Longleat Safari Park near Warminster has said it's open for business despite quarantining its monkey enclosure after one of the primates was found to be infected with the deadly simian herpes virus - which is fatal to humans.

Keepers at Longleat, which is visited by 800,000 people every year, made the discovery during a routine test.

They immediately closed their Monkey Jungle drive-through enclosure and placed all 100 Rhesus Macaques in quarantine after a female tested positive.

The rest of the colony have now been proven free of the disease but the attraction remains closed as a safety precaution pending further tests.

Simian herpes can be transmitted from monkeys to humans through a bite, scratch or spit and 80 per cent of people who contract it die because there is no cure.

Keith Harris, head warden at Longleat, today confirmed the closure of the monkey enclosure and revealed they are now investigating how the virus arrived.

He said: "After carrying out routine testing of the monkey colony one single female tested positive for simian herpes.

"The whole group has now been tested and all have proven to be negative bar this one female.

"Despite this, Longleat has taken the decision to keep the Monkey Jungle closed to drive-through traffic until further tests on this individual have been undertaken.

"Longleat is working with all relevant professional authorities to try and establish how the positive reading has occurred in a closed negative colony."

The Monkey Jungle at Longleat was closed on November 2 last year while tests on its 100-strong colony were carried out.

But the drive-through enclosure was shut down for good just ten days later when one result from a female monkey came back positive.

In December 1997, research worker Elizabeth Griffin, 22, died of the simian herpes B virus at the Yerkes Regional Primate Centre at Emory University, Atlanta, USA.

She had been splashed in the eye with monkey spittle two weeks earlier and did not seek medical attention.

Although the disease is rare, with only 40 recorded cases in the world, humans infected with the bug have an 80 per cent fatality rate.

Monkeys, however, show no ill effects from the virus, which causes flu-like symptoms before attacking the central nervous system and brain.