Oral fluid as a non-invasive alternative diagnostic medium for disease monitoring in pigs

Abstract

Current pig disease serological surveillance often involves blood sampling which is costly to the farmer due to veterinary fees and labour. Oral fluid (OF) has been highlighted as a promising non-invasive alternative to blood serum for diagnostics, however research into the collection and handling of samples, as well as validation against the current Gold Standard serum is required. This thesis aimed to address these key areas to support the application of OF diagnostics in the pig industry. Collection methodologies were investigated, including the use of flavours on cotton chewing ropes to increase sample yield, and the provision of multiple ropes to increase sample representation in larger groups. Flavour did not affect OF yield, however the provision of multiple ropes did improve representation in weaner, but not finishing pigs. A method to store porcine OF samples at ambient temperature for diagnosis of Porcine Reproductive and Respiratory Syndrome virus (PRRSv) infection via reverse transcription polymerase chain reaction (RT-PCR) was developed. Flinders Technology Associates (FTA) cards preserved PRRSv RNA within spiked OF samples stored at ambient temperature for up to 4 weeks. An existing protocol designed for use with serum was modified for the detection of anti-Salmonella antibody in porcine OF. Field testing resulted in 56% sensitivity and 97% specificity compared with serum. In order to validate the use of OF to assess PRRS status, blood and OF samples were collected from pigs in eight commercial pig production flows, comprising 29 pig units of breeder, nursery and finisher stages. Comparison with current Gold Standard serum testing yielded 90% sensitivity and 76% specificity by pen. This was followed by a longitudinal OF study of pigs from 8 units through nursery and growing stages to track PRRS antibody dynamics over time. Three specific patterns of anti-PRRSv antibody were detected in different populations of pigs between, as well as within the same pig flows studied. iii The results of this research will support the successful implementation of OF diagnostics for health management in pigs and has identified areas where further work is necessary.