Marble Spleen Disease
Marble spleen is caused by an adenovirus, and tends to affect older poults or adult birds. A typical sign of Marble spleen is sudden mortality of birds in good condition. Spleens become mottled and enlarged, and a bloody fluid is found in the lungs, essentially this means that the birds drown in their own body fluid. There is no specific treatment but the infection usually runs its course in approximately two weeks. Mortality is usually between 5% and 10% but can get as high as 50%.
There is a turkey adenovirus vaccine available which appears to give some protection against the challenge.