Optimizing oral fluid-based surveillance for an evolving swine industry
Date
2024-12
Authors
Tarasiuk, Grzegorz
Major Professor
Advisor
Zimmerman, Jeffrey
Giménez-Lirola, Luis
Karriker, Locke
Main, Rodger
Rotolo, Marisa
Committee Member
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Abstract
Beginning in the early 1900s and continuing today, pork producers have transitioned toward housing pigs indoors in order to better shelter the animals and optimize productivity [1,2]. Nevertheless, the disease pressures in these ever-larger populations and the costs associated with clinical and subclinical infections is significant, e.g., the economic impact of PRRSV was estimated at $664 million annually in the US [3]. To respond to the health challenges posed by infectious agents, surveillance methods have been developed to detect and follow their spread. In particular, aggregate samples, e.g., oral fluids, have become increasingly popular among producers and veterinarians because they are easily collected and facilitate routine surveillance of farms [4]. Oral fluids are amenable to the detection of a wide variety of viral and bacterial pathogens of swine, including some of the most economically impactful, e.g., African swine fever virus, classical swine fever virus, foot-and-mouth disease virus, Porcine circovirus type 2, Porcine Reproductive and Respiratory Syndrome virus, pseudorabies virus, swine influenza virus, and others [5].
Despite the acceptance of oral fluid diagnostics by pork producers and veterinarians, sensu stricto, pig behaviors associated with oral fluid sample collection are not well documented. With the goal of optimizing oral fluid sampling across the industry, we first set out to understand the current swine industry and, in particular, the range of pens sizes used in production systems. To that end, Chapter 3 describes two surveys conducted in swine producers and veterinarians in which it was found that the average pen size for grow-to-finish farms was 75 to 82 pigs. Due to this information, subsequent field studies were conducted across a range of pen sizes. Thus, Chapter 5 describes pig participation in oral fluid sampling in terms of the effect of previous experience with rope sampling ("training"), variable number of ropes suspended in the pen, and increasing sampling time in pens of different sizes. Notably, this research focused on pig behavior and not on diagnostic target detection; albeit higher pig participation in oral fluid collection would likely lead to a higher probability of population-based detection. The results showed that training, providing additional ropes, and extended sampling time each increased pig participation across pen sizes.
Likewise in this research, we addressed a fundamental question of oral fluid sampling in pigs. That is, it is well documented that diagnostic targets present in oral fluids may represent systemic infection or replication in buccal tissues. However, in swine and other animals, it is widely postulated that diagnostic targets in oral fluid samples may also reflect their presence in the environment. This is because normal swine behavior includes rooting, biting, smelling, and tasting the environment [6]. Diagnostic targets encountered in the environment during this exploratory process may be retained in the oral cavity, deposited in the oral fluid sample, and detected by testing [7]. However, despite the wide acceptable of this point of view, scientific data was lacking.
Scientific documentation of the process of collecting environmental targets and depositing them in an oral fluid sample is best done using a non-infectious and non-toxic tracer. In Chapter 2, we reviewed non-infectious traces (rhodamine B, tetracyclines, and iophenoxic acid) in free-ranging pig populations and their wide use evaluating the delivery of oral vaccines and/or bioactive compounds. However, tracers used in free-ranging pigs are not suitable for farm-raised pigs because of the residuals that remain in meat intended for human consumption. In Chapter 4, we describe the use of a non-infectious and safe tracer (red food coloring) which we subsequently used to document the transfer of a target both directly from pigs and indirectly from their environment into pen-based oral fluid samples. The results showed detectable levels of red food coloring in oral fluid samples from 78 of 89 pens (87.6%), including 43 of 47 (91.5%) pens in which pigs were directly exposed to the tracer and 35 of 42 (83.3%) pens in which the tracer was placed in the environment. Thus, oral fluid samples contain both pig-derived and environmental targets.
Overall, this reach has contributed measurably to our understanding and use of oral fluid sampling in the field.
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dissertation