Chronic suppurative pulmonary infection with Streptococcus suis and Trueperella pyogenes and concurrent colonic mucosal immune alterations in two domestic pigs: a case report

Streptococcus suis and Trueperella pyogenes are opportunistic bacteria associated with suppurative respiratory disease in pigs. Information on concurrent intestinal immune changes during naturally occurring respiratory infection is limited. We describe the clinical, pathological, microbiological and intestinal immune findings in two pigs that developed severe respiratory disease during quarantine. Two 3-month-old male uncastrated Polish Landrace pigs were monitored during a 14-day quarantine period. One developed respiratory signs on day 9 and the second on day 12, with progressive respiratory disease; one pig also developed lameness and joint inflammation. Both were euthanized because of worsening dyspnea and cyanosis. Necropsy and histopathology revealed multifocal suppurative bronchopneumonia with pulmonary abscessation and chronic morphological features. S. suis and T. pyogenes were isolated from lung abscesses in both animals. Mild lymphoplasmacytic colitis and reactive hyperplasia of mesenteric lymph nodes were also identified despite the absence of gastrointestinal signs. Faecal examination, bacterial culture and 16 S rRNA sequencing provided no evidence of primary enteric infection. Colonic flow cytometry demonstrated a predominance of CD8⁺ T cells among intraepithelial lymphocytes and interindividual differences in CD4⁺ T-cell subsets and IFN-γ- and IL-17-producing cells. The cases demonstrate severe suppurative respiratory disease associated with S. suis and T. pyogenes co-infection, accompanied by subclinical intestinal histological and immunological changes. The chronic pulmonary lesions suggest that clinical deterioration represented an exacerbation of a pre-existing process. The intestinal findings may reflect systemic inflammatory responses and are compatible with, but do not demonstrate, a gut–lung interaction. These observations are hypothesis-generating and require confirmation in controlled studies with larger cohorts.