THE ECOLOGY AND FUTURE DISTRIBUTION OF WEST NILE VIRUS IN THE CANADIAN PRAIRIE PROVINCES
Date
2013-07-26
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Degree Level
Doctoral
Abstract
This thesis describes aspects of the ecology of West Nile virus (WNV) including factors contributing to the distribution of WNV, possible future distribution, and effects of WNV on host abundance in the Canadian prairies provinces: Alberta, Saskatchewan, and Manitoba.
Using mosquito surveillance data collected between 2005 and 2008, models integrating abiotic and biotic factors were constructed to predict the weekly and monthly scales of WNV infection rate in Culex tarsalis, which is the primary vector of WNV in the Canadian prairies.
At the weekly scale, the WNV infection rate in Cx. tarsalis increased with increasing Cx. tarsalis abundance and mean temperature lagged from 1 to 8 weeks, but decreased with an increasing mean precipitation lagged from 2 to 6 weeks. Furthermore, precipitation was a ‘distorter variable’ which altered the association between Cx. tarsalis abundance and the WNV infection rate.
Study at the monthly scale showed that higher mean temperature and time lagged mean temperature elevated were associated with increased numbers of Cx. tarsalis and higher WNV infection rates. However, increasing precipitation was associated with higher abundance of Cx. tarsalis and lower WNV infection rate. In addition, this study found that increased temperature fluctuation and wetland land cover were associated with decreased WNV infection rate in Cx. tarsalis.
Climate change could drive dramatic alterations in the spatial and temporal distribution and overall incidence of vector-borne diseases. The constructed models and biological thresholds were used to predict the distribution of Cx. tarsalis and WNV infection rate in the prairie provinces under a range of potential future climate and habitat conditions. In the current endemic regions, the projected WNV infection rate under the median outcome scenario in 2050 was 18 times higher than under current climate conditions. Seasonal occurence of Cx. tarsalis infected with WNV extended from June to August to include May and September. Moreover, models predicted northward range expansion for Cx. tarsalis and WNV.
The declines of susceptible bird abundance caused by WNV may further influence the bird community composition and, in turn, affect the incidence of WNV through a dilution effect. The North American Breeding Bird Survey data was used to evaluate the effect of WNV on the abundance of selected birds in the Canadian prairies, as well as the effects of bird community composition on the WNV risk. There was no significant decline in bird abundances of selected birds following the emergence of WNV. These findings suggest that the effect of WNV on selected bird abundance and bird community composition is insignificant. In addition, there is no evidence to support the association between bird community composition and WNV infection rate in Cx.tarsalis in the Canadian prairies.
Lastly, findings in this thesis and current knowledge were integrated to create a decision making flowchart for the prevention of WNV infection in the prairie provinces.
Description
Keywords
West Nile virus, Canadian prairies, Modeling, Climate change, Bird diversity
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Large Animal Clinical Sciences
Program
Large Animal Clinical Sciences