The tortoise and the herpesvirus

An intuition by Frédéric Gandar, a PhD student at the University of Liege and his thesis supervisor Alain Vanderplasschen to focus on a research topic that has rarely been explored in the scientific world, has paid dividends. The study of Testudinid herpesvirus 3 ( TeHV-3), a herpesvirus causing high mortality rates in several protected species of tortoises (including Hermann’s tortoise), has resulted in several discoveries and has also made front-page in the Journal of Virology(1). Up to the present, the 250 or so herpesviruses studied – these are found in oysters as well as in humans – are divided into six distinct genomic structures. All of them, that is, except Testudinid herpesvirus 3. Frédéric Gandar and Alain Vanderplasschen could not believe their eyes, but they had discovered a new herpesvirus genome structure. This would be the seventh. Virology reference books will need to be updated! And this does not even take into account immune evasion or phylogeny-related discoveries. The researchers are currently working on a vaccine against this disease that is decimating tortoise species many of which are endangered.

COVER herpes virus tortuesThe renowned Journal of Virology is the cream of publications in matters relating to virology. Not only has the young doctoral student been published in this journal but he appeared on the front page of the 2015 November edition. “Being published in this journal with a herpesvirus affecting tortoises is no mean feat”! Says his thesis supervisor, Alain Vanderplasschen. “This subject was actually a handicap, which makes the achievement even greater”. The immunology and vaccinology researcher at the Faculty of Veterinary Medicine of the University of Liege has no hesitation in admitting that nobody in industry would be likely to invest in this research. The reality is that the death of tortoises is not likely to be a source of concern for many people. This subject area is not financially interesting for pharmaceutical companies so they are not interested in investing.

Fortunately for Frédéric Gandar, Alain Vanderplasschen is not an industrialist. Even though there was no likelihood of an economic dividend for his department, he invested in the project in collaboration with Professors Didier Marlier, head of the Exotic Pets Clinic and Marianne Diez, head of the Nutrition Department. Following five years of work, the investment has proved judicious: the researchers hope to perfect a vaccine that will be capable of immunising tortoises against the plague that is killing them in such great numbers.

The plague in question is Testudinid herpesvirus 3, TeHV-3. If a group of young tortoises comes into contact with the virus, the result will be fatal for 80% to 100% of them. At first, there will be no visible signs to show that they are infected. After an incubation period of around twenty days the first symptoms will appear: nasal discharge, weakness, white spots in the mouth. Secondary infections will then appear. Then the nervous system is affected avoiding tortoises from eating and moving around. Finally, the infection affects all the organs, the spleen, the kidneys and the brain. Death is inevitable after around ten days. Those that survive become “asymptomatic carriers”. Without any visible warning, the virus will be carried by them all their lives and will spread to other tortoises they meet.

When collection rhymes with propagation

The first descriptions of this disease in scientific literature goes back to the 1980s. The propagation of the disease probably accelerated at the same time as people began to collect these reptiles which live mainly in the Mediterranean Basin. Fans of these animals are prepared to spend from 200 to 250 Euros for a classic species or even up to 1,500 Euros for certain specimens. These are the types of figures that apply in the official market. But there is also a parallel unofficial market. Carefree tourists buy tortoises at the corner of the street when they are on holiday or may even pick them up on the side of the road to bring them home in their luggage, blissfully unaware that they are infected. As a result of these practices the virus can spread much more quickly than by natural means. “People are often unaware of the fact, but many species are suffering due to the fact that they have become animals of collection”, says Alain Vanderplasschen. “Certain diseases have become global whereas they would have developed much more slowly in nature, thus perhaps giving the species in question time to adapt to the disease. Because of collection, very different species can come into contact with each other artificially in terrariums…It’s like putting a crocodile and a caribou together in the same place! It is not impossible that what is happening to Testudo tortoises is the expression of the non-adaptation of a virus to a new host and therefore the consequences of a recent transfer of a virus from one species of animal to another”.

(1) Gandar F., Wilkie G., Gatherer D., Kerr K., Marlier D., Diez M., Marschang R., Mast J., Dewals B., Davison A., Vanderplasschen A., The genome of a tortoise herpesvirus (Testudinid Herpesvirus 3) has a novel structure and contains a large region that is not required for replication in vitro or virulence in vivo. Journal of Virology, 89, 22, october 2015.

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