Exactly how the highly pathogenic avian influenza that destroyed millions of turkeys and chickens in Iowa, Minnesota and other states this spring and summer spread remains a mystery, according to a new USDA report.
The H5N2 strain that hit poultry producers this spring is considered the worst animal-disease outbreak in U.S. history and caused an estimated $3.3 billion in economic impact. USDA officials have cautioned that the risks are high that the virus could return this fall when temperatures drop and wild birds begin moving south again.
The Animal and Plant Health Inspection Service report, however, indicates scientists still are looking at a number of potential pathways to the spread of the flu. “With the data from both reports, APHIS concludes that there is not substantial or significant enough evidence to point to a specific pathway or pathways for the current spread of the virus,” the report said.
The lessons learned by USDA, farmers and other stakeholders are being discussed at a two-day conference on avian influenza this week in Des Moines sponsored by several major poultry associations. The event, however, is closed to media, as sponsors indicated, “in order to facilitate open, frank discussion.”
Just last week officials in the state of Iowa indicated some farms that lost their bird populations are just now beginning to re-stock their operations and may be two years away from returning to full production.
In the latest report, APHIS examined the characteristics and biosecurity measures of infected turkey farms, as well as wildlife near the farms.
APHIS looked at 81 turkey farms across the Midwest and found those farms “typically follow biosecurity protocols, which are established by the company with which they work.”
Those procedures include spraying vehicle tires with disinfectant as they enter farms, requiring visitors and employees to wear coveralls and disposable boot covers before entering barns, using disinfectant footbaths at barn entrances, using rodent control, and caring for younger birds before caring for older birds.
“Fomites, (an object or substance capable of carrying infectious organisms) such as equipment, are probably playing a role in this outbreak,” APHIS said. “In the majority of cases in this study, feed trucks, live haul loaders, pre-loaders, and other items were shared by multiple farms. While equipment sharing makes economical and logistical sense, it also increases the risk of lateral spread of HPAI between farms.”
The report said wild birds were observed inside of barns at 35% of the farms, “with the frequency ranging from daily to occasionally.
“While most of the 81 farms surveyed had biosecurity protocols in place, only 43% of case farms reported that biosecurity audits or assessments were conducted on the farm by the company or a third party. Farms can decrease their HPAI (highly pathogenic avian influenza) risk by verifying that biosecurity procedures are being followed properly.”
In addition, APHIS conducted a case study on egg-layer flocks in Iowa and Nebraska. The study found that a number of risk factors for avian flu introduction and factors associated with lowering the risk of introduction were identified.
“Factors associated with an increased risk of becoming infected with HPAI included being located within one of the 10-kilometer control zones,” APHIS said. “Using rendering of dead birds as a disposal method; sharing of company trucks, trailers, bird removal and egg removal vehicles; sharing of equipment between farms like egg rack, pallets and flats; and visits by company service personnel who entered barns.”
APHIS found those factors associated with a lower risk of infection included being more than 100 yards from a public gravel or dirt road, having on-farm vehicle-washing stations, and “being more than 100 miles from the egg-processing facility used by the farm.”
WILD BIRD POPULATION
APHIS also collected more than 2,600 samples from nearby wild bird populations.
“APHIS will continue to investigate how the HPAI virus is introduced and spread and will provide updated results regularly,” APHIS said in the report. “We are also 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.”
APHIS identified several potential pathways, including results indicating that highly pathogenic bird flu can become airborne. The virus was detected in air samples collected inside infected barns and “immediately outside of the infected premises.”
APHIS said “limited detection of viable virus does not necessarily indicate that the virus was not viable since the sampling process could contribute to the inactivation of the virus.” In addition, researchers found “considerable” surface environmental contamination across multiple surfaces outside the premises of a layer flock.
“The implications of these findings in terms of understanding the transmission of HPAI between flocks need further investigation and we hypothesize that both the transport of airborne particles and the deposition of infectious airborne particles on the surfaces around infected premises represents a risk for the spread of HPAI to other locations,” the report said.
APHIS said interviewers found an interesting connection between four companies interviewed.
“Companies with four or more operations represented 16 of the 28 case surveys and seven of the 30 control surveys,” the report said. “This company model is a common production type in the Iowa layer system and those surveyed here are representative of the greater layer-hen industry in Iowa. Sharing of feed and other company trucks that make several trips back and forth from the main company site, which houses hens and often feed mills, to serve smaller pullet sites is one potential route of spread within an organization.”