Spread of an Experimental Salmonella Derby Infection in Antibiotic-Treated or Lawsonia intracellularis Vaccinated Piglets

SIMPLE SUMMARY: Today, pigs repeatedly suffer from diarrhoea which requires treatment with antibiotics. Infections with Lawsonia intracellularis are one of the most common diseases, which, although usually subclinical, have a negative impact on performance. The alternative to antibiotic treatment is vaccinations against Lawsonia intracellularis, not least because antibiotic treatments are suspected of promoting the spread of certain zoonotic pathogens. A study was carried out with piglets from a farm that had a problem with Lawsonia intracellularis infections. In half of the animals, antibiotic treatments with tylosin were carried out in piglet rearing. In the other group, the piglets had been vaccinated against Lawsonia intracellularis as suckling piglets. Individual animals from both groups were subsequently artificially infected with Salmonella as piglets. A total of 72 animals were included in the study, 12 of which were primarily infected. The other animals had the possibility of becoming infected via direct animal contact or the faeces of infected animals. The detection of Salmonella in stool and intestinal lymph nodes was significantly higher in animals previously treated with antibiotics. Treatment with tylosin may significantly increase the spread of the Salmonella infection not observed after early Lawsonia intracellularis vaccination. ABSTRACT: Lawsonia intracellularis infections are a common reason for antibiotic treatment in pig production. Experimental studies in animals naturally infected with Lawsonia intracellularis comparing the course of an experimental Salmonella infection in piglets previously treated with tylosin or vaccinated against Lawsonia intracellularis are scarce. A total of 72 seven-week-old Salmonella-free pigs were taken from a herd with a Lawsonia intracellularis history in piglet rearing. The pigs were divided into two groups with three replicates each. Animals had either been previously treated with tylosin (10 mg/kg body weight) for seven days (AB(+)VAC(−)) or had been vaccinated as suckling pigs by drenching (Enterisol(®)Ileitis; AB(−)VAC(+)). Two animals per replicate were primarily infected with Salmonella Derby (1.04 × 10(8) colony-forming units per animal). The detection of Salmonella in faeces (p < 0.0001, odds ratio: 3.8364) and in the ileocaecal lymph nodes (p = 0.0295, odds ratio: 3.5043) was significantly more frequent in AB(+)VAC(−) animals. Overall, the odds ratio for detecting Salmonella in any substrate or organ was significantly higher in the AB(+)VAC(−) group animals (p = 0.0004, odds ratio: 5.9091). Treatment with tylosin can significantly increase the spread of a Salmonella infection, which is not observed after early Lawsonia intracellularis vaccination.