The Thai Journal of Veterinary Medicine


This study was to investigate the virulence and pathogenicity of Thai isolated Mycoplasma gallisepticum (MG)inoculated into embryonated eggs and the chance of virulence study in embryonated eggs instead of experimentalchickens. One hundred and twenty eight-day-old embryonated eggs were divided into 4 groups as follows. Group 1consisting of 12 eggs served as sham negative control and was inoculated with 0.1 ml of broth into yolk sac. Group 2(2.1, 2.2 and 2.3), 3 (3.1, 3.2 and 3.3) and 4 (4.1, 4.2 and 4.3) were inoculated with 0.1 ml of MG strains F, 6/85 and Thaiisolated into yolk sacs, respectively. Each subgroup consisted of 12 eggs and the number of microorganisms differedbetween each subgroup, 108, 106 and 104 CFU/ml, respectively. Early death period (3-6 days post inoculation) andlate death period (7 days and later post inoculation) were observed. When the chicks were 7 days old, blood collectionwas done for serology by SPA and ELISA. Then all of them were necropsied for gross thoracic airsac lesion score andmicroscopic tracheal lesion score, and the airsacs of all chicks were swabbed for DNA detection by PCR assay. Resultsrevealed that the early and late death periods of all groups ranged from 0-4 and 2-7 eggs, respectively, and thenumber of survival chicks 0-6 days old and 7 days old were 0-3 and 1-9, respectively. The mean of thoracic airsaclesion score of dead and survival chicks was 0-1.33 without significant difference, however, significant difference wasfound when group 1 was compared with groups 3.2, 3.3, 4.1 and 4.2 (p<0.05). The mean of tracheal lesion score was0.81-2.56 without significant difference. The number of positive reactors against SPA and ELISA was 0 and 1,respectively. The number of positive results against PCR assay was ranged 0-4. However, MG DNA of groups 1 and2.3 was not observed. This study suggested that evaluation of the virulence and pathogenicity of Thai isolated MGcould cause a lesion of thoracic airsac, and embryonated eggs could be used instead of experimental chickens invirulence study.



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