Dr. Bailey Arruda of Iowa State University recently completed Swine Health Information Center-funded research on development and evaluation of a dual matrix serum/oral fluid atypical porcine pestivirus (APPV) ELISA using known status samples. As part of its mission to protect the health of the US swine herd, SHIC funded this research to provide tools for an emerging disease which has not affected domestic pigs significantly though it presents potential for concern. APPV is the most common cause of congenital tremor (CT) in pigs. This is the first study to experimentally infect swine with APPV and monitor the infection dynamics over time out to 70 days post inoculation (DPI). There is limited information concerning the ecology, epidemiology, and pathophysiology of APPV. Currently, there is no available serologic assay to evaluate the immunity of a dam or herd. Such an assay would provide meaningful information to assess the effectiveness of preventative measures such as acclimation and vaccination as well as improve our understating of the infection dynamics and herd impact of APPV.
CT is a disease of neonatal pigs characterized by bilateral, clonic contractions of skeletal muscle seen within hours of birth, stopping when piglets are at rest. APPV is transmitted from the dam to fetuses resulting in all, or a subset, of piglets with CT. Gilts and low parity sows are frequently reported to have CT litters, however, CT litters can be seen with multiparous sows as well. Outbreaks of CT litters are most commonly observed in herds that are newly stocked, have changed genetics, or have a high gilt replacement rate with some reports stating up to 50% of litters are affected. In such outbreaks, it is not uncommon to have litter mortality reported to be 30 to 40%. Regardless of parity, CT litters are likely due to insufficient dam immunity at a critical timeframe of gestation. The most common route of exposure and infection in dams is presently unknown. Semen as well as cohorts may be involved.
Results of the experimental inoculation provide evidence that APPV viremia can be prolonged – at least 60 days could be expected following intentional exposure. Additionally, based on the results of this study, it appears oral fluid is an appropriate, and likely highly sensitive sample type, to monitor herd status by RT-qPCR. Lastly, both oral fluid and serum iELISA assays can be used to evaluate individual and herd status prior to and following intervention strategies. Per Dr. Arruda, this project provided important foundational knowledge concerning the infection dynamics of APPV in experimentally infected swine while also providing the necessary samples to develop and evaluate serologic assays that will assist in furthering our understanding of APPV and preventing CT litters.
APPV was first detected at 10 DPI in the serum of four inoculated animals. By 35 DPI, APPV was detected in the serum of every APPV-inoculated animal and all animals remained positive until the end of the study at 70 DPI. APPV was detected in 63% and 83% of oral fluids at 14 and 17 DPI, respectively. By 24 DPI, all oral fluid samples were positive and remained positive until the end of the study at low Cq values (17.3-20.0). APPV was first detected in nasal swabs from four animals at 17 DPI with nasal shedding detected in animals at 42, 49, and 56 DPI. APPV was not detected in any sample type from negative control pigs.
As a result of this SHIC-funded research, significantly more information on APPV as well as the tools to diagnose it are now available to benefit US swine veterinary practitioners and producers. This effort to fill a knowledge and resource gap represents SHIC’s ongoing commitment to protecting and enhancing the health of the US swine herd, including work on diseases not presently creating production or financial barriers.
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