Dolphins share Toxoplasma gondii Type II genotypes with terrestrial animals: Evidence of terrestrial T. gondii contamination in marine environments

Abstract

Toxoplasma gondii is a protozoan parasite that can infect all warm-blooded animals, leading to toxoplasmosis. Dolphins are invaluable sentinel species informing potential risks of zoonotic pathogen infection in humans through raw or undercooked seafood consumption. Between 2019 and 2023, 14 dolphins from coastal New South Wales, Australia were examined as part of ongoing marine animal health monitoring programs. Based on the histological lesions of inflammation associated with protozoal structures, Toxoplasma gondii infection is interpreted to have contributed to morbidity and mortality of four of these dolphins as identified via real-time PCR for B1 and REP genes on genetic material extracted from lung and brain samples. Additional genetic characterisation was performed on three T. gondii dolphin samples utilising multiplex multilocus nested PCR-RFLP (Mn-PCR-RFLP) targeting 13 genetic markers: B1, SAG1, 5’ and 3’ SAG2, alt. SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and Apico. A Type II variant genotype, also called ToxoDB PCR-RFLP genotype #3, was identified in four tissues. Three of the samples displayed a unique genotype on the SAG3 marker, and one of the samples showed unique genotypes on both B1 and c22-8 markers. Our findings suggest that T. gondii of the same genotype has been circulating in New South Wales for the past decade. Although temporal data is limited, all examined animals were found stranded during multi-year La Niña events. The notable increase in rainfall in 2022 is considered a potential factor leading to T. gondii infections in these dolphins, likely due to run-off containing feline faecal contamination highlighting the widespread impact of invasive species in Australia.