Circulation of the low pathogenic avian influenza subtype H5N2 virus in ducks at a live bird market in Ibadan, Nigeria

BACKGROUND To monitor carrier hosts of avian influenza in Nigeria, we randomly collected cloaca swab specimens from 155 ducks at a live bird market (LBM) in Ibadan, southwest Nigeria, between July 2011 and July 2012. METHODS The samples were analyzed by real-time reverse transcription-polymerase chain reaction (RT-PCR) and virus isolation was carried out in embryonated chicken eggs. Partial sequencing of the antigenic cleavage site of the haemagglutinin (HA) gene was performed, multiple sequence alignment was carried out using ClustalW, and a phylogenetic tree was constructed using the neighbor joining method. RESULTS Twenty (13%) of the 155 samples were positive for avian influenza subtype H5N2 by real-time RT-PCR and three isolates were obtained from embryonated chicken eggs. Partial sequencing of the amino acid cleavage site of the HA genes of two isolates corresponded to a PQRETGL*F sequence that is common in low pathogenic avian influenza (LPAI). Phylogenetically, the HA genes of the two influenza viruses are monophyletic and clustered with H5N2 viruses detected in wild ducks from Africa. CONCLUSION The occurrence of LPAI in domestic ducks in Nigeria underscores the importance of continuous surveillance and monitoring of the virus (in a country that is considered to be free of avian influenza) in order to prevent the emergence of virulent strains that may spread to commercial poultry and humans.