Can Shrimp Diseases be Beaten by Bacterial Interference?

New Mexico-based Pebble Labs is using bacteria to express\r\nRNAi in the plants and animals that live alongside that bacteria, effectively\r\nturning on their own natural defenses against diseases, viruses, fungi and even\r\nsome pests. Courtesy photo.

The global shrimp-farming sector is one of aquaculture’s\r\ngreat success stories, despite its ongoing battles with viral aquatic diseases\r\nthat can render once-thriving ponds empty and wasted.

One of the most devasting shrimp diseases worldwide over the\r\npast few decades has been White Spot Syndrome Virus (WSSV), a dsDNA viral\r\ninfection that plagues penaeid shrimp like the widely produced Pacific white\r\nshrimp (Penaeus vannamei) and can kill off entire populations in a very short\r\nperiod of time. The contagious disease is caused by a collection of related\r\nviruses that all create similar symptoms. Many of the losses – some $1 billion\r\na year – have piled up on smallholder farmers throughout Asia and Central and\r\nSouth America.

Solutions to WSSV are scarce – once a pond is infected,\r\nfarmers have little choice but to conduct an emergency harvest before the virus\r\nruns its course. A biotechnology company based in New Mexico is working to\r\naddress this problem, starting not with virus control but rather by harnessing\r\nnatural bacteria within the shrimp itself to block the transmission of the\r\ndisease – a process known as RNA interference, or RNAi.

“We’re using a technology where we have the ability to\r\nmodify and provide RNAi, which is the messenger that interacts with DNA,\r\ndirectly to plants and animals,” explained David Morgan, president of Pebble Labs, which is applying much of\r\nthe same science that researchers are using to address human diseases. “We use\r\nit to affect the development of pathogens in particular in species, and we get\r\nthe RNAi into the plant or animal by way of bacteria.”

It’s a little like using probiotics to improve bacterial\r\nflora. But rather than eating yogurt to regulate gut health, Pebble Labs is\r\nusing bacteria to express RNAi in the plants and animals that live alongside\r\nthat bacteria, effectively turning on their own natural defenses against\r\ndiseases, viruses, fungi and even some pests.

“Using this platform technique, which we call Directed\r\nBiotics, we’re using naturally occurring bacteria which are already present in\r\nthe shrimp population,” Morgan said. “We modify those bacteria, they deploy the\r\nRNAi into the shrimp and that RNAi will effectively knock out some of the more\r\nserious diseases that are affecting shrimp.”

WSSV infection and molt stage

Characteristically, WSSV causes small white spots to appear\r\non the shrimp’s body, indicative of calcium salts that are building up under\r\nthe shell. Over time, these deposits can damage the shrimp’s gills and\r\nother internal organs, eventually leading to death. As shrimp farming has\r\nexpanded in tropical parts of Southeast Asia in recent years, WSSV cases have grown right alongside it, thriving as it does in warm\r\nclimates.

Pebble Lab’s MermaidBio line is designed to address\r\nprevention of WSSV and other diseases without the use of antibiotics. It\r\npromises a natural solution that fights common diseases while protecting the\r\n“purity, quality and safety of seafood products and their ecosystem,”\r\nincreasing production and creating a more sustainable seafood supply chain.\r\nRight now, different application techniques are being tested, but the\r\nexpectation is that the RNAi solution can be incorporated into fish feed,\r\nminimizing the work that farmers will need to do to introduce the product into\r\ntheir facilities.

And, yes, the company believes that its Directed Biotics\r\nplatform could one day replace antibiotics in fish farming entirely. The\r\npotential applications for this type of technology are broad, and Pebble Labs\r\nis working on new solutions for agriculture as well, but the company’s initial\r\naquaculture focus is on preventing WSSV as well as Early Mortality Syndrome\r\n(EMS) in shrimp.

Like white spot syndrome, EMS is effectively 100 percent\r\nlethal once contracted and has had a presence in Vietnam, Malaysia and Thailand\r\nsince at least 2009. In testing, Pebble Labs says its RNAi technique has been\r\nable to depress the infection rate of EMS by about 60 percent, compared to\r\nexisting treatments that have never been able to crack 10 percent containment.\r\nIt’s not complete control but represents a substantial improvement that Morgan\r\nhopes will have a material impact on the shrimp market.

“So, here are two very large challenges in shrimp production\r\nthat we have a technology solution for,” he said, “and that is attracting quite\r\na bit of attention. So much so that we’re in the last stages of concluding an\r\nagreement with one of the largest animal health companies in the world involved\r\nto be a commercial partner in their aquaculture program.”

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Pebble Labs is already getting out of the lab and into ponds\r\nthis year, testing out its platform on a wide variety of environmental\r\nproduction regimes. Once that’s done, the company expects to get a product on\r\nthe market in 2021.

Source: Global Aquaculture Alliance