To detect a parvovirus you just need to lighten up, say Italian scientists.

Aldo Roda and co-workers at the University of Bologna have developed an ultrasensitive way of detecting parvovirus B19 infections. The virus is responsible for a range of clinical syndromes in humans, including aplastic crisis. Aplastic crisis causes suppression of red blood cell production and is a particular threat to children with sickle cell disease, for whom infection can result in severe anaemia. 

By exploiting three detection techniques in combination, Roda's team has engineered a system that they claim is more sensitive than any previously developed in situ assays. The method is sensitive enough to detect the virus within cells and at early stages of infection.

In Roda's assay, infected cells are exposed to short strands of a synthetic version of DNA: peptide nucleic acid, or PNA. PNA has a neutral backbone rather than the negatively charged one of DNA and RNA, eliminating electrostatic repulsion effects and allowing fast, strong binding to DNA and RNA. The PNA strands bind to the viral nucleic acids and are then labelled with an enzyme (alkaline phosphatase) using a linker molecule already on the PNA.

The key to the new system is chemiluminescence, light produced by a chemical reaction. Used in detection, it is extremely sensitive and the signal can be quantified. By adding a substrate that chemiluminesces on binding to the alkaline phosphatase label, the PNA and hence viral nucleic acids can be detected.

Importantly, Roda's method does not require amplification or even extraction of the viral DNA and RNA from the cells, reducing sample handling and potentially shortening assay times. According to the team, the system could eventually be used to monitor persistent low-level viral replication in chronic infections and to study virus replication kinetics and the effects of antiviral drugs.

Freya Mearns