Study links Toxoplasma genotypes to brain lesions in striped dolphins
Bottom line
A new Frontiers in Veterinary Science study adds fresh evidence that Toxoplasma gondii is reaching pelagic marine mammals off Southern Italy. Researchers necropsied 93 stranded cetaceans recovered along the coasts of Campania and Calabria from 2018 to 2023 and found T. gondii DNA in the brains of 12 animals, all striped dolphins. Genotyping identified two parasite lineages, with genotype II in 10 dolphins and genotype III in 2, while neuropathology showed lesions ranging from mild non-suppurative meningitis or meningoencephalitis to severe necrotizing encephalitis. The authors say the findings support land-to-sea transmission and reinforce striped dolphins as sentinels for terrestrial pathogens in a One Health context. (frontiersin.org)
Why it matters: For veterinary professionals, the study strengthens the case for including toxoplasmosis in the differential diagnosis for neurologic disease in stranded cetaceans, especially striped dolphins. It also extends a line of Italian research dating back to earlier Ligurian Sea cases, where cerebral toxoplasmosis and genotype II or atypical type II strains had already been documented in stranded striped dolphins. Taken together, the work suggests that postmortem brain sampling, molecular testing, histopathology, and immunohistochemistry remain essential for teasing apart T. gondii from other important causes of cetacean meningoencephalitis, including morbillivirus, herpesvirus, and Brucella spp. (frontiersin.org)
What to watch: Watch for follow-up surveillance asking how pelagic dolphins are being exposed, whether genotype patterns shift over time, and how these findings inform coastal runoff and One Health monitoring programs. (frontiersin.org)
Key facts
- Study type
- Frontiers in Veterinary Science study
- Species affected
- Striped dolphins
- Sample size
- 93 stranded cetaceans necropsied
- Positive cases
- 12 dolphins had Toxoplasma gondii DNA in the brain
- Geography
- Coasts of Campania and Calabria, Southern Italy
- Genotypes detected
- Genotype II in 10 dolphins, and genotype III in 2
- Pathology
- Lesions ranged from mild non-suppurative meningitis or meningoencephalitis to severe necrotizing encephalitis
- Interpretation
- Findings support land-to-sea transmission and striped dolphins as sentinels for terrestrial pathogens
A newly published Frontiers in Veterinary Science paper reports Toxoplasma gondii in 12 stranded striped dolphins recovered along the coasts of Campania and Calabria in Southern Italy, adding new genotype and neuropathology data to a long-running concern in Mediterranean cetacean health. Across 93 cetaceans necropsied between 2018 and 2023, all positive animals were striped dolphins, and the brain lesions documented in most evaluable cases were consistent with protozoal encephalitis, from mild inflammation to severe necrotizing disease. (frontiersin.org)
The study builds on earlier Italian reports that linked T. gondii to cerebral disease in stranded striped dolphins along the Ligurian Sea coast. A 2010 Vet Pathology paper described severe nonsuppurative meningoencephalitis in stranded dolphins, with T. gondii cysts and zoites in brain tissue and no evidence that morbillivirus contributed to those deaths. A subsequent genotyping study found type II and atypical type II isolates in Ligurian cases, helping establish that toxoplasmosis in Mediterranean dolphins is not just incidental exposure but can be associated with clinically relevant CNS disease. (pubmed.ncbi.nlm.nih.gov)
In the new Southern Italy dataset, the authors screened brain tissue by real-time PCR and reported positive cycle threshold values ranging from 21 to 30. Genotyping using eight microsatellite markers identified genotype II in 10 of 12 dolphins and genotype III in 2 of 12. Histology and immunohistochemistry were available for 10 cases, and 7 were IHC-positive; tissue cysts were seen near lesions in the more severely affected brains. Geographically, 9 positive dolphins stranded along Calabria and 3 along Campania, and all positives came from the 70 striped dolphins included in the broader 93-cetacean necropsy series. (frontiersin.org)
The broader literature helps explain why that matters. Reviews and opinion pieces have framed stranded cetaceans as useful sentinels for marine ecosystem health and terrestrial pathogen spillover, especially because T. gondii is a recognized threat to free-ranging marine mammals worldwide. At the same time, older commentary has noted an unresolved epidemiologic question: striped dolphins are typically pelagic, so their exposure pathway may not be as straightforward as it is for more coastal species. That leaves room for competing explanations, including runoff-driven contamination, prey-mediated exposure, or other open-sea transmission dynamics. This is an inference from the literature rather than a direct conclusion of the new paper. (frontiersin.org)
Expert reaction specific to this new paper was limited in publicly indexed coverage, but the study sits within a growing One Health discussion around T. gondii circulation in Southern Italy. Related recent Frontiers work has examined the parasite in wild birds from the same region, underscoring the value of cross-species surveillance when trying to understand environmental circulation and genotype diversity. That context supports the new paper’s argument that marine mammal findings shouldn’t be viewed in isolation from terrestrial wildlife, runoff, and ecosystem interfaces. (frontiersin.org)
Why it matters: For veterinarians working in wildlife, aquatic animal health, pathology, and public health interfaces, this paper is a reminder that toxoplasmosis belongs high on the list when stranded cetaceans present with neurologic lesions. It also reinforces the need for complete diagnostic workups rather than attributing encephalitis to a single familiar pathogen. Differential diagnosis papers in cetaceans have emphasized overlap among lesions caused by morbillivirus, herpesvirus, Brucella spp., helminths, and T. gondii, which means molecular assays, histopathology, and targeted IHC remain central to case interpretation. From a herd-health and surveillance perspective, the bigger message is environmental: land-based pathogen pressure can surface in marine species far from the farm or household source. (pubmed.ncbi.nlm.nih.gov)
What to watch: The next step is likely more integrated surveillance, pairing marine mammal necropsy findings with terrestrial and coastal monitoring to clarify exposure routes, genotype distribution, and whether genotype III becomes more prominent in Mediterranean strandings. If that work expands, veterinary teams may get a clearer picture of whether these dolphins are acting primarily as sentinels of coastal contamination, or of a more complex offshore transmission ecology. (frontiersin.org)