Sequential pathology of genital tract in chickens experimentally infected with Mycoplasma gallisepticum

Unsexed day-old White Leghorn chicks hatched from eggs pre-treated with erythromycin were infected via the yolk sac with a 48-hr broth culture of pathogenic Mycoplasma gallisepticum (S6). Fourteen of the 57 experimental female birds had gross lesions in the oviduct, characterized by the presence of grayish-white caseous plugs of various sizes in a segment or throughout the length of the oviduct. Forty-six of the infected female birds had microscopic lesions, detected primarily as mild heterophilic infiltration, lymphocytic aggregates, lymphoid follicles, diffuse lymphocytic infiltration, pleocellular response, or a combination of any of these depending on the stage and extent of infection. The caseous plugs were formed by tissue debris, fibrin, necrotic heterophils, and sometimes a few lymphocytes and macrophages. Changes that accompanied the necrotic exudate were atrophy of the mucosa, hypertrophy of the oviduct wall, or sometimes necrosis of the folds of mucosa. No significant gross and microscopic lesions were detected in ovaries, although 3 of the 33 infected male chickens had histological lesions in the testes. Gross and microscopic changes of mycoplasmosis were also found in the respiratory tract. M. gallisepticum could be consistently reisolated from oviduct(s) up to five weeks PI; thereafter, isolations were intermittent. From the ovaries or testes the organism could be isolated consistently up to one week PI only. Agglutinins were detected in the sera of infected chickens as early as one week PI, when the mean titer was 1:5, and it reached a maximum of 1:128 at six weeks PI. Thereafter the titer gradually declined, but the demonstrable agglutinins were present until 25 weeks PI.