Pathological and microbiological findings from mortality of the Chinese giant salamander (Andrias davidianus)

Abstract

The Chinese giant salamander, Andrias davidianus, is a nationally protected and cultured species in China. Recently, a severe epizootic occurred in cultured Chinese giant salamanders in Hubei, Hunan, Sichuan, Shaanxi, and Zhejiang provinces of China, causing substantial economic losses. The typical clinical signs of diseased larval animals were jaw and abdominal swelling and subcutaneous hemorrhaging. Diseased adult animals exhibited skin hemorrhages, ulceration of the hind limbs, and multiple hemorrhagic spots in the visceral organs. Histopathological observation indicated tissue necrosis and cytoplasmic inclusions in the spleen, liver and kidney, suggestive of viral disease. A viral agent was isolated from affected tissues in cell culture. The virus was determined to be pathogenic after experimental infection. Electron microscopy revealed iridovirus-like virions with a size of 140-180 nm in diameter inside the kidney of naturally infected animals and in cell culture. The major capsid protein (MCP) of the virus exhibited 98-99 % sequence identity to ranaviruses. Additionally, phylogenetic analysis indicated that the virus belonged to the genus Ranavirus. Comparative analysis of the MCP gene sequence with those of other viruses previously isolated from Chinese giant salamanders revealed that these isolates were highly similar, although a few variations were observed. The virus was preliminarily named Chinese giant salamander iridovirus (GSIV).

Comparative Pathology of Ranaviruses and Diagnostic Techniques

“…1a, b ). Hemorrhages are most often present on the ventral surfaces near the vent, rear legs, and gular regions, but can also be observed around the eyes, ear drum, tongue, tail, and feet (Balseiro et al 2009 ;Cheng et al 2014 ;Cunningham et al 2007 ;Docherty et al 2003 ;Geng et al 2010 ;Kik et al 2011 ;Meng et al 2014 ;Sutton et al 2014a ). Raised skin plaques or polyps have been described in tiger salamanders ( Ambystoma tigrinum ) and Chinese giant salamanders (Jancovich et al 1997 ;Bollinger et al 1999 ;Geng et al 2010 ).…”

“…Other fi ndings in the skin of anurans and caudates can include ulceration or rough discolored gray areas (e.g., Bollinger et al 1999 ;Cunningham et al 2007 ;Kik et al 2011 ). Swelling of the legs, body, and head from accumulation of fl uid (i.e., edema) within the tissues, lymph sacs, and body cavity is commonly seen in amphibians, and is especially evident in larvae (e.g., see Wolf et al 1968 ;Miller et al 2011 ;Meng et al 2014 ).…”

“…Splenomegaly and hepatomegaly have also been reported (Kik et al 2011 ) and may be related to congestion and hemorrhage. Intestinal hemorrhage has been seen in mortality events and in experimentally challenged anurans and caudates (Bollinger et al 1999 ;Geng et al 2010 ;Cheng et al 2014 ;Meng et al 2014 ). In Brazil, hemorrhage and necrosis are seen in the vestibular region of ranavirus-positive bullfrogs displaying vestibular syndrome (R. Mazzoni, CRMV-GO, personal communication).…”

“…4a-c ). In amphibians, a wide tissue tropism has been observed and additional changes that have been reported include degeneration and ulceration of the epidermis (Cunningham et al 2007 ;Geng et al 2010 ;Cheng et al 2014 ;Meng et al 2014 ), necrosis of the GI mucosa (Bollinger et al 1999 ), necrosis of lymphoid tissue (Bollinger et al 1999 ;Balseiro et al 2009 ;Meng et al 2014 ), necrosis of neuroepithelial tissue (Docherty et al 2003 ), skeletal muscle degeneration , necrosis of the pancreas (Balseiro et al 2010 ;Kik et al 2011 ), multicentric hemorrhage, vestibular hemorrhage and necrosis (R. Mazzoni, CRMV-GO, personal communication), and an ocular malformation (Burton et al 2008 ). In chelonians, common fi ndings include fi brinoid vasculitis, myositis, and necrotizing pharyngitis, esophagitis, and stomatitis ( Fig.…”

“…Conventional PCR has been used to detect ranaviral infection in fresh or fi xed tissue specimens from surveillance studies and mortality events, as well as the identifi cation of cultured virus Gray et al 2009 ;Meng et al 2014 ). Phylogenetic mapping of banked DNA sequences (GenBank) representing isolates from throughout the world reveals signifi cant sequence identity, which has been exploited in designing primers for detection of ranaviruses by PCR.…”