Environ. Sci. Technol. Lett. 2023, XXXX, XXX, XXX-XXX
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Our understanding of how HPAI viruses like H5N1 persist in the environment - while incomplete - continues to grow, and we now know that under the right circumstances they can survive for extended periods of time outside of a living host.
A few examples include:- In 2012's EID Journal: Persistence Of H5N1 In Soil, we looked at several studies that found H5N1 could remain viable on various surfaces, and in different types of soil, for up to 13 days (depending upon temperature, relative humidity, and UV exposure).
- In 2017, researchers showed that - when refrigerated - H5N1 infected poultry could remain infectious for months (see Appl Environ Microbiol: Survival of HPAI H5N1 In Infected Poultry Tissues).
- And in 2020 we looked at a study from researchers at the USGS (see Proc. Royal Society B: Influenza A Viruses Remain Viable For Months In Northern Wetlands - USGS), which found long-term (up to 7 months) survival of influenza A viruses in wetlands in both Alaska and Minnesota.
- 3 weeks ago in Emerg. Microbes & Inf.: Feather Epithelium Contributes to the Dissemination and Ecology of clade 2.3.4.4b H5 HPAI Viruses in Ducks, we saw evidence of `. . . environmental shedding and dissemination of H5 HPAIVs through the infected plumage of domestic ducks' which the authors warned `. . . may constitute an underestimated route of transmission'.
Over the past dozen years we've also seen number of studies investigating long-distance airborne spread of avian flu, including 2019's Nature: Airborne Transmission May Have Played A Role In Spread Of U.S. 2015 HPAI Epizootic and 2022's HPAI (H5N8) Clade 2.3.4.4b Virus in Dust Samples from Poultry Farms, France, 2021.
In 2020's Nature Comms: Influenza A Transmission Via `Aerosolized Fomites', we looked at laboratory evidence that influenza A viruses (and probably others) can be transmitted via airborne or `aerosolized fomites'.
Despite more than 2 decades of research, HPAI H5 (and other novel viruses) still have a lot of secrets left to uncover. One of the barriers has been the relatively low sensitivity of environmental testing methods.
In the past we've looked at advances in aerobiology, and today we look at a new method of sampling and detecting HPAI viruses in fresh surface water.
By inoculating eggs with filtered and concentrated water samples, and then extracting RNA, researchers saw a significant increase in positive results over traditional testing methods.
Laura E. Hubbard*, Carrie E. Givens,Erin A. Stelzer,Mary L. Killian, Dana W. Kolpin, Christine M. Szablewski, and Rebecca L. PoulsonCite this: Environ. Sci. Technol. Lett. 2023, XXXX, XXX, XXX-XXXPublication Date:November 15, 2023© 2023 The Authors. Published by American Chemical Society.This publication is licensed under CC-BY-NC-ND 4.0.Avian influenza viruses (AIVs) infect both wild birds and domestic poultry, resulting in economically costly outbreaks that have the potential to impact public health. Currently, a knowledge gap exists regarding the detection of infectious AIVs in the aquatic environment.
In response to the 2021–2022 Eurasian strain highly pathogenic avian influenza (HPAI) A/goose/Guangdong/1/1996 clade 2.3.4.4 lineage H5 outbreak, an AIV environmental outbreak response study was conducted using a One Health approach. An optimized method was used to temporally sample (April and May 2022) and analyze (culture and molecular methods) surface water from five water bodies (four wetlands and one lake used as a comparison location) in areas near confirmed HPAI detections in wild bird or poultry operations.
Avian influenza viruses were isolated from water samples collected in April from all four wetlands (not from the comparison lake sample); HPAI H5N1 was isolated from one wetland. No virus was isolated from the May samples.
Several factors, including increased water temperatures, precipitation, biotic and abiotic factors, and absence of AIV-contaminated fecal material due to fewer waterfowl present, may have contributed to the lack of virus isolation from May samples. Results demonstrate surface water as a plausible medium for transmission of AIVs, including the HPAI virus.
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Sample Collection and ProcessingSample collection and processing included the following steps: (1) filtration (primary concentration), (2) filter elution, (3) centrifugation (secondary concentration), (4) centrifugation (tertiary concentration), (5a) egg inoculation (virus isolation), and (5b) extraction (RNA isolation) (Figure S1).
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The molecular results demonstrate that the current commercially available molecular methodology used for diagnostic AIV detection may not detect AIV in large volume wetland water sample concentrates. Following the current diagnostic molecular procedures, our environmental positive detections would have been missed without the addition of VI to determine infectivity. These results support the need for virus isolation in addition to molecular techniques when assessing AIV presence in surface water as many of the VI positive samples would have been categorized as negative if only rRT-PCR was used to assess AIV presence.
Our VI and sequencing results confirm the presence and recovery of infectious AIV, including HPAI, from wetlands. The results also underscore the need for (1) improved extraction techniques for reduction or removal of PCR inhibitors in concentrated water samples and (2) incorporating an internal positive control in rRT-PCR.
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Further research is needed to improve the collective understanding of AIV in the environment, including persistence and potential for transmission via water to birds and mammals, supporting early detection of HPAI viruses and other AIVs, and mitigation to reduce the spread of disease into domestic poultry and potentially to other wildlife. This information also has potential human health implications, especially in public use waterways, where people may have direct exposure to AIV with primary or secondary contact. Methods to detect AIV using rRT-PCR more consistently from these concentrated surface waters would help improve environmental detection.
Although the spread of HPAI from bird-to-bird via contaminated surface water is the most obvious concern, we've seen ample evidence that semiaquatic mammals (otters, mink, muskrats, polecats, voles, etc.) are highly susceptible to avian flu infection (see Nature: Semiaquatic Mammals As Intermediate Hosts For Avian Influenza).
Other terrestrial mammals may drink from these waters as well. While most of these will be dead-end infections, every spillover to a mammalian host provides the virus with another opportunity to adapt.
Given the spread and rapid evolution of HPAI viruses over the past few years, we need to up our game. That means increased surveillance, better testing methods, and timely sharing of information.
While we may be falling behind in some of these endeavors, it's nice to be able to report progress being made in others.
