The government advises travellers to countries where mosquito-borne illnesses are able to spread to use insect repellent, wear protective clothing, and stay in lodgings where there are mosquito screens on windows and doors. Photo: James Gathany/Center for Disease Control

Travellers are warned to be on the alert for dengue fever, with cases on the rise in the Pacific.

The Cook Islands have been particularly affected, with more than 500 cases reported since the outbreak began in May last year.

Other countries reporting increased dengue activity include Samoa, Tuvalu, Nauru, Kiribati and American Samoa.

The government advises travellers to countries where mosquito-borne illnesses are able to spread to use insect repellent, wear protective clothing, and stay in lodgings where there are mosquito screens on windows and doors.

People who become unwell during or within three weeks of returning from their trip are advised to seek immediate medical advice.

Clinical director of Etu Pasifika, Dr Maryann Heather, has recently treated a patient with dengue fever.

"The main thing is to have a high index of suspicion, especially since there are ongoing outbreaks in the islands," she said.

Dr Heather said dengue could present as a vague viral illness, often accompanied by symptoms like headaches and pain behind the eyes, abdominal pain, nausea or vomiting, muscle and joint pain, skin rash, general lethargy, tiredness, and high fever.

"Symptoms can last up to two to seven days and can be mild or severe. One in four people infected with dengue will get sick."

She said dengue was caused by mosquitoes, specifically those that bite during the day, which transmit the virus to others.

"While dengue can be confirmed through blood tests (dengue serology), it is mostly clinical and awareness of dengue fever outbreak in Pacific countries," she said.

She said there was no specific treatment for dengue, but supportive care was important, including rehydration and taking paracetamol for fever, aches, and pains, along with taking time to recover.

"If you aren't improving or concerned, you should seek medical attention, especially if you think you have dengue fever after returning from the islands."

She said dengue was most common during the wet season in the islands, when there was a lot of rain.

"Prevention focuses on reducing mosquito exposure by eliminating stagnant water around the house, wearing light-coloured clothing, and using insect repellent."

"It's crucial to educate and warn people travelling back to the islands so they are aware that dengue fever is present, especially since it is seasonal."

The Ministry of Foreign Affairs and Trade said that in 2025, in response to requests from four Pacific Island countries, New Zealand's International Development Cooperation assisted in the response to dengue outbreaks and prevention and preparedness efforts for dengue. This included providing funding and deploying professionals.