Experimental Infection of Streptococcus suis Isolate in Pig in Bali – Indonesia Produced Mild Clinical Signs but Severe Multiorgan Lesions

Abstract

There has been uncertainty about Streptococcus suis (S. suis) causing disease in pig. Different inoculation routes might lead to different pathologic courses. Here, we provide data on experimental infection of weaning pigs with S. suis isolated from pigs with severe infections through intranasal (IN) and intravenous (IV) inoculation. Nine weaning landrace piglets were used as experimental animals. Three were inoculated with S. suis intranasally and three intravenously, each with 1x109CFU S. suis, while the other three were left uninoculated as control animals. Prior to inoculation, the animals were anesthetized using ketamine hydrochloride (10mg/BW) delivered intramuscularly. All control animals remained healthy throughout the study. Fever was observed in all IN and IV animals from 3 to 9 days post infection (dpi). Appetite loss was observed at 3 to 9dpi in the IN group and at 3 to 7dpi in the IV group. Diarrhea occurred in one animal in each group from 3-5dpi. Lameness was observed for one animal in the IN group. Body weights (bwt) on Day 14 of the IN, IV, and control group piglets were 11.93±0.83, 9.80±1.83, and 14.70±0.53kg, respectively. After 14 days, only four animals, three from the IN group and one from the IV group, showed pathological lesions of pneumonia and hemorrhage in the myocardium. Necropsied animals from both inoculation route groups showed inflammation in various organs. Using polymerase chain reaction, we identified S. suis from the culture of heart samples taken from animals with hemorrhage in the myocardium. We concluded that although producing a mild clinical course, S. suis isolated from severely diseased pigs causes multiorgan histological lesion development and slower weight gain. Appropriate vaccines against S. suis should reduce its financial and zoonotic impact.