Wagdy Sawahel
Date : 3 September, 2007
Source: Science Development Network (www.sciencedev.net)
In tropical countries the diagnosis of viral infections of humans or animals is often hampered by the lack of suitable clinical material and the necessity to maintain a cold chain for sample preservation up to the laboratory.
Researchers have developed a simple system using filter papers for rapid sample collection, and the molecular detection and genotyping of viruses when stored over long periods at elevated temperatures.
They demonstrated the validation of this method using two animal viruses, African swine fever, a large double-stranded DNA virus and Peste des Petits Ruminants, a negative single-stranded RNA virus.
Emmanuel Couacy-Hymann co-author of the paper at Côte-d’Ivoire-based Laboratoire Central de Pathologie Animale told Science development network (SDN) “This method is greatly relevant for developing countries. And the method is ready to be used”
Chris Verhofstede at Belgium-based Ghent University told SDN “The possibility of using dry spots on filter paper for the collection and long term storage of blood will eliminate one of the major obstacles for the widespread use of amplification-based assays for diagnosis of infectious diseases in the developing countries. It will allow blood collection in rural areas and the easy and cheap storage and transportation to a laboratory, even is this laboratory is located far away from the place of sampling. “
Verhofstede added “Besides, the possibility of storing blood on a small piece of filter paper will enable the long term storage of human or animal material on a limited space, allowing to build up large blood banks for current or future epidemiological surveys.”
He indicated that a very important finding of the study is the possibility of using the filter paper spots directly in the amplification reaction, without the need for an extraction procedure. This will result in a significant reduction of workload and cost.
“However, one has to keep in mind that many amplification based reactions are highly prone to inhibition by contaminants and that the sensitivity for contaminants can be quite different from assay to assay. A global conclusion about the usefulness of dry blood spots for the PCR based diagnosis of infectious diseases is therefore a bit hasty and careful validation and comparison with standard techniques of each application is needed and must be recommended. „ he pointed out.
Kim Steegen, researcher at AIDS Reference Laboratory of Belgium-based Ghent University told SDN “Dried blood spots (DBS) are an ideal medium for blood collection in rural areas because of the simplicity, loss of viral infectivity and the exclusion of a cold chain. The feasibility of detecting and identifying DNA and RNA genomes after long-term storage under tropical conditions is a important asset for their use in developing countries. However, the results of this paper should be treated with caution due to the limited sample size. Also the exclusion of extraction steps might be feasible in this case but cannot always be generalised to other equally important viruses. Moreover when viral quantification is needed, which is the case for the follow-up of many viral infections, like HIV, HCV etc, the exclusion of an extraction step is doubtful. “
Steegen said “Although the use of DBS in resource-limited settings in a big improvement towards the simplification of collecting samples, still high tech assays are needed to process the samples (PCR, genotyping). Therefore, the search for simpler assays should continue as well.”
Link to full research paper
Long-term storage at tropical temperature of dried-blood filter papers for detection and genotyping of RNA and DNA viruses by direct PCR
