There is evidence that climate change can influence the occurrence and severity of Summer Eczema (Insect Bite Hypersensitivity, IBH) in horses. The connection is considered biologically plausible and is supported by studies, even though climate change is not the sole cause.
What is Summer Eczema?
Summer eczema is an allergic reaction to the saliva of biting insects, especially midges of the genus Culicoides. Affected horses develop severe itching, particularly on:
- Mane crest
- Tail dock
- Belly seam
- Head and ears (depending on the insect species)
How does climate change influence summer eczema?
1. Longer insect season
Milder winters and earlier springs allow midges to become active earlier and remain active later in autumn. This extends the time horses are exposed to the insects.
Evidence: The development and activity of Culicoides species depend heavily on temperature and humidity. Warmer conditions prolong their active period.
2. Increase in insect population
Higher temperatures accelerate larval development. Moist soils after heavy rain or floods create additional breeding grounds.
However, extreme drought or prolonged heat can also reduce local populations. The effect therefore varies regionally.
3. Spread to new regions
Several Culicoides species are spreading northwards in Europe and to higher altitudes. This means that diseases that were previously rare are now more common in areas that were less affected.
Other influencing factors
Climate change alone does not cause summer eczema. Other crucial factors include:
- genetic predisposition
- individual immune response
- housing conditions
- proximity to wetlands
- pasture management
What does this mean for horse owners?
The following measures are considered particularly effective:
- Apply an eczema rug before the midge season begins.
- Reduce turnout during dusk and at night, as midges are particularly active then.
- Choose pastures with as much wind as possible (midges fly poorly in wind).
- Avoid damp areas and standing water near the stable where possible.
- Use insect repellents targetedly.
- For severely affected horses, establish a treatment plan with a veterinarian early on.
Conclusion
Current scientific knowledge suggests that climate change indirectly increases the risk of summer eczema by altering living conditions for midges and extending their activity period. However, whether individual horses are actually more affected also depends on their genetic predisposition, the regional insect population, and housing conditions.
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Scientific sources include:
- World Organisation for Animal Health – Information on the biology and distribution of Culicoides as disease vectors.
- European Food Safety Authority – Assessments on the spread of Culicoides and the effects of climatic factors.
- Intergovernmental Panel on Climate Change – Reports on the effects of climate change on vectors and vector-borne diseases.
- Mellor PS, Boorman J, Baylis M. Culicoides biting midges: their role as arbovirus vectors. Annual Review of Entomology (2000).
- Schaffartzik A. et al. Studies on Insect Bite Hypersensitivity (IBH) in horses, published in veterinary journals.