Effect of Early-Life Treatment of Piglets with Long-Acting Ceftiofur on Colonization of Streptococcus suis Serotype 7 and Elicitation of Specific Humoral Immunity in a Farm Dealing with Streptococcal Diseases

Abstract

In newborn piglets treatment with long-acting ceftiofur is a common approach to reduce losses due to streptococcal diseases on farms, even if problems start after weaning. The purpose of this study was to examine the influence of a single early-life treatment on Streptococcus (S.) suis colonization, transmission, immunoreaction, and drug resistance over an observation period of 14 weeks. In a farm with a history of streptococcal disease and isolation of a S. suis cps 7 mrp+, arcA+ isolate from diseased piglets, half of each litter was treated with a long-acting ceftiofur on day 1. S. suis-isolates were profiled and serum samples were tested for opsonizing antibodies. Treated and untreated pigs did not differ according to average daily weight gains, S. suis-isolation rates and level of opsonizing antibodies. Although the invasive cps 7 strain was not detected in a single piglet over 14 weeks, all animals developed bactericidal activity. No resistance to ceftiofur, but resistance to tetracyclins (100%), and trimethoprim/sulfamethoxazole (53%) was shown. Our results indicate that early treatment with ceftiofur does not prevent colonization and transmission of S. suis or the induction of bactericidal humoral immunity in nursery and fattening pigs. The necessity of continuous usage should be reconsidered.

Keywords: antibodies; bactericidal killing assay; colonization; drug resistance; early life ceftiofur treatment; pig; streptococcus suis serotype 7; transmission.

Figure 1

High-graded purulent polyarthritis in 6–7 week-old piglet caused by Streptococcus suis cps 7 (mrp+, arcA+, sly−).

Figure 2

Detection rate of S. suis (dark green (control) or blue (treatment): cps 7, light green (control) or blue (treatment): other serotypes) at birth, day 7 of life and week 14 in the treatment and the control group in percent, detected on tonsils. Piglets in both groups were colonized almost equally when coming out of the birth channel before ceftiofur treatment. At week 14 all piglets were colonized on tonsils. No statistical differences could be seen between treatment and control group.

Figure 3

Results of the bactericidal killing assay using blood from S. suis cps 7 free piglets with sera collected at week 7 and 14 of life from piglets in the treatment and control group and the invasive mrp+ cps 7 strain. A survival factor < 1 indicates killing of S. suis, a survival factor > 1 indicates bacterial proliferation. No differences between treatment group and control group were seen in week 7 (p = 0.9) and week 14 (p = 0.1).

Figure 4

Time flow of the study. Piglets were weaned at four weeks of age.