Susceptibility of zebrafish (Danio rerio) to a model pathogen, spring viremia of carp virus

To improve our understanding of the genetic basis of fish disease, we developed a pathogen model, using zebrafish (Danio rerio) and spring virema of carp virus (SVCV). Replicate groups of 10 fish were acclimated to 20 or 24 degrees C, then were exposed to SVCV concentrations of 10(3) to 10(5) plaque-forming units per milliliter (PFU/ml) of water and observed daily. In a second trial, fish were acclimated to 15 degrees C, and replicate groups of 10 fish were exposed to SVCV at a concentration of 10(5) PFU/ml; however, the temperature was raised 1 degrees C/wk. Moribund fish were collected for histologic examination, and dead fish were assayed for virus by use of cell culture and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. Mortality exceeded 50% in fish exposed to 10(5) PFU of SVCV/ml at the lower temperatures. Clinical signs of disease became evident seven days after viral exposure and were observed most consistently in fish of the 10(5) PFU/ml groups. Affected zebrafish were anorectic and listless, with epidermal petechial hemorrhages followed by death. Use of plaque assays and RT-PCR analysis confirmed presence of SVCV at titers > or = 10(4) PFU/g of tissue. Histologic lesions included multifocal brachial necrosis and melanomacrophage proliferation in gills, liver, and kidneys. These results indicate that zebrafish are susceptible to infection by SVCV under conditions that mimic a natural route of exposure.