Understanding the factors governing host species barriers to virus transmission 
has added significantly to our appreciation of virus pathogenesis. Jaagsiekte 
sheep retrovirus (JSRV) is the causative agent of ovine pulmonary adenocarcinoma 
(OPA), a transmissible lung cancer of sheep that has rarely been found in goats. 
In this study, in order to further clarify the pathogenesis of OPA, we 
investigated whether goats are resistant to JSRV replication and carcinogenesis. 
We found that JSRV induces lung tumors in goats with macroscopic and 
histopathological features that dramatically differ from those in sheep. 
However, the origins of the tumor cells in the two species are identical. 
Interestingly, in experimentally infected lambs and goat kids, we revealed major 
differences in the number of virus-infected cells at early stages of infection. 
These differences were not related to the number of available target cells for 
virus infection and cell transformation or the presence of a host-specific 
immune response toward JSRV. Indeed, we also found that goats possess 
transcriptionally active endogenous retroviruses (enJSRVs) that likely influence 
the host immune response toward the exogenous JSRV. Overall, these results 
suggest that goat cells, or at least those cells targeted for viral 
carcinogenesis, are not permissive to virus replication but can be transformed 
by JSRV.