Herpes Virus

Article by Stuart McArthur.

Herpes Virus Infection Associated with Lymphoma in Testudo hermanni

During 1996 an outbreak of disease associated with lymphoproliferative disease (viral lymphoma), immunosuppression, respiratory disease and paralysis was investigated at Holly House Veterinary Surgery, Leeds, England. The outbreak occurred in a large breeding colony of about 45 mainly Testudo hermanni tortoises. The colony was composed of several separate groups, one of which had temporarily contacted four sick leopard tortoises (Geochelone pardalis) and an African hingeback (Kinixys erosa). The affected unit was made up of 25 Testudo hermanni tortoises. The other unaffected tortoises were one Testudo graeca ibera, five leopard tortoises (Geochelone pardalis), four Testudo horsfieldii, one Kinixys erosa, two Geochelone sulcata and a further 16 juvenile Testudo hermanni. These were kept in individual species groups, isolated from each other and the main affected group. During the disease outbreak the entire colony was divided into two groups. Those known to have contacted sick tortoises were nursed on the original site, and those animals assumed to be clear of exposure were quarantined in small groups of two or three animals in new sites where no other chelonians were present. The disease achieved 100 per cent mortality and morbidity rates in the exposed groups, but the isolated animals currently remain unaffected after eight months' quarantine. One juvenile Testudo hermanni that left the affected group eight months previously was returned to the affected group with early signs of the disease. The course of disease in this individual was similar to those that remained in the group and a histopathological diagnosis of lymphoma was also made from this individual. This suggested the possibility of a long symptomless incubation period. The leopard tortoises were the first to show the disease; the main group of Testudo hermanni demonstrated significant symptoms after a time lag of several months. The presenting signs in the leopard tortoises included hypersecretion of ocular and nasal fluids, anorexia, muscle wastage, and fore and hind limb paralysis. Later a spastic neck muscle paralysis retained the necks of two leopard tortoises in flexion. Post mortem findings included lymphoma, jaundice, tracheitis, pneumonia, hepatitis, bile duct rupture and renal failure. The disease in the leopard tortoises tended to be chronic.

The Testudo hermanni tortoises generally showed a more acute onset of signs that included non-specific symptoms of collapse. These animals had pale greyish mucous membranes, dyspnoea and a whitening of the eyes that cleared over a period of a week or so in most animals. Some of the Testudo hermanni tortoises died within 12 hours of displaying these signs. Other animals were nursed through the initial crisis. Those that remained stable for some weeks were then either overwhelmed by non-specific infections or went into acute hepatic and renal failure. This was demonstrated from blood biochemistry and haematology. Many of these animals required human euthanasia; the remainder died despite treatment. Treated animals were given Enroflaxin (Baytril:Bayer) at a dose rate of either 5mg/kg daily or 10mg/kg daily by intramuscular injection along with cyclical courses of Ketoconazole (Nizoral Suspension:Jaansen) at 15mg/kg orally for five days at a time. Intensive fluid therapy was undertaken and environmental and nutritional support was actively given. Liquidised vegetable diets were regularly tubed into some animals and more active animals were force-fed a vegetarian diet by hand. While this treatment did not cure the affected animals it did stabilise them and certainly appeared to decrease overwhelming secondary infections. Six post mortem examinations of recently dead or euthanased tortoises yielded histopathology consistent with lymphoproliferative disease (lymphoma) affecting spleen and/or liver. Samples were sent to two independent external laboratories, both of whom reached a similar diagnosis: lymphoma relating to a lymphoid infiltration of affected organs with occasional mitotic cells. Lymphoma was present in both leopard and Testudo hermanni tortoises, indicating that the causative agent had crossed a species barrier.

Further samples from these post mortem, lymphoma-positive animals were despatched to the Ministry of Agriculture, Fisheries and Food, Central Veterinary Unit, Avian Virology Unit, where electron microscopy easily demonstrated significant numbers of herpes virus particles in both spleen and liver tissue. It has also been possible to grow the virus on CAM at a variety of temperatures, and further typing of the virus is being carried out. Affected tortoises also demonstrated degenerative changes affecting the trachea and lung tissue. Microbiology findings were consistent with overwhelming bacterial and fungal infections. Animals which had been nursed for some time showed further changes relating to muscle wasting and fatty degeneration of the liver. Some had large numbers of intestinal parasites. Samples from sick tortoises under intensive treatment revealed occasional positive pharyngeal swabs for Chlamydia spp and a variety of presumably secondary bacterial and fungal agents. A PCR faecal test for chlamydial agents was also positive in several animals. Blood from 14 affected animals under treatment was tested serologically for Mareks disease (an avian onchogenic herpes virus causing lymphoma with paresis) but this did not reveal any positive results. There appear to be significant similarities between the progress of Mareks disease in birds and the symptoms of this onchogenic herpes virus infection in tortoises. Virus cultures under way may yet demonstrate related antigens between these two viruses and hence it may become possible to use a Mareks disease vaccine in the face of similar outbreaks in breeding colonies of endangered chelonia. However, safety and efficacy may be hard to assess.

There are many reports of herpes virus infections in chelonia. It is also possible that currently unexplained disease epidemics globally in many species of both tortoises and turtles are due to a similar if not related herpes virus infection. The use of endoscopic organ biopsy in live animals and subsequent histopathology, viral culture and investigation may allow viral screening of colonies to identify potential carriers of virus infections. Such investigations would require considerable financial input from an interested sponsor but could identify the cause of fatal disease epidemics that occur after a tortoise colony is exposed to a different species tortoise assumed to carry a latent, symptomless infection. Serology may become a useful way in which affected individuals could be identified. However, the response to Mareks disease serology was disappointing and leaves this area open to further research. It may be worthwhile to treat similar chelonian infections with antiviral agents such as Acyclovir, currently used to treat children with chicken pox caused by a herpes virus infection. However, if this proved to be of therapeutic value we would not know for how long recovered animals may still excrete virus and remain infectious to animals with which they come in contact. Recently in the UK there have been a large number of cases of unexplained hind- and forelimb paralysis of Mediterranean tortoises. These could be consistent with a neurotropic onchogenic herpes virus. This would indeed be a chelonian parallel to avian Mareks disease. It is possible that the virulence and pathogenicity of a herpes virus may vary significantly with the species affected, some species being symptomless, some showing neuropathies or upper respiratory signs such as runny nose syndrome (RNS), and the remainder suffering fatal disease. We continue to be interested in viral investigations and would encourage veterinarians, or those managing colonies which have experienced disease outbreaks similar to those described above, to contact us with a view to understanding the epidemiology of this type of infection. We are particularly interested in those dealing with outbreaks in wild populations of tortoises and marine turtles globally, and would be most interested in assisting those who have encountered similar problems in breeding projects with endangered species.

Article is for information resource only, and to aware, inform or stress others of any Herpes Virus Infections within Chelonia