Virus replication and cell modifications in organ cultures of tumor tissue from chickens with Marek's disease

Organ cultures of lymphomas from chickens infected with Marek's disease (MD) virus were examined by electron microscopy at various periods after explantation. Non-enveloped herpes-type virions were observed in explants 18 days after the culture was initiated. Cytolytic virus was replicated often in lymphoblastoid cells and occasionally in other cell types (permissive and nonpermissive transformed). The permissive cells were numerous, but nonpermissive transformed cells were also present as indicated by the longevity of some cultures. The presence of both permissive and transformed cell types in the organ cultures and reasons for their sequential appearance were discussed. The results unequivocally demonstrated that lymphoid cells of tumors induced by MD virus were sites of virus replication under proper culture conditions.

Newer knowledge in comparative virology--its contribution to human health research

Like other comparative sciences, and despite its recent beginning comparative virology has already contributed useful applications and observations to human health research. Teachings derived from the study of Marek's disease found application in that of Burkitt's lymphoma, and may lead to a possible vaccine against the human disease. Equally useful information came from the study of canine distemper in the development of a chorio-allantoic membrane attenuated measles vaccine, and in our knowledge of subacute sclerosing panencephalitis (SSPE) of humans; from the study of reovirus-like agents of infant mice and neonatal calves in that of an acute nonbacterial gastro-enteritis of infants and young children; and from that of the cancer-producing viruses of chickens, cats, and dogs to a better understanding of some human neoplasias. Finally, Aleutian mink disease may be an excellent natural model for the study of the collagen diseases of man, and scrapie of sheep one for that of a human chronic degenerative disease of the central nervous system of humans such as Kuru. Comparative virology has proved quite productive in a relatively short period, and is unlikely to be neglected in the future.

[Mark's disease: V. Experimental behavior of 3 isolates taken place in the country]

Three experiments were designed to determine the parameters of virus infection, antibodies and mortality with three different MD isolates inoculated in one day old birds from commercial origin. The animals were divided in three inoculated lots (1-2-3) and three control groups (4-1, 4-2, 4-3) and were followed weekly from hatching through 17 weeks. The former were inoculated respectivelly with FOV-6, FCV-8 and FCV-9. Each day old bird received between 50-75 FPU/bird by I.P. route. Samples were taken from circulating blood of five birds by cardiac puncture with an heparinized syringe (20 U/ml), were centrifuged and the white cells inoculated to 5-15 four day old embryos by yolk salk route for virus detection; plasma was assayed by immunodiffusion against MD antigen in order to detect precipitating antibodies, and mortality was recorded after microscopical examination. Infection appeared to persist indefinitelly in the host chicken flock and coexist with (100%) precipiting antibodies, (Fig. 1-2-3). First virus isolation was accomplished after 4 weeks post-inoculation and the 100% porcentage of antibodies, was found only 1-3 weeks after the first peak of viraemia. With the most pathogenic isolate FCV-6 (ig. 1) the antibody response was significantly delayed. Maternal antibodies decreased more rapidly in inoculated than in control birds. Accumulative mortality showed isolate FCV-6 and FCV-8 as pathogenic strains and FCV-9 strain as less pathogenic. Mortality begun 1-3 weeks after the first peak of virus detection in the flock, independently of the pathogenic pattern of the isolate, but frecuencies of death were markedly different.

Virologic and serologic studies of zoo birds for Marek's disease virus infection

One hundred and eleven zoo birds representing 49 species in 14 orders were examined for Marek's disease (MD) herpesvirus (MDHV) infection. MDHV was isolated from 10 birds, all belonging to genus Gallus. The precipitating antibodies against MDHV were demonstrated only in the Gallus birds, when 51 selected birds including 34 Galliformes and 17 other birds representing 12 species from nine orders were examined. The 10 MDHV isolates all induced morphologically similar plaques in cell cultures closely resembling those of HN strain, a low pathogenic isolate of MDHV. Six of the 10 isolates, when inoculated into an experimental line of chickens highly susceptible to MD, caused only a minimal degree of histologic lesions without causing clinical MD, gross MD lesions, or deaths from MD. Natural hosts of MD are probably Galliformes, primarily affecting Gallus and less often other genera of Galliformes.

Properties of a chicken lymphoblastoid cell line from Marek's disease tumor

Properties of a chicken lymphoblastoid cell line (MSB-1) from a Marek's disease tumor were studied. The cell line grew well at 41 degrees C in medium RPMI-1640 supplemented with 10% bovine fetal serum and had a doubling time of 8-12 hours. Cells grown in stationary suspension culture did not attach to the vessel and had the morphology of typical lymphoblasts. At 37 degrees C, the cell line grew initially but ceased to divide after several subcultures. In the subcultures maintained for 48-72 hours, 1-2% of the cells produced Marek's disease virus (MDV)-specific intracellular and mambrane antigens and contained herpesvirus particles when examined by the electron microscope. Cocultivation of these cells with duck or chicken embryo fibroblast cultures resulted in transfer of infection and production of microplaques typical of MDV. Peripheral nerve lesions and lymphoid tumors characteristic of Marek's disease were caused by inoculation of susceptible chicks with MSB-1 cells or duck cells infected with strain BC-1 of MDV recovered from the MSB-1 cell line. No specific tumors were produced at the site of inoculation, and infection was readily transmitted to cagemates. Tumors were also produced in the skeletal muscles and seemed to be largely virus induced. MSB-1 cell line was free of C-type virus particles.

Viremic responses of genetically susceptible and resistant chickens to experimental infection with acute, mild, or both strains of Marek's disease herpesvirus

The development and persistence of viremia were followed in two lines of Single-Comb White Leghorns: one experimental line (WSU-VS) highly susceptible, and one commercial line (C-WL) relatively resistant to Marek's disease(MD). In the resistant C-WL chicken, viremia with a mild strain of MD herpesvirus (MDHV) persisted in all viremic birds through 8 weeks postinoculation (PI), while viremia with an acute strain of MDHV did not, resulting in a decrease in number of viremic birds after 2 weeks PI. In the susceptible WSU-VS chicken, viremia with acute MDHV persisted in all viremic birds whereas viremia with mild MDHV was detected in a decreasing number of birds after 6 weeks PI. The pattern of viremia observed in the dually infected groups simulated a combination of the responses of the two groups respectively inoculated with mild and acute MDHV. Whether inoculation was with acute MDHV alone, or together with mild MDHV, levels of viremia with acute MDHV were appreciably higher in the WSU-VS than in the C-WL chicken. In both lines, levels of viremia were higher with acute MDHV than with mild MDHV but viremia with acute MDHV could not be demonstrated in the C-WL bird at 6-8 weeks PI. Levels of viremia with mild MDHV were consistently and similarly low in both WSU-VS and C-WL chickens.

Natural pox and herpes as a dual virus infection in chickens

A natural dual viral infection was confirmed in chickens of University of Illinois Poultry Farm by histopathologic, immunologic, and electron-microscopic examination of formalin-fixed tracheal tissue. Histopathologic examination of the tracheal mucosa revealed eosinophilic cytoplasmic inclusions characteristic of fowlpox and intranuclear inclusions suggestive of Marek's disease. Treatment of the formalin-fixed tracheal tissue with peroxidase and fluorescent-labeled antibody against Marek's disease virus revealed specificity of the reaction. Electron microscopy showed viral particles of two morphologic forms, i.e., pox and herpes. A single cell having dual infection with herpes virus in the nucleus and pox virus in the cytoplasm was also encountered on electron-microscopic examination.

Marek's disease herpesvirus-induced DNA polymerase

Infection of duck embryo fibroblasts by Marek's disease herpesvirus (MDHV), strain GA, led to the induction of a novel DNA polymerase. This novel DNA polymerase, designated MDHV-induced DNA polymerase, could be distinguished from the DNA polymerase activities of uninfected duck embryo fibroblasts by its chromatographic behavior on phosphocellulose, by its sedimentation coefficient, and by its catalytic properties. The characteristics of MDHV-induced DNA polymerase which had been purified by phosphocellulose chromatography were investigated. The sedimentation coefficient of the enzyme, as determined by sucrose density gradient centrifugation in the presence of 0.25 M KCl, was 5.9S. From this sedimentation coefficient, the molecular weight of MDHV-induced DNA polymerase was estimated to be 100,000. MDHV-induced DNA polymerase could not effectively use either poly(dA).oligo(dT)(12-18) or poly(dC).oligo(dG)(12-18) as a template-primer. The DNA polymerases from uninfected duck embryo fibroblasts could use these synthetic template-primers. MDHV-induced DNA polymerase also could not use poly(rA).oligo(dT)(12-18) or poly(rC).oligo(dG)(12-18) as template-primers or oligo(dT)(12-18) as a primer, indicating that it was not a polymerase of the type R-DNA polymerase, reverse transcriptase, or a terminal nucleotidyl transferase. In vitro synthesis of DNA by MDHV-induced DNA polymerase was markedly inhibited by the addition of (NH(4))(2)SO(4) to the reaction mixture.