Effect of virus infectivity titer following centrifugation and filtration during virus extraction from fish samples

A 0.45-μm membrane filter is generally used to remove bacterial contamination during virus extraction from fish samples. However, the number of fish viruses is drastically reduced after filtration with a 0.45μm filter. In this study, we investigated the effect of filters on virus infectivity titer and the change in virus titer and bacterial number following different centrifugation conditions to determine a suitable procedure for virus extraction from fish samples. 104.05 and 105.05TCID₅₀/ml of infectious hematopoietic necrosis virus (IHNV) and 104.05 and 104.55TCID₅₀/ml of Oncorhynchus masou virus (OMV) were not detectable after filtration with two types of 0.45-μm filters, except the IHNV titer was reduced by about 10 fold after filter use (company A). No significant difference was found in the virus titer following centrifugation at 880×g (30 min) or 3,500×g (30 min), whereas IHNV and OMV titers were reduced by about 10 and 10-1000 fold by centrifugation at 14,000×g (30 min) and 14,000×g (10 and 30 min), respectively. A total of 97.7-99.9% Escherichia coli were eliminated by centrifugation at 880 ×g (30 min) and 3,500×g (30 min). These results show that fish viruses were affected by filtering, even though the effect differed by virus species and filter type. Therefore, centrifugation at 3,500×g (30 min) and use of medium with antibiotics may be useful for virus extraction along with a reduction in bacteria.