B. R. Burmester

Studies on the etiology of Marek's disease. II. Finding of a herpesvirus in cell culture.

Summary Duck embryo fibroblast (DEF) monolayer cultures seeded with whole blood from birds inoculated with the JM strain of Mareks disease (MD) and which showed a cytopathic effect (CPE), also contained intranuclear herpes-like virus particles. Complete virus particles with envelope essential for infectivity of herpesviruses were not found in either the infected cells or the extracellular materials of cultures containing such cells. All cultures showing CPE contained virus particles, and when inoculated into susceptible chicks caused MD. Cytopathic effect and viral synthesis could not be induced in fresh DEF cultures with spent media from infected cultures passed through 450 mμ Millipore filters. The perfect correlation obtained between CPE, presence of virus particles, and reproduction of MD by these cells suggests a cause and effect relationship and circumstantially implicates this virus in the etiology of MD.

Studies on the Etiology of Marek's Disease. I. Propagation of the Agent in Cell Culture

Summary A focal cytopathic effect (CPE) was observed in duck embryo fibroblast (DEF) cultures 11-25 days postinoculation with blood from the JM strain of Mareks disease (MD). All cell suspensions from such cultures reproduced MD when inoculated into chicks, while all of the morphologically normal DEF cultures were noninfectious. The CPE and infectivity were maintained in DEF cultures for 182 days. Both the induction of CPE in cell cultures and MD in chickens required intact cells in the inoculum. These data indicate that the JM strain of MD was successfully propagated in DEF cultures and produced a characteristic CPE.

Differential effect of maternal antibodies on efficacy of cellular and cell-free Marek's disease vaccines.

The protective efficacy of cell-free and cell-associated turkey herpesvirus (HVT) vaccines against Mareks disease (MD) was determined by a quantitative protective dose 50% (PD(50)) assay in susceptible chicks from HVT-vaccinated, MD-exposed dams or from genetically comparable, isolation-reared, specific pathogen free dams. Comparison within trials showed that cell-associated and cell-free vaccines were equally efficacious in chicks lacking maternal antibodies (median PD(50)s were about 1-4 plaque-forming units (PFU) ). However, in chicks with maternal HVT/MD antibodies, PD(50)values were increased by 2- to 8-fold for cell-associated vaccine and by 15-to 80-fold for cell-free vaccine. The apparent requirement in antibody-positive chicks for greater doses of cell-free than of cell-associated vaccine to give 50% protection may be of practical importance in establishing the optimum number of PFU in a field dose.

Lymphoid leukosis viruses and GS antigen in unincubated chicken eggs.

Lymphoid leukosis viruses and viral group-specific antigen were found in albumen of unincubated chicken eggs stored at 8 degrees C. Infectious virus was detected for up to 22 days and antigen was stable for 63 days. Tests for virus were conducted on albumen withdrawn from eggs prior to incubation and on extracts of embryos from the same eggs. When albumen was from eggs stored no longer than 6 days, virus was isolated from 20% more albumen samples than embryo extracts. The techniques described should be useful in programmes to eradicate lymphoid leukosis viruses from commercial poultry.

Transmission of Marek's disease with oral washings and feces from infected chickens.

Summary Mareks disease was transmitted with oral washings and fecal extracts from 4-week-old, JM-inoculated chickens to day-old chickens by inoculation. All birds inoculated with oral washings or fecal extracts by the intra-abdominal route were positive while in-tranasal instillation of these materials gave responses of 0% and 21 % respectively during a 10-week experimental period. An attempt to transmit Mareks disease by a direct transfer of oral fluids with cotton swabs from donor to recipient chicks was unsuccessful.

Growth in tissue culture of cytopathogenic agent from strain of virus which produces avian lymphomatosis.

Summary A cytopathogenic agent isolated from RPL 12 in chicken embryo liver tissue cultures is reported. The virus produces a marked CPE on liver parenchymal cells. Virus serially passed in tissue culture, when inoculated into susceptible chicks, produced visceral lymphomatosis. Neutralization tests with antiserum against RPL 12 indicate a relationship of tissue culture virus with RPL 12; however, positive identity of the cytopathogenic agent with the virus causing visceral lymphomatosis has not been established.

Immunity To Visceral Lymphomatosis in Chicks Following Injection of Virus into Dams

Summary Results obtained in experiments involving 14 immunized hens and 300 test chicks indicate that the virus of visceral lymphomatosis is capable of inducing antibodies in adult chickens, and that these antibodies are transmitted to the chick via the egg, giving the former a significant immunity to challenge inoculation.

In vitro and in vivo Neutralization of the Virus of Visceral Lymphomatosis

Summary Evidence is presented for the production of antibodies which neutralize the oncogenic activity of the virus of visceral lymphomatosis, by hens injected with virulent virus. Serum from such hens injected into chicks has produced a passive immunity.

Viability of a Transmissible Fowl Tumor (Olson) upon Storage at Low Temperatures.

Conclusion When the transmissible fowltumor (Olson) was frozen slowly and stored at −65°C to −76°C for 10 to 391 days, no significant reduction or alteration in its capacity to produce typical tumors in the pectoral muscle was detected by methods employed.

Modification of Complement Fixation Test for Estimation of Rous Sarcoma Virus Antibodies in Turkey and Chicken Serums

Summary A complement fixation test with Rous sarcoma virus is described and some preliminary results reported. Although the sensitivity of the test appears to be somewhat lower than in vitro tissue culture neutralization tests, the correlations obtained are quite good.