A new S. suis serotype 3 infection model in pigs: lack of effect of buprenorphine treatment to reduce distress

Abstract

Background Streptoccocus suis (S. suis) is a major porcine pathogen causing meningitis, septicemia, arthritis and endocarditis. These diseases severely impair welfare of pigs. Experimental studies in pigs are important to better understand the pathogenesis and to identify protective antigens, as so far there is no vaccine available protecting against various serotypes (cps). Due to the severity of disease, application of appropriate refinement strategies in experimental S. suis infections is essential to reduce distress imposed on the piglets without jeopardizing the scientific output. The objectives of this study were to evaluate buprenorphine treatment as a refinement measure and serum cortisol levels as a distress read out parameter in a new S. suis cps3 infection model in pigs. Results Intravenous application of 2 × 108 CFU of S. suis cps3 (sly+, mrp+) to 6-week-old piglets led to severe morbidity in approximately 50% of the animals. Main pathological findings included suppurative meningoencephalitis and arthritis as well as fibrinosuppurative endocarditis. Buprenorphine treatment (0.05 mg/kg every 8 h) did not prevent signs of severe pain, high clinical scores, moderate to severe pathologies or high levels of serum cortisol in single severely affected piglets. Significant differences in the course of leukocytosis, induction of specific antibodies and bactericidal immunity were not recorded between groups with or w/o buprenorphine treatment. Of note, clinically unobtrusive piglets showed serum cortisol levels at 2 and 5 days post infectionem (dpi) comparable to the levels prior to infection with cps3. Cortisol levels in serum were significantly increased in piglets euthanized due to severe disease in comparison to clinically unobtrusive pigs. Conclusions Different clinical courses and pathologies are induced after intravenous challenge of piglets with 2 × 108 CFU of this S. suis cps3 strain. The chosen protocol of buprenorphine application does not prevent severe distress in this infection model. Important parameters of the humoral immune response, such as the level of IgM binding to S. suis cps3, do not appear to be affected by buprenorphine treatment. Serum cortisol is a meaningful parameter to measure distress in piglets experimentally infected with S. suis and to evaluate refinement strategies. In this intravenous model, which includes close clinical monitoring and different humane endpoints, clinics and cortisol levels suggest convalescence in surviving piglets within 5 days following experimental infection.

Comparative analysis of the interactions of different Streptococcus suis strains with monocytes, granulocytes and the complement system in porcine blood

“…We investigated survival and C3 labeling of the different cps 2 , 9, and 14 strains in blood and plasma, respectively ( cps 7 was not investigated as it was known that these strains are efficiently killed in blood of pigs at this age [ 6 ]). The samples were drawn from 8-week-old piglets from a herd known to be infected with different cps such as 1, 1/2, 2, 7 and 9 [ 37 ]. Furthermore, piglets at this age in this herd carry IgM antibodies binding to cps 7, cps 1 and cps 14 [ 6 , 25 ].…”

A critical review on experimental Streptococcus suis infection in pigs with a focus on clinical monitoring and refinement strategies

“…However, defining piglets to be free from specific serotypes or antibodies does not exclude a substantial level of background immunity. Since nearly all pigs within a herd are colonized with S. suis in the upper respiratory tract, specific or unspecific cross-reactive antibodies are detectable in serum of these pigs [ 14 , 58 ]. Some publications describe the usage of specific-pathogen-free (SPF) pigs ( n = 12/68) (Fig.…”

“…Different approaches have been used to measure pain in pig experiments such as grimace scales [ 94 , 95 ] or scoring systems including typical signs of pain, e.g. change in normal behavior or movement, pain vocalization and reduced feed intake [ 58 , 96 , 97 ]. These methods have to be well validated to surely measure pain and not behavior related to anxiety or fear [ 96 ].…”

“…cortisol or glucose are related to stress and pain [ 96 , 98 , 99 ]. As recently shown blood cortisol levels are significantly elevated in piglets suffering from severe S. suis disease [ 58 ]. However, there are limitations due to the influence of the circadian rhythm and the handling of the animals on the cortisol level [ 100 ].…”