Dolphin Morbillivirus and Toxoplasma gondii coinfection in a Mediterranean fin whale (Balaenoptera physalus)
© Mazzariol et al; licensee BioMed Central Ltd. 2012
Received: 26 September 2011
Accepted: 7 March 2012
Published: 7 March 2012
Although Morbillivirus and Toxoplasma gondii have emerged as important pathogens for several cetaceans populations over the last 20 years, they have never been identified together in a Mysticete. In particular, morbilliviral infection has been never described in the Mediterranean fin whale population.
On January 2011 an adult male of fin whale (Balaenoptera physalus) stranded along the Tyrrhenian coastline of Italy. During necropsy, tissue samples from heart, skeletal muscle, mesenteric lymph nodes, liver, spleen, lung, and kidney were collected and subsequently analyzed for Morbillivirus and Toxoplasma gondii by microscopic and molecular methods. Following the detailed necropsy carried out on this whale, molecular analysis revealed, for the first time, the simultaneous presence of a Dolphin Morbillivirus (DMV) and T. gondii infection coexisting with each other, along with high organochlorine pollutant concentrations, with special reference to DDT.
This report, besides confirming the possibility for Mysticetes to be infected with DMV, highlights the risk of toxoplasmosis in sea water for mammals, already immunodepressed by concurrent factors as infections and environmental contaminants.
Among the several threats to which free-ranging cetaceans are exposed, Morbillivirus and Toxoplasma gondii are believed to represent a serious hazard to their health and conservation . Nevertheless, morbilliviral infections have been rarely described in mysticetes [2–4], while T. gondii has been also reported as a disease-causing protozoan agent in immunocompromised Odontocetes [5, 6] affected by a severe meningo-encephalitis, as recently documented in the Mediterranean striped dolphin (Stenella coeruleoalba) population .
The present study represents the third report of Morbillivirus infection in a fin whale worldwide , thus confirming the susceptibility of Mysticetes to this virus, as also suggested by the seropositivity previously described in an Icelandic fin whales  and in a minke whale from the Mediterranean Sea . Furthermore, this report is a further proof of the diffusion of morbilliviral infection among cetaceans of the Mediterranean Sea basin, namely pilot whales (Globicephala melas), striped dolphins, and bottlenose dolphins (Tursiops truncatus) along Spanish, French and Italian coastlines [10–13]. During the dramatic morbilliviral epidemic in the Mediterranean Sea from 1990 to 1992, coinfection with T. gondii, an opportunistic pathogen for cetaceans, was reported in striped dolphins . In Mysticetes, the only previous report of infection is limited to seropositivity against T. gondii in a humpback whale (Megaptera novaeangliae) from the Atlantic Ocean . To the best of our knowledge, this is the first DMV and T. gondii coinfection described in a baleen whale. In our fin whale specimen, the molecular identification of T. gondii supports the hypothesis of a severe impairment of the immune system, likely induced by the coexisting morbilliviral infection . In contrast to what established during the investigations on the 2006-2008 morbilliviral epidemic in the Mediterranean Sea , the consistent body concentrations of OC contaminants measured in the fin whale under study, which were higher than those found in free-ranging animals [17, 18], were considered as a likely worsening factor, accompanied by concurrent kidney dysfunction and prolonged fasting, similarly to what occurred during the 1990-1992 epidemic . Furthermore, the absence of evident pathological changes related to T. gondii in the heart and in the mesenteric lymph nodes, which appeared non-compromised, suggests an acute protozoan infection.
The transmission pathways through which cetaceans acquire T. gondii infection are currently unknown, although T. gondii oocysts have been recently demonstrated in run-off waters, shellfish, and filter-feeding fish [5, 19, 20]; furthermore, oocysts may survive in sea water and remain infective for up to 6 months . No data are available on the route of transmission of T. gondii infection in the fin whale described here; however, the animal may have acquired the pathogen while swimming in shallow waters in the days immediately preceding the stranding, with such possibility highlighting the risk of toxoplasmosis for immunodepressed mammals in the marine environment.
Considering the features and the size of the Mediterranean fin whales' population [22, 23], DMV and T. gondii, especially when occurring in association to each other and under the influence of anthropogenic activities on cetacean populations living in Mediterranean waters , may pose a serious threat for this already endangered species.
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