Objective Avian leukosis virus subgroup J (ALV-J) and reticuloendotheliosis virus (REV) can be transmitted vertically through chicken embryos, and there have been reports of chicken embryos that are co-infected with the two viruses, however, the pathogenicity of co-infection between the two through chicken embryos has not been studied. An experimental animal model of vertical transmission of ALV-J and REV was established to study the pathogenicity of vertical transmission of ALV-J and REV and its effect on the purification test of avian leukaemia, with a view to providing a reference for the promotion of the synergistic purification of multiple pathogens.

Method An infection model for chicks carrying ALV-J, REV and co-infected with the two viruses was constructed respectively by means of chicken embryo inoculation, and the pathogenicity of co-infection of REV and ALV-J in vertical transmission was analyzed by the indexes of hatching rate, mortality rate, body weight, fetal-feces ALV-p27 antigen detection rate, and viraemia positive rate.

Result The hatching rate of the chicken embryos in the co-infection group of ALV-J+REV was 65.71%, which was lower than that in the mono-infection group and CK; the mortality rate in the co-infection group was higher than that in the mono-infection group and CK. The average weights of chicken in the CK, ALV-J group, REV group and ALV-J+REV group were 59.25, 50.83, 49.67, 43.78 g, indicating that co-infection increased the inhibition of growth. The results of ALV plasma virus isolation showed that the positive rates of ALV-J group and ALV-J+REV group were 100% at each day age, while the rate of CK was 0%. The results of anal swabs collected for the detection of ALV-27 antigen showed that the positive rates of ALV-J + REV group were 91.30%, 93.75%, 90.90% and 100% at day age (s) of 1, 3, 7 and 14, respectively, and the positive detection rate of ALV-J p27 in anal swabs was lower than that of plasma virus isolation. Comparison of the results of the immune organ development showed that, both ALV-J mono-infection and REV mono-infection could lead to the atrophy of chicken immune organs, while co-infection of them aggravated the degree of atrophy. The viral load of immune organs showed that the co-infection of REV and ALV-J promoted the proliferation of ALV-J in immune organs, while ALV-J also promoted the proliferation of REV in immune organs.

Conclusion Co-infection of ALV-J and REV reduced embryo hatching rate, increased chick mortality and enhanced growth inhibition compared with mono-infection of ALV-J and REV, and the effect was more pronounced on inducing atrophy of immune organs such as the thymus, spleen and bursa, and both promoted mutual replication during co-infection.