On June 15th APHIS released a 38-page partial epidemiology report on the spread of HPAI H5 across the United States (see APHIS: Partial Epidemiology Report On HPAI H5 In The US) that cited a number of plausible factors that might explain the rapid spread of the HPAI between farms, particularly in the Midwest.
While investigators had been unable to find one or even a group of factors that satisfactorily explain this AI spread, factors under consideration included movement of poultry, poultry products, equipment and personnel between farms and the possibility that prevailing winds may have carried contaminated dust particles from farm to farm.
Today APHIS has released an updated – 99 page PDF – Epidemiological Report that contains a great deal more information – including details of a case-control study - but does not nail down any `specific pathway or pathways for the current spread of the virus’.
Published: Jul 24, 2015
July 21, 2015—The United States Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) today released an updated highly pathogenic avian influenza (HPAI) epidemiology report.
The report has been updated to include:
- interpretation of data from 81 turkey flocks investigated for HPAI;
- preliminary results from a case-control study conducted in layer operations in Iowa and Nebraska; and,
- preliminary results of a study of wildlife near affected and unaffected premises.
The updated report can be read here, http://www.aphis.usda.gov/animal_health/animal_dis_spec/poultry/downloads/Epidemiologic-Analysis-July-15-2015.pdf.
EXECUTIVE SUMMARY – UPDATED
For the past several months, the USDA’s Animal and Plant Health Inspection Service (APHIS) has conducted epidemiological investigations and other studies with the goal of identifying transmission pathways of highly pathogenic avian influenza (HPAI). This report includes updates to the report released by APHIS on June 5, 2015.
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. This edition of the report includes data on the characteristics and biosecurity measures of infected turkey farms and a case control study to compare these measures between infected and non-infected farms. We have also sampled wildlife near affected and unaffected farms.
In a case series investigating 81 turkey farms across the Midwestern United States, we found turkey farms typically follow biosecurity protocols, which are established by the company with which they work. Common procedures include spraying vehicle tires with disinfectant at the farm entrance, requiring visitors and employees to wear coveralls and disposable boot covers (or dedicated footwear) before entering the barns, using disinfectant footbaths at barn entrances, using rodent control, and caring for younger birds before caring for older birds. The objective is to establish a clean-dirty line where outside contaminants are not carried into the barn.
Fomites, such as equipment, are probably playing a role in this outbreak. 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. Wild birds, another possible route of disease transmission, were observed inside barns on 35 percent 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 risk by verifying that biosecurity procedures are being followed properly.
In a case-control study focused on egg layer flocks in Iowa and Nebraska, a number of risk factors for HPAI introduction and factors associated with lowering the risk of introduction were identified in our preliminary analysis.
- Factors associated with an increased risk of becoming infected with HPAI included being located within one of the 10-kilometer control zones; 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.
- Factors associated with a lowered risk of infection included being more than 100 yards from a public gravel or dirt road, having wash stations for vehicles on the farm, and being more than 100 miles from the egg processing facility used by the farm.
Also in this edition are preliminary results of a study of wildlife near affected and unaffected premises. Testing is ongoing on the over 2,600 samples collected.
APHIS will continue to investigate how the HPAI virus is introduced and spread and will provide updated results regularly. 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. With the results of this and the June 5 report, which included wind and airborne virus studies as possible causes of viral spread as well as a genetic analysis of the viruses detected in the United States, we have identified several possible pathways. Comprehensive and stringent biosecurity practices remain crucial to reducing the risk of HPAI infection.