The fast-spreading Zika virus is likely being under-diagnosed in South-East Asia, infectious disease experts have warned in several reports, including that of an Australian who was infected after a monkey bite in Bali.
The virus, which is being investigated for links to potentially fatal defects in unborn babies in South America, is believed to have been transmitted primarily by mosquitos, with only rare reports of exceptions.
Global fight ramps up against Zika
Governments around the world mobilise to combat the Zika virus, which is spreading rapidly from Brazil where it is blamed for thousands of devastating birth defects.
But the authors of a report into the case of a 27-year-old Australian man last year have proposed that a monkey bite he received at the Ubud Monkey Forest could have been to blame.
The man was diagnosed with acute Zika virus after arriving at the Royal Darwin Hospital with fever and a rash seven days after the bite, the report states. He'd also been bitten by mosquitos while holidaying in Bali.
The authors of the report, including doctors from the hospital and academics from the Victorian Diseases Reference Laboratory and the Menzies School of Health Research, wrote that while mosquito-borne transmission was possible,the monkey was a plausible route of transmission.
They also noted the virus has similar symptoms to other viruses, such as dengue fever, and the limited availability of the test to detect Zika virus in Indonesia.
"Transmission of Zika virus by monkey bite or other (non-mosquito) routes, and attribution of illness to dengue or other infections, may be more frequent than the absence of prior reports suggests," says the report, published in the Southeast Asian Journal of Tropical Medicine and Public Health in May 2015.
Meanwhile, researchers studying an outbreak of dengue fever at Jambi Province in central Sumatra in early 2015 also pointed out the possibility Zika was being under-diagnosed due to similarities with the common symptoms of other diseases.
While the recent links between Zika and birth defects is causing alarm, experts say 80 per cent of people do not experience sickness when they get the virus. When people are affected, the symptoms are usually mild and include a rash and fever. Most people clear the virus from their blood within a week.
They had stumbled on a 27-year local man who contracted the disease despite having never travelled outside of Indonesia. A report into the case was this week uploaded to the Eijkman Institute for Molecular Biology Indonesia's website ahead of publication in a Centre for Disease Control journal in May.
Frilasita Aisyah Yudhaputri from the institute's virus research unit said while the virus was believed to have existed in Indonesia for some time, the Asian strain of Zika was "mild" and not believed to cause birth defects.
"The one we found is the Asian strain, … the same found in Thailand, the Philippines and Cambodia.It is not the one related to microcephaly (a congenital condition associated with incomplete brain development.)," she said.
A 2013 report into a previously healthy 52-year-old Australian woman who returned home from Jakarta with Zika misdiagnosed as Dengue also suggested it is possible many cases were being missed.
The report said that at the time, this was the first case of a Zika virus infection reported in a returned traveller to Australia although evidence of the virus had been reported in Java, Indonesia.
"However it is likely that many cases are either undiagnosed (because of mild symptoms) or misdiagnosed, presumably most commonly as dengue fever, given their clinical similarities," the report in the American Journal of Tropical Medicine and Hygiene stated.
Dr Mike Catton, from the Doherty Institute's Victorian Infectious Diseases Reference Laboratory, said it was difficult to know whether Zika was being under-diagnosed in Indonesia but said he believed it was unlikely that a "large outbreak" like that being experienced in South America could be overlooked.
He said of 1500 Australians the institute had tested after returning from overseas with an illness, only seven tested positive for Zika since 2012.
"I think that testing is likely to be picking up Zika if it's there in Australian return travellers," he said.
The Department of Foreign Affairs and Trade has not adjusted its travel advice for Indonesia because the transmission of the virus is not considered to be "ongoing" there, a spokeswoman said.