Alien crab species as potential carriers of pathogens impacting marine megafauna's health and conservation

Climate change, with special emphasis on global warming, is believed to be a key driver of the accelerated rate of alien species expansion into the Mediterranean Sea basin and, more in general, into all marine and oceanic ecosystems (Zenetos and Galanidi 2020). 
Published in Microbiology

Share this post

Choose a social network to share with, or copy the shortened URL to share elsewhere

This is a representation of how your post may appear on social media. The actual post will vary between social networks

As a matter of fact, the last 8 years (2015-2022) have been the hottest ones ever experienced by Mother Earth throughout the last 140 years (Di Guardo 2023a).

In order to provide a numerical representation of the magnitude of such an alarming phenomenon, 70 new species were added from 2017 to 2019 to the list of those inhabiting the Mediterranean Sea (Zenetos and Galanidi 2020), including the blue swimming crabs Callinectes sapidus, of common occurrence in the central Adriatic Sea (Cerri et al. 2020), along with Portunus segnis, which has just been reported in the same geographical area (Grati et al. 2023).

The colonization of marine and oceanic ecosystems different from those where a given species, either vertebrate or invertebrate, is endemically and “traditionally” found has several implications, among which the subsequently arising alterations of sea food webs and food chains are of special concern, together with an increased risk of introduction of “new” infectious agents potentially carried by alien species into the marine and ocean environments hosting them. Furthermore, since extreme weather events like the exceedingly frequent floods represent the “alter ego” of global warming  within the climate change scenario characterizing the present “Anthropocene Epoch”, adequate attention should be also paid to the land-to-sea transfer of a large number of oro-faecally transmitted viral, bacterial, fungal and protozoan pathogens impacting the health and conservation status of marine vertebrate organisms, with special emphasis on inshore or coastal species. This is the case, among others, of Toxoplasma gondii, a zoonotic and protozoan agent of global concern to free-living cetaceans, whose health and conservation status appear to be increasingly threatened by human activities as well as by several anthropogenic and non-anthropogenic factors, often acting synergistically with each other (Di Guardo 2023b).

Noteworthy, three new Flavivirus genus members - RNA viruses classified into the Flaviviridae family - have been recently discovered in crustaceans (Gammarus chevreuxi flavivirus, Gammarus pulex flavivirus and Crangon crangon flavivirus), with Wenzhou shark flavivirus (WSFV) variants having been additionally documented in several gazami crab (Portunus trituberculatus) populations. These findings strongly support the assumption that WSFV moves horizontally between sharks and gazami crabs in ocean ecosystems (Parry and Asgari 2019). P. trituberculatus, the most fished crab worldwide and an intensely investigated crustacean model, is widely distributed in Indian and West Pacific oceans, with an ubiquitous presence of it in southeast/east Asian countries as well as in northern and eastern Australian coastal waters (Carpenter et al. 1998).

While the ability of flaviviruses to infect a range of vertebrate species has been either gained or lost throughout time (Shi et al. 2018), the aforementioned study has provided clear-cut evidence of an intriguing vertebrate-invertebrate host association in flaviviral evolution, although it was not possible to establish whether WSFV jumped from sharks to P. trituberculatus or viceversa (Parry and Asgari 2019). In this respect, it has previously been shown that other RNA viral agents like rhabdoviruses have occasionally moved between distantly related species, subsequently spreading into closely related hosts (Longdon et al. 2015). While it is still unknown if any pathological changes are caused by WSFV in susceptible host species, it should be also emphasized that viral genomes and/or antigens are abundantly present within all body tissues from infected sharks (Shi et al. 2018).

Several shark species are known to populate the Adriatic and, more in general, the Mediterranean Sea, with the health and conservation status of a number of them being increasingly threatened by both anthropogenic and non-anthropogenic factors, which largely justifies their inclusion into the "Red List" of the "International Union for the Conservation of Nature" (IUCN) (Bradai et al. 2012).

Based upon the documented occurrence in the central Adriatic Sea of C. sapidus (Cerri et al. 2020) and P. segnis (Grati et al. 2023), both of which are closely related to P. trituberculatus, it would be interesting to investigate whether WSFV or other "cousin" flaviviruses circulate also between these two alien crab species as well as between them and one or more shark species and populations residing in the same geographic areas.

In this respect, it should be additionally underscored that West Nile virus (WNV), a relevant zoonotic, arthropod-borne flaviviral pathogen infecting humans and a huge number of mammalian, avian, reptilian and amphibian species (Habarugira et al. 2020), has been deemed able to infect aquatic mammals, with WNV-infected common seals (Phoca vitulina) and killer whales (Orcinus orca) developing a fatal polioencephalomyelitis (Del Piero et al. 2006) and a non-suppurative encephalitis (St. Leger et al. 2011), respectively, in a similar fashion to WNV-infected horses (Cantile et al. 2000) and human.patients (Constant et al. 2023).

As a concluding remark, while the circulation of flaviviruses between marine and oceanic vertebrates and invertebrates, along with their potential susceptibility to flaviviral infections, undoubtedly represent challenging and intriguing issues warranting ad hoc and in-depth research efforts in the next future, I also believe that a "One Health"-based approach should be the necessary prerequisite to adequately investigate such complex host-pathogen interaction and coevolutionary dynamics, provided that human, animal and environmental health are tightly and mutually linked to each other.




Bradai MN, Saidi B, Enajjar S (2012), Elasmobranchs of the Mediterranean and Black Sea: Status, ecology and biology. Bibliographic analysis. Studies and Reviews. General Fisheries Commission for the Mediterranean, Food and Agriculture Organization of the United Nations, Rome, Italy, pp. 103


Cantile C, Di Guardo G, Eleni C, Arispici M (2000), Clinical and neuropathological features of West Nile virus equine encephalomyelitis in Italy. Equine Veterinary Journal 32: 31-35, doi:10.2746/042516400777612080


Carpenter KE, Niem VH, Norsk utviklingshjelp, South Pacific Forum Fisheries Agency, Food and Agriculture Organization of the United Nations (1998), The living marine resources of the Western Central Pacific, Volume 1, Food and Agriculture Organization of the United Nations, Rome, Italy


Cerri J, Chiesa S, Bolognini L, Mancinelli G, Grati F, Dragičević B, Dulčic J, Azzurro E (2020), Using online questionnaires to assess marine bio-invasions: A demonstration with recreational fishers and the Atlantic blue crab Callinectes sapidus (Rathbun, 1986) along three Mediterranean countries. Marine Pollution Bulletin 156: 111209, j.marpolbul.2020.111209


Constant O, Maarifi G, Barthelemy J, Martin MF, Tinto B, Savini G, Van de Perre P, Nisole S, Simonin Y, Salinas S (2023), Differential effects of Usutu and West Nile viruses on neuroinflammation, immune cell recruitment and blood-brain barrier integrity. Emerging Microbes and Infections 12: 2156815, doi:10.1080/22221751.2022.2156815


Del Piero F, Stremme DW, Habecker PL, Cantile C (2006), West Nile flavivirus polioencephalomyelitis in a harbor seal (Phoca vitulina). Veterinary Pathology 43: 58-61, doi: 10.1354/vp.43-1-58


Di Guardo G (2023a), Land-to-sea pathogen transfer. Veterinary Record 192: 216-217, doi:10.1002/vetr.2814


Di Guardo G (2023b), Sci. Adv.: Global warming, extreme weather events, and scientific research (Letter to the Editor/e.Letter). Science Advances, 


Grati F, Froglia C, Souissi JB, Bolognini L, Azzurro E (2023), The blue swimming crab Portunus segnis (Forskål, 1775) reaches the Adriatic Sea: A distant and disjointed occurrence. BioInvasions Records 12, bir.2023.12.4.15


Habarugira G, Suen WW, Hobson-Peters J, Hall RA, Bielefeldt-Ohmann H (2020), West Nile virus: An update on pathobiology, epidemiology, diagnostics, control and "One Health" implications. Pathogens. 9: 589, doi:10.3390/pathogens9070589


Longdon B, Murray GG, Palmer WJ, Day JP, Parker DJ, Welch JJ, Obbard DJ, Jiggins FM (2015), The evolution, diversity, and host associations of rhabdoviruses. Virus Evolution 1: vev014, doi: 10.1093/ve/vev014

Parry R, Asgari S (2019), Discovery of novel crustacean and cephalopod flaviviruses: Insights into the evolution and circulation of flaviviruses between marine invertebrate and vertebrate hosts.

Journal of Virology 93: e00432-19, doi: 10.1128/JVI.00432-19


Shi M, Lin XD, Chen X, Tian JH, Chen LJ, Li K, Wang W, Eden JS, Shen JJ, Liu L, Holmes EC, Zhang YZ (2018), The evolutionary history of vertebrate RNA viruses. Nature 556: 197-202, doi: 10.1038/s41586-018-0012-7


St Leger J, Wu G, Anderson M, Dalton L, Nilson E, Wang D (2011), West Nile virus infection in killer whale, Texas, USA, 2007. Emerging Infectious Diseases 17: 1531-1533, doi: 10.3201/eid1708.101979


Zenetos A, Galanidi M (2020), Mediterranean non indigenous species at the start of the 2020s: Recent changes. Marine Biodiversity Records 13: 10,

Please sign in or register for FREE

If you are a registered user on Research Communities by Springer Nature, please sign in

Follow the Topic

Life Sciences > Biological Sciences > Microbiology