Such an impressive, transoceanic spread of living organisms was greatly enhanced by micro-nanoplastics, which likely acted as “rafts” for them (1).
Among the large number of (mostly) invertebrate species affected by the aforementioned phenomenon, special emphasis should be also placed upon microbial pathogens, some of which are known to impact the health and conservation of free-ranging cetaceans (2). A paradigmatic example in this direction is represented by Toxoplasma gondii, a protozoan and zoonotic agent of major concern (3), which may also infect striped dolphins (Stenella coeruleoalba), with subsequent development of severe brain lesions leading to stranding and death (4). Although a "general consensus" seems to exist on a "land-to-sea flow" as the most plausible mechanism through which T. gondii oocysts, similarly to other oro-fecally transmitted microorganisms, may gain access to the marine environment (2), this becomes questionable when dealing with striped dolphins and other T. gondii-susceptible species of aquatic mammals living in the open sea (5). In other words, how striped dolphins and other pelagic cetaceans may acquire T. gondii infection is still far from being understood. Consequently, among the different hypotheses drawn to explain this phenomenon, the existence of an "alternate" (mainly, if not exclusively) intra-marine biological protozoan's cycle has been also hypothesized (5). Since "alternate" cycles of a similar nature have not been demonstrated to occur, thus far, for both T. gondii and many other protozoan and non-protozoan pathogens, it would be worthwhile to investigate whether tsunamis, seaquakes, and (more in general) seawater movements may account for the dispersal into marine and oceanic ecosystems, also for very long distances, of T. gondii and other oro-fecally transmitted microbial agents, along with their (vertebrate and invertebrate) hosts.
Noteworthy, T. gondii has been additionally identified in several edible fish species sold on the
market (6) and, since no clear-cut evidence is hitherto available to the best of my knowledge
on fish susceptibility to this infection, such an alarming finding of public health concern provides
further support to the assumption that T. gondii-contaminated micro-nanoplastics behaved as the
likely infection’s vehicle after having been eaten by fish. Indeed, an association in the marine environment of the zoonotic protozoan parasites T. gondii, Cryptosporidium parvum, and Giardia enterica with polyethylene microbeads and polyester microfibers has been recently described, with more parasites adhering to microfiber surfaces as compared with microbeads (7).
In conclusion, while the herein hypothesized “T. gondii/micro-nanoplastics synergism” warrants
further study, an integrated approach based upon the complementary “One Health” and “One Ocean, One Health” concepts/principles would be highly recommended (also) for elucidating the complex dynamics driving the mutual “animal/human host-parasite-foodweb interactions” within the marine ecosystem.
- J.T. Carlton, J.W. Chapman, J.B. Geller, et al. Tsunami-driven rafting: Transoceanic species dispersal and implications for marine biogeography. Science 357, 1402-1406. DOI: 10.1126/science.aao1498 (2017).
- M.-F. Van Bressem, J.-A. Raga, G. Di Guardo, et al. Emerging infectious diseases in cetaceans worldwide and the possible role of environmental stressors. Dis. Aquat. Organ. 86, 143-157. DOI: 10.3354/dao02101 (2009).
- J.G. Montoya, O. Liesenfeld. Toxoplasmosis. Lancet 363, 1965-1976. DOI: 10.1016/S0140-6736(04)16412-X (2004).
- G. Di Guardo, U. Proietto, C.E. Di Francesco, et al. Cerebral toxoplasmosis in striped dolphins (Stenella coeruleoalba) stranded along the Ligurian Sea coast of Italy. Vet. Pathol. 47, 245-253. DOI: 10.1177/0300985809358036 (2010).
- G. Di Guardo, S. Mazzariol. Toxoplasma gondii: Clues from stranded dolphins. Vet. Pathol. 50, 737. DOI: 10.1177/0300985813486816 (2013).
- A.M.F. Marino, R.P. Giunta, A. Salvaggio, et al. Toxoplasma gondii in edible fishes captured in the Mediterranean basin. Zoonoses Public Health 66, 826-834 (2019).
- E. Zhang, M. Kim, L. Rueda, et al. Association of zoonotic protozoan parasites with microplastics in seawater and implications for human and wildlife health. Sci. Rep. 12, 6532. https://doi.org/10.1038/s41598-022-10485-5 (2022).