Climate change impacts and vulnerability in Europe 2016

Climate change impacts on society
5.2.5 Vector-borne diseases
Key messages
• The transmission cycles of vector-borne diseases are sensitive to climatic factors, but disease risks are also affected by
factors such as land use, vector control, human behaviour, population movements and public health capacities.
• Climate change is regarded as the principal factor behind the observed move of the tick species Ixodes ricinus — the
vector of Lyme borreliosis and tick-borne encephalitis in Europe — to higher latitudes and altitudes. Climate change is
projected to lead to further northwards and upwards shifts in the distribution of Ixodes ricinus.
• It is generally suspected that climate change has played (and will continue to play) a role in the expansion of other disease
vectors, notably the Asian tiger mosquito (Aedes albopictus), which can disseminate several diseases including dengue,
chikungunya and Zika, and Phlebotomus species of sandflies, which transmit leishmaniasis.
• The unprecedented upsurge in the number of human West Nile fever infections in the summer of 2010 in south-eastern
Europe was preceded by extreme hot spells in this region. High temperature anomalies in July were identified as
contributing factors to the recurrent outbreaks in the subsequent years.
Relevance
Climate change can lead to significant shifts in the
geographic and seasonal distribution ranges of
vector‐borne diseases in Europe (Semenza and Menne,
2009), but there remain significant knowledge gaps
related to attributing historical shifts in infectious
disease transmission to climate change, as well as to
projecting future transmission patterns (Altizer et al.,
2013; Rodó et al., 2013; Ostfeld and Brunner, 2015;
Parham et al., 2015).
Climate can affect vector-borne diseases by affecting
the life cycles of disease vectors and the replication
rates of viruses and parasites inside vectors and
human hosts. Temperature increases may shorten
the life cycles of vectors and the incubation periods of
vector-borne pathogens, thereby potentially leading
to larger vector populations and higher transmission
risks, but beyond certain thresholds pathogen growth
in vectors might be interrupted. Over the longer term,
seasonal changes could affect both vectors and host
animals, as well as human behaviours and land-use
patterns, thereby further influencing the geographical
distribution, seasonal activity and overall prevalence of
vector-borne diseases in Europe (Lindgren et al., 2012).
Furthermore, climatic suitability is essential for the
arrival, establishment and spread of 'exotic' diseases
that are not currently established in continental Europe
(Randolph and Rogers, 2010). However, in addition to
climate change, the risk of communicable diseases is
also affected by a wide range of ecological, economic
and social factors, such as land-use patterns and
agricultural practices; biological diversity; the capacity
of public health systems; travel, trade and migration;
and human behaviours affecting individual risk factors
(Jones et al., 2008; Suk and Semenza, 2011; McMichael,
2013). Thus, vulnerabilities to health systems and
populations must also be accounted for alongside
climatic changes when assessing future infectious
disease risks (Suk et al., 2014).
Past trends: tick-borne diseases
Tick-borne encephalitis (TBE) and Lyme borreliosis
(Lyme disease) are the two most important tick-borne
diseases in Europe, both of which are transmitted
primarily by Ixodes ricinus. Lyme disease is the most
common vector-borne disease in the EU, with a
reported incidence of approximately 65 000 cases
per year. However, there is no standardised case
definition or diagnosis for Lyme disease in Europe,
so this number represents only a best estimate. The
number of reported cases of TBE in the EU was 2 560
during 2012. The mean annual reporting of TBE cases
has increased by approximately 400 % in European
endemic areas over the past 30 years, although this is
almost certainly the result of more robust detection
methods and diagnosis (Medlock et al., 2013; ECDC,
2014).
A key determinant of the number of reported cases is
the abundance of ticks, a factor which is sensitive to
climatic variables, notably temperature and humidity.
Currently, Ixodes ricinus is present across much of
continental Europe (Map 5.2). There have already
been reports on the northerly migration of the tick
species in Sweden (Jaenson et al., 2012), and to higher
altitudes in the Czech Republic and Austria (Daniel
et al., 2003; Heinz et al., 2015). Range shifts have also
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