Authorities in Queensland are monitoring 83 horses across six properties in what has developed into the worst string of Hendra cases since the disease was identified in 1994.
In all, 12 horses across Queensland and New South Wales have died from the infection in less than a month.
Companion horses are automatically placed under a testing regime and subjected to fortnightly blood tests of a six-week period to confirm they are clear of the bat-borne virus.
Queensland's chief veterinary officer, Dr Rick Symons, said it would take three rounds of negative test results to clear each property of Hendra virus infection.
"We will then release the quarantine. This takes around 35 days from the time the property was quarantined," Symons said.
"In total, about 250 tests will need to be run to clear all of these animals.
"No test results from the horses we are currently monitoring have returned as positive and none of these animals are currently showing any clinical signs of Hendra virus infection.
"As has been our approach throughout these incidents, we will keep the community informed of the progress of the results and of any significant findings."
Symons said there had clearly been a heightened awareness among vets and horse owners about the possibility of Hendra virus infection when horses became sick.
Biosecurity Queensland is now receiving about 25 samples for testing per week from locations throughout the state.
Before the current incidents, Biosecurity Queensland was receiving five samples per week.
In New South Wales, a total of four horses have died from the disease in the current run of cases.
Two died on one property near Wollongbar and single horse deaths occurred on properties near Macksville and Lismore.