IT has killed at least 12 dogs and left two others seriously ill.
Now a mystery toxin that struck fear into the hearts of dog owners across the New Forest is thought to have poisoned another two pets.
One dog managed to fight off the substance but another animal had to be put down.
It comes a year after the first outbreak, sparking fears that the next few months will see another spate of deaths.
But experts are no nearer identifying the toxin, which causes skin lesions and acute kidney failure in its victims.
Most of the initial fatalities occurred at various locations across the Forest between December 2012 and March 2013.
The timing of the two new cases suggest that the cause could be seasonal in nature but the poison’s origin remains a mystery – despite extensive testing carried out by various organisations last year.
Vets alarmed at the possibility of a fresh outbreak are urging dog owners in the Forest to be vigilant.
One of the practices involved in treating the poisoned pets and investigating their deaths is Winchester-based Anderson Moores.
Commenting on the two new incidents vet David Walker said: “The first dog developed skin lesions and went on to suffer kidney problems. It was hospitalised for more than a week but managed to pull through.
“The second animal became ill incredibly quickly and was in hospital for only 48 hours before it had to be put down.”
The dogs are understood to have been infected in the Sway and Wilverley areas of the Forest.
Mr Walker added: “Some of the first cases were presented this time last year and it’s incredibly concerning that it might be starting again.
“A huge amount of testing was done in 2013 but failed to provide a conclusive answer.
“Our message to pet owners is to be vigilant and consult a vet immediately if their dog develops skin lesions.”
One of the 2013 victims was three-year-old Gemma, who died after being exercised at Linwood, near Ringwood.
A Jack Russell called Squibby is one of only three pets known to have survived the toxin. She developed a swollen paw after going for a run near Latchmore Brook and spent nine days on a drip.
No other animal species appears to have been affected by the poison.
The mystery took a new twist last year after it was revealed that similar cases had been reported elsewhere in the UK, including Cornwall, County Durham and Surrey.