Longitudinal Active Avian Influenza Surveillance in Bangladesh From 2017-2022 Reveals Differential IAV and H5 Infection and Viral Burden Associated With Bird Species, Sex, and Age

Abstract

Influenza viruses are a major global health burden with up to 650,000 associated deaths annually. Beyond seasonal illness, influenza A viruses (IAVs) pose a constant pandemic threat due to novel emergent viruses that have evolved the ability to jump from their natural avian hosts to humans. Because of this threat, active surveillance of circulating IAV strains in wild and domestic bird populations is vital to our pandemic preparedness and response strategies. Here, we report on IAV surveillance data collected from 2017 to 2022 from wild and domestic birds in Bangladesh. We note evidence to suggest that male birds show a higher risk of IAV, including highly pathogenic avian influenza (HPAI) A(H5) virus, positivity than female birds. The data was stratified to control for selection bias and confounding variables to test the hypothesis that male birds are at a higher risk of IAV positivity relative to female birds. The association of IAV and A(H5) largely held in each stratum, and double stratification suggested that the phenomena was largely specific to ducks. Finally, we show that chickens, male birds, and juvenile birds generally have higher viral loads compared to their counterparts. These observations warrant further validation through active surveillance across various populations. Such efforts could significantly contribute to the enhancement of pandemic prediction and risk assessment models.

Keywords: avian influenza; pandemic preparedness; risk assessment; sex-specific bias; surveillance.

Figure 1

Influenza A positivity by age of birds. IAV positivity is displayed for avian samples grouped by age rounded to quarter year increments. IAV, influenza A virus.

Figure 2

Violin plots of qRT-PCR Ct values for bird sexes. Violin plots illustrating the distribution of qRT-PCR M-gene Ct values between bird sexes in (a) the entire dataset and in specific habitats classified as (b) farm, (c) free-range farm, and (d) LBMs. The color-coding represents chicken (blue), duck (orange), quail (green), and environmental (feces) samples (red). Asterisks indicate significant differences (α = 0.05) between the indicated distributions as determined by Kolmogorov–Smirnov two-sample tests. Ct, cycle threshold; LBMs, live bird markets; M, matrix; qRT-PCR, reverse transcriptase polymerase chain reaction.

Figure 3

Violin plots of qRT-PCR Ct values for sample ages. Violin plots illustrating the distribution of qRT-PCR M-gene Ct values across different age classifications in (a) the entire dataset and in specific habitats classified as (b) farm, (c) free-range farm, and (d) LBMs. The color-coding represents samples from birds in their HY (blue), after their HY (orange), and unknown ages (green). Asterisks indicate significant differences (α = 0.05) between the indicated distributions as determined by Kolmogorov–Smirnov two-sample tests. AHY, after hatch year; Ct, cycle threshold; HY, hatch year; LBMs, live bird markets; M, matrix; qRT-PCR, reverse transcriptase polymerase chain reaction.

Figure 4

Violin plots of qRT-PCR Ct values for sample hosts. Violin plots illustrating the distribution of qRT-PCR M-gene Ct values across different host species and environmental samples in (a) the entire dataset and in specific habitats classified as (b) farm, (c) free-range farm, and (d) LBMs. The color-coding represents chicken (blue), duck (orange), quail (green), and environmental (feces) samples (red). Asterisks indicate significant differences (α = 0.05) between the indicated distributions as determined by Kolmogorov–Smirnov two-sample tests. Ct, cycle threshold; LBMs, live bird markets; M, matrix; qRT-PCR, reverse transcriptase polymerase chain reaction.