Chemical inactivation of foot-and-mouth disease virus in bovine tongue epithelium for safe transport and downstream processing

Epithelial tissue or vesicular fluid from an unruptured or recently ruptured vesicle is the sample of choice for confirmatory laboratory diagnosis of foot-and-mouth disease (FMD). However, in ‘FMD-free’ countries the transport and downstream processing of such samples from potentially infected animals present a biosafety risk, particularly during heightened surveillance, potentially involving decentralised testing in laboratories without adequate biocontainment facilities. In such circumstances, rapid inactivation of virus, if present, prior to transport becomes a necessity, while still maintaining the integrity of diagnostic analytes. Tongue epithelium collected from cattle infected with FMD virus (FMDV) of serotype O (O/ALG/3/2014 – Lineage O/ME-SA/Ind-2001d) or A (A/IRN/22/2015 – Lineage A/ASIA/G-VII) was incubated in the PAXGene Tissue System Fixative (pH 4) and Stabiliser (pH 6.5) components respectively, in McIlvaine’s citrate-phosphate buffer (pH 2.6) or in phosphate-buffered saline (PBS, pH 7.4) at room temperature for 2, 6, 24 or 48 h. Following incubation, tissues were homogenised and tested by virus isolation and titration using LFBK_αVβ6 cells. The integrity of FMD viral RNA was assessed by RT-qPCR (3D^pol coding region), Sanger sequencing of the VP1 region and transfection of LFBK_αVβ6 cells to recover infectious virus.

Viable virus could be recovered from samples incubated in PBS for at least 48 hours. The PAXgene Tissue System Stabiliser component yielded variable results dependent on virus serotype, requiring at least 6 hours of incubation to inactivate A/IRN/22/2015 in most samples, whereas the Fixative component required up to 2 hours in some samples. McIlvaine’s citrate-phosphate buffer rapidly inactivated both viruses within 2 hours of incubation. There was no demonstrable degradation of FMD viral RNA resulting from incubation in any of the buffers for up to 48 hours, as assessed by RT-qPCR, and 24 hours by sequencing and transfection to recover infectious virus. McIlvaine’s citrate-phosphate buffer (pH 2.6) is easy to prepare, inexpensive and inactivates serotype A and O FMDV in epithelial tissue within 2 hours, while maintaining RNA integrity for downstream diagnostic processes and virus characterisation.