APHIS Issues Final Epidemiology Report for Avian Influenza Affected Poultry in Indiana

March 16, 2016

In mid-January, a combined outbreak of highly pathogenic avian influenza and low pathogenic avian influenza (HPAI and LPAI) occurred in Indiana. The outbreak in commercial turkeys was first detected by an increase in mortality followed by laboratory confirmation of H7N8 HPAI. After initial efforts to control the disease, a series of epidemiologic, geospatial, genetic, and wildlife investigations was started. These studies are being conducted collaboratively with the poultry industry, the Indiana State Board of Animal Health, and the United States Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS). This is the second report of the findings available to date to assist in understanding the introduction and disease transmission pathways. Ultimately, the goal is to reduce the risk of continued spread in this outbreak and to help in future efforts to prevent disease incursions. This report is the final epidemiologic report for this incident, although additional analyses may be undertaken and reported through other mechanisms.
Genetic analyses determined that all H7N8 viruses detected from this event are of North American wild bird lineage, and the HPAI and LPAI viruses are highly similar across all eight genes excluding the multi-basic amino acid insertion at the cleavage site in the HPAI virus. Genetic analysis also suggests a point source introduction followed by lateral/secondary spread.
An investigation of cases and controls using an in-person administered questionnaire examined physical and management characteristics of infected premises. Differences were identified between case farms and barns compared to control farms and barns. Several risk factors found in a previous HPAI case-control study were found to occur on more case farms and in case barns than on control farms and in control barns. These factors included distance to dead bird disposal and litter compost areas, presence of wild mammals, and visitors entering barns.
Additionally, daily mortality sheets were obtained from both case and control farms. Mortality patterns from these farms between September 7, 2015, and January 17, 2016, were compared. This comparison showed differences in mortality between case and control farms for 2 weeks in October 2015 and again in November 2015. However, there were no major differences in mortality patterns between case and control farms in closer temporal proximity to the identified H7N8 HPAI outbreak.
APHIS has completed sampling and testing of wildlife near infected premises. The results indicate no evidence of existing virus in the samples from wild birds and mammals tested.
Initial geospatial analysis looked at county-level factors that may have contributed to the introduction of the virus into Dubois County, Indiana. The weather in Dubois County was warmer and wetter than past years, which may have contributed to the introduction and persistence of the virus. Additional analysis identified a geospatial pattern observed between infected premises and a driving route. More detailed geospatial analysis is ongoing.