OCCURRENCE OF KERATOCONJUNCTIVITIS APPARENTLY CAUSED BY MYCOPLASMA-GALLISEPTICUM IN LAYER CHICKENS

Natural cases of keratoconjunctivitis, apparently caused by Mycoplasma gallisepticum (MG), in layer chickens are described. The disease occu rred in a commercial flock consisting of 36,000 pullets (Babcock), fir st appearing around 30 days of age. Clinically, affected chickens show ed unilateral or bilateral swelling of the facial skin and the eyelids , increased lacrimation, congestion of conjunctival vessels, and respi ratory rales. Some of the severely affected chickens closed their eyes . The morbidity reached 27.8%, and it was estimated that approximately 10% died from reduced feed intake due to impaired vision. Ten 70-day- old chickens with clinical diseases were examined for lesions. There w as acute to subacute keratoconjunctivitis in all of the chickens, and some exhibited laryngitis. Adherence of mycoplasma organisms to epithe lial cells of the conjunctiva, cornea, and larynx was frequently obser ved. These organisms had an ultrastructure characteristic of MG and sh owed a positive reaction with rabbit polyclonal antibodies against the S6 strain of MG by immunohistochemical analysis. MG was isolated from tissue homogenates of the eyelids and tracheas of the affected chicke ns. Many of the chickens had atrophic bursae, and infectious bursal di sease virus antigens were detected in necrotic bursal follicles by imm unostaining. Therefore, immunosuppression due to infectious bursal dis ease was implicated in the pathogenesis of keratoconjunctivitis in the present cases.