New Era Vets said it was treating the animal for strangles, which can be transmitted by contact between infected horses or by some other agent, including humans, equipment, and other animals.
The horse has been isolated since it arrived in the Island two weeks ago and New Era said they were confident it was an isolated case.
In a statement on Facebook it said: ‘We have a horse under treatment which has provisionally tested positive for strangles. The horse has been isolated since its arrival in the Island approximately two weeks ago and there has been no movement on or off the yard since its arrival.
‘It was tested for respiratory diseases as soon as the first symptoms appeared and strict bio-security has been in place since initial examination. The horse and yard owner have been extremely co-operative and have behaved entirely responsibly.’
It added: ‘Under these circumstances the likelihood of disease spread is low, and we are not recommending restrictions on any riding events at present. We would, however, remind horse owners of the importance of basic bio-security, as this and other infectious diseases are widespread in UK and France at the moment and could appear in the Island at any time.
‘Strangles is a bacterial disease which is highly infectious between horses and can be transferred by people or shared objects. It is not a notifiable disease, so there are no government controls over movements etc during an outbreak, only voluntary restrictions.’
Strangles had not been seen in Jersey for 25 years until last year when a miniature horse in St Ouen was diagnosed.
Retired race horse Purley Queen then contracted the disease in an unrelated case, which led to the postponement of a meeting of the Jersey Race Club.
Acting on the advice of veterinary officials, all race horses were blood-tested for the infection and racing resumed the following week.
Last month outbreaks of the unrelated infection equine flu led to a six-day horse-racing shut-down in the UK and further cases have been confirmed in recent days.In the first six months of 2019 eight times as many flu cases have been reported among UK horses as in the whole of last year.
New Era said while there were no legal powers to control imports of horses from the UK to Jersey, they strongly recommended delaying importation until the equine flu situation in the UK was clearer.
They added that anyone still wanting to import a horse should get a full vet health check for the animal and make sure the horse has had a flu vaccination within the last six months.
Strict isolation is then recommended for two to three weeks following arrival in Jersey.
The Jersey Race Club season is due to get under way on Easter Monday, 22 April.
