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, 9 (1), 11755

Airborne Transmission May Have Played a Role in the Spread of 2015 Highly Pathogenic Avian Influenza Outbreaks in the United States

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Airborne Transmission May Have Played a Role in the Spread of 2015 Highly Pathogenic Avian Influenza Outbreaks in the United States

Yang Zhao et al. Sci Rep.

Abstract

The unprecedented 2015 outbreaks of highly pathogenic avian influenza (HPAI) H5N2 in the U.S. devastated its poultry industry and resulted in over $3 billion economic impacts. Today HPAI continues eroding poultry operations and disrupting animal protein supply chains around the world. Anecdotal evidence in 2015 suggested that in some cases the AI virus was aerially introduced into poultry houses, as abnormal bird mortality started near air inlets of the infected houses. This study modeled air movement trajectories and virus concentrations that were used to assess the probability or risk of airborne transmission for the 77 HPAI cases in Iowa. The results show that majority of the positive cases in Iowa might have received airborne virus, carried by fine particulate matter, from infected farms within the state (i.e., intrastate) and infected farms from the neighboring states (i.e., interstate). The modeled airborne virus concentrations at the Iowa recipient sites never exceeded the minimal infective doses for poultry; however, the continuous exposure might have increased airborne infection risks. In the worst-case scenario (i.e., maximum virus shedding rate, highest emission rate, and longest half-life), 33 Iowa cases had > 10% (three cases > 50%) infection probability, indicating a medium to high risk of airborne transmission for these cases. Probability of airborne HPAI infection could be affected by farm type, flock size, and distance to previously infected farms; and more importantly, it can be markedly reduced by swift depopulation and inlet air filtration. The research results provide insights into the risk of airborne transmission of HPAI virus via fine dust particles and the importance of preventative and containment strategies such as air filtration and quick depopulation of infected flocks.

Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Backward air trajectories of four example days (4/8 – 4/11/2015) prior to the infection confirmation date (4/12/2015) of the first Iowa case. Red, blue and green lines are the 24-h (12am-12am, Local Standard Time or LST), 16-h (12am-4pm, LST) and 8-h (12am-8am, LST) trajectories, respectively. The round red dot represents the first case location; other dots are cases (green for turkey, red for laying hen, purple for backyard) that had been confirmed positive before the first Iowa case and the infected flocks had not yet been depopulated.
Figure 2
Figure 2
Proportions of HPAI infected cases and case-days in Iowa that were possibly attributable to airborne transmission. The total number of Iowa cases is 77, and the total number of case-days is 1,617 (77 cases, each was examined 21 days prior to the date of infection confirmation).
Figure 3
Figure 3
Ninety-five percent confidence interval (95% CI), maximal and minimal concentrations of airborne avian influenza virus carried by PM10 (A) and PM2.5 (B) at the infected farms in Iowa. Concentrations were estimated based on the default values. Top and bottom horizontal lines of each rectangular box are the upper and lower limits of 95% CI, respectively. Free ends of the top and bottom vertical lines are the maximal and minimal virus concentrations, respectively. Red dash line and blue solid line are the MIDs for laying hen and turkey, respectively.
Figure 4
Figure 4
Distribution of Iowa cases at four infection risk categories using default and ceiling values in concentration modeling for virus carried by PM10. For ceiling values, distribution was estimated by pushing each parameter to its ceiling value, separately and combined.
Figure 5
Figure 5
Distribution of Iowa cases at four infection risk categories by farm type. Combined ceiling values of virus shedding rate, emission rate, and half-life are applied.
Figure 6
Figure 6
Flock sizes of infected Iowa farms at four infection risk categories. Error bars are 95% confident intervals. Combined ceiling values of virus shedding rate, emission rate, and half-life are applied.
Figure 7
Figure 7
Distance between each Iowa case and its nearest previously infected farm in four airborne infection risk categories. Combined ceiling values of virus shedding rate, emission rate, and half-life were applied. Error bars are 95% CIs.
Figure 8
Figure 8
Case distribution at four infection risk categories when applying 24-h depopulation and inlet air filtration strategies to minimize airborne transmission risks. Combined ceiling values of virus shedding rate, emission rate, and half-life for PM10 are applied.

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