In a preliminary epidemiology report on the spread of highly pathogenic avian influenza, USDA's Animal and Plant Health Inspection Service said this week that there are likely several ways the virus could be transmitted between birds and farms, including lapses in biosecurity practices and environmental factors.
The report includes initial findings through June 5 from investigations of more than 80 commercial poultry farms.
Despite the identification of several possible transmission methods, APHIS said it cannot associate HPAI transmission with one factor or group of factors in a statistically significant way at this time, and will continue to update this report regularly as more analyses are completed.
APHIS scientists believe wild birds were responsible for introducing HPAI into commercial poultry. While wild birds are the original pathway for the virus' introduction into the United States, it appears the virus was spreading in other ways as well, given the number and proximity of farms affected by HPAI.
The report provides evidence that a certain cluster of farms was affected by identical viruses, pointing to possible transmission among those farms. In addition, genetic analyses of the HPAI viruses suggest that independent introductions as well as transmission between farms were occurring in several states concurrently.
For example, APHIS has observed the following: sharing of equipment between an infected and non-infected farm; employees moving between infected and non-infected farms; lack of cleaning and disinfection of vehicles moving between farms; and reports of rodents or small wild birds inside the poultry houses.
Based on an analysis by APHIS, environmental factors may also play a part in transmitting HPAI. APHIS found that air samples collected outside of infected poultry houses contain virus particles, indicating that the virus could be transmitted by air.
Preliminary analysis of wind data shows a relationship between sustained high winds and an increase in the number of infected farms approximately five days later. APHIS is conducting additional analyses to better characterize environmental factors that may contribute to virus spread.
APHIS said it plans to continue sharing what it learns with state and industry partners through regular conversations and meetings, including an Industry/USDA/State Animal Health Meeting in July where the agency will focus specifically on biosecurity.
APHIS will continue to host monthly calls with state agriculture officials, weekly calls with industry and state veterinary officials, and daily calls with officials in HPAI-affected states.
Read the full report, Epidemiologic and Other Analyses of HPAI-Affected Poultry Flocks: June 15, 2015