Dog owners are being warned about the possible recurrence of Seasonal Canine Illness (SCI), which is expected to return from late August.
The Animal Health Trust (AHT) is urging dog owners to seek medical attention if their dogs show any signs of the disease, which include vomiting, diarrhoea and lethargy.
Dogs appear to catch the disease after walking in woodlands and symptoms usually appear between 24 and 72 hours.
SCI claimed the lives of several dogs during the autumn of 2009, 2010 and 2011. Previously affected sites include Clumber Park and Sherwood Forest in Nottinghamshire, Rendlesham Forest in Suffolk, and the Sandringham Estate and Thetford Forest in Norfolk.
Dr Richard Newton, of the AHT, said: "Our SCI investigation has been ongoing since we were first alerted to the illness.
"Thankfully the number of dogs which are surviving has increased. We hope this is due to more owners being aware of the signs of SCI and accessing veterinary help as soon as possible."
Dog owners who use any of the five sites being investigated are being asked to fill out an online questionnaire as even if they do not become ill, the information gathered will help the AHT's investigation. This can be found on the AHT website.
Anyone who suspects their dog may be suffering from SCI is advised to seek immediate vet treatment.