Molecular evidence for Toxoplasma gondii in the brain of striped dolphins (Stenella coeruleoalba) stranded along the Ligurian Sea coast of Italy

Abstract

Toxoplasma gondii is a protozoan agent of increasing concern for both free-ranging and captive cetaceans. Nonetheless, information on epidemiology, biology, genetics and pathogenic potential of T. gondii for aquatic mammals is incomplete. This work provides molecular evidence for T. gondii in the brain tissue from five striped dolphins (Stenella coeruleoalba) found stranded in 2007-2008 along the Ligurian Sea coast of Italy. These animals showed a more or less severe, subacute to chronic, non purulent, multifocal meningo-encephalitis. Additionally, the cerebral parenchyma of 3 animals harboured protozoan cysts and zoites which were immunohistochemically linked to T. gondii. Consequently, a preliminary molecular investigation was undertaken to confirm the presence of the protozoan in these dolphins. Genomic DNA was extracted from the brain tissue of the animals and the extracts were examined with a nested PCR specific for the B1 gene of T. gondii. Three out of the 5 animals scored positive upon B1-PCR. Sequences were subsequently searched against the GenBankTM Database using the Basic Local Alignment Search Tool. The three sequences were identical to each other and showed 100% homology with the corresponding B1 sequence of T. gondii, with no insertions/deletions nor substitutions. The other 2 dolphins were negative upon B1-specific PCRs and also upon PCRs targeting other T. gondii genes (i.e. GRA and UPRT). To explore more in depth the genetic make-up of this protozoan, complementary studies are presently ongoing on GRA and UPRT genes of the 3 animals which were molecularly confirmed (i.e. B1-PCR) as infected by T. gondii. In conclusion, further studies are needed to elucidate a number of epidemiological and biological features of T. gondii infection in free-ranging cetaceans, with special emphasis on “pelagic” species such as striped dolphins.