Signalment:  

Seven, 6- to 8-inch long goldfish (Carassius auratus) In June 2010, a fish kill occurred at a lake in south east South Dakota. This pond's primary function is a storm sewer retention basin, and the kill occurred a couple days after a big rain event. The rain event was likely the stressor that started the die off. The die off involved a high percentage of goldfish, but dead bullheads and crappies were also seen. Mortality in these other species is common during the transition from spring to summer in our natural lakes and ponds. The goldfish first appeared in the lake about two years before the die off. The exact source of the goldfish is not known; however, it is assumed that someone released their pet fish. Dead goldfish were submitted to Animal Disease

Research and Diagnostic Laboratory at South Dakota State University by the South Dakota Department of Game Fish and Parks for diagnostic workup due to concern with possible viruses that attack species such as koi, carp, and goldfish.

Gross Description:  

Some of the dead goldfish gills had limited multifocal hemorrhages and pale foci that appear to be necrosis. All fish had empty stomachs and full gallbladders. A couple of fish had edema and reddening of the lateral skin.

Histopathologic Description:

The gills have severe pleocellular inflammation with some proliferation and multifocal necrosis. There is severe multifocal meningoencephalitis. The inflammation is most extensive in the meninges and the ventricles. The head kidney, kidney, and spleen have severe multifocal to coalescing necrosis of hematopoietic tissue. Many intranuclear basophilic inclusion bodies are present. 

Morphologic Diagnosis:  

Submitted kidney slides: Acute severe multifocal to coalescing necrotizing inter-stitial nephritis with intranuclear inclusion bodies.

Etiology: Cyprinid Herpesvirus 2, confirmed by PCR.

Lab Results:  

Pools of gill, liver, and spleen were cultured and large growths of Aeromonas hydrophilia were isolated from all pools. Viral examination included the collection of kidney, gill, and spleen from the goldfish, and after processing, inoculating EPC cells at 15°C for VHS (viral hemorrhagic septicemia); and EPC cells at 25°C for SVCV (spring viremia of carp virus), LMBV (largemouth bass virus), or KHV (koi herpes virus). After a week the EPC cells at 25°C had cytopathic effect (CPE). Supernatant from the cell culture was filtered and put on EPC cells again and CPE was present again at a week. These cells were harvested and polymerase chain reaction (PCR) for VHS and SVCV was run and was found to be negative. Kidney, spleen, and gill homogenate was sent to Veterinary Diagnostic Laboratory at the University of Minnesota; it was examined for koi herpes virus with PCR and found to be negative. Minnesota also put homogenate on KF‐1 cells at 15°C and 25°C for 42 days being passed on day 14 and day 28 and the results were negative. Finally, pools of kidney, spleen, gill, liver, and intestine were sent to Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis; they were positive for Cyprinid Herpesvirus 2 (CHV‐2) using PCR.

Condition:  

Cyprinid herpesvirus-2, goldfish

Contributor Comment:  

Herpesviral hematopoietic necrosis (HVHN) is a disease of goldfish Carassius auratus auratus. It is caused by Cyprinid herpesvirus 2 (CyHV-2), a member of the cyprinid herpesvirus group that includes carp pox (CyHV-1) and koi herpesvirus (CyHV-3). Cyprinid Herpesvirus 2 is found worldwide. Most goldfish populations carry the virus and disease outbreaks are sporadic and brought on by stress. Mortality associated with HVHN can approach 100 percent. The virus causes severe necrosis of hematopoietic tissue. Necrosis and inflammation is also found in the gills.(3,5)

JPC Diagnosis:  

1. Kidney, hematopoietic tissue: Necrosis, diffuse, with moderate hyperplasia and numerous intranuclear inclusion bodies. 

2. Kidney, tubules: Degeneration, necrosis and loss, diffuse, with rare intranuclear inclusion bodies.

Conference Comment:  

Infection and goldfish mortality associated with CyHV-2 has been described throughout the world including in North America, Japan, Australia, the United Kingdom, Italy,(2) China and France; global fish trade is an important pathway for viral spread. Outbreaks are triggered by handling stress, transportation, and variations in water temperature.(1)

The three cyprinid herpesviruses are closely related to anguillid herpesvirus 1; all 4 viruses are grouped within the genus Cyprinivirus. Cyprinid herpesvirus-3 (CyHV-3) is highly contagious and is also termed koi herpesvirus disease. It is an OIE reportable disease and is also present throughout the world due to global fish trade; it can be devastating to the production of koi and common carp. Characteristic signs of disease include erratic swimming, gasping for air, poor appetite, discoloration and fin erosions. Histologic lesions include gill, liver and renal necrosis with intranuclear inclusion bodies. 

Hyperplasia of gastric gland epithelium, intestinal villi, and respiratory cells may also be seen, resulting in lamellar fusion. Survivors of CyHV-3 outbreaks and other unaffected fish species can act as carriers. The virus is transmitted horizontally and fish density may play a role in severity and spread of infection in an outbreak. Cyprinid herpesvirus-1 causes papillomatous skin lesions in infected koi; the virus is lethal in young fish, but is generally not lethal in adult koi.(4)

Consistent histopathologic findings in CyHV-2 infection include necrosis of hematopoietic tissue in the spleen and/or kidney (necrosis may or may not be present in both locations), with or without the presence of characteristic herpesviral inclusion bodies. Other reported microscopic findings include: branchial epithelial hyperplasia, necrosis(1,2) and hypertrophy; necrosis and inflammation in the intestine; and lesions in the heart.(1) Viral DNA has been interstitium with eosinophilic cellular and demonstrated in subclinically affected animals with the presence of single cell necrosis in hematopoietic tissue, suggesting a possible role of latent infection in the pathogenesis of this disease.(2)

The most prominent lesion in these sections is the diffuse necrosis within the expanded renal hematopoietic tissue, and the presence of numerous prominent intranuclear inclusions within hematopoietic precursor cells and occasionally within renal tubule epithelium. The tunica media of few vessels is discontinuous and infiltrated by low numbers of inflammatory cells, however, the moderator pointed out that this is likely an innocent bystander lesion in areas of necrosis and not a true vasculitis. There is multifocal renal tubule epithelial degeneration, necrosis and rare regeneration. Herpesviral intranuclear inclusion bodies are also present within circulating leukocytes, which can be seen in the lumen of several small vessels. The moderator also discussed the presence of mild compensatory hematopoietic tissue hyperplasia and erythrophagocytosis. 

References:

1. Boitard PM, Baud M, Labrut S, Boisseson C de, et al. First detection of Cyprinid Herpesvirus 2 (CyHV-2) in goldfish (Carassius auratus) in France. J Fish Dis. 2015; July, 14; E pub ahead of print. DOI 10.1111; jfd.12400.

2. Giovannini S, Vergman SM, Keeling C, Lany C, et al. Herpesviral Hematopoietic Necrosis in Goldfish in Switzerland: Early Lesions in Clinically Normal Goldfish (Carassius auratus). Vet Pathol. 2015; Nov 9; Online first. DOI: 10.1177/0300985815614974.

3. Goodwin AE, Khoo L, LaPatra SE, Bonar C, et al. Goldfish hematopoietic necrosis Herpesvirus (Cyprinid herpesvirus 2) in the USA: molecular confirmation of isolates from diseased fish. J Aquat Anim Health. 2006;18:1118.