Race horses in Hong Kong have been infected with equine herpes in the territory’s worst outbreak of the disease, a year before the special administrative region of China is due to host the equestrian event of the Beijing Olympics, the local jockey club said.

A total of 132 horses have fallen sick since February 9 - showing symptoms of mild fever, blood problems and swelling in the legs - and five horses pulled out of races yesterday.

Wilson Cheng, spokesman for the Hong Kong Jockey Club, said: “We’ve never had an outbreak involving so many horses.”

The horses fell sick despite being vaccinated against the virus, but Cheng said that was not a dangerous sign.

“Even if you’re vaccinated against the flu, it doesn’t mean you’re totally immune. You may get mild symptoms, but they can be quickly controlled,” he said.

The Jockey Club said the sick horses recovered within a few days and most returned to training within a week.

It said Hong Kong’s strong surveillance and disease control measures helped limit the impact of a “potentially serious" outbreak.

The South China Morning Post quoted Brian Stewart, a veterinary official for the Jockey Club, as saying the herpes appeared to be spread by shared horse equipment.

The outbreak comes three weeks before the prestigious Queen Elizabeth II Cup race on April 29 and a year ahead of the Beijing Olympics. After Beijing won the bid to host the 2008 Games, it received permission to move the equestrian events to Hong Kong because of concerns about equine diseases on the mainland.

A spokesman for the Olympic equestrian event in Hong Kong said organisers aren’t worried about the equine herpes virus outbreak because it has ordered stringent quarantine measures. Competing horses, which will be kept apart from the local horses, must be quarantined for a week before they depart for Hong Kong and another 10 days after they arrive.

The herpes outbreak is the second major horse safety scare in Hong Kong in recent weeks. On March 21, Jockey Club workers discovered a 12-metre hose that branched out into metal tubes embedded in a race course, a device police said could inflict serious injury to horses.