An epidemiological study of avian influenza A (H5) virus in nomadic ducks and their raising practices in northeastern Bangladesh, 2011‐2012

Abstract

BackgroundIn Bangladesh, nomadic duck flocks are groups of domestic ducks reared for egg production that are moved to access feeding sites beyond their owners’ village boundaries and are housed overnight in portable enclosures in scavenging areas. The objectives of this study were to measure the prevalence of influenza A virus RNA and H5‐specific antibodies in nomadic ducks and to characterize nomadic duck raising practices in northeastern Bangladesh.MethodsWe tested duck egg yolk specimens by competitive ELISA to detect antibodies against avian influenza A (H5) and environmental fecal samples by real‐time reverse‐transcription polymerase chain reaction (rRT‐PCR) to detect influenza A virus RNA and H5 subtype.ResultsThe median age of the ducks was 24 months (range: 8‐36 months) and the median flock size was 300 ducks (range: 105‐1100). Of 1860 egg yolk samples, 556 (30%, 95% confidence interval (CI): 28‐32) were positive for antibodies against H5 and 58 flocks (94%) had at least one egg with H5‐specific antibodies. Of 496 fecal samples, 121 (24%, 95% CI: 22‐29) had detectable influenza A RNA. Thirty‐three flocks (53%) had at least one fecal sample positive for influenza A RNA.ConclusionsNomadic ducks in Bangladesh are commonly infected with avian influenza A (H5) virus and may serve as a bridging host for transmission of avian influenza A (H5) virus or other avian influenza A viruses subtypes between wild waterfowl, backyard poultry, and humans in Bangladesh.

Prevalence and Distribution of Avian Influenza Viruses in Domestic Ducks at the Waterfowl-Chicken Interface in Wetlands

“…Studies had shown a significant association between farmer’s education with AI and zoonotic awareness, whereas knowledgeable farmers tend to take different precautionary measures to control infectious diseases [ 57 ]. In this study, AI seroprevalence and viral RNA prevalence were higher in free-range duck flocks than that of household duck flocks, which is consistent with previous studies [ 27 ]. It is likely that the frequent movement of free-range ducks in the wetlands provides more exposure and interaction with wild migratory birds and other wild waterfowl leading to higher infection rates.…”

“…The AI seroprevalence was 58.5% in ducks having contact with wild waterfowl and viral RNA prevalence was 9.6%. Previous studies have shown that free-range ducks contact with wild waterfowl was affected by IAVs during winter [ 27 ]. The correlations between the risk of HPAI outbreaks and the presence of domestic waterfowl was established in previous studies [ 47 ].…”

“…In contrast, free-range ducks scavenge in a large flock (100–1000) in post-harvest paddy fields and water bodies during the day and stay in temporary enclosures overnight. The large water bodies serve as a site for intermingling between free-range ducks and wild waterfowl populations, resulting in the transmission of IAVs [ 27 ]. For the farmers’ families, it is a common practice to share dwelling places with ducks and chickens [ 13 ] and such close proximity between humans and avian species may results in the emergence of novel IAV strains of pandemic potential circulating between humans, ducks and chickens.…”

Prevalence of Avian Influenza A(H5) and A(H9) Viruses in Live Bird Markets, Bangladesh

“…However, care must be taken when comparing these results because studies used different study designs and sample screening protocols over different periods. Bird-level prevalence for contaminated LBMs was much higher than for virologic surveys conducted in backyard and commercial farms in Bangladesh (1,4,33,34). This finding suggests that virus transmission was amplified along the value chain from farms to LBMs.…”

A Decade of Avian Influenza in Bangladesh: Where Are We Now?

“…Unusual mortalities caused by H5N1 have been reported in commercial poultry [5], waterfowl [6], and in crows [7]. Evidence of past exposure to H5 virus in nomadic ducks has been reported [8]. A total of eight human cases attributed to the subtype have also been reported since 2008 [9].…”