Dolphin Morbillivirus and Toxoplasma gondii coinfection in a Mediterranean fin whale (Balaenoptera physalus)

Abstract

Background: 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.

Case presentation: 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.

Conclusion: 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.

Figure 1

Steps of the necropsy carried out on the stranded whale. Biometrical measurements were taken before starting post-mortem analyses (A). A severe cutaneous parasitic infestation by Pennella spp. (B) was evident during external examination and a poor body condition was assessed due to a reduction of the blubber layer (C).

Figure 2

Molecular analyses yielded a positive result for Morbillivirus-specific genome sequences. RT-PCR targeting Morbillivirus nucleoprotein (N) gene gave positive results from the whale's spleen (lane 2), liver (lane 3), and lung (lane 4), while the heart was negative (lane 1); positive and negative controls (C + and C-, respectively) are also shown in figure A along with the DNA ladder marker. Each result was confirmed by means of both sequence and RFLP: the latter is shown in figure B with the positive reaction for spleen (lane 1), liver (lane 2), and lung (lane 3). Immunohistochemistry (IHC) using a commercially available mouse monoclonal antibody (MoAb) solution (1:500) against canine distemper virus (CDV) nucleoprotein antigen (VMRD Inc), which recognizes the same epitope from different members of the Morbillivirus genus (including DMV) was negative, possibly due to bad tissue preservation.

Figure 3

Molecular and immunohistochemical studies confirmed the presence of T. gondii in the whale's tissues. PCR techniques amplifying a conserved region of coccidian parasites yielded positive results for T. gondii in the heart (lane 1), skeletal muscle (lane 2), mesenteric lymph node (lane 3), and kidney (lane 4); positive and negative controls (C + and C-, respectively) are also shown in figure A along with the DNA ladder marker. IHC by means of a commercially available goat polyclonal anti-T. gondii antiserum solution (1:1000; VMRD Inc, Pullman, WA) showed rare T. gondii cysts embedded into both the myocardial (B; 400×, bar = 20 μm) and the renal tissue.