Herpesvirus Determination in Free-Ranging Cetaceans Stranded in the Mediterranean Sea Between June 2010 and June 2013
Abstract
Herpesvirus can infect a wide range of animal species: mammals, birds, reptiles, fish, frogs and bivalves,1 producing different lesions and diseases. Several cases of herpesvirus infection have been described in marine mammals, but there are still many unresolved issues such as the percentage of positive animals, the differences depending on age and sex and the relationship between the presence of the virus and the appearance of lesions.
In this study, in order to amplify the knowledge of herpesvirus in free-ranging cetaceans, a systematic and complete screening of all samples obtained from animals stranded in the Mediterranean coast of Valencia Community (Spain) between June 2010 and June 2013, were evaluated for herpesvirus presence. Forty-seven stranded cetaceans were analyzed: 35 striped dolphins (Stenella coeruleoalba), eight bottlenose dolphins (Tursiops truncatus), three Risso's dolphins (Grampus griseus), and one Cuvier's beaked whale (Ziphius cavirostris). Individuals were classified in six age groups based on the total length of the animal, the presence of thymus and the radiological analysis of the pectoral flipper2: adult, subadult, juvenile, calf, suckling calf and neonate. All necropsies were performed according to the standard protocol of the European Cetacean Society.3 Because of the corpus conservation condition, necropsies were not always possible; in these cases, some samples were collected at the beach. In total, 966 samples were collected and stored at -80°C. For all tissue samples obtained, herpesvirus determination was carried out by using a panherpesvirus nested PCR targeting the DNA polymerase gene.4 PCR product of all positive samples were purified and sequenced, using the obtained sequences in a phylogenetic analysis performed by using MEGA 5.2 software.5 Herpesvirus determination revealed that from the 47 evaluated cetaceans, 38 were positive in at least one tissue (80.85%): 28 striped dolphins (28/35, 80.00%), seven bottlenose dolphins (7/8, 87.5%), two Risso's dolphins (2/3, 66.67%) and the Cuvier's beaked whale (1/1, 100%). From the 966 evaluated tissues, 121 were positive for herpesvirus determination (12.53%), most of them belonging to the subfamily Gammaherpesvirinae. Results based on sex and age revealed that the percentage of positive tissues from the total evaluated is higher in females than in males, and only the suckling calves and neonates showed a lower percentage comparing them with the rest of the age groups. And, interestingly, most of the positive cetaceans presented herpesvirus in more than one tissue, occurring in several cases (51.85%) that sequences of virus belonged to the subfamilies Alphaherpesvirinae and Gammaherpesvirinae were found in different tissues of the same individual.
In summary, the conclusion could be that herpesvirus is usually present in free-ranging cetaceans in the Mediterranean sea, even though the number of positive tissues per animal is normally low, most individuals are positive for herpesvirus diagnosis in at least one tissue.
Acknowledgements
The authors thank Belén Rivera and Rocío Sánchez for their assistance. This work has been supported by a collaborative agreement involving the Oceanografic Aquarium of the Ciudad de las Artes y las Ciencias (Valencia); the VISAVET Center of Complutense University of Madrid; and the Pfizer Foundation. Mar Melero is the recipient of a predoctoral fellowship from the PhD student grant programme of Complutense University of Madrid. Consuelo Rubio-Guerri is the recipient of a predoctoral fellowship from the FPU programme of the Spanish Ministry of Education.
* Presenting author
+ Student presenter
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