Correction: I mistakenly attributed this study to the Journal of Virology, and not the Virology Journal, in the title (now corrected). My apologies for the confusion, and my thanks for the head’s up from Hon S. Ip, Section Head of the Diagnostic Virology Laboratory at the USGS.
Along with a lot of other writers who have been following the arrival of HPAI H5 into North America these past 10 months, I’ve been forced to use the word `Presumably’ a lot.
As in, `The HPAI H5 virus arrived in North American last fall, presumably carried in from Asia by migratory birds.’ and ` Over the spring both H5N2 and H5N8 affected numerous poultry farms across the western and central United States, many presumably infected by infected migratory or wild birds.’
While we lack a `smoking bird’ bird for both these assumptions, right now they are the best explanation for what we’ve observed. Last July, in APHIS/USDA Announce Updated Fall Surveillance Programs For Avian Flu, we looked at two new surveillance plans (Here and Here) that is hoped will help better answer some of these questions.
Today, however, we have a commentary from four USGS researchers, who propose some tweaks to these recently released surveillance plans, placing a greater emphasis on sampling in regions that have the greatest risk for poultry losses, and attempting to `define the mechanisms of transfer to enhance biosecurity’.
This commentary spends a good deal of time on the need to identify potential `bridge species’, those that may acquire the HPAI virus from waterfowl and then transfer it into enclosed poultry operations. These may range from other bird species, to rodents or other small mammals, and possibly even insects.
A few studies we’ve looked at in the past on potential bridge species include:
The full open access article may be read at the link below.:
28 September 2015
© 2015 Flint et al.
It is unknown how the current Asian origin highly pathogenic avian influenza H5 viruses arrived, but these viruses are now poised to become endemic in North America. Wild birds harbor these viruses and have dispersed them at regional scales. What is unclear is how the viruses may be moving from the wild bird reservoir into poultry holdings. Active surveillance of live wild birds is likely the best way to determine the true distribution of these viruses. We also suggest that sampling be focused on regions with the greatest risk for poultry losses and attempt to define the mechanisms of transfer to enhance biosecurity. Responding to the recent outbreaks of highly pathogenic avian influenza in North America requires an efficient plan with clear objectives and potential management outcomes.
The original United States interagency strategic plan for detection of Asian highly pathogenic H5N1 avian influenza was developed nearly a decade ago, with focus on the early detection of an exotic virus . The current outbreaks of HPAI H5N8 and H5N2, caused by foreign origin viruses, have very quickly become widely distributed within North America, thus negating the need for early detection at the broad scale.
Two new avian influenza surveillance and monitoring documents have been recently released that address early detection at local and regional scales. One focuses on detection of HPAI in waterfowl in high priority watersheds and the spread of viruses to new areas of concern . The other encompasses a strategy for early detection of avian influenza viruses of significance in wild birds in general, and encourages sampling of areas with high poultry density .
We propose taking these plans a step further by suggesting a 2-tiered surveillance strategy focusing on waterfowl and bridge species in the vicinity of poultry operations. This 2-step sampling design would address the mechanism(s) of virus transfer and provide data that can inform management actions that minimize the impact of these viruses on domestic poultry.
Surveillance activities should go beyond simply documenting and tracking where HPAI H5 viruses occur, but rather target sampling in areas where management outcomes can be applied that enhance biosecurity. The existing HPAI surveillance plan for waterfowl focuses on early detection of viruses in specific areas (Fig. 1, box 1), selected on the basis of watershed characteristics, dabbling duck populations and movements, and previous AI activity .
For example, that plan calls for a greater sampling effort in areas of Utah and Nevada with prioritized watersheds and mixing of dabbling ducks but little commercial poultry production, than in the portions of Iowa and Minnesota where commercial poultry losses associated with H5N2 exceeded 40 million birds in spring 2015 , .
We propose that sampling be stratified in relation to the risk of economic damage to the poultry industry associated with these viruses by targeting areas of highest poultry density (Fig. 2) . When HPAI is detected in a region, either in wild birds or poultry, directed sampling should immediately expand to include potential bridge species appropriate to specific locations and time (Fig. 1, box 2).
Poultry facilities attract flies, rodents, and other pests and an investigation of 81 HPAI-positive turkey farms in the Midwestern U.S. in 2015 indicated that wild birds were observed within facilities on 35 % of farms , . Wildlife surveys and poultry facility investigations can be used to identify high priority bridge species , ,. Identification of the pathways by which HPAI can move from waterfowl into commercial poultry holdings can then be used to enhance and actively target biosecurity  (Fig. 1, box 3).
We emphasize that in our conceptual model of HPAI movement, biosecurity is the only factor that could be controlled (Fig. 1). As such, a logical goal of a surveillance program would be to facilitate enhancement of biosecurity. Understanding which bridge species may be involved, when, how, and why they enter poultry facilities is necessary to define potential counter strategies. Clearly the response to avian vs mammalian bridge species would be different. It may also be productive to pursue identification of bridge species associated with low pathogenic AI infections, as these are common in wild waterfowl and occur annually in commercial poultry . Detailed studies of epidemiological links between wild waterfowl and commercial poultry may provide a means to target biosecurity and lessen the economic impacts of the HPAI viruses currently circulating in in North America. Timely analyses of collected samples and rapid response to positive detections from surveillance results are also essential to facilitating management outcomes.