54 of Minnesota’s 84 Outbreaks Are Clustered in 3 Counties
Although migratory and wild birds are believed responsible for the delivery of HPAI H5 viruses to North America last fall and the subsequent spread of H5N8, H5N2, and H5N1 to at least 18 states, the clustering of infected farms (particularly in Minnesota and Iowa) has many wondering if there isn’t a second – as yet unidentified - mode of transmission at work.
While Minnesota has recorded 84 outbreaks across 21 counties, more than 1/3rd of those are from one county (Kandiyohi n=32), while the three county nexus of Stearns, Meeker & Kandiyohi account for nearly 65% of all of the cases.
Similarly, in hard hit Iowa, out of 44 farms infected across 12 counties, 2 counties (Buena Vista & Sioux) account for fully half their total.
In the past, human activities – the movement of personnel, or equipment, or poultry related items – has been viewed as the likely source of local `lateral’ transmission between farms, but so far epidemiological investigations have failed to find any solid evidence of such.
Somehow, despite elaborate biosecurity measures, the virus continues to make its way into scores of farms. And with the likely return of the virus next fall, figuring this out is a priority.
One idea, increasingly being considered, is the possibility that the virus is being dispersed – at least across short distances - `on the wind’. Carried on dust particles from one farm to another (see last April’s Bird Flu’s Airborne `Division’ for a discussion of previous studies on this possibility).
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May 08, 2015
Evidence of the H5N2 avian influenza virus has been found in air samples collected in and near infected Minnesota poultry barns, a researcher said today, supporting the suspicion that the virus may go airborne for short distances, while Iowa reported seven new H5 outbreaks involving 4 million chickens and an unknown number of turkeys.
In addition, Wisconsin authorities today reported finding H5N2 in an owl along Green Bay, while hard-hit Minnesota had its second day this week without any new poultry outbreaks.
Air sampling findings
Montse Torremorell, DVM, PhD, of the University of Minnesota said she and three colleagues did a pilot air sampling study at three Minnesota farms with infected poultry.
"Our results indicated that influenza genetic material can be detected in air samples collected inside and immediately outside of infected poultry facilities. We still don't know whether virus was viable or not, and those analyses are in progress," said Torremorell, who holds the Allen D. Leman Chair in swine health and productivity.
"So far we have shown that HPAI [highly pathogenic avian influenza] can be aerosolized from infected facilities," she added. "However, the implications of these findings in terms of understanding the transmission of HPAI between flocks needs further investigation." The study focused on a total of four poultry barns on the three farms.
Torremorell said the study was commissioned by the US Department of Agriculture's Animal and Plant Health Inspection Service (APHIS). The agency's National Veterinary Services Laboratories (NVSL) in Ames, Iowa, are testing the samples to see if they contain any viable virus particles.
Humidity, ambient air temperatures, UV ray exposure levels . . . even the pH of whatever medium the virus clings to as it rides the air currents . . . are all likely factors affecting the viability (and longevity) of avian flu viruses in the environment.
While ideal conditions are likely to be short-lived - if you add the right amount of air movement and relatively closely clustered farms – you might have a legitimate route for lateral transmission.
For earlier blogs on the viability of influenza viruses (avian and human) in the environment, you may wish to revisit: