ZOONOSES: BLURRED LINES OF EMERGENT DISEASE AND ECOSYSTEM HEALTH Drivers of zoonotic disease emergence
Researchers studying records that date from 1940 to 2004 detected an increase in the rate of emerging infectious disease over those years. Of the 335 documented events, 60.3 per cent were zoonotic and 71.8 per cent of the zoonoses originated in wildlife.11
Generally scientists consider three different types of
change that allow virulent pathogens to initiate a new move from animal host to human host: changes in the environment, in either host, or in the pathogen itself.
Changes in the environment are usually the result of human activities, ranging from land use change to changing climate. Encroachment on natural ecosystems through resource exploitation, agricultural activity, and human settlements provides opportunities for pathogens to spillover from wild animals to people, especially when the natural disease resistance that may result from rich biological diversity is lost.5,12,13
Climate change is a major factor for disease
emergence. It influences the environmental conditions that can enable or disable the survival, reproduction, abundance, and distribution of pathogens, vectors, and hosts, as well as the means of disease transmission and the outbreak frequency.17
Growing evidence suggest that outbreaks or
epidemic diseases may become more frequent as climate continues to change.17-19
Changes in animal or human hosts are often the result of human action as well. Zoonotic transmission from wildlife hosts directly to human host is uncommon: domestic animals can bridge the gap.20
Top 3 reported zoonoses, based on 13,293 research publications dated from 1912 to 2013
Geographic distribution of top three reported wildlife-livestock interfaces, based on an analysis of 13,293 research publications dated from 1912 to 2013
Examples of zoonoses emerging when land is cleared
for human activity can be found in many regions and on most continents.5,14-16
Source: Wiethoelter et al. (2015)44
Source: Wiethoelter et al. (2015)44 Primary drivers of past disease emergence
Other 4%
Human
demography and behaviour 4%
Climate and weather 6%
Increasing demand for milk and
meat, driven mainly by fast-growing populations of urban consumers in developing countries, is projected to double by 2050.21
The Livestock Revolution paradigm is leading to rapid
increases in livestock populations in developing countries, which increases the likelihood of disease transmission.22 Demand for livestock products leads to more intensive production, that is greater populations of high yielding and
22
Medical industry changes 11%
War and famine 7%
Agricultural industry changes 15%
International travel and commerce 13%
Source: Loh et al. (2015)43
Land use changes 31%
Breakdown of public health 3%
Primary drivers of disease emergence associated with the past emerging zoonotic disease events
Bushmeat 3%
Food industry change 2%
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