Evaluation of PRRS and ASF virus dissemination between pigs when using conventional needles and a needle-free device

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Background & Objectives

African swine fever (ASF) is a highly contagious viral disease of domestic and  wild pigs, responsible for massive losses with a mortality rate that can reach  100% in pig populations and that can have serious economic consequences  due to export restrictions. ASF has generated one of the main crises in the pig  industry in recent years. On the other hand, Porcine reproductive and  respiratory syndrome virus (PRRSV) is also one of the diseases which causes  the greatest economic losses to the swine industry.

Intramuscular administration using needles has been the main route of  vaccination in pigs, although risks associated with conventional needles are  high. PRRSV, for instance, was transmitted by conventional needles and was  able to induce the disease in naïve pigs (1).

The objective of this study was to evaluate ASF and PRRSV transmission with  conventional needles and a needle-free device.

Materials & Methods
Forty-two, 3-week-old pigs were procured from an ASF-free and PRRSV-free  herd. Eighteen pigs were randomly allocated into 6 groups called seeders,  with 3 pigs in each, namely IM/ASF, ID/ASF, IM/PRRSV, ID/PRRSV and 2 control  groups, NoChal/ASF and NoChal/PPRSV (Table 1). Twenty-four age-matched  pigs were divided into 4 groups of 6 each as sentinels: IM/ASFsent,  ID/ASFsent, IM/PRRSVsent and ID/PRRSVsent (Table 2).

At 0 days post exposure (DPE), the IM/ASF and ID/ASF groups were  contact-exposed to ASF-infected pigs and the IM/PRRSV and ID/PRRSV  groups were intranasally inoculated with 4 ml of HP-PRRSV-2 (106 TCID50/ml,  2 ml/nostril). At 7 DPE (0 days post injection (DPI)), 2 ml PBS was  administered via the intramuscular route (IM) to the IM/ASF and IM/PRRSV  groups using needles, whilst the ID/ASF and ID/PRRSV groups were given 0.2  ml PBS intradermally (ID) using a needle-free device (HIPRADERMIC®, HIPRA,  Spain).

Also at 7 DPE, the same needles or needle-free device were used to inject the  same volume of PBS to sentinel pigs (1 exposed pig to 2 sentinels) with the  same route of injection used for each. Blood samples were collected from the  seeders at 0, 7, 14, 21 and 28 DPE and from the sentinels at 0, 7, 14, 21 and 28  DPI. ASF and PRRSV viraemia was evaluated using RT-qPCR.

Results

The ASF and PRRSV exposed groups had the highest viraemia at 7 DPE.  Following injection, the IM/ASFsent and IM/PRRSV sent groups were PCR  positive at 7 DPI. In contrast, sentinel pigs of both the ID/ASF sent and  ID/PRRSV sent groups were PCR negative throughout the experiment.

Conclusions & Discussion

Our findings revealed the potential for ASF and PRRSV transmission through  needles during vaccination. On the other hand, the needle-free device  inhibits both ASF and PRRSV transmission and could be used as an  alternative route of vaccination, avoiding transmission.

References

1. Madapong A et al. 2021 Safety of PRRSV-2 MLV vaccines administrated via  the intramuscular or intradermal route and evaluation of PRRSV  transmission upon needle-free and needle delivery. 11, 23107.