Characterization of influenza A viruses isolated from wild waterfowl in Zambia

Abstract

Although the quest to clarify the role of wild birds in the spread of the highly pathogenic H5N1 avian influenza virus (AIV) has yielded considerable data on AIVs in wild birds worldwide, information regarding the ecology and epidemiology of AIVs in African wild birds is still very limited. During AIV surveillance in Zambia (2008-2009), 12 viruses of distinct subtypes (H3N8, H4N6, H6N2, H9N1 and H11N9) were isolated from wild waterfowl. Phylogenetic analyses demonstrated that all the isolates were of the Eurasian lineage. Whilst some genes were closely related to those of AIVs isolated from wild and domestic birds in South Africa, intimating possible AIV exchange between wild birds and poultry in southern Africa, some gene segments were closely related to those of AIVs isolated in Europe and Asia, thus confirming the interregional AIV gene flow among these continents. Analysis of the deduced amino acid sequences of internal proteins revealed that several isolates harboured particular residues predominantly observed in human influenza viruses. Interestingly, the isolates with human-associated residues exhibited higher levels of virus replication in the lungs of infected mice and caused more morbidity as measured by weight loss than an isolate lacking such residues. This study stresses the need for continued monitoring of AIVs in wild and domestic birds in southern Africa to gain a better understanding of the emergence of strains with the potential to infect mammals. The GenBank/EMBL/DDBJ accession numbers for the sequences reported in this study are AB569476-AB569571.

The zoonotic potential of avian influenza viruses isolated from wild waterfowl in Zambia

“…The methods used to investigate the replicative and pathogenic capacity of these viruses in mice were essentially the same as those previously described [28], with slight modifications. Here, 6-week-old female BALB/c mice (15 mice per group) were inoculated i.n.…”

“…Since the replicative and pathogenic profiles of Zb03 (H6N2) and Zb10 (H6N2) were determined previously (i.e., Zb10 (H6N2), possessing 4 human signature residues, replicated better and caused more severe disease in mice than Zb03 (H6N2) which lacks such residues) [28], these viruses were excluded in this mouse experiment. On day 1 p.i., all the viruses tested were 8 recovered from the lungs of all infected mice with virus titers ranging from 10 3.5 to 10 5.3 EID 50 /g (Table 3).…”

“…AIVs used in this study ( [28,29]. Before being used in this study, these viruses were passaged once in 10-dayold specific-pathogen-free (SPF) embryonated eggs and then titrated to determine the EID 50 calculated by a method described previously [26].…”

“…Here, 6-week-old female BALB/c mice (15 mice per group) were inoculated i.n. with 0.05 ml of Zb01 and virus titration in organs were done as described previously [28].…”

“…However, this notion has not been comprehensively tested. We previously reported that some AIV strains isolated from wild waterfowl in Zambia harbored residues frequently observed in human influenza viruses [28]. In experimental infection of mice, two AIV strains possessing the human signature residues showed higher levels of virus replication in the lungs of infected mice and caused more morbidity as measured by weight loss than a strain lacking such residues.…”