Two cases of monkeypox have been confirmed, one in Melbourne and another in Sydney.
The case in Melbourne is a man in his 30s who developed mild symptoms before returning home from London on May 16, and then sought medical attention.
He remains in isolation at the Alfred Hospital with mild symptoms.
Monkeypox is a viral infection which does not spread easily between people and tends to be mild in presentation.
Dozens of cases have been either confirmed or are under investigation across the US, Canada, Europe and the UK in recent weeks.
It has raised alarm because the disease is usually only found in west and central Africa, and rarely spreads elsewhere.
Meanwhile NSW health authorities have confirmed the virus has been identified in a man who recently returned to Sydney from Europe.
The man, in his 40s, went to his GP with mild symptoms several days after landing in NSW.
It was determined his symptoms were clinically compatible with monkeypox and urgent testing was carried out.
It's the first case to be confirmed in the state.
Chief Health Officer Kerry Chant said the virus was not a cause for panic given its low level of transmissibility between humans.
"Usually, you need to have quite prolonged face-to-face contact," Dr Chant said.
"It is not the same spread mechanism as COVID or the flu, where it [transmission] is more fleeting."
However, Dr Chant said, people should still remain vigilant about potential symptoms of the virus.
"It starts off with fever, muscle aches and pains. You can get those in large lymph nodes, headaches, feeling tired and lethargic," she explained.
"And then it can be followed by a rash one to three days longer. Often the rash starts on the face."
The man and a close contact are now isolating at home with care and support being provided by NSW Health and his GP.
Plane passengers being contacted by health authorities
People who were on the same flights back to Australia as the man who has tested positive in Melbourne are being contacted by Victorian health authorities, and are being asked to isolate only if they develop symptoms.
The affected flights are:
- Flight EY10 which departed London on May 14 and landed in Abu Dhabi at 6:15am
- Flight EY462 which departed Abu Dhabi on May 15 and landed in Melbourne at 5:45am on May 16.
Victoria's Department of Health has begun contact tracing, and some of the man's close contacts will be offered a vaccine, which can be effective up to four days after potential exposure.
The state's Chief Health Officer Brett Sutton also urged people who were on those flights to watch for symptoms.
"Those symptoms are flu-like symptoms, they can be headache, fever, muscle aches and pains," he said.
"Generally people are more unwell than with a mild cold so it can be quite significant constitutional symptoms.
"Then a rash occurs with those typical chicken pox-like lesions that occur — so fluid-filled, pus-filled."
Professor Sutton said there were early indications the "few dozen cases" across Europe and North America were a version of the disease from west Africa that is milder than other forms.
But he said that version of monkeypox still had a fatality rate of between 1 and 5 per cent.
"The transmission of the virus can be through the fluids, the material within lesions in those pox," he said.
"There can also be respiratory transmission for people who are in close contact with each another... or close skin-to-skin contact."
Professor Sutton said the risk of transmission was "not great" and described the monkeypox virus as "rare".
NSW chief health officer Kerry Chant said an alert had been issued to GPs, hospitals and sexual health services across the state to be aware of cases being identified overseas.
"Cases are occasionally reported in non-endemic countries in returning travellers or their close contacts, or in owners of imported pets," Dr Chant said.
"People can contract monkeypox through very close contact with people who are infected with the virus.
"The infection is usually a mild illness and most people recover within a few weeks."
Health experts have added that it's highly unusual for monkeypox to be detected across multiple continents, given the virus does not easily spread from person to person.
University of New South Wales Global Biosecurity Professor Raina MacIntyre, said there's seemingly no known link between the cases.
"At this stage, it looks like there's not a clear relationship from one case to the next and so people are trying to speculate as to why this is and has there been a whole lot of transmission that hasn't been noticed which would be you know asymptomatic transmission."
Monkeypox was first found in monkeys in 1958, but rats are now considered the main carrier.
