A dog belonging to one of my friends may have Canine Seasonal Illness (CSI). I'd never heard of CSI before and as it seems to be important to get your dog to the vets asap if it shows symptoms it seemed like one to be aware of - especially if like me you walk your dog in the woods a lot. I've tried to list the main points I found out about it. It seems to have only been reported in the UK. It is new - Sandringham Estate, Norfolk reported it to the Animal Health Trust in 2010 Cases occur from August to November. Dogs with CSI exhibit symptoms 24-72 hours after being in woodland. The most common symptoms are sudden onset lethargy, diarrhoea and vomiting. Some cases are fatal though as awareness has increased fatalities have reduced. The cause is unknown. Many dogs walk in woodlands where CSI occurs without getting CSI. For more information, you can visit this website of the Animal Health Trust.