Is Porcine Periweaning Failure-to-Thrive Syndrome an Infectious Diseases?

Abstract

Porcine Periweaning Failure-to-Thrive syndrome (PFTS) is a clinical syndrome of newly weaned pigs with unknown etiology and characterized by anorexia, lethargy and progressive debilitation. The hypothesis of this thesis is that PFTS is an infectious disease. Investigation in an index farm affected by PFTS from Saskatchewan Canada ruled out most common swine pathogens as the etiology and identified several lesions that were consistent across many cases. A larger study including multiple farms in North America was then undertaken. A total of 8 farms were investigated, within which 5 met the clinical definition of PFTS. Gross and histological examinations were performed on 8 case and 4 control pigs on each farm. Detection of relevant porcine pathogens, complete blood count, serum chemistry, and serum cytokine analysis were performed on each pig. Thymic atrophy, superficial gastritis and small intestinal villous atrophy were significantly more prevalent in case pigs compared to control pigs. All case pigs had at least two of these three lesions. All case and control pigs were negative for porcine reproductive and respiratory syndrome virus, swine influenza virus and were free of porcine circovirus associated diseases. Although several pathogens, such as porcine cytomegalovirus, haemagglutinating encephalomyelitis virus, porcine enteric calicivirus, group A rotavirus, enteroviruses and Cystoisospora suis were detected in some of the case and control pigs, none were associated with clinical status. Clinical pathology findings of case pigs was consistent with anorexia and dehydration, such as increases in haematocrit, blood urea, serum bilirubin, albumin, beta-hydroxybutyrate and decreases in blood glucose, calcium and phosphorous. Case pigs had similar levels to IL1-β than control pigs, which suggested that PFTS was not a result of excessive cytokines. In subsequent experiments, a snatched-farrowed porcine-colostrum-deprived (SF-pCD) pig model was developed and tissue homogenates were used to inoculate SF-pCD pigs in an attempt to reproduce the clinical signs of PFTS. The SF-pCD pigs were immunologically characterized and shown to be suitable for inoculation studies. However, inoculation of tissue homogenate from PFTS pigs failed to reproduce the clinical signs of PFTS in SF-pCD pigs. All together, PFTS is a clinical syndrome with consistent pathological and serum analytical changes among affected pigs. Despite the efforts of this research to establish an infectious etiology, there is a lack of evidence that PFTS is an infectious disease.