The possible role of other animal host species in the transmissions of reassortant viruses in Indonesia should not be neglected. In particular, one of the reassortant viruses was isolated from a dead cat in Jakarta, where H5N1 outbreaks in poultry and sporadic human infections have been reported [42] . Moreover, unusual high mortality of cats in the vicinity of H5N1 HPAI outbreaks has been reported [43] . An unofficial report also detected H5N1 HPAI sero-positivity in around 20% of 500 blood samples taken from stray cats near poultry markets in Java and Sumatera [44] . In addition to small cats in Germany [45] , Iran [46] , and Indonesia [42] , dogs and zoo tigers were also found infected with H5N1 HPAI viruses in Thailand [47, 48] . Furthermore, previous experimental studies have demonstrated that cats can be infected with H5N1 HPAI virus [49, 50] , and that cat-to-cat transmission is possible [49, 51] . Could cats, or other non-avian species, have played a role in spreading the reassortant viruses in Java? Similarly, could cats act as amplifying hosts facilitating viral expansion and cross-species transmission, as civets did in the SARS outbreaks [52] ? Future experimental studies on these reassortant viruses, that assess viral transmissibility between species, together with epidemiological studies, such as viral monitoring within Indonesian animal populations using serological tests and PCR detection, would give more clues to these questions. H5N1 HPAI viruses have been endemic and evolved into different genetic lineages that have spread across Indonesia. Areas where more than one lineage of virus is co-circulating, such as Jakarta, are most likely to generate novel viruses by inter-lineage reassortment. These reassortant viruses have distinctive evolutionary and transmission dynamics, as shown in this study. We suggest that more intensive and timely field surveillance and analysis of influenza viruses, including H5N1 HPAI and human H3N2, H1N1, and H1N2 epidemic strains, should be employed, so that bio-security can be undertaken promptly and appropriate strains can be selected for vaccine production whenever a novel reassortant strain emerges. The reassortant viruses reported in this study should be also added to the watch list for the future epidemiological surveillance.