The histo- and ultra-pathological studies on a fatal disease of Prussian carp (Carassius gibelio) in mainland China associated with cyprinid herpesvirus 2 (CyHV-2)

Instead of the usual host, the goldfish, cyprinid herpesvirus 2 (CyHV-2), has been detected in the Prussian carp (Carassius gibelio) from Hungary, the Czech Republic and mainland China in recent years, which has caused the massive mortality of C. gibelio and appears to be spreading worldwide. From May to July of 2011 and 2012, the massive mortality of C. gibelio was observed in many aquatic breeding ponds in northern Jiangsu province, eastern China. Moribund fish showed petechial and eccymotic hemorrhages in gills and around the base of the fins and white color of fins. Histological examination revealed that tissues from gill, kidney and spleen presented symptoms of infiltration of hemocytes and the lesions. Transmission electron microscopy of these cells demonstrated naked herpes-like virus nucleocapsids (95-110 nm) in their nuclei, while the cytoplasm contained multiple aggregates of enveloped viral particles (170-200 nm). CyHV-2 infected gill, kidney and spleen and multiplied or enveloped in both nucleus and cytoplasm of leukocytes or hematopoietic cells. Maturation of CyHV-2 occurred in the cytoplasm, particularly associated with Golgi apparatus, indicating that the virus from C. gibelio probably contains viral glycoproteins. PCR method was used for detecting the virus by using CyHV-2 primers and produced positive results in the tissues of gill, kidney and spleen but negative results in the fins, liver and intestine, which coincided with histological and morphological results. The present work presents the ultrastructural pathology of this serious disease in C. gibelio caused by CyHV-2. It will be helpful to further understand the mechanism of CyHV-2 infection of this new fish host.