BELOVED family pet Lottie died just 24 hours after returning from a walk in Highnam woodland and falling ill.
Now her owners are desperate to find out what killed her and are urging other dog walkers to look out for the signs of seasonal canine illness (SCI), which they fear took her life.
The killer bug was flagged up on BBC show Countryfile and Jennifer and Anthony Marsh, from Highnam, recognised the symptoms suffered by their nine-year-old Labrador, who died last month.
Lottie was regularly walked in Lassington Woods, and Jennifer believes the illness could have been picked up there.
"We took her for two walks that day. When she got home she was very lethargic, had diarrhoea and sickness," she said.
"That night I heard her being sick downstairs and she had vomited up some blood. We took her to the emergency vet who put her on a drip, but she didn't recover and died later that day. It was only when we watched the Countryfile programme that highlighted seasonal canine illness that we recognised the symptoms."
SCI was first recognised in autumn 2009 and has recurred every autumn since. Most cases occur in the last two weeks of August and the first two in September.
Affected dogs develop symptoms between 24 and 72 hours after walking through woodland. Five areas have had the majority of cases – all outside Gloucestershire – the Sandringham Estate and Thetford Forest in Norfolk, Sherwood Forest and Clumber Park in Nottinghamshire and Rendlesham Forest in Suffolk.
Jason Burgess, from the Wood Veterinary Group in Bristol Road, said the bug could be to blame.
"The condition doesn't appear to be passed between dogs and there have been cases where dogs are walked in groups where only one dog is affected and other groups where all dogs are affected.
"Treatment at present involves symptomatic treatment as the exact cause is unknown. Owners who suspect their dog has SCI should contact their vet immediately."
One theory is that the dogs could have had an allergic reaction to bites from harvest mites, but a direct link is yet to be established.
Charlotte Robin, SCI Research Co-ordinator at the Animal Health Trust, said 300 questionnaires from dog owners have been completed to date, with 80 suspected cases of SCI from study sites.
What's SCI? Seasonal canine illness comes on very quickly, usually within 24 to 72 hours of having walked in a woodland area. The most common clinical signs reported are: -Vomiting -Diarrhoea -Tummy (abdominal)pain Lethargy (or reluctance to move) -Loss of appetite -Shaking or trembling -High temperature (fever)