Lymphocystis viruses identified in fish
2016-12-01 17:17:22   copyfrom:    hits:

Gilthead seabream infected with lymphocystis (Photo: Universidad Autónoma de Madrid)SPAINThursday, December 01,

Gilthead seabream infected with lymphocystis. (Photo: Universidad Autónoma de Madrid)


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Thursday, December 01, 2016, 01:20 (GMT + 9)


A study involving the Autonomous University of Madrid (UAM) suggests a polyviral origin of lymphocystis, an infectious disease that affects at least 150 species of fish and causes significant economic losses in aquaculture. In addition, it offers the first identification of papillomavirus in fish.

The European Union's fish farms produce about 109,000 tonnes of gilthead seabream (Sparus aurata) a year, representing a turnover of more than EUR 500 million annually. And one of the main threats to the sector is precisely viral infections, among which one of the most widespread is lymphocystis.

This disease is characterized by the formation of tumorations in the skin as a result of an increase of up to 100 times in the affected cell volume, and so far it has been thought that it was only caused by iridovirus infection.

Spanish researchers used DNA ultrasecution techniques to study the lymphocystis-associated virus community. In this way, they were able to assemble the complete genome of a new species of iridovirus, which turned out to be very different from two other genomes of the same genus hitherto sequenced.

In addition to describing this new iridvirus species, LCDV-Sa, the team was able to identify a large number of SaPV1 and SaPyV1 virus sequences, belonging to the papillomavirus and polyomavirus families, respectively.

"By joining these sequences we have been able to complete the genome of the first papillomavirus detected in fish, as well as the genome of one of the first polyomaviruses found in these animals," said the team members.

The discovery of this first fish papillomavirus suggests that the evolutionary origin of this family is much older than previously thought, dating back at least 500 million years ago.

The SaPV1 papillomavirus also has a unique characteristic within the family. "Their major capsid protein is expressed through an RNA splicing mechanism," the authors explain.

The prevalence of these three viruses in 22 Mediterranean gilthead seabream specimens shows that the LCDV-Sa iridovirus is present in both diseased and healthy animals, although less in the latter. The other two viruses identified were only detected in diseased animals, with at least one of them being associated with the LCDV-Sa virus, suggesting that their presence might be necessary for the onset of the disease.

"This work proposes the participation of viruses from different families in the development of a disease and opens the door to the development of new lymphocytic control strategies, based on the use of vaccines against fish polyomaviruses or papillomaviruses," the authors add.

The results, published in the Journal of Virology, thus coincide with other previous studies suggesting the involvement of other environmental factors in the development of the disease.

Researchers from the UAM, the Animal Health Research Centre of the National Institute of Agricultural and Food Research and Technology, Severo Ochoa Molecular Biology Centre and the University of Malaga are participating in the study.

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