cross-species infection, which then can contribute the different transmission of different hepadnaviruses. Replacing the special region of the envelope protein of one hepadnavirus with another hepadnavirus's. HHBV by DHBV:infect ducks and derived primary hepatocytes WMHBV by HBV:infect human hepatocytes Subviral sphere particles: They are assumed to have the ability of absorbing virus-neutralizing antibodies to facilitate the virus spread and maintenance in the host. Potentials Co-infection A lot of studies have well characterized the horizontal transmission of HBV through parenteral routes and co-infections with different genotypes of HBV have also been reported, including genotypes A and D, genotypes A and G, and genotypes B and C. In Asia, genotypes B and C account for almost all HBV infections. Infection with genotype C may induce more severe liver diseases than infection with genotype B. Recombination between genotypes B and C can occur as the result of co-infection of the two genotypes and recombinant strains may possess an enhanced disease-inducing capacity compared with genotype B. It has also been reported that the predominance of recombinant strains between genotypes B and C might be associated with the development of hepatocellular carcinoma in young carriers in Taiwan. Recombination Though the hepadnaviruses have a very limited host range, with the potential cross-species transmission of hepadnavirus among primates and some families of birds, combined with recombinants, it might change the hepadnavirus host specificity. Interspecies recombination between hepadnaviruses from cross-species hosts would provide a large variation of virus genome, which will change the pathogenicity and transmissibility, and enlarge the host range; the first evidence of potential recombination between chimpanzee HBV and human HBV genome was documented, recombination between human and non-human primate HBV strains, between GiHBV strains from different genera of gibbons, and between birds HBV strains from different avian sub-families were confirmed. All those experiments provided data allowing us to better understand the background, virus hosts, and zoonotic transmission of the non-human primate HBVs. References Virology Hepadnaviridae