The Animal Health Trust (AHT) is warning dog owners in the UK over seasonal canine illness (SCI) after reporting that cases have occurred on all five of its study sites since August 2012.
Earlier this year, the AHT warned that cases of SCI had been identified in national parks in Nottingham, Suffolk and Norfolk.
The disease can be treated with pet meds but can be fatal if left untreated. Symptoms include vomiting, diarrhoea and lethargy between 24 and 72 hours after walking in woodland.
To learn more about SCI, the AHT launched an online questionnaire for dog owners who have walked in the affected sites.
Charlotte Robin, SCI research co-ordinator at the AHT, said: "We need dog owners to help us in two ways. Firstly, by completing our online SCI questionnaire - the more information we can gather through the questionnaires the better chance we have of identifying the cause of this mystery illness.
"Secondly, we hope dog owners will help us to spread the word about SCI to other dog owners."
If owners suspect their dog is suffering from SCI, they are advised to seek medical treatment immediately.