Survival and detection of bivalve transmissible neoplasia from the soft-shell clam Mya arenaria (MarBTN) in seawater

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 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 BTN cells are highly sensitive to salinity, with acute toxicity at salinity levels lower than those found in their environment. BTN cells also survive longer at lower temperatures, with >48% of cells surviving a week in seawater at temperatures from 4°C to 16°C, and 49% surviving for more than two weeks 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 BTN-specific DNA in the environment. We observed release of BTN-specific DNA into the water of aquaria from tanks with highly BTN-positive clams, and we detected BTN-specific DNA in seawater samples collected from BTN-endemic areas, although the level detected was much lower. Overall, these data show that BTN cells can survive well in seawater, and they are released into the water by diseased animals, supporting the hypothesis that BTN is spread from animal-to-animal by cells through seawater.

Horizontal transmission of disseminated neoplasia in the widespread clam Limecola balthica from the Southern Baltic Sea

“…Due to the absence of adaptive immunity in bivalves, biochemically changed NCs do not provoke effective pathogen-directed defence systems in these animals and those cells are able to clone themselves and disseminate into the tissues of other hosts , Ujvari et al 2016. The mechanism of NCs transmission is not fully described yet, but it is believed that single clonal cancerous cells that originate in one neoplastic individual are expelled from its body in, either by direct release of DNA from heavily neoplastic animals (Giersch et al 2021) or possibly through spawning or death events, and are then transmitted to other individual(s) via seawater uptake. This hypothesis is supported by studies showing successful inoculation of NCs and/or haemolymph from neoplastic to healthy bivalve through injection which resulted in further DN development and also transmission of NCs through cohabitation in different bivalve species (thoroughly discussed in Carballal et al 2015 andMetzger et al 2015).…”

“…The studies of viability of NCs fromM. arenaria shows that these cells are able to survive in the water column for several hours (Sunila & Farley 1989) or even up to 8 weeks in lower temperatures (Giersch et al 2021). The success of implantation to another organism is determined by the water circulation and density of animals (Elston et al 1990) and most probably with the filtrating potential of species.…”