Introduction
Waterborne transmission is considered a significant route for avian
influenza viruses (AIV) dissemination (Lebarbenchon et al., 2011). This
indirect route of transmission is known as one of the main determinants
of disease dynamics, since water can be simultaneously contaminated by
different viral strains and infect multiple animals, including wild
birds (Numberger et al., 2019; Roche et al., 2009).
Waterfowl are recognized as the natural reservoir of IAV and play a key
role in the viral spread and diversity (Montalvo-Corral & Hernández,
2010). Infected wild ducks shed feces with high AIV concentrations into
aquatic environments (Dovas et al., 2010). Viruses shedding into the
water have the potential to infect any other waterfowl within bird
populations by drinking or filtering the virus-contaminated water
(Keeler et al., 2014). Therefore, viral transmission among wild aquatic
birds mainly occurs via the fecal-oral route through contaminated water
(Brown et al., 2007).
Environmental water where resident and migratory waterfowl congregate
has a significant role in the AIV ecology and epidemiology (Numberger et
al., 2019). Viruses shed before migration can persist in the water over
winter and become a source of infection to birds returning during spring
(Brown et al., 2007). This environmental persistence may enable short-
and long-term maintenance of AIV among spatially or temporally separated
wild bird populations (Lickfett et al., 2018).
Wild bird habitats close to livestock production systems also represent
high-risk zones for AIV interspecies transmission (Achenbach & Bowen,
2011; Harris et al., 2017). Barnyard fowls from backyard farms can use
open waters and become indirectly infected by wild waterfowls
congregated in the same habitats (Cappelle et al., 2011). Likewise,
other farm animals, such as pigs, can be AIV infected by contaminated
surface water collected from natural or artificial ponds and used for
cleaning barns and watering animals (Karasin et al., 2000; Ma et al.,
2007).
In addition to the wild duck-livestock animal interface, live bird
markets constitute high-risk sites for harboring and spreading AIV (Khan
et al., 2018). Wet markets promote close contact between different
animal species which facilitates the genetic reassortment of influenza
viruses (Vergne et al., 2019). Wild and domestic birds (including
infected birds) use to share cages, feed, and water trays. Therefore,
birds from live bird markets can be co-infected with different AIV
subtypes (Khan et al., 2018).
Globally, multiple subtypes of low- and high-pathogenic avian influenza
(LPAI and HPAI) have been identified based on epidemiological
surveillance (Machalaba et al., 2015). Environmental AIV surveillance is
considered a convenient, noninvasive, and sensitive method for
conducting AIV detection (Leung et al., 2007). Avian influenza
surveillance in poultry-related environments, including live poultry
markets, wild bird habitats, slaughterhouses, and poultry farms is
conducted annually in some countries (Zhang et al., 2019). However, the
global diversity and distribution of AIVs in environmental water widely
used by waterfowl and poultry have been scarcely studied. In this study,
we aim to address this knowledge gap by characterizing the AIV diversity
and its spatial distribution in water samples from areas considered to
be at high risk for avian influenza outbreaks (i.e., wild bird habitats,
live bird markets, poultry farms) on a global scale.