Almost the full range of 16 haemagglutinin (HA) and nine neuraminidase subtypes of avian influenza viruses (AIVs) has been detected either in waterfowl, land-based poultry or in the environment in Bangladesh. AIV infections in Bangladesh affected a wide range of host species of terrestrial poultry. The highly pathogenic avian influenza (AI) H5N1 and low pathogenic AI H9N2 were found to co-circulate and be well entrenched in the poultry population, which has caused serious damage to the poultry industry since 2007. By reviewing the available scientific literature, the overall situation of AIVs in Bangladesh is discussed. All Bangladeshi (BD) H5N1 and H9N2 AIV sequences available at GenBank were downloaded along with other representative sequences to analyse the genetic diversity among the circulating AIVs in Bangladesh and to compare with the global situation. Three different H5N1 clades, 2.2.2, 2.3.2.1 and 2.3.4.2, have been detected in Bangladesh. Only 2.3.2.1a is still present. The BD LP H9N2 viruses mostly belonged to the H9 G1 lineage but segregated into many branches, and some of these shared internal genes with HP viruses of subtypes H7N3 and H5N1. However, these reassortment events might have taken place before introduction to Bangladesh. Currently, H9N2 viruses continue to evolve their HA cleavage, receptor binding and glycosylation sites. Multiple mutations in the HA gene associated with adaptation to mammalian hosts were also observed. Strict biosecurity at farms and gradual phasing out of live-bird markets could be the key measures to better control AIVs, whereas stamping out is not a practicable option in Bangladesh. Vaccination also could be an additional tool, which however, requires careful planning. Continuous monitoring of AIVs through systematic surveillance and genetic characterisation of the viruses remains a hallmark of AI control.

H9N2 is the most widespread avian influenza virus subtype in poultry worldwide. It infects a broad spectrum of host species including birds and mammals. Infections in poultry and humans vary from silent to fatal. Importantly, all AIV, which are fatal in humans (e.g. H5N1, H7N9) acquired their ‘internal’ gene segments from H9N2 viruses. Although H9N2 is endemic in the Middle East (ME) and North Africa since the late 1990s, little is known about its epidemiology and genetics on a regional level. In this review, we summarised the epidemiological situation of H9N2 in poultry and mammals in Iran, Iraq, Kuwait, Qatar, United Arab Emirates, Oman, Bahrain, Yemen, Saudi Arabia, Jordan, Palestine, Israel, Syria, Lebanon, Turkey, Egypt, Sudan, Libya, Tunisia, Algeria and Morocco. The virus has been isolated from humans in Egypt and serosurveys indicated widespread infection particularly among poultry workers and pigs in some countries. Some isolates replicated well in experimentally inoculated dogs, mice, hamsters and ferrets. Insufficient protection of immunised poultry was frequently reported most likely due to concurrent viral or bacterial infections and antigenic drift of the field viruses from outdated vaccine strains. Genetic analysis indicated several distinct phylogroups including a panzootic genotype in the Asian and African parts of the ME, which may be useful for the development of vaccines. The extensive circulation of H9N2 for about 20 years in this region where the H5N1 virus is also endemic in some countries, poses a serious public health threat. Regional surveillance and control strategy are highly recommended.

Low pathogenic avian influenza virus (LPAI) subtype H9N2 in poultry has occurred in many countries since the mid-1990s. Outbreaks due to H9N2 have occurred in Korea, Germany, Italy, Ireland, South Africa and the USA. Most recently, H9N2 infections have been reported in several Asian countries, the Middle East and Africa, causing widespread outbreaks in commercial chickens. In these countries, vaccine has been distributed with the aim of controlling the disease. However, H9N2 infections have become endemic in commercial poultry in a significant number of countries. This review is aimed to shed light on the current situation of the LPAI world-wide.