Single and mixed infections of avian infectious bronchitis virus and Mycoplasma gallisepticum

Comparative studies of the clinical signs, pathological changes, multiplication of the pathogens and serological responses were made of groups of chickens infected with either or both avian infectious bronchitis virus and Mycoplasma gallisepticum. Electron microscopic examination of thin sections of infected tracheas showed that the multiplication of M. gallisepticum was greatly enhanced in the tracheas of chickens which had been previously or simultaneously infected with avian infectious bronchitis virus. The enhanced multiplication of mycoplasmas resulted in more severe clinical signs, pathological effects and serological responses. These findings confirm the general belief that avian infectious bronchitis infection may precipitate latent mycoplasma infection. Similar experiments were made in the allantoic sacs of 10-day embryonated hens' eggs. The results again show that there was at least a one hundred-fold increase in the multiplication of M. gallisepticum in eggs simultaneously or previously infected with avian infectious bronchitis virus. These findings emphasize the importance of using mycoplasma-free eggs for the production of virus vaccines.