All horse movements are banned as state officials work to break the 2-2 deadlock in positive and negative tests.
Fears have eased slightly, with the two results from one lab both proving negative, but another laboratory has returned positive tests.
The lockdown will remain in place until biosecurity staff are satisfed the repiratory illness in the horse in not equine flu.
Symptoms in the horse are not severe and biosecurity staff are contacting other horses known to have been in contact with the sick animal in recent days.
Given the highly contagious nature of the disease, each hour that passes without further reports of sick horses only improves the odds of the sick horse being free of the disease.
In New South Wales and Queensland, the number of infected properties continue to climb. There are 4259 such properties in NSW, with 407 labelled "dangerous contact" and 462 officially "suspect".
Queensland had 1014 infected properties as of yesterday, an increase of 67 on the day before. The recognised infected area now covers 2354 square kilometres.
Vaccination programmes are continuing in both states.
The NSW Department of Primary Industries is seeking to identify horses currently unaffected by the disease within the purple and red zones, with plans to vaccinate these animals.
NSW biosecurity officials say the priorities for vaccination are in the following order: