A myopathy associated with protozoan schizonts in chickens in commercial farms in peninsular Malaysia

A myopathy associated with elongated intramuscular protozoan schizonts of uncertain classification was observed in chickens in commercial farms. Of 152 affected fowls originating from 21 flocks in 12 farms, 149 were 24 weeks of age or older and 136 were broiler breeder birds. Both sexes were affected. The disease was only observed during the months of October, November and December, 1976 and 1977. The monthly mortality rate in affected adult flocks rose by 0.5% to 4% and the egg production declined by 5% to 15% during this period. Most affected birds were in good body condition or overweight. Gross lesions were usually present in all skeletal muscles and the cardiac muscle. They resembled nutritional myopathy, sarcosporidiosis, leucocytozoonosis or haemorrhagic syndrome. Microscopically visible elongated schizonts were demonstrated in skeletal muscles and the cardiac muscle in 49 of 55 birds examined histologically. The possible aetiology with respect to known parasites of muscles in fowls is discussed.