Chapter 4 - Leukosis

This condemn category includes several neoplastic diseases caused by various viruses. All of them produce tumors in domestic poultry and present similar gross lesions. The age and species of bird affected by the leukotic tumors suggest which viral agent is involved. This information can only be used to make a presumptive diagnosis, however, because there is considerable overlap. The most common manifestations of the leukosis complex are as follows:

• Marek's disease, which is an important disease found only in chickens less than six months of age
• Lymphoid leukosis, which is most common in semi-mature and mature chickens
• Reticuloendotheliosis, which occasionally producers liver and spleen tumors in turkeys, and, rarely, runting disease in chickens
• Lymphoproliferative disease, which affects turkeys, producing a greatly enlarger spleen as well as tumors in other organs.

There is no evidence that viruses of the leukosis complex are pathogenic for humans.

As shown in Figure 4.1, the incidence of carcass condemnation due to leukosis is very low, and has continued to decrease overtime (0.92% of total condemnations in 2001 to 0.06% in 2007).