Scientists investigating seasonal canine illness (SCI), which can kill dogs walked in woodland during autumn, are closing in on the cause.
A pilot study by the Animal Health Trust (AHT) aims to see if harvest mites are to blame.
The mystery illness is most common between August and November.
Dogs show symptoms of vomiting, diarrhoea and lethargy within 24 to 72 hours of being walked in woodland.
In 2010 two dogs died of suspected SCI after walking in Clumber Park, near Worksop.
In 2011 the AHT received two more reports of non-fatal cases at Clumber Park.
Last year saw a spike in reported cases, possibly down to increased awareness and publicity around SCI , with 28 reported cases at Clumber.
But overall the number of fatal cases has fall each year.
Warning signs are now displayed each autumn at Clumber Park.
This year the AHT has had 68 suspected cases of SCI reported at its five study sites Clumber Park and Sherwood Forest, and Rendlesham Forest, Sandringham Estate and Thetford Forest in East Anglia.
Fourteen of these were linked to Clumber Park.
Suspected causes like man-made poisons, toxic mushrooms and plants, blue-green algae and bracken spores are now virtually ruled out.
But a number of this year’s cases showed evidence of harvest mite infestation.
“To enable us to eliminate harvest mites as a potential cause of SCI, we are advising dog owners to treat their dogs with a fipronil spray directly before walking in woodlands,” said Charlotte Robin, SCI research co-ordinator.
“Dog owners need to be aware that using fipronil spray may not protect their dog from SCI. What we are trying to do with this study is eliminate harvest mites and other external parasites from our enquiries.”
• For more information see www.aht.org.uk/sci