Subgroup J has recently emerged in broilers to cause deaths by myeloid tumours. All 3 subgroups are transferred vertically or horizontally. ALV-J is more of a problem because whereas with ALV-A almost all birds recover if infected posthatch with ALV-J many become persistently viraemic. J is now being eliminated from elite flocks which will be used to breed disease-free stock. As with FeLV the virus does not persist in the environment.