Rapid qPCR test designed for clam farmers to spot disease early

New qPCR test detects hemocytic neoplasia early in hard clams, improving harvests and sustainability in shellfish aquaculture

Researchers at the Aquatic Diagnostic Laboratory (ADL) at Roger Williams University’s (RWU) Center for Economic and Environmental Development (CEED) have developed a new diagnostic method that detects hemocytic neoplasia – even in its early stages – in Mercenaria mercenaria, the widely farmed hard clam also known as the quahog.

Hemocytic neoplasia is a contagious, cancer-like condition affecting the hemolymph – the clam’s equivalent of blood – and is commonly found in both soft and hard-shell clams in New England. Although not a risk to human health, the disease can cause high mortality rates in farmed hard clam populations before they reach harvest size.

Hard clams are the second most valuable cultured shellfish species in Rhode Island and the broader region, after oysters. While the extent of losses to the disease in Rhode Island remains unquantified, significant impacts have been documented in wild clam populations in parts of nearby Massachusetts’ waters.

“This diagnostic method can be done in two weeks and will be a game-changer for shellfish farmers,” said Michael Torselli, an ADL research technician. “It gives a much faster response of whether aquaculture clams have the disease or not, and then that allows farmers to make decisions about what to do with their populations a lot more quickly.”

Traditionally, hemocytic neoplasia has been diagnosed through histological analysis, a process in which tissue samples are examined under a microscope – a method that can take up to six weeks and requires sacrificing the animal.

But the RWU ADL researchers developed an alternative approach using quantitative polymerase chain reaction (qPCR) to test hemolymph samples. This new method is not only non-lethal but also more sensitive, capable of detecting the disease at lower levels and less costly than conventional diagnostic techniques.

“We’re hoping a lot of farmers take advantage of the test to be proactive about the disease and how it spreads,” said Torselli. “This can have a major positive impact on the shellfish industry.”

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Although hemocytic neoplasia affects hard clams, researchers emphasize that the disease poses no risk to human health and does not impact the safety of consuming affected shellfish. The primary concern, they note, is economic: the disease can significantly reduce harvest yields, making it difficult for shellfish farmers to produce enough marketable clams to sustain profitable aquaculture operations.

“Once the clams have this cancer, they’re not going to survive for very long,” said Abigail Scro, ADL Molecular Research and Lab Manager. “This test will at least let you know that if your clams are market size, that they should be sold quickly.”

The underlying cause of hemocytic neoplasia in clams remains unknown. However, researchers believe the new diagnostic method could support long-term monitoring efforts and provide valuable data to help answer that question. They also hope that, once their findings are published, other laboratories will adopt and adapt the technology for use in conservation, aquaculture management, and further scientific research.

“We would like even an earlier warning system someday,” said Scro. “We hope to offer this qPCR method as a routine diagnostic option for farmers using our services at the RWU Aquatic Diagnostic Laboratory, and to have this new method USDA-APHIS certified in the future.”

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