Pathogenicity of Mycoplasma iowae for chick embryos

An investigation was carried out into the pathogenicity of four strains of Mycoplasma iowae for chick embryos. Doses ranging from approximately 10(6) to 10 colony-forming units of M. iowae per egg were inoculated via the yolk sac at 7 days of incubation. Groups of 10 or more eggs per dose were used. The eggs were incubated through to hatch, and dead embryos and hatched chicks were examined for abnormalities and mycoplasma recovery. All four strains of M. iowae caused embryo mortality but two were especially virulent - one killed all the embryos while the other killed all but one. Most deaths occurred towards the end of incubation and the main abnormalities were dwarfing and congestion. Some embryos were oedematous, especially around the head, and livers and spleens were often mustard-coloured. Hatched chicks had a low incidence of air sac lesions. Mycoplasmas, identified by immunofluorescence as M. iowae were isolated from almost every exposed embryo and chick, and from almost every site sampled. No mycoplasmas were isolated from broth-inoculated controls.