Of the numerous other transmissible and nontransmissible tumors known to occur in poultry, a few have limited importance. Most strains of leukosis/sarcoma viruses also induce nonlymphoid tumors (including sarcomas), erythroblastosis, myeloblastosis, myelocytoma, hemangiomas, nephroblastoma, osteopetrosis, and related neoplasms. The nature of the tumors and their frequency depend on virus strain, chicken strain, age, dose, and route of infection. Occasional outbreaks of predominantly one type of tumor are seen in the field. Recently, myelocytoma has occurred sporadically in field flocks, especially in broiler breeders. The Rous sarcoma virus, a member of this group, has been widely studied in the laboratory. Each strain usually causes a predominantly neoplastic disease and can be distinguished on the basis of pathogenicity. Some viruses (eg, Rous sarcoma and erythroblastosis viruses) contain a viral oncogene that is responsible for their ability to induce neoplasms within a short incubation period, but such viruses are rare in the field. Others are defective for replication and require a nondefective helper virus.
Squamous cell carcinomas occur at relatively high frequencies in some broiler flocks and are a cause of condemnations. Typically, the lesions are seen during processing as crater-like eruptions on the defeathered skin. An etiological agent has not yet been identified, and the true neoplastic nature of the lesion has not been confirmed. Transmissibility of this tumor has neither been demonstrated nor ruled out.
Adenocarcinomas of the ovary or oviduct are relatively common incidental tumors in mature chickens. These neoplasms often are characterized by multiple miliary implant tumors on the mesentery and other visceral surfaces, frequently accompanied by ascites. These tumors are not known to be virus induced or to be transmissible.
Lymphoproliferative Disease in Turkeys