The isolation of novel viral genomes from serum or plasma samples presents a significant technical challenge. In the September 25 Proceedings of the National Academy of Sciences, Tobias Allander and colleagues at the National Institute of Allergy and Infectious Diseases, Bethesda, USA, describe a sensitive method for identifying viruses in serum samples (Proc Natl Acad Sci USA 2001, 98:11609-11614).

The method is based on the fact that viral genomes are generally protected from DNase degradation by protein capsids and lipid envelopes. Allander et al. developed a technique using DNase treatment of serum followed by nucleic acid extraction, restriction enzyme digestion and sequence-independent single primer amplification (SISPA).

This methodology, that they named DNase-SISPA, can detect viruses at titres of less that 10⁶ viral genome equivalents per millilitre. Allander et al. applied the DNase-SISPA technique to clone two new bovine parvoviruses from bovine serum.