Risk assessment of PRRSV-1 MLV vaccine strains transmission via residual presence in intramuscular syringes and needle-free injection devices

Abstract Background Transmission of the Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) may occur through both direct and indirect routes. Hematogenous transmission of PRRSV has been described from infected to susceptible pigs via repeated use of the same needle with intramuscular syringes or the use of needle-free injection devices (NFID). Indirect transmission may also occur through injection devices that can act as fomites. The purpose of this study was to evaluate the risk of residual PRRSV-1 modified live (MLV1) vaccine strains in automatic intramuscular syringes with needle (AIMS) or in NFID after implementation of cleaning and disinfection procedures. Three different MLV1 vaccines were evaluated. Injection devices were sampled (internal injection mechanism and external surface) unwashed (UW), after washing (W) or after washing and disinfection (WD) procedures, just after the vaccination (D0) or after seven days of quarantine (D7). The samples were tested by PRRSV RT-PCR and by virus isolation. Results In the unwashed condition, PRRSV genome was detected on external surfaces and internal mechanisms of almost all AIMS and NFID devices. Infectious VP046 bis strain was recovered from the interior of an AIMS 7 days after use. Whatever the vaccine used, after washing only or washing and disinfection, a marked decrease in PRRSV genome load was noticed in injection mechanisms of injections devices. For AIMS, PRRSV RNA was still detectable, always with Ct > 30 (mean Ct 34.0 ± 2.2). For NFID, PRRSV genome was detected in all injection mechanisms as well, but with Ct < 30 (except one NFID - mean Ct 27.0 ± 2.5). On external surface, PRRSV was not detected for any AIMS after maintenance procedures, but was detected on 75% of NFID with Ct > 30 (mean Ct 35.6 ± 2.3). After seven days of storage, no PRRSV genome was detected on external surfaces and in injection mechanisms of AIMS, however, it was still detected in almost all injection mechanisms of NFID with Ct < 30 (mean Ct 26.4 ± 3.4). Virus isolation tests all yielded negative results for both washed only and washed and disinfected devices. Conclusion The risk of transmission of PRRSV-1 MLV vaccine strains through their residual presence in injection devices appeared to be reduced when proper washing and disinfection protocols were applied between vaccination sessions. However, given the limited sensitivity of virus isolation on MARC-145 cells, an in vivo evaluation of the viability of residual virus detected by PCR would be necessary to confirm the effectiveness of these protocols.