New Zealand as a model for vector borne disease emergence : Effects of social and environmental factors on dengue

Abstract: The geographic distribution of dengue fever has increased worldwide in recent years and is at present the most widespread vector borne viral disease in the world (Halstead 2002). Because of its rapid spread and increasing seriousness of its complications it is considered to be the most troubling vector borne disease (Wilcox and Colwell 2005, Phillips 2008). Dengue fever is the one vector borne disease that poses the greatest threat to New Zealand. Imported cases are being reported in ever increasing numbers and all the components for a mosquito borne disease cycle is already present (Ministry of Health 1997). Furthermore, New Zealand’s geographic isolation makes it a unique location for studying the emergence of vector borne diseases, such as dengue. The objective of this thesis was - by using case studies on dengue fever on a global scale and the potential emergence of the disease in isolated New Zealand as examples – to explore the interlinkages between global changes (climate change and rapid urbanisation), globalisation (rapid travel and trade), and their local impacts on vulnerability and health (i.e. changes in local climate, travel and trade patterns and demographic changes that affect emergence and transmission of disease). This was done by 1) reviewing the ecological and environmental conditions necessary for dengue transmission; 2) examining key social and environmental factors contributing to the recent global increase in dengue fever and dengue hemorrhagic fever (DHF) and 3) drawing projections to 2070 in order to build future scenarios for epidemic dengue risks in New Zealand. Regression analysis were used to analyse 16 years of area specific dengue rates from 232 geographical areas in relation to key social and environmental factors proposed to contribute to dengue emergence. The results were tested on the mainland of New Zealand in order to build future scenarios for epidemic dengue risks in New Zealand for 2070. The outcome from the regression analysis proved to have a good ability to predict dengue rates based on national characteristics and it predicted a nearly fourfold increase in risk of epidemic for New Zealand’s North Island based on climate projections for 2070. The projected increase in population density however, had much less of an effect on the perceived risk than the projected climate change despite an estimated increase of 33% in population density. This is the first study that makes an attempt to measure the relative importance of different social and environmental variables proposed to contribute in the recent global increase in dengue.