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The natural disease has been described only in turkeys, commercial hybrid strains of which appear to differ in susceptibility. Chickens can be infected experimentally but are less susceptible than turkeys. Ducks and geese are refractory to experimental infection. Lymphoproliferative disease has been identified in England and Israel and probably has occurred in several European countries; its presence in the USA has not been confirmed.
Etiology:The etiological agent probably is a retrovirus that is antigenically and genetically distinct from those causing lymphoid leukosis and reticuloendotheliosis. This virus has not been cultivated in vitro, but virus particles can be seen in tissues of infected turkeys; plasma is a good source of infective material.
Transmission and Epidemiology:Contact transmission has been demonstrated among turkeys. Although vertical transmission has not yet been proved, this possibility also should be considered. The incidence of infection is far greater than the incidence of disease; high rates of infection can be demonstrated in certain flocks with no mortality. Infected turkeys often develop a persistent viremia that can be detected by the presence of a reverse transcriptase in the plasma or by enzyme immunoassays. A polymerase chain reaction assay is available.
In natural outbreaks, up to 25% of turkeys may die from neoplastic disease when 7-18 wk old. Males may be more susceptible than females. Poults are more susceptible to experimental inoculation at 4 wk than at hatching. Lesions appear first in the spleen and thymus and can be recognized as early as 2 wk after infection.
Clinical Findings and Lesions:Affected birds die suddenly; some may be depressed before death. The most characteristic lesion is a greatly enlarged spleen, which is often pale or marbled. Gray-white tumor foci can be seen in the liver, thymus, gonad, pancreas, kidney, intestine, lung, and heart. In some cases, the peripheral nerves are enlarged. The tumor lesions are composed of a pleomorphic mixture of lymphoid cells, reticulum cells, and plasma cells.
Diagnosis:Diagnosis depends on the presence of characteristic gross and microscopic lesions. The tumors differ in their pleomorphic cellular composition from those of reticuloendotheliosis, which are composed of uniform lymphoreticular cells. The presence of reticuloendotheliosis virus should be excluded by appropriate tests for virus or antibodies. The plasma of turkeys with lymphoproliferative disease often contains a virus-associated reverse transcriptase that has a higher activity in the presence of magnesium ions than manganese ions; with reticuloendotheliosis virus, the opposite is true. A polymerase chain reaction assay may be used to confirm the presence of the virus in the tumor tissue and may play an important role in differential diagnosis.
Control:No control methods have been developed.
See Also:
Neoplasms
Marek’s Disease
Lymphoid Leukosis
Reticuloendotheliosis
Other Tumors
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