Parasites on paper--The use of FTA Elute((R)) for the detection of Dirofilaria repens microfilariae in canine blood.

Storage of blood samples for subsequent DNA extraction without loss of integrity can be difficult under field conditions. Filter-based technologies are known to deliver good results for viral, bacterial and protozoan material but have not been tested for blood-dwelling stages of nematodes. In this study Whatman FTA Elute (Whatman plc, Middlesex, UK) filter technology was tested for its ability to stabilise DNA from blood samples of dogs naturally infected with Dirofilaria repens for storage prior to PCR. The concentration of microfilariae per 100microl of blood was evaluated and the blood was diluted to determine the lowest detectable number of parasites by real-time PCR (qPCR). In parallel, negative dog blood was prepared in the same way. A parasitaemia of 6+/-0.43 larvae per 100microl of blood containing EDTA could be detected using the FTA Elute filter cards, although quantification of the larvae by using the qPCR was not possible. Inasmuch as the average microfilaremia in a pool of positive dogs was 311+/-21.72 larvae per 100microl, these cards provide an effective tool for parasitological field studies because blood samples are stable for extended periods of time at room temperature without loss of DNA integrity.