The influence of climate on influenza A virus (IAV) introductions in Minnesota turkeys: Spring 2007 - 2015

Xi Guo1, Nitipong Homwong2, Jeanette Munoz-Aguayo3, Cristian Flores3,

Carol J. Cardona1

Introduction

• Climate affects the transmission cycle of infectious diseases• The landscape that gives rise to the transmission of influenza A virus

(IAV) between wild and domesticated avian species is greatly impacted by the climate.

• The behavior of the wild waterfowl, the natural host of IAV, is also affected by the climate condition.

• In the spring of 2015, highly pathogenic avian influenza (HPAI) H5N2 was introduced to turkeys in Minnesota (MN). Prior to 2015, there were seven low pathogenic avian influenza (LPAI) introductions occurred in the same area and the same season in the turkey flocks.

List of Spring introductions of IAV

*The dates were based on an estimation of the date of infection from positive serological and virological findings

Case ID Year Date Subtype County

1 2007 03/22* H7N9 Brown

2 2009 05/06* H7N9 Redwood

3 2011 05/13* H7N9 Wright

4 2012 04/26* H8N4 Kandiyohi

5 2013 05/08* H3N2/H9N2 Kandiyohi

6 2014 05/09 H4N2 Kandiyohi

7 2015 02/27 H5N2 Pope

8 2015 03/22 H5N2 Lac Qui Parle

9 2015 04/08 H5N2 Kandiyohi

10 2016 03/14 H1N1 Kandiyohi

Objective

To characterize the climate conditions associated with the Spring introductions of IAV in MN turkeys.

Data source

Daily climatic variables including maximum temperature, minimum temperature and snow depths during 1960-2015 were retrieved from the National Climatic Data Center (NCDC) archives. The weather stations selected for data analysis were within 20 miles of the case sites, which were clustered into five regions.

Weather data analysis • Spearman correlation was performed between the week of the

introduction cases and the weather indicators including temperature 7 to 9°C, heading degree days (HDD) 18 to 20 days, and the yearly average temperature.

• Wilcoxon Ranked-sum tests were performed to compare the sum of introduction years and non-introduction years.

• Permutation tests were performed to validate the significance between the mean difference of temperature and snow depth between introduction years and non-introduction years.

Result - Temporal pattern of temperature

Result - Temporal pattern of temperature

• The relationship between Case 7 and the lowest point resembles the temporal pattern illustrated by Liu et al (Plos one, 2007), recapitulating the same climate condition for HPAI introductions.

• The temperature pattern of other LPAI cases is different from Case 7, suggesting different mechanism of HPAI and LPAI introductions.

Result - Weather indicator correlation

Weather indicator Spearman correlation p value

Spearman correlation coefficient

The  week  when  weekly  average  temperature  was  the  closest  to  7  °C   0.2005 0.5062

The  week  when  weekly  average  temperature  was  the  closest  to  8  °C   0.0083* 0.8447

The  week  when  weekly  average  temperature  was  the  closest  to  9  °C   0.0532 0.7000

The week when weekly average temperature was the closest to the

yearly average 0.1344 0.5768

The week in which weekly average HDD was the closest to 18 0.0083* 0.8447

The week in which weekly average HDD was the closest to 19 0.0137* 0.8149

The week in which weekly average HDD was the closest to 20 0.2005 0.5062

Result - Weather indicator correlation

• The relationship between Case 7 and the lowest point resembles the temporal pattern illustrated by Liu et al (Plos one, 2007), recapitulating the same climate condition for HPAI introductions.

• The temperature pattern of other LPAI cases is different from Case 7, suggesting different mechanism of HPAI and LPAI introductions.

Result - Snow depth analysis

Result - Snow depth analysis

Case   Rank  (From  low  to  high)   Wilcoxon  P  value  1 26  out  of  56   0.90

2 21  out  of  56   0.66

3 40  out  of  56   0.50

4 27  out  of  54   1.00

5 54  out  of  56   0.12

6 49  out  of  56   0.21

7 11  out  of  56   0.29

8 4  out  of  55   0.14

Case 7 and 8 have lower snow depths than non-introduction years. Other cases have average level of snow depths among all the year.

Conclusion and future direction • The similar temporal patterns of Case 7 and the HPAI cases

from other locations suggest a universal climatic condition that drives the occurrence of HPAI outbreak.

• Several weather indicators correlate with the timing of the introductions. These indicators could help to predict the timing of the next IAV introduction in turkey flocks.