Novel poxvirus discovered in crocodile tegus (Crocodilurus amazonicus)

Skin lesions, represented by multiple, up to lentil-sized, elevated, partially ulcerated foci. Photo: Institute of Virology/Vetmeduni Vienna

Skin lesions, represented by multiple, up to lentil-sized, elevated, partially ulcerated foci. Photo: Institute of Virology/Vetmeduni Vienna  1

A novel poxvirus (family Poxviridae) has been discovered in Crocodilurus amazonicus (family Teiidae), a lizard species with a body length of up to 120 cm. Researchers from the Institute of Virology at Vetmeduni Vienna have now succeeded in generating the first genome sequence of the virus, which shows that the reptile poxvirus has its closest phylogenetic relationship to avian poxviruses (Avipoxvirus). The discovery highlights the potential for virus exchanges between avian and reptilian species and could be relevant in the context of species conservation programmes.

In 2019, five Crocodilurus amazonicus, owned by a private collector in Austria, exhibited skin lesions and weight loss. Due to the severity of the clinical signs, one animal had to be euthanized and was sent for further diagnostic evaluation to the pathologists of the Research Institute of Wildlife Ecology at Vetmeduni Vienna. The animal had multiple elevated, partially ulcerated skin lesions with a diameter of up to 4 mm on the back and the areas of head, neck and tail that did not extend into the underlying muscle. Large numbers of poxvirus-like particles were detected within these lesions. A sample taken from a skin lesion tested positive for the presence of poxvirus DNA.

Surprisingly close relationship to avian pox virus

Although lesions and infections have been described in various reptiles before, including crocodilians, tortoises, chameleons and tegus, they have not yet been characterized at the genetic level, except for poxviruses in Nile and saltwater crocodiles. The present study, which was recently published in Archives of Virology, is the first report of the genome sequence of a poxvirus in a crocodile tegu – and shows it to be most closely related to avian poxviruses. First author Kerstin Seitz from the Institute of Virology at Vetmeduni Vienna: “The close relationship of the poxvirus in this study to the avian poxviruses is surprising given the more than 150-million-year phylogenetic separation between avian and reptilian species and the differences in body temperature.” Viruses are usually well adapted to the body temperature of their hosts. Birds have a body temperature between 38°C and 42°C, while the body temperature of crocodile tegus is dependent on the ambient temperature. “The great phylogenetic distance to crocodilian poxviruses may indicate that reptile poxviruses evolved at different times. Additional studies are needed to examine the diversity of reptile poxviruses and their species specificity and potential as disease agents,” says last author Christiane Riedel from the Institute of Virology at Vetmeduni Vienna.

Viruses with high relevance for public health

Poxviruses are large enveloped viruses containing a double-stranded DNA genome. They are important pathogens of high public health relevance. Poxviruses are able to infect a wide range of host species, ranging from insects to mammals. Within the family Poxviridae, two subfamilies (Chordopoxvirinae and Entomopoxvirinae) have been defined based on their hosts, which are either vertebrates or insects. The subfamily Chordopoxvirinae is divided into 18 genera, which include a total of 52 species. Poxviruses infecting non-mammalian species belong to the genera Avipoxvirus and Crocodylidpoxvirus. As also observed in mammalian hosts, poxviruses of avian and crocodilian species are primarily associated with skin lesions but can also affect the upper respiratory and gastrointestinal tract. Poxvirus infections of reptiles other than crocodilians have been described in the literature, but no sequence information or further characterization of these viruses had been available so far.
 

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