Ticks, Diseases and Climate Change
Utrecht Centre for Tick-borne Diseases
Members of 44 institutions in 28 countries comprise the Integrated Consortium
on Ticks and Tick-borne Diseases (ICTTD), and collaborate to study the effects of
climate change on the global distribution of ticks and tick-borne diseases.
One of the aims of the consortium is to better understand the tick-host-pathogen
interactions within diverse ecosystems wherein ticks survive and transmit disease.
GIS-referenced data on ticks and pathogens are mapped and used to validate
statistical models to predict climate-dependent changes.
Ticks transmit a greater variety of pathogenic micro-organisms than any
other arthropod vector group and are among the most important vectors of
diseases affecting humans and animals. Human tick-borne diseases have gained
enormously in notoriety since the discovery of Lyme borreliosis (LB), now
recognised as the most commonly reported tick-borne disease of humans in
Europe and North America, accounting for tens of thousands of new cases yearly
in both regions. Other zoonotic tick-borne illnesses of viral origin are characterised
by encephalitis and haemorrhagic fevers and cause high mortality in humans.
In the (sub)tropics, ticks and diseases are a major constraint to animal production.
Boophilus ticks transmit babesiosis and anaplasmosis to cattle, and severely affect
their productivity, particularly of Bos taurus-type cattle.
Ticks spend most of their life living off their hosts, where ambient temperature
and humidity determine their geographic range and survival. Increasing
temperatures with climate change may shorten their lifecycle, but increase their
reproduction rate. Very high temperatures can reduce survival and mortality
increases under drier conditions.
Climatic conditions dictate the dynamics of tick-borne diseases by affecting the
distribution of ticks and their seasonal occurrence. Reliable predictive models are
required to measure the direct effect of climatic change on the abundance of ticks
and tick-borne diseases.
The ecology of tick-borne diseases is complex, as is the influence of climate
on spatial and temporal variations in ticks and tick-borne diseases. The relative
impact of climate is often difficult to discern from variations in other factors that
are not directly climatic.
The LB ‘epidemic’ in Europe and North America has occurred because of an
increase in abundance and range of infected Ixodes ticks, but is also the result
of better surveillance and awareness. This epidemic has been associated with
climate-independent land use changes, from farm land to woodlands, which
resulted in increased abundance of hosts for ticks and the LB agent.
Climate change may affect not only tick survival, but have indirect effects on
host ecology and abundance, causing emergence of tick-borne diseases in some
regions, and their disappearance in other areas. Human behaviour - increased
recreational activities and travel - have also contributed to an increased number
of humans bitten by ticks. The LB epidemic shows how man-made ecological
changes can result in disease emergence.
There are two approaches. First, where records of tick and tick-borne pathogen
occurrence exist, statistical pattern matching of climatic and landscape variables
can provide insight into projected distributions. Second, climate-driven simulation
models of tick populations can be used to establish the geographic footprint
of ticks and tick-borne pathogens, particularly where ticks are not currently
The geographic range of the Ixodes ticks, I. scapularis, (the vector of LB in North
America) is expected to move further northwards into Canada based on a
simulation model. Statistical models also suggest that this northward range
expansion may be matched by northward movement of the southern limit of the
In Latin America, a mean increase of 2°C in temperature may contribute to
dramatic changes in habitat suitability for the Boophilus tick, B.microplus,
extending its distribution further south into Central Argentina, but disappearing
In southern and eastern Africa, an autochthonous species of the Boophilus ticks, B.
decoloratus, retreats from vast areas increasingly occupied by B. microplus, a more
dangerous disease carrier. It is not clear what the influence of climate change on
this change is and will be.
A major challenge is the collection of field data on the occurrence of ticks now
and in the future, to calibrate and validate suitable models, and to monitor
anticipated changes in tick-borne disease risk with the final aim of making
ICTTD-3 is a Coordination Action supported by the European Union through
project no. 510561 and is coordinated by the Utrecht Centre for Tick-borne
Diseases, Faculty of Veterinary Medicine, Utrecht University, in The Netherlands.
The project is a forum for genomics, biosystematics, molecular diagnostics,
epidemiology and remote-sensing, and has developed an integrated database for
ticks, hosts and pathogens (THPbase) for characterisation of ticks and diagnosis of
||Integrated Consortium on Ticks and Tick-borne Diseases
Utrecht Centre for Tick-borne Diseases
Professor Frans Jongejan
For further information:
Tel: + 31 6 20 97 11 10