"The heterogeneous population of lymphoid cells in MD lymphomas, as seen in haematoxylin-and-eosin-stained
sections, or in impression smears of lymphomas stained by May–Grünwald–Giemsa, is an important feature in
differentiating the disease from lymphoid leukosis, in which the lymphomatous infiltrations are composed of
uniform lymphoblasts. Another important difference is that, in lymphoid leukosis, gross lymphomas occur in the
bursa of Fabricius, and the tumour has an intrafollicular origin and pattern of proliferation. In MD, although the
bursa is sometimes involved in the lymphoproliferation, the tumour is less apparent, diffuse and interfollicular in
location. Peripheral nerve lesions are not a feature of lymphoid leukosis as they are in MD. The greatest difficulty
comes in distinguishing between lymphoid leukosis and forms of MD sometimes seen in adult birds in which the
tumour is lymphoblastic with marked liver enlargement and absence of nerve lesions. If post-mortems are
conducted on several affected birds, a diagnosis can usually be made based on gross lesions and histopathology.
However there are other specialised techniques described. The expression of a Meq biochemical marker has
been used to differentiate between MD tumours, latent MDV infections and retrovirus-induced tumours (Schat &
Nair, 2008). The procedure may require specialised reagents and equipment and it may not be possible to carry
out these tests in laboratories without these facilities. Other techniques, such as detection by immunofluorescence
of activated T cell antigens present on the surface of MD tumour cells (MD tumour-associated
surface antigen or MATSA), or of B-cell antigens or IgM on the tumour cells of lymphoid leukosis can give a
presumptive diagnosis, but these are not specific to MD tumour cells."
http://www.oie.int/fileadmin/Home/eng/Health_standards/tahm/2.03.13_MAREK_DIS.pdf
http://www.merckmanuals.com/vet/poultry/neoplasms/lymphoid_leukosis_in_poultry.html
Okay...the first link is the one associated with the excerpt above and the bottom link has me more baffled than before. Symptoms aren't adding up. Again, I'm missing something.