Polyserositis mostly affects 4−8 weeks old piglets and is usually caused by Glaesserella parasuis, and/or Streptococcus suis, and/or Mycoplasma hyorhinis. The present study aimed to investigate the prevalence and etiology of polyserositis in a tricky pig herd. The concurrent effect of vaccination for Glässer’s disease was also assessed. A total of 46 sows and 387 piglets were herein investigated, subdivided into three groups based on their immune status (i.e., vaccination of sows and piglets). All the piglets found spontaneously dead between the 2nd and 16th week of age were recorded and necropsied. Whenever polyserositis was diagnosed, biomolecular investigations were carried out to detect the above-mentioned pathogens. Mycoplasma hyorhinis was detected most frequently (n = 23), often as the only causative agent (n = 15), whereas S. suis was observed in 8 cases (6 as the only pathogen). Moreover, Glaesserella parasuis was demonstrated in 6 piglets, always in combination with Mycoplasma hyorhinis and/or Streptococcus suis. Vaccination did not significantly affect mortality rates. Overall, our data indicate that polyserositis is likely caused by an intricate puzzle of pathogens, even when dealing with a small herd and during a short time span. That makes it challenging to achieve the correct diagnosis and to properly manage this health issue.
Keywords: Glaesserella parasuis; Mycoplasma hyorhinis; Streptococcus suis; etiology; polyserositis; swine; vaccine.