Shedding light on avian influenza H4N6 infection in mallards: modes of transmission and implications for surveillance.

Kaci K Vandalen,Heather J Sullivan,Nicole L Mooers,Alan B Franklin,Susan A Shriner,Anthony R Fooks

doi:10.1371/journal.pone.0012851

Kaci K Vandalen, Heather J Sullivan + Show 4 more

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https://doi.org/10.1371/journal.pone.0012851

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Abstract

BackgroundWild mallards (Anas platyrhychos) are considered one of the primary reservoir species for avian influenza viruses (AIV). Because AIV circulating in wild birds pose an indirect threat to agriculture and human health, understanding the ecology of AIV and developing risk assessments and surveillance systems for prevention of disease is critical.Methodology/Principal FindingsIn this study, mallards were experimentally infected with an H4N6 subtype of AIV by oral inoculation or contact with an H4N6 contaminated water source. Cloacal swabs, oropharyngeal swabs, fecal samples, and water samples were collected daily and tested by real-time RT-PCR (RRT-PCR) for estimation of viral shedding. Fecal samples had significantly higher virus concentrations than oropharyngeal or cloacal swabs and 6 month old ducks shed significantly more viral RNA than 3 month old ducks regardless of sample type. Use of a water source contaminated by AIV infected mallards, was sufficient to transmit virus to naïve mallards, which shed AIV at higher or similar levels as orally-inoculated ducks.ConclusionsBodies of water could serve as a transmission pathway for AIV in waterfowl. For AIV surveillance purposes, water samples and fecal samples appear to be excellent alternatives or additions to cloacal and oropharyngeal swabbing. Furthermore, duck age (even within hatch-year birds) may be important when interpreting viral shedding results from experimental infections or surveillance. Differential shedding among hatch-year mallards could affect prevalence estimates, modeling of AIV spread, and subsequent risk assessments.

Highlights

Avian influenza viruses (AIV) is a term used to describe influenza Type A viruses, which have been isolated from a wide range of avian species throughout the world [1]
The avian influenza viruses (AIV) subtype H4N6 is one of the most common subtypes found through surveillance of wild waterfowl in North America [1,16,17] and a wild bird isolate of an H4N6 virus was used in this study to infect mallards (Anas platyrhychos)
Viral RNA shedding in orally inoculated ducks The threshold for detection of our reverse-transcription polymerase chain reaction (RRT-PCR) assay was determined to be approximately 100 EID50

Summary

Introduction

Avian influenza viruses (AIV) is a term used to describe influenza Type A viruses, which have been isolated from a wide range of avian species throughout the world [1]. While RRT-PCR cannot determine the infectiousness of samples, the molecular assay is quicker, more sensitive and less expensive than virus isolation for AIV screening [14]. The AIV subtype H4N6 is one of the most common subtypes found through surveillance of wild waterfowl in North America [1,16,17] and a wild bird isolate of an H4N6 virus was used in this study to infect mallards (Anas platyrhychos). Because AIV circulating in wild birds pose an indirect threat to agriculture and human health, understanding the ecology of AIV and developing risk assessments and surveillance systems for prevention of disease is critical

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