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Shared needles are a possible iatrogenic and hematogenous inanimate vector of African Swine Fever virus (ASFV) in farm conditions.
Methods: To evaluate that possible transmission, sixty, 4-week-old pigs were procured from an ASF free herd free. Upon arrival, pigs were randomly divided into two sets. Set 1 served as seeder pigs, and were randomly allocated to 4 groups. The other pigs were divided into 8 groups, and served as sentinels. Seeder pigs were oronasally challenged with ASFV at high (108 copy numbers/mL), moderate (106 copy numbers/mL) or low (101 copy numbers/mL) challenge titer, except a subgroup that remained unchallenged (negative control). At 7 days post challenge (peak viremia), all four seeder groups were intradermally and intramuscularly injected with a vaccine adjuvant using a needle-free device and conventional needles, respectively. The same needle or needle-free device was then used to inject the same volume of adjuvant into set 2 (n = 48) pigs. All pigs were observed for clinical disease daily and assayed for the presence of ASFV DNA by quantitative PCR.
Results: All seeder groups developed viremia (except the control pigs). ASFV viremia was detected in all sentinel groups injected via the intramuscular route. Transmission rate from the intramuscular route via conventional needles was positively correlated with virus titer in blood circulation of seeders. Sentinels intramuscularly exposed to needles from high titer challenged seeders displayed more severe and acute clinical disease compared to that of exposed to low titer challenged seeders. No viremia nor clinical signs were observed in the sentinel groups injected via the intradermal route.
Conclusion: This study confirmed the hematogenous transmission of African Swine Fever virus between pigs through needle-sharing.
Salman M, Lin H, Suntisukwattana R, et al. Intradermal needle-free injection prevents African Swine Fever transmission, while intramuscular needle injection does not. Scientific Reports. 2023; 13: 4600. https://doi.org/10.1038/s41598-023-31199-2