7/24/19
Although the majority of animal research is done with mice or rats, expanding the biodiversity helps medical research. I have previously written about predatory marine snails in medical research. Here I would like to discuss some other marine creatures.
A few weeks ago, I found myself in Cedar Key, Florida; The #1 Producer of the USA’s Farm Raised Clams. Although we may often associate clams with seafood, they reminded me of a fantastic review article I had recently read, “From the raw bar to the bench: Bivalves for models of human health” — published in the journal of Developmental and Comparative Immunology. The article was filled with great information on how research on bivalves can help human health.
First off, what’s a bivalve? I personally had never heard of this term before, but soon learned that just about everyone knows what a bivalve is. They are soft-bodied invertebrates with a hinged shell. This includes organisms like oysters, clams, and mussels.
Most research focuses on production, or farming, while other more basic research has investigated the bivalves’ ability to filter water ecosystems (see video). Both areas of research have led to an impressive base for applying their unique biology to biomedicine.
Clams and Cancer
The first area of research I would like to go over is with clams and transmissible clonal cancer. Transmissible cancer is a type of cancer where the cancerous cells can jump from one animal to the next without involvement of a virus — they’re contagious! Although this type of cancer is very rare in humans — only occurring from transplants or transmitted during pregnancy to the fetus — it is quite prevalent in dogs (canine transmissible venereal tumor), Tasmanian devils (devil facial tumor disease), and clams (bivalve transmissible neoplasia).
Transmissible cancers are a type of cancer with extreme metastasis, or ability to spread. Specifically, transmissible cancer cells can live without a host for a short period of time and then occupy a new host and evolve. At least 15 different species of bivalves are susceptible to transmissible cancer. This biodiversity allows scientist to uncover how some clams are susceptible while others are resistant. Such research could help us develop therapies for blocking this type of cancer in dogs, Tasmanian devils, and even humans.
Also, because transmissible cancer is an extreme case of metastasis, scientists can study general principles behind metastasis. As most of us know, one of the scariest facts about cancer is that it can spread throughout the entire body. By understanding and blocking extreme cases of metastasis, we may be able to use these techniques to block less extreme cases of metastasis in other animals.
Mollusks and Malaria
Another area of research is on mollusks and malaria. Oysters are the particular mollusk used for this research because they are prone to a disease called perkinsosis, or dermo. Perkinsosis causes massive mortality in oyster populations by degrading the oyster tissues. The disease is caused by the protist, Perkinsus marinus, which can be ingested by the oyster and then infests the oysters’ blood cells. Interestingly, P. marinus is analogous to malaria in vertebrates.
Senior Research Scientist José A. Fernández Robledo demonstrated that P. marinus expresses the same genes that cause malaria in mammals. However, rather than being transmitted via the blood, the protist is ingestible. Interestingly, when the protist is ingested by mice it interacts with the systemic immune system — just like malaria — but it doesn’t lead to disease and is virtually innocuous. Fernández Robledo is currently pursuing research to genetically engineer P. marinus to deliver a vaccine to the systemic immune system of mammals via ingestion, particularly malaria. Unlike vaccines delivered by injection, oral ingestible vaccines make vaccination of large populations less expensive and safer, without the necessary use of needles.
These two examples are just some of the ways bivalve research is important for medical research. Other uses include bone regeneration; because of their ability to form pearls, and antibiotics; because of their ability to filter-feed. So next time you find yourself near the ocean or comment on the clarity of a lake or river, remember the importance of bivalves in medical research and how unusual creatures can reveal some fascinating insights into human health.
Justin Varholick
Special thanks to Dr. José A. Fernández Robledo for help with this article.
Additional Readings
Cancer is Contagious in Clams: What about us?
https://www.nytimes.com/2016/06/28/science/contagious-cancer-clams.html
Tasmanian devils ‘adapting to coexist with cancer. https://www.bbc.com/news/science-environment-47659640
Humanized HLA-DR4 Mice Fed with the Protozoan Pathogen of Oysters Perkinsus Marinus (Dermo) Do Not Develop Noticeable Pathology but Elicit Systemic Immunity. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0087435
Fernández Robledo, José & Yadavalli, Raghavendra & Gerdol, Marco & Greco, Samuele & Allam, Bassem & Pales-Espinosa, Emmanuelle & Stevick, Rebecca & Gomez-Chiarri, Marta & Zhang, Ying & Heil, Cynthia & Tracy, Adrienne & Bishop-Bailey, David & Metzger, Michael. (2018). From the raw bar to the bench: Bivalves as models for human health. Developmental & Comparative Immunology. 92. 10.1016/j.dci.2018.11.020.
Ben-Horin, Tal & Bidegain, Gorka & Huey, Lauren & Narvaez, Diego & Bushek, David. (2015). Parasite transmission through suspension feeding. Journal of invertebrate pathology. 131. 10.1016/j.jip.2015.07.006.
Speaking of Research 