The USDA’s APHIS has released a 38-page partial epidemiology report on the spread of HPAI H5 today, along with a press release summarizing their early findings. Although it has been pretty apparent that wild birds introduced the virus to North America, and have played a part in their dispersal, the number and tight clustering of affected farms suggest other factors are at work as well.
- Last year, in Bird Flu Spread: The Flyway Or The Highway? we looked at the impacts of migrating birds vs. the movement of poultry, poultry products, equipment and personnel between farms, both of which have long been cited as promoting the spread of avian influenza.
- In April, in Bird Flu’s Airborne `Division’, we looked at studies that linked prevailing winds with the localized spread of avian flu viruses in previous outbreaks, while last month in H5N2 Roundup & Detection In Environmental Air Samples at experiments conducted by the University of Minnesota.
As you see, from the following excerpt from the epidemiology report’s executive summary – while investigators have been unable to find one or even a group of factors that satisfactorily explain this AI spread, all of these are factors are still under consideration.
APHIS scientists believe wild birds were responsible for introducing HPAI into commercial poultry. However, given the number and proximity of farms affected by HPAI, it appears the virus is spreading in other ways as well. For instance, one analysis provides evidence that a certain cluster of farms was affected by identical viruses, pointing to possible transmission among those farms. In addition, genetic analyses of the HPAI viruses suggest that independent introductions as well as transmission between farms are occurring in several States concurrently.
Although APHIS cannot at present point to a single statistically significant pathway for the current spread of HPAI, a likely cause of some virus transmission is insufficient application of recommended biosecurity practices. For example, APHIS has observed sharing of equipment between an infected and noninfected farm, employees moving between infected and noninfected farms, lack of cleaning and disinfection of vehicles moving between farms, and reports of rodents or small wild birds inside poultry houses. We are compiling these observations and will present our findings in a subsequent update of this report. Until then, USDA is collaborating with affected industries and States to implement more stringent biosecurity procedures while continuing to work on identifying and mitigating other possible disease pathways in poultry farms nationwide.
Environmental factors may also play a part in transmitting HPAI. APHIS found that genetic material from the HPAI virus could be detected in air samples taken inside and outside infected poultry houses, supporting the idea that the virus can be transmitted through air. Further reinforcing this concept is preliminary analysis of wind data that shows a relationship between sustained high winds (25 mph or greater for 2 days or longer) and an increase in the number of infected farms 5 to 7 days later.
In other words, there’s a lot more investigating ahead. You’ll find a press release on the APHIS site (link below) which also summarizes their findings.