A sequential study of bone lesions caused by isolates of an avian osteopetrosis virus, MAV-2(0)

Forensic investigation of a 1986 outbreak of osteopetrosis in commercial brown layers reveals a novel avian leukosis virus-related genome

Avian leukosis virus (ALV) is known to cause several neoplastic conditions in chickens, such as B-cell lymphomas, myelocytomas, erythroblastosis, and other types of neoplasia including osteopetrosis. We describe herein the identification of unique ALV-related proviral DNA sequences in an archived chicken bone affected with osteopetrosis. The osteopetrotic bone was obtained from an affected 46-week-old brown layer during an outbreak of osteopetrosis in Costa Rica in 1986. Analysis of proviral DNA in the 23-year-old osteopetrotic bone revealed unique exogenous ALV-related sequences that were named CR-1986 (Costa Rica, 1986). The 5' and 3' long terminal repeats (LTR) in the proviral DNA were identical to each other. The U3 regions in the LTRs were most similar to equivalent sequences in ALV-J, while U5 was identical to known endogenous ALV-E sequences. The predicted CR-1986 envelope protein was most similar to the envelope of myeloblastosis associated virus type 1 (MAV-1), although the percentage of amino acid sequence similarity to MAV-1 was low (90.4%). The variable and hypervariable regions of gp85 displayed several mutations compared to representative strains of ALV. The gp37 (transmembrane or TM) envelope protein showed three leucine to serine mutations that may represent important changes in the conformation of this protein, a finding that is currently being investigated. Several recombination events may have contributed to the emergence of CR-1986 because each analyzed segment was similar to a different ALV. CR-1986 may represent a unique ALV based on distinctive characteristics of its predicted envelope protein in comparison to previously reported ALVs.

Assessment of the influence of NaF or 1,25-(OH)2 vitamin D3 on the proliferative bone effect of an avian osteopetrosis virus, MAV-2(O)

1,25-(OH)2 vitamin D3 (D3) and sodium fluoride (NaF) were given to chicken embryos and newly hatched chickens infected with a slow onset strain of avian osteopetrosis-inducing virus [MAV-2(O)] to determine if either agent influenced MAV-2(O)-induced proliferation of bone. Embryos were administered MAV-2(O) and treated with: 1) up to 240 micrograms NaF or up to 100 ng D3 as embryos; 2) up to 1.8 g NaF/kg or up to 9.5 micrograms D3/kg after hatching: or 3) 240 micrograms NaF as embryos and up to 1.8 g NaF/kg after hatching. Administration of MAV-2(O) alone resulted in expansion of the cortical diameter of bone. Coadministration of NaF or D3 with MAV-2(O) did not influence the change in cortical diameter seen with MAV-2(O) alone at 18 days of incubation, and 3 and 6 weeks after hatching. Increased osteoid relative to bone (hyperosteoidosis), with NaF and MAV-2(O) compared to MAV-2(O) alone, and NaF compared to untreated controls reflected delayed mineralization of osteoid, a known fluoride effect. We conclude that the administration of NaF or D3 did not influence the incidence, severity or time of onset of the MAV-2(O)-induced proliferative changes of bone.

Analysis of hematopoietic and lymphopoietic tissue during a regenerative aplastic crisis induced by avian retrovirus MAV-2(O)

Infection of 10-day-old chickens with an avian osteopetrosis virus resulted in a severe regenerative aplastic crisis. Hematopoietic and lymphopoietic tissues of chickens infected with myeloblastosis-associated virus (of subgroup B, inducing osteopetrosis, MAV-2(O] were analyzed for integrated and unintegrated viral DNA sequences, cell population shifts, weight changes, and morphological alterations. By 6 days postinfection (p.i.), DNA from bone marrow cells and peripheral blood leukocytes (PBL) contained between 0.50 and 0.70 copies of viral DNA per haploid genome. Erythrocytes and splenic leukocytes contained less than 0.10 copies/haploid genome. Granulocytes and precursor mesomyelocytes were absent from bone marrow, but numbers of erythrocytes, erythroblasts, and reticulocytes were normal. By 9 days p.i., bone marrow was severely hypoplastic and both granulopoietic and erythropoietic colonies were depleted. By 12 days p.i., erythrocytes and granulocytes were maximally depressed in peripheral blood and the amount of integrated virus in bone marrow and PBL decreased to less than 0.20 copies/haploid genome. In contrast, erythrocytes contained integrated viral DNA of up to 0.30 copies/haploid genome, indicating infection of erythrocyte precursors. At 18 days p.i., viral DNA was detected only in erythrocytes. Unintegrated viral DNA was not detected in any organs. Anemia was accompanied by splenomegaly and erythrophagocytosis. Viral DNA was never detected in thymus or bursa. Differential counting and flow cytometry of cells from bursa, thymus, and spleen, and of blood lymphocytes did not detect significant population shifts. These results suggest that MAV-2(O) infection of immunocompetent chickens occurs primarily in myelopoietic tissues, and tissues are selectively infected.