endorsed tests for multiple pathogen detection, in terms of sensitivity and specificity. There is nothing that compares or comes close.

When samples arrive at Genics, they undergo a QC process, are extracted to remove DNA and RNA, and then go through the PCR-based MultiPath process.

Q: How often do you recommend sending a sample, and why?

MS: This depends on the reasons for sampling and how we are adding value to the customer’s business. It might be weekly; it might be every six months. All health plans are customized for each farm.

Q: How does this technology benefit shrimp farmers?

MS: For the first time, it makes multiple pathogen detection affordable. Historically shrimp farmers wait until they have sick shrimp, and then they only test for one or two pathogens that they think might be the cause, not paying attention to any others. Shrimp often have 3-5 pathogens at any one time. Once you have sick shrimp, it is too late.

Because Shrimp MultiPath™ is so affordable, farmers can test statistically significant sample sets for early detection before clinical signs appear.