African swine fever virus (ASFV) is a dsDNA virus that can cause high mortality in pigs of all ages. ASFV is primarily transmitted oro-nasally or indirectly by feeding garbage containing infected ingredients, biological vectors or fomites. Spray-dried plasma (SDP) is a highly digestible, high-protein level ingredient that is widely used in feed because it benefits growth performance, gut function, and immune parameters (1). The objective of this study was to evaluate the potential benefits of feeding SDP to naïve pigs in direct contact with pigs infected with ASFV Georgia 2007/01 strain.

In this experiment two groups of pigs were fed a diet either with or without SDPP. ASFV infected pigs were introduced into each treatment group of pigs and were monitored for signs of infection.

During the first trojan exposure, no in-contact animals in either group became infected with ASFV and did not develop ASFV-specific antibodies (probably due to the short exposure time). However, all pigs fed with SDP showed low, albeit detectable, specific T-cells responses on day 15. In clear contrast, only 2 of the 10 pigs fed the control diet showed detectable T-cell responses, indicating a lower immune priming. With these unexpected results, we decided to add additional trojans on day 23. New trojans in the control group died 5 to 8 days post injection. However, 2 of 3 trojans in the SDP group survived until the end of the study (day 12 post-challenge or day 35 of the study).

After the second trojan exposure (day 23 of study), rectal temperature (RT) of contact pigs in the control group increased > 40.5°C by day 30 of the study, however, in the SDP group of pigs this increase in RT was not observed until 4 days later (day 34 of study). Average PCR Ct values were lower in the different tissues of control contact pigs compared with the SDP group (Figure 1).

Figure 1: Average ASFV PCR+ Ct values of different tissue samples from contact pigs at the end (day 35 or day 12 after second exposure) of the study. The lower Ct values the higher virus amount in the tissues.

Ct values of groups within a row differ; #P<0.1; *P<0.05; **P< 0.01.

Conclusion

Under the conditions of this study, feeding spray-dried porcine plasma to pigs contributed to reducing ASFV transmission and progression, most likely by enhancing the ASF-specific T-cell responses, previously demonstrated as key rulers for ASFV protection (2). Feeding SDP can be a strategic nutritional intervention to improve protection against ASFV. In addition, feeding SDP during endemic ASFV situations with less virulent strains may help to reduce and delay transmission by direct contact.

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Article made possible through the contribution of J. Polo et al. and APC

Feeding spray-dried porcine plasma (SDPP) to pigs contributed to delayed experimental African swine fever transmission and progression