Toxoplasma gondii in stranded marine mammals from the North Sea and Eastern Atlantic Ocean: Findings and diagnostic difficulties

Abstract

a b s t r a c tThe occurrence of the zoonotic protozoan parasite Toxoplasma gondii in marine mammals remains a poorly understood phenomenon. In this study, samples from 589 marine mammal species and 34 European otters (Lutra lutra), stranded on the coasts of Scotland, Belgium, France, The Netherlands and Germany, were tested for the presence of T. gondii. Brain samples were analysed by polymerase chain reaction (PCR) for detection of parasite DNA. Blood and muscle fluid samples were tested for specific antibodies using a modified agglutination test (MAT), a commercial multi-species enzyme-linked immunosorbent assay (ELISA) and an immunofluorescence assay (IFA). Out of 193 animals tested by PCR, only two harbour porpoise (Phocoena phocoena) cerebrum samples, obtained from animals stranded on the Dutch coast, tested positive. The serological results showed a wide variation depending on the test used. Using a cut-off value of 1/40 dilution in MAT, 141 out of 292 animals (41%) were positive. Using IFA, 30 out of 244 tested samples (12%) were positive at a 1/50 dilution. The commercial ELISA yielded 7% positives with a cut-off of the sample-to-positive (S/P) ratio ≥ 50; and 12% when the cut-off was set at S/P ratio ≥ 20. The high number of positives in MAT may be an overestimation due to the high degree of haemolysis of the samples and/or the presence of lipids. The ELISA results could be an underestimation due to the use of a multispecies conjugate. Our results confirm the presence of T. gondii in marine mammals in The Netherlands and show exposure to the parasite in both the North Sea and the Eastern Atlantic Ocean. We also highlight the limitations of the tests used to diagnose T. gondii in stranded marine mammals.

Clinical, pathological, and laboratory diagnoses of diseases of harbour porpoises (Phocoena phocoena), live stranded on the Dutch and adjacent coasts from 2003 to 2016

“…Kirkwood et al [15] observed brain lesions in 2% of the animals and Jauniaux et al [14] reported brain lesions in 4% of the animals. In previous studies, carcinoma [42], Toxoplasma [43, 44], and A. fumigatus [32] have been diagnosed as causes of brain lesions. In comparison, we observed A. fumigatus or Aspergillus sp.…”

Exposure of yellow-legged gulls to Toxoplasma gondii along the Western Mediterranean coasts: Tales from a sentinel

“…Also, because gulls live in close proximity to human populations, they have access to refuse tips (Ceia et al, 2014; Navarro et al, 2016; Ramos et al, 2009; Real et al, 2017; Steigerwald et al, 2015). Recently, it has also been suggested that marine prey, and filter feeders in particular, may accumulate oocysts (Massie et al, 2010), explaining therefore the ubiquity of this parasite in the marine environment (Dubey et al, 2005; Honnold et al, 2005; van de Velde et al, 2016; Verma et al, 2018).…”

Dolphins Stranded along the Tuscan Coastline (Central Italy) of the “Pelagos Sanctuary”: A Parasitological Investigation

“…Nevertheless, in this study the seroprevalence of T. gondii was higher in striped dolphins (33.33%, 5/15), a pelagic species, than in bottlenose dolphins (10.00%, 1/10). Differences between serological and PCR results can be explained by the heterogeneous distribution of T. gondii and parasite absence in the low amount of nervous tissue (few mgs) used for molecular analysis, especially in the case of low infection intensity [ 50 ]. It is interesting to note that the only subject found PCR positive in this study showed the highest serological titre.…”

“…It is interesting to note that the only subject found PCR positive in this study showed the highest serological titre. Nevertheless, PCR negativity to T. gondii of nervous tissues from serologically positive dolphins has been previously reported [ 19 , 50 ]. Furthermore, it is also possible that the positivity observed in some animals in this study was due to infections caused by other protozoa antigenically related to T. gondii and reported in dolphins, such as Neospora caninum and Sarcocystis spp.…”