Frightening outbreak of deadly fever linked to climate crisis

The climate crisis has led to a sharp rise in dengue fever cases in the Pacific islands, with infection rates reaching their highest in a decade and several countries declaring a state of emergency, experts say.

Pacific island countries and territories have reported 16,502 confirmed cases and 17 deaths since the start of 2025, according to the Pacific Syndromic Surveillance System (PSSS), which collaborates with the World Health Organization (WHO) and other agencies. The region's case rate is at its highest since 2016, according to the WHO. Fiji, Samoa and Tonga are among the worst-hit countries, The Guardian reports.

Dr Paula Vivili, deputy director general of the Pacific Community (SPC), said that historically, dengue outbreaks have been seasonal. “However, due to climate change, transmission seasons are lengthening and in some areas there is a year-round risk of dengue infection,” Vivili said.

Dengue fever, a viral disease spread by Aedes mosquitoes, causes high fever, severe headaches, joint and muscle pain, rashes and, in severe cases, death, The Guardian reports. Rising temperatures, rainfall and humidity create ideal conditions for Aedes mosquitoes to breed, even in areas previously unsuitable for transmission.

“Dengue fever is one of the first real climate-related diseases that we can attribute to climate change,” says Dr. Joel Kaufman, an epidemiologist and director of the Center for Exposure, Disease, Genomics, and the Environment at the University of Washington.

“Rainfall increases the water level of mosquito eggs laid just above the surface, which then hatch into larvae – part of the natural breeding cycle. Heavy rains can also cause water to stagnate in springs, creating more opportunities for mosquito breeding,” the epidemiologist said.

Dr Kaufman warned that the outbreaks point to a wider public health problem: “This will certainly be at the forefront of many types of human diseases that become more common and severe as the planet warms.”

Since the outbreak was declared in April, Samoa has confirmed six dengue deaths, including two siblings, and more than 5,600 cases. Fiji has recorded eight deaths and 10,969 cases so far this year. Tonga has recorded more than 800 cases and three deaths since the outbreak was declared in February.

The outbreaks highlight the region's vulnerability to climate-sensitive diseases, which are expected to worsen as global temperatures rise, The Guardian notes.

According to the Intergovernmental Panel on Climate Change (IPCC), Pacific Island countries produce just 0.03% of global greenhouse gas emissions but face some of the most serious climate-related health threats, including vector-borne diseases.

According to New Zealand's National Institute of Water and Atmospheric Research (NIWA), parts of the Pacific Ocean, including Palau, Papua New Guinea and the Solomon Islands, have seen heavy rainfall in recent months, while severe drought has affected parts of the Marshall Islands, Papua New Guinea, Nauru and Fiji. Forecasts show these contrasts will continue into October.

While increased rainfall has been linked to ideal breeding conditions for mosquitoes, Kaufman notes that extreme weather events can also contribute to the spread of mosquito-borne diseases. According to NIWA, significant parts of the Pacific experienced severe to very dry conditions in the first half of the year.

“We might think that drought would reduce the number of mosquito-borne infections, but that doesn’t seem to be happening,” says Dr. Kaufman. “Instead, there’s an acceleration of transmission.”

“Existing disease surveillance systems are rarely sufficient to combat dengue fever, as evidenced by the continued rise in dengue cases in the region and globally,” acknowledges Dr. Bobby Reiner, a disease ecologist at the Institute for Health Metrics and Evaluation at the University of Washington.

Mosquito control measures are methods used to reduce the population of Aedes mosquitoes that spread dengue fever, such as removing breeding sites, applying larvicides, or spraying insecticides. They may also include biological control, personal protective measures, and community clean-up campaigns to prevent mosquito bites and transmission.

However, Rainer notes that many mosquito control measures have never been shown to reduce transmission, and most responses have been reactive and often “wastefully chasing an outbreak, arriving too late.”