Responses of pigs to a re‐challenge with Actinobacillus pleuropneumoniae after being treated with different antimicrobials following their initial exposure

Abstract

Four groups of six specific pathogen-free (SPF) pigs were inoculated intranasally with Actinobacillus pleuropneumoniae serotype 2 and treated with either enrofloxacin, tetracycline or penicillin at the onset of clinical disease, or left untreated. A fifth group was left uninoculated. The inoculated control and the penicillin-treated groups developed severe disease, but the groups treated with enrofloxacin and tetracycline recovered rapidly. All the inoculated pigs, except those treated with enrofloxacin developed serum antibodies to A pleuropneumoniae. On day 28, all five groups were challenged with A pleuropneumoniae without any subsequent treatment. The previously uninoculated control group and the enrofloxacin-treated group developed severe disease, but the three seropositive groups remained unaffected.

Effects of different antimicrobial treatments on serum acute phase responses and leucocyte counts in pigs after a primary and a secondary challenge infection withActinobacillus pleuropneumoniae

“…However, these two pigs did develop moderate levels of serum antibodies to A pleuropneumoniae serotype 2. The protective role of antibodies against A pleuropneumoniae infections has been reported previously (Cruijsen and others 1995, Sjölund and others 2009), and is further supported as the two pigs that did not mount an acute phase response were no more severely affected than the other pigs with respect to clinical signs and lesions at postmortem examination. The mild clinical signs observed in these pigs implies that a strong immune response is correlated with more severe signs of disease in A pleuropneumoniae infections.…”

“…The clinical signs, leucocyte counts and serological responses of the experimental inoculations with A pleuropneumoniae have previously been described in detail (Sjölund and others 2009). In brief, the clinical scores for the pigs in the enrofloxacin-treated group only differed from the uninoculated control group 20 hours after the first inoculation.…”

“…In Sweden, the disease has been successfully controlled for many years using batch-wise rearing together with biosecurity measures (Holmgren and others 1999, Holmgren and Lundeheim 2002), but it appears to be re-emerging as herd sizes have increased (Heldmer and others 2006, Beskow and others 2008). Acute infections may be controlled with antibiotic treatments (Hoflack and others 2001), and the efficacy of treating A pleuropneumoniae infections with fluoroquinolones is well documented (Smith and others 1991, Wallgren and others 1999a, Lauritzen and others 2003, Sjölund and others 2009). Other drugs with differing efficacies have also been used (Wallgren and others 1999a, Lauritzen and others 2003, 2005, Hart and others 2006).…”

Evaluation of diagnostic assays for the serological detection ofActinobacillus pleuropneumoniaeon samples of known or unknown exposure

“…Previously, it has been shown that pigs experimentally inoculated with A. pleuropneumoniae serovar 2 and injected with enrofloxacin after onset of clinical sign had evidence of interference with antibody production to A. pleuropneumoniae. 44 In the present study, ceftiofur was used for treatment of clinically affected pigs, and it is possible that the antigenic load in treated pigs was reduced, resulting in a reduced or even absent humoral immune response. A previous report on the evaluation of ELISAs for A. pleuropneumoniae also showed that antibodies against some serovars could not be detected.…”

“…Because antimicrobial treatment may interfere with antibody production, 44 seroconversion to A. pleuropneumoniae was verified by additional assays in selected pigs. All samples from a pig collected after inoculation were excluded if there was no indication of seroconversion by all 4 assays utilized in this study and by the confirmatory assay(s).…”