Mycoplasma gallisepticum (MG) can cause respiratory disease in chickens and result in serious economic losses in the chicken industry. The use of live vaccines has been a favorable option for the control of MG infection in multi-age commercial layers and broiler breeders. There are three live vaccines, including ts-11, 6/85, and F strain, that have been commonly used in various parts of the world, including South Korea. The definitive diagnosis of the infection, therefore, requires the differentiation of wild-type field strains of MG from the vaccine strains used. Thus, we aimed to develop a novel multiplex PCR assay to discriminate between vaccine strains (ts-11, 6/85, and F strain) and wild-type field strains of MG isolated from infected chickens. We designed four novel primer sets that are each specific to MG species, ts-11, 6/85, and F strain. The multiplex PCR assay using the primer sets differentially identified wild-type and vaccine strains of MG but did not detect other avian bacteria. The detection limit of this assay was 250 fg/μL of genomic DNA of each strain tested. In addition, this assay was applied to 36 MG strains isolated from chickens over the past 20 years in South Korea. As a result, the assay identified 22 wild-type strains and 14 vaccine strains. Consequently, the novel multiplex PCR assay can discriminate between vaccine and wild-type field strains of MG and could be a valuable tool for the diagnosis of MG infection in MG-vaccinated chicken flocks.

A safe and effective method for eradicating poultry red mite (PRM; Dermanyssus gallinae) is urgently needed, as existing treatments show a low efficacy or hazardous effects on chickens. We evaluated the efficacy of a combined treatment with ivermectin and allicin (IA) against PRMs in chickens and drug residues in non-target samples. The efficiency of PRM eradication by IA was compared with those of natural acaricides in vitro. Ivermectin (0.25 mg/mL) + allicin (1 mg/mL) (IA compound) was sprayed on isolator housing hens with PRMs. The PRM mortality rate, clinical symptoms, and ivermectin residue in hens were analyzed. IA showed the highest PRM-eradication efficacy among all tested compounds in vitro. The insecticidal rates of IA were 98.7%, 98.4%, 99.4%, and 99.9% at 7, 14, 21, and 28 days of treatment, respectively. After inoculating PRMs, hypersensitivity, itching, and a pale-colored comb were observed in control animals, which were absent in treated hens. No clinical symptoms from IA and ivermectin residues were found in hens. IA effectively exterminated PRMs, demonstrating its potential for industrial use to treat PRMs.

Fowl typhoid, caused by Salmonella Gallinarum (SG), remains an important poultry disease. We characterized 136 SG isolates, one per farm, from diagnostic submissions of diseased chickens to the national veterinary laboratory in South Korea from 2002 to 2026, comparing two periods (2002–2010 and 2011–2026). Antimicrobial susceptibility was determined by broth microdilution, the spvB polyproline linker (PPL; the region joining the two functional domains of the SpvB virulence factor) was sequenced, and genetic relatedness was assessed by XbaI–pulsed-field gel electrophoresis (PFGE). Resistance to nalidixic acid was most frequent (93.4%), followed by streptomycin (83.1%) and ciprofloxacin (71.3%). Resistance to ampicillin, tetracycline, and nalidixic acid was less frequent in 2011–2026 (false discovery rate-adjusted p < 0.05), and these associations persisted after adjustment for chicken type. Multidrug resistance was detected in 52.2% of isolates, without significant change between periods. However, 13 of the 34 multidrug-resistant isolates from 2002–2010 were resistant to four or more antimicrobial classes, whereas all 37 from 2011–2026 were resistant to exactly three classes. Five PPL lengths of 13–21 prolines were identified, and their distribution differed between periods (p = 0.016). Isolates carrying ≥17 prolines were more frequent in 2011–2026 than in 2002–2010 (p < 0.01). PFGE yielded 61 pulsotypes in 27 clusters, with two dominant clusters detected across years and chicken types. These findings indicate that the PFGE-defined SG population showed temporal phenotypic changes within Korean poultry flocks, underscoring the need for continued surveillance of resistance and genotype.