The Thai Journal of Veterinary Medicine


Mycoplasma gallisepticum (MG) causes chronic respiratory disease in poultry. MG organisms consist of several virulence genes which are related to infection. The aim of this study was to analyze the virulence genes and determine the pathogenicity of Thai MG isolates. In this study, there were 3 experiments; nineteen MG isolates; and 2 reference strains, F and S6 strains, analyzed to detect 4 virulence genes (LP, gapA, pvpA and mgc2) by PCR assay (experiment 1). The pathogenicity study of sham negative control group, S6 strain, 3 selected isolates (AHRL 31/46, 54/46 and 58/46) and F strain, respectively, were inoculated into 6 groups of 21-day-old chickens, 21 birds in each group (experiment 2), and 6 groups of 8-day-old chicken embryonated eggs (CEEs), 15 eggs in each group (experiment 3). In experiment 2, at 42 days old, all birds were bled for MG ELISA, swabbed for MG PCR assay and necropsied to evaluate gross thoracic air sac and microscopic tracheal lesion scores. In experiment 3, after hatching, all chicks of each group were separately raised until 7 days old. At 7 days old, all birds were swabbed and necropsied as previously described. Results revealed that all MG isolates and reference strains had all virulence genes. The pathogenicity study in chickens was similar to that of CEEs. The Thai MG AHRL 58/46 isolate could induce the most severe clinical signs and lesions of air sacs and tracheas compared with those of the other groups. This study revealed that Thai MG isolates could cause disease in chickens.



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