Abstract
Many pathogens can cause cancer, but cancer itself does not normally act as an infectious agent. However, transmissible cancers have been found in a few cases in nature: in Tasmanian devils, dogs, and several bivalve species. The transmissible cancers in dogs and devils are known to spread through direct physical contact, but the exact route of transmission of bivalve transmissible neoplasia (BTN) has not yet been confirmed. It has been hypothesized that cancer cells from bivalves could be released by diseased animals and spread through the water column to infect/engraft into other animals. To test the feasibility of this proposed mechanism of transmission, we tested the ability of BTN cells from the soft-shell clam (Mya arenaria BTN, or MarBTN) to survive in artificial seawater. We found that MarBTN cells are highly sensitive to salinity, with acute toxicity at salinity levels lower than those found in the native marine environment. BTN cells also survive longer at lower temperatures, with 50% of cells surviving greater than 12 days in seawater at 10 °C, and more than 19 days at 4 °C. With one clam donor, living cells were observed for more than eight weeks at 4 °C. We also used qPCR of environmental DNA (eDNA) to detect the presence of MarBTN-specific DNA in the environment. We observed release of MarBTN-specific DNA into the water of laboratory aquaria containing highly MarBTN-diseased clams, and we detected MarBTN-specific DNA in seawater samples collected from MarBTN-endemic areas in Maine, although the copy numbers detected in environmental samples were much lower than those found in aquaria. Overall, these data show that MarBTN cells can survive well in seawater, and they are released into the water by diseased animals. These findings support the hypothesis that BTN is spread from animal-to-animal by free cells through seawater.
Highlights
Introduction distributed under the terms andMost cancer stays with the organism from which it came, arising and dying within a single host, but in a few cases, cancer has evolved to transmit from one animal to the acting as a pathogen as well as a cancer
disseminated neoplasia (DN) was first confirmed to be a transmissible cancer in soft-shell clams (Mya arenaria) [5], and later, multiple independent lineages of transmissible cancer were identified in bivalve species worldwide [12]
To test whether bivalve transmissible neoplasia (BTN) cells are released from diseased animals into the environment, we developed an environmental DNA qPCR assay. eDNA is DNA collected from environmental samples rather than from individual organisms
Summary
Introduction distributed under the terms andMost cancer stays with the organism from which it came, arising and dying within a single host, but in a few cases, cancer has evolved to transmit from one animal to the acting as a pathogen as well as a cancer. A leukemia-like disease in multiple bivalve species, called disseminated neoplasia (DN) or hemic neoplasia, was shown to be a transmissible cancer in several bivalve species [5]. DN was first confirmed to be a transmissible cancer in soft-shell clams (Mya arenaria) [5], and later, multiple independent lineages of transmissible cancer were identified in bivalve species worldwide [12]. Seven lineages of the bivalve transmissible neoplasia (BTN) in eight bivalve species have been reported [5,12,13,14,15,16,17], showing that the majority of DN cases in bivalves are likely to be a transmissible cancer, a few cases of primary DN have been reported [12,14,15]
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