Spray-dried porcine plasma supports the health and immune status of pigs and could potentially be used in feed as a nutritional intervention against African swine fever transmission and progression of infection.
JOE CRENSHAW, JAVIER POLO, JOY CAMPBELL, YANBIN SHEN and LUIS RANGEL* report trials that evaluate the potential health benefits of feeding spray-dried porcine plasma to pigs infected with African swine fever virus (ASFv), and also on the protection afforded an ASFv vaccine prototype.
African swine fever virus (ASFv) can cause high mortality in domestic swine and affects global trade of pork with severe economic consequences for producers, affiliated industries, and communities involved in pork production. Swine producers in endemic regions afflicted by ASF continue to search for strategies to protect their swine herd from getting or having a recurrence of ASF. Traditional efforts to build immunity against ASF have been unsuccessful. Lack of officially authorized vaccines complicates the control of ASF. However, several vaccine prototypes are under development but only one vaccine against ASF has been officially approved and registered for use in Vietnam.
Nutritional interventions against ASFV transmission and progression of infection
Are there any nutritional strategies that can help build immunity and support the efficacy of vaccination protection against ASF? Dietary spray-dried plasma has been shown to protect mucosal integrity and promote optimal immune response including Th-1 and cytotoxic CD8 T-cells. Results from two new companion articles published in the peer-reviewed journal, Vaccines, imply that feed supplemented with spray-dried porcine plasma (SDPP) favorably alters the immune response of both vaccinated and non-vaccinated pigs exposed by contact with trojan pigs intentionally infected with the pandemic Georgia 2007/01 strain of ASF virus. These studies were conducted in biosecurity level 3 facilities at the Centre de Recerca en Sanitat Animal (CReSA), Barcelona, Spain.
Figure 1: ASF viral load in tissues of non-vaccinated pigs fed diets with or without SDPP.
Trial 1: Health benefits
The initial study was done using non-vaccinated pigs to evaluate if there were any health benefits associated with feeding SDPP to pigs exposed by contact with pigs intentionally infected with ASF. Non-vaccinated pigs located in separate rooms were either fed a diet with 8% SDPP or a diet without SDPP throughout the study. After an adaptation period, ASF-infected pigs were placed in contact with both groups of the non-vaccinated pigs for four days then removed. Surprisingly, neither group of non-vaccinated pigs developed fever or became viremic after 18 days of observation. Therefore, the study was extended, and another group of ASF-infected pigs were placed in contact with the non-vaccinated pigs. This time both groups of non-vaccinated pigs eventually became infected, however the group of pigs fed the SDPP diet had lower virus load in tissues (Figure 1) with a delayed development of fever (Figure 2) during the 12 days of observation after the second exposure.
Another interesting observation was that nine days after the first exposure to ASF-infected pigs, the non-vaccinated pigs fed the SDPP diet had a more robust number of ASFv-specific IFN-γ secreting cells in their blood, which may have contributed to the delayed onset of ASF infection and fever in this group of pigs. Stimulation of these ASFv-specific IFN-γ secreting cells is a desired response for enhancing the protective efficacy of a vaccine against ASF.
Figure 2: Average rectal temperatures over time of non-vaccinated contact pigs fed diets with or without SDPP after second exposure period.
Trial 2 – Vaccine efficacy
In the next study, the effects of feeding SDPP on the protection efficacy of the ASFv vaccine prototype BA71∆CD2 was evaluated. This prototype is a live attenuated vaccine developed through collaborative efforts of a global multidisciplinary group and provides protection against both homologous and heterologous ASFv strains. The attenuated virus can be grown in stable cell lines to facilitate large scale production of the vaccine. For this study, two groups of pigs were acclimated to diets with or without 8% SDPP, then intranasally inoculated with the vaccine, and three weeks later kept in direct contact with pigs infected with the pandemic Georgia 2007/01 ASFv strain. During the 20-day exposure period, vaccinated pigs fed the diet with SDPP showed absence of fever, while a few of the vaccinated pigs fed the control diet started having increased temperature the last four days of the study (Figure 3).
Figure 3: Average rectal temperature of vaccinated pigs and non-vaccinated ASF-infected trojan pigs fed diets with or without spray dried porcine plasma.
Furthermore, the ASFv genome was absent in blood and fecal swabs from pigs fed the SDPP diet during the exposure period, but most of the vaccinated pigs fed the control diet showed presence of virus genome in blood and fecal swabs. In addition, ASFv was not detected in any organ tissue samples from pigs fed the SDPP diet at 20 days post-exposure, but pigs fed the control diet showed some tissue infectivity (Figure 4).
Figure 4: Percentage of vaccinated pigs fed diets with or without SDPP that were PCR positive for ASF genome in various tissues.
For pigs fed the SDPP diet there were higher specific IFN-γ secreting cells in their blood in response to both the vaccine and pandemic strains of ASFv at day 9 post-exposure (Figure 5). The immunomodulatory effects of dietary SDPP were evident in serum cytokine profiles before vaccination, and at various days after vaccination or after exposure. Collectively, these dietary SDPP-driven alterations in serum cytokines suggest an enhancement of the vaccine-induced ASFv-specific cellular response. Further research on mucosal immunity and its interconnections with systemic immune responses are needed to better characterize the mechanisms impacted by dietary SDPP.
Figure 5: Number of ASFV-specific IFN-γ secreting cells in blood from vaccinated pigs fed diets with or without SDPP at 9 days post-exposure for pandemic wild strain (Georgia 2007/01) and vaccine modified strain (BA71∆CD2) viruses.
Feeding diets containing SDPP enhanced the efficacy of the prototype ASFv BA71∆CD2 vaccine and provides a novel nutritional strategy to improve the health status of pigs under ASFv conditions, and potentially for other disease conditions as well.
*Dr Joe Crenshaw (firstname.lastname@example.org) Director of Technical Services, Dr. Joy Campbell, Senior Director of Research and Development, Dr. Javier Polo, Vice President Research & Development, Yanbin Shen, Global Director of Technical Services and NA, Luis Rangel, Director of Technical Services – Latin America, are all with APC. References are available from the lead author.
By the Asian Agribiz Technical Team -16 June, 2023, AM