Avian leukosis virus infection and shedding in brown leghorn chickens treated with corticosterone or exposed to various stressors

Some chickens which are viraemic with subgroup J avian leukosis virus have antibody-forming cells but no circulating antibody

New immunoperoxidase-based assays for splenic IgG -antibody-forming cells (AFC) and serum IgG-antibody were used to look for antibody to HPRS-103 in meat-type birds. Meat type birds are known to be less likely to produce neutralising antibody and to be less likely to clear virus from their serum than layer-type birds after infection at hatch. In this work all 12 of the brown leghorn layer-type birds and 5/12 of the line 21 meat-type birds had produced AFC and serum antibody and had cleared serum virus at 63, 82 and 110 days of age. None of the seven viraemic line 21 birds contained serum antibody but three produced AFC. The four viraemic line 21 birds which lacked AFC occurred later in the experiment and had a higher level of virus than the three viraemic line 21 birds which possessed AFC. This suggests that most line 21 birds do not control HPRS-103 and eventually become anergic.

Role of contact and genetic transmission of endogenous virus-21 in the susceptibility of chickens to avian leukosis virus infection and tumors

The role of contact and genetic transmission of endogenous virus-21 (EV21) on response of chickens to avian leukosis virus (ALV) infection and tumors was studied. F1 progeny of a cross between RPRL late-feathering (LF) line EV21+ males and RPRL early feathering (EF) line 15B1 females harboring or lacking EV21 were used. The EF chicks lacking EV21 were inoculated with a field strain of subgroup A ALV at hatch and contact exposed to LF, EV21+ hatchmates for various time intervals. In a second experiment, EV21 contact-exposed and unexposed EF chicks as well as LF, EV21+ hatchmates were inoculated with ALV at various ages. Chickens were tested for ALV-induced viremia and antibody and were observed for tumors until 24 wk of age. Antibody to EV21 in EF chickens contact-exposed to LF, EV21+ hatchmates varied from 10 to 65%, and was detected by 10 wk of age. By 24 wk of age, ALV-induced viremia and tumors in EF chickens varied from 5 to 30%, and from 15 to 32%, respectively, regardless of exposure to EV21. The incidence of ALV-induced tumors was significantly higher in LF chickens genetically infected with EV21 than in EV21 contact-exposed or unexposed EF chickens, but only in chickens inoculated with ALV at hatch. The data suggest that contact infection with EV21 has no influence on ALV infection and tumors. The data also suggest that genetic transmission of EV21 may increase susceptibility of chickens to ALV infection and tumors following infection with ALV at hatch, but not at 4 wk of age or older.

The influence of ev6 on the immune response to avian leukosis virus infection in rapid-feathering progeny of slow- and rapid-feathering dams

Endogenous virus (EV) locus ev6 encodes only virus envelope glycoprotein. The influence of ev6 on the immune response to contact infection with hatchmates infected with avian leukosis virus (ALV) was compared in replicate hatches. The ALV Subgroup E-resistant, rapid-feathering (RF) female chickens produced by slow-feathering (SF) and RF dams with and without ev6 were exposed at hatch to hatchmates infected with ALV Subgroup A (Strain RPL-40). The RPL-40 viremia, shedding, and virus neutralizing antibodies were measured among pullets from two hatches at 22 wk of age. Although significant (P less than .05) differences between hatches in the immune response to contact infection were noted among ev6+ pullets, significantly fewer ev6+ pullets seroconverted than their ev6- hatchmates. At 22 wk of age, significantly more lymphomas were also found among ev6+ pullets than among ev6- hatchmates. In flocks wherein both parents and progeny were homozygous resistant to Subgroup E virus, there was no deterimental maternal effect on RF progeny from SF dams that carried ev21. These results also confirm that selection for genetic cellular resistance to Subgroup E ALV infection eliminates congenital transmission of EV21.

Interactions between endogenous virus loci ev6 and ev21. 1. Immune response to exogenous avian leukosis virus infection

The effects of ev6, ev21, sex, and hatch, were studied with respect to avian leukosis virus (ALV) viremia, cloacal shedding, and antibody response among RPL-40 virus-infected White Leghorns that carried ev6 and ev21 in all combinations. Among the four possible ev genotypes, chickens that carried only ev21 were the most immunologically tolerant to RPL-40 infection. Incidence of RPL-40 viremia was lowest among hatchmates that lacked both ev genes. Analysis of variance indicated significant interactions between ev6 and ev21 with respect to all responses. Among ev21+ slow-feathering (SF) chickens, the incidence of viremia and shedding of RPL-40 was reduced in the presence of ev6 when compared with ev6- hatchmates. Conversely, among ev21- rapid-feathering (RF) chickens, ev6 significantly enhanced the incidence of RPL-40 viremia when compared with ev6- hatchmates. The endogenous virus, ev6, markedly reduced recovery of the endogenous virus (EV21) from plasmas of slow-feathering chickens. When both flocks were terminated at 21 wk of age, significantly more ev21+ SF females had died from or developed RPL-40-induced tumors than ev21- hatchmates.

Interactions between endogenous virus loci ev6 and ev21. 2. Congenital transmission of EV21 viral product to female progency from slow-feathering dams

The influence of the endogenous virus ev6 on congenital transmission of EV21, the infectious viral product encoded by locus ev21, and the immune response to exogenous avian leukosis virus (ALV) infection was studied in rapid-feathering (RF) female progeny from four classes of slow-feathering (SF) (ev21+ and RF (ev21-) dams with and without ev6. Apart from transmitting infectious EV21 and ev6 to progency, dam ev genotype did not influence the immune response or shedding of RPL-40. The endogenous virus envelope glycoprotein encoded by ev6, however, completely restricted shedding and congenital transmission of infectious endogenous virus EV21, from SF dams. After 19 wk of exposure to ALV strain RPL-40 infected cage mates, only 11% of the congenitally infected female progeny mounted neutralizing antibodies against RPL-40, whereas 73% of their noncongenitally infected sisters seroconverted. More ev6+ female progeny, however, were shedders of RPL-40 and developed tumors than ev6- sisters. Among progeny from the four classes of dams, EV21 congenitally infected hens had the highest incidence (31%) of RPL-40-induced tumors.