A female veterinarian who euthanased a racehorse infected with the potentially deadly Hendra virus has a nervous wait to be cleared of the virus after a needlestick injury.

The Department of Primary Industries vet was putting down a thoroughbred, who had recovered from the virus but was deemed a biosecurity threat, when she received a needlestick injury on Friday.

She was admitted to Brisbane's Princess Alexandra hospital and continues to be monitored for any Hendra-related symptoms as doctors wait for blood test results.

She is the third person to be admitted to the hospital for medical surveillance since last month's Hendra outbreak at a Brisbane bayside clinic.

Veterinarian Ben Cunneen and a nurse fell ill with the virus last month after treating horses at the Redlands Veterinary Clinic.

Brisbane Southside Population Health Unit medical officer Brad McCall would not comment on the patients' condition.

But McCall said before the Redlands case there had been four known human cases of the virus - two died and two recovered.

"We have limited information (on this virus) but we do know two people have had this infection and remain well to this day," McCall said.

The Redlands Bay Clinic outbreak is the worse case of infection since horse trainer Vic Rail and 14 horses died from the virus in September 1994.

The latest horse to be put down was the only infected horse from the clinic to recover but despite calls from the owner that the horse be used for research, was put down because of biosecurity fears.

Tamworth was the fifth horse to either die or be put down at the clinic, which continues to be under strict quarantine control.

Biosecurity Queensland chief veterinary officer Ron Glanville said Tamworth's latest blood tests had returned negative for Hendra virus, which was a hopeful sign for the vet who received the needlestick injury.