The U.S. Department of Agriculture’s Animal & Plant Health Inspection Service (APHIS) has released the epidemiology report for cases of highly pathogenic avian influenza (HPAI) and low-pathogenic avian influenza (LPAI) in poultry this spring.

This kind of analysis helps identify how the disease spread and how to help prevent it in the future. APHIS noted it has made great strides in HPAI emergency response since the 2014-15 outbreak. Rapid response times and a 24-hour depopulation goal of confirmed HPAI cases has helped minimize the spread of disease. Vigilant biosecurity practices remain a top priority to protect domestic poultry from the disease.

On March 4, APHIS’s National Veterinary Services Laboratories confirmed a case of HPAI H7N9 on a commercial broiler breeder farm in Tennessee. A second case of HPAI H7N9 in Tennessee was confirmed on March 15 on another commercial broiler breeder farm. This virus was NOT the same as the China H7N9 virus that emerged in 2013 and affected poultry and people in Asia, APHIS emphasized.

Additionally, APHIS found H7 LPAI in six backyard flocks: three in Alabama, two in Tennessee and one in Kentucky. APHIS also found H7 LPAI in six commercial broiler breeder flocks: one in Tennessee, three in Alabama, one in Kentucky and one in Georgia.

Following these avian influenza findings, APHIS joined forces with the affected states and the poultry industry to complete a series of epidemiologic, genetic and wildlife investigations.

In the new report, APHIS outlined the findings to date, which include:

* The identification of a closely related H7N9 LPAI virus in a blue wing teal in Wyoming in 2016 that was likely a precursor to the 2017 strain of H7N9. The teal was part of a live-bird banding effort from Wildlife Services' wild bird surveillance program.

* Results of genetic analyses determined that all H7N9 viruses detected from this event were of North American wild bird lineage.

* The comparison of the HPAI and LPAI H7N9 viruses showed that they were highly similar, so it's likely that the LPAI virus was first introduced in commercial poultry and later mutated into HPAI.

* Initial results from wild bird samples on infected premises have not confirmed influenza A virus, but there is limited evidence from the samples that some birds may have been previously exposed to it.

* Genetic and epidemiologic evidence suggests the possibility of more than a single introduction of virus from wild birds to commercial poultry with limited lateral spread from farm to farm.

* Risk factors include rodents and wild mammals near barns, housing conditions and biosecurity protocol breaches that could bring the virus from the environment into the barns.

APHIS said it will continue to collect and analyze data to help refine its prevention, detection and response efforts based on the best available science and lessons learned. The full report can be viewed here.