What is Seasonal Canine Illness (SCI)

Seasonal Canine Illness (SCI) is a rare but serious condition that can affect dogs of any age or breed, typically during the autumn months (August–November). It develops quickly and can be life-threatening, with symptoms sometimes worsening within hours. 

The exact cause of SCI is unknown. Some dogs affected have recently walked in woodland areas, and there is ongoing concern about harvest mites, although other theories such as algae exposure or agricultural chemicals have been suggested. 

Written by Dr. Mariella Roberts, Veterinary Surgeon, Animal Trust Vets CIC | Published October 2025 | Review date October 2028 | This advice is for UK pets only and is not a replacement for seeing a vet