Dengue fever is scorching through the Pacific Islands, with Fiji reporting nearly 2000 cases and American Samoa reporting a year's supply of cases last month alone.
Samoa, Tonga, New Caledonia, Kiribati and Palau are also reporting unusually high levels of the virus.
Dengue fever, transmitted to humans through mosquito bites, is severely painful, debilitating and at times deadly.
The outbreak has swept across Fiji in recent weeks. The central region, with almost 1300 cases, and the west are worst hit.
Health authorities in American Samoa say the virus has killed a 10-year-old boy and affected almost 200 so far this year. Most of those cases have occurred in the past six weeks.
Last year the nation had 109 cases.
The New Zealand Government's travel advice warning to the Pacific Islands is cautioning travellers about the recent upsurge of the fever.
Thailand and Brazil's Rio de Janeiro also have high levels, it says.
"As there is no vaccine to protect against dengue fever, travellers are advised to use insect repellent, wear protective clothing, and stay in lodgings where there are mosquito screens on windows and doors."
Those returning from the Islands who fear they may have contracted the virus on their trip, or feel unwell in their first two weeks back, are urged to seek immediate medical advice.
Ministry of Health public health medicine senior adviser Dr Andrea Forde said New Zealand did not have health checks at the border.
"So there is no way of determining whether a New Zealander returning from overseas is infected with a specific disease like dengue until they seek medical care."
Dengue fever outbreaks tended to come and go in the Pacific, said Dr Teuila Percival of Auckland University's Pacific Health Research Centre.
Dr Percival herself contracted the fever in Samoa years ago, and said despite its low fatality rate dengue was "not something you ever want to get".
"It is horrible. At its worst it can kill, it can make you basically bleed from everywhere, into every organ. But at its mildest it's still horrible."
She said the common form of the fever felt like a severe flu.