Metabolic insights and background from naturally affected pigs during Streptococcus suis outbreaks

Abstract

Streptococcus suis (S. suis) is an endemic zoonotic pathogen still lacking adequate prevention in pigs. The present case study looked back to the occurrence and consequences of S. suis outbreaks in our swine research facilities in search of new metabolic and physiological insight. From a series of outbreaks, a dataset was created including 56 pigs sampled during disease detection based on clinical signs. Pigs suspected with S. suis infection were defined as diseased (n = 28) and included pigs defined as neurologically diseased (n = 20) when severe neurological signs (central nervous system dysfunctions, i.e., opisthotonos, ataxia, and generalized tremor) were observed. Another set of 28 pigs included respective pen mates from each case and were defined as control. Representative deaths were confirmed to be caused by S. suis. Tonsillar swabs were collected and analyzed by quantitative polymerase chain reaction (qPCR) for total bacteria, total S. suis, and S. suis serotypes (SS) 2 (and/or 1/2) and 9. Blood and sera were analyzed to quantify blood gases, minerals, and S. suis reactive immunoglobulins against current isolates. Data collected included litter sibling associations, birth and weaning body weight (BW), and average daily gain (ADG) 7 d after the disease detection. In general, the disease increased pH, sO₂ and the incidence of alkalosis, but reduced pCO₂, glucose, Ca, P, Mg, K, and Na in blood/serum compared to control. The SS2 (and/or SS1/2) prevalence was significantly (P < 0.05) increased in neurologically diseased pigs and its relative abundance tended (P < 0.10) to increase in tonsils. In contrast, the relative abundance of total S. suis was lower (P > 0.05) in diseased pigs than control pigs. Levels of S. suis reactive IgG2 were lower, but IgM were higher (P < 0.03) in neurologically affected pigs compared to control. Furthermore, there was an increased proportion of sibling pigs that were diseased compared to control. In conclusion, our results evidence that naturally affected pigs were associated to average performing pigs without any predisease trait to highlight but a sow/litter effect. Besides, neurologically affected pigs had increased S. suis (SS2 and/or 1/2) prevalence and relative abundance, a respiratory alkalosis profile, and mineral loss.

Keywords: Streptococcus suis; immunoglobulins; meningitis; minerals; nursery pig.

Figure 1.

Main differences in venous blood biochemical analysis and mineral analysis in neurologically diseased pigs¹ (n = 20) and control pen-mates (n = 28). ¹Defined as pigs showing clinical signs of severe central nervous system dysfunctions as opisthotonos, ataxia, and generalized tremor were defined as neurologically diseased. Symbols: LSMEANS between neurologically diseased and control tended to differ P ≤ 0.10 (t) or differed at P < 0.05 (*) or at P < 0.01 (**).

Figure 2.

Relative abundance of total S. suis within total bacteria counts in tonsillar swab measured by qPCR (cells/tonsillar swab). ^a–b Different superscripts indicate a significant difference between categories (P = 0.030; Wilcoxon two-sample test).

Figure 3.

Relative abundance of S. suis serotypes 2 (and/or 1/2) and nine within total S. suis measured by qPCR (cells/tonsillar swab). ^x–yDifferent superscripts showed a tendency to categories (P = 0.086; Wilcoxon two-sample test). P-values for all diseased: serotype 2 P = 0.192, serotype 9 P = 0.436, and unknown serotypes P = 0.476; P-values neurologically diseased: serotype 2 P = 0.083, serotype 9 P = 0.859, and unknown serotypes P = 0.867.

Figure 4.

Total Ig (A), IgM (B), IgG1 (C) and IgG2 (D) levels1 in pigs either diseased² as suspected of S. suis (n = 20) with neurological signs, or in control pen-mates (n = 28) at different times post-weaning when cases were detected in the nursery phase. ¹Points indicate means for n cases on a same day post-weaning and among the values for three isolates (isolate as random effect and pig as a repeated measure). ²Defined as severe diseased pigs including central nervous system dysfunctions (opisthotonos, ataxia, and generalized tremor). The shadded areas indicates 95% confidence interval.