The extraction of Peste Des Petits Ruminants Virus RNA from paraffin-embedded tissues using a modified extraction method

Peste des petits ruminants (PPR) which is caused by small ruminant morbillivirus (PPRV) has an important economic impact on small ruminant farming due to high mortality rates, weight loss and restrictions on the export of small ruminants products. Molecular assays are commonly used in the diagnosis of the disease. Extraction of RNA from formalin-fixed paraffin-embedded (FFPE) tissues is challenging because of the RNA is often degraded by formalin fixation process. Although commercial kits have been developed for extraction of nucleic acids from FFPE tissues, they are expensive than other extraction kits. In this study, a modified extraction method was evaluated for detection of PPRV from FFPE tissues. A total of 20 FFPE tissue samples including 15 PPRV positive and 5 PPRV negative FFPE tissue samples were used. Two years ago, these selected FFPE tissue samples were analysed by nucleoprotein gene based one step real time RT-PCR method before they were fixed with formalin and embedded in paraffin. FFPE tissue samples were extracted using modified extraction method and were tested by fusion (F) gene based one step RT-PCR. PPRV specific RNA was detected in 12 FFPE tissue samples whereas 3 positive samples were found negative by one-step RT-PCR. Furthermore, 5 negative FFPE tissue samples were also found negative. Three false negative results were from samples with high real-time RT-PCR cycle threshold. Therefore, false negative results could be related with lower viral loads which might be lower than detection limit of the one-step RT-PCR. The results of the study show that modified extraction method could be used for RNA extraction from FFPE tissues which had been stored for 2 years.