Climate change: a ticking time bomb for vectorborne diseases

Author(s): Jesslyn Thay , Date: 28 October 2021

One Health day is acknowledged globally on 3rd November, as a day to raise awareness of interconnectivity of human, animal and planetary health, and how solving health problems needs a more holistic approach with veterinary, environmental and human health professionals all working alongside one another.

In celebration of COP 26 – a global conference on climate change, the UKRI hosted an interactive webinar - Climate Change Bites: how disease-spreading bugs will impact our health and food security under climate change. - with a panel of multidisciplinary experts to discuss the challenges that climate change brings to world health through the movement of disease vectors and crop pests.

The “climate change bites” varied panel reflected the connectedness of One Health with plant disease experts, human disease experts, zoonotic disease experts, ecologists and veterinarians discussing how climate change, and resulting different land use, is affecting the health of humans, animals and the environment – and how we are all extrinsically linked with earth’s weather and climate.

Invasive vectors making a new home

As the climate around us changes, many habitats previously unhospitable to disease vectors are becoming warmer, allowing populations to overwinter and breed in areas that were traditionally unsuitable. Prime examples are invasive mosquitoes, but ticks, biting midges, sand flies and snails, have all seen their habitats increase as the climate warms.  

The ECDC has charted the movement of several invasive insect and tick vectors across Europe over the course of the past two decades. The most notable being the increase in Aedes mosquitoes (Ae. aegypti, Ae. albopictus, Ae. atropalpus, Ae. japonicus and Ae. koreicus) insects responsible for transmitting many vector-borne diseases including: yellow fever virus, dengue virus, chikungunya virus and Zika virus. Their habitat range has spread and are widely found across southern Europe due to concurrent mild winters allowing overwintering of populations.

Urban environments are becoming safe havens for invasive vectors such as the Aedes sp mosquitoes. Experts found that urbanisation (defined by population density or by artificial geographical space) correlates with a significantly higher risk and abundance of Aedes mosquitoes, mainly due to urban environments providing good breeding sites and extending adult survival time through protection against seasonal change.

Ticks and climate change – on the move

Increases in tick populations, in areas where the vectors have traditionally been absent has been noted across North Africa, Eastern Europe and areas of the Middle East. Different species of ticks prefer different environments, but as the climate warms more habitats meet the conditions needed for populations to survive and grow.

Worldwide the majority of people who become infected with a tick-borne disease often are in close contact with livestock or game animals or frequent areas inhabited by wild animals – particularly scrubland and temperate forests. 

Changing land use impacts the levels of vegetation in tick habits making conditions more favourable for nymphs, whereas livestock and game animals such as deer are responsible for transporting ticks across vast distances.

Tick-borne diseases – established and emerging

Wider ranges for ticks increase the population and this increases the risk of them carrying diseases such as Lyme diseaseCrimean-Congo haemorrhagic fever (CCHF)BabesiosisTick-borne encephalitis and Human granulocytic anaplasmosis (HGA), therefore increasing infectious disease risk in humans and animals in contact with ticks.

Tick-borne diseases are found across the globe, with endemic zoonotic viruses found across North America, Central America and the Caribbean and similar diseases widespread across Siberia and Asia. Some endemic diseases are established in localised areas, but there are new emerging diseases being identified regularly – both viral and bacterial.

Climate change mitigation and ticks

In southern India the endemic tick-borne viral haemorrhagic fever Kyasanur Forest Disease claims lives each year. Climate change, changing land use for agriculture – such as plantations, and deforestation are forcing more people into the forest, therefore in contact with ticks carrying the virus.

Experts on the ground noticed that a climate change mitigation campaign of reforestation in southern west India, in areas where Kyasanur Forest Disease is prevalent, is providing more habitat for ticks – causing an increase in cases in forest-dwelling communities.

People dependant of the forest for their livelihoods still work and live in the forest, but as the forest becomes less fragmented the ticks’ ranges have increased, meaning more people are vulnerable to contact with ticks carrying the virus.

Looking forward

To help prevent deaths from vector-borne diseases there needs to be an increasing awareness of insect-borne and tick-borne diseases. This cannot be achieved through public health education and community engagement programs alone, but through cooperation among authorities, data collection and sharing, in addition to creation of partnerships between different disciplines will help overcome some of the risks posed by climate change in the One Health battle against vector-borne disease.

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