Diseases caused by herpesviruses have been reported in different species of turtles. Many of these reports are based on observations of single or isolated cases,2-6,9,12 but several epizootics caused by herpesviruses were also reported.7,8,10,11,13 In Europe, a herpesvirus infection which causes typical pathological lesions in land tortoises seems to be responsible for significant morbidity and mortality among these animals in captivity.5,9,10,11 A similar disease associated with herpesvirus particles was also described in the United States.4,7,12 However, current data about the prevalence of herpesvirus infections in land tortoises are lacking.
In a retrospective study we investigated the occurrence of herpesvirus infections in land tortoises which had been necropsied since 1988 at the Department of Zoo Animal Pathology, Institute of Animal Pathology, Berne. Moreover, systematical examinations on the distribution of herpesvirus induced lesions have been performed since 1995.
From 1988 to 1996 a total of 914 postmortem examinations of land tortoises were carried out. In 142 cases (15.5%), a herpesvirus infection was diagnosed based on the presence of typical eosinophilic intranuclear inclusion bodies in histological sections. Selected and ambiguous cases were examined by electron microscopy to confirm the histological diagnosis. Among the 142 affected animals were 99 spur tailed tortoises (Testudo hermanni, 69.7%), 29 spur thighed tortoises (T. graeca, 20.4%), eight leopard tortoises (T. pardalis, 5.6%), four marginated tortoises (T. marginate, 2.8%), one four-toed tortoise (T. horsfieldii, 0.7%), and one yellow-footed tortoise (T. denticulata, 0.7%). Many of the animals had been captive-bred in Switzerland, but some were also imported.
Pathological lesions were mainly characterized by lesions in the upper digestive tract. An ulcerative to diphtheroid-necrotizing stomatitis and glossitis was seen in most of the cases. Histologically, epithelial necrosis in the oral cavity, the pharynx, and the esophagus were found. Eosinophilic intranuclear inclusion bodies were present in and around degenerating epithelium. The second most frequently affected organ system was the respiratory tract. Intranuclear inclusion bodies were found in areas of epithelial necrosis in the trachea and lung. Bacterial superinfections frequently caused a severe inflammatory reaction. Moreover, intranuclear inclusion bodies in neurones and glial cells of the brain were detected in about 25% of our cases. Other organs that were inconsistently found to be affected are the stomach, small and large intestine, cloaca, liver, and spinal cord. In all of these organs intranuclear inclusion bodies were detected. Electron microscopy revealed intranuclear and intracytoplasmic herpesvirus-like particles.
In our study no sex or age predisposition was evident. However, an increase in the frequency of the disease was noted in spring when tortoises wake up from hibernation.
Our data demonstrate that herpesvirus infections frequently occur in captive land tortoises in Switzerland and suggest a wide distribution of this disease. A similar situation can be assumed for other European countries. Like in mammals and birds, reptilian herpesviruses possibly induce latent and persistent infections of their hosts. Virulent herpesviruses could be easily distributed and be introduced into immunological naive populations, resulting in a high mortality. Therefore, the disease is of concern for owners, breeders, the pet trade, zoos, and conservation programs.
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