First highlighted as a problem in the 1960s, the mosquito-borne disease is increasing at a higher rate than any other communicable disease, according to the World Health Organisation.

Last year, Bangladesh experienced its largest-ever outbreak, with 300,000 cases.

In the first three months of 2024, governments in Latin America confirmed more than 3.5 million cases and 1000 deaths.

Last year was also a record year, with 4.5 million cases reported in the region.

What is dengue fever?

Dengue is a mosquito-borne, viral infection that is common in warm, tropical climates, according to the WHO. (The mosquitos that transmit dengue aren't present in New Zealand, in large part thanks to it's relatively cold temperatures.)

Infection is caused by any one of four serotypes, or closely-related dengue viruses. Infection with one gives long-term protection from that serotype, but can make infections from the other serotypes more serious.

A blood test is required for diagnosis.

Most cases are mild, though some can result in hospitalisation or even death.

Symptoms develop from four days after being bitten by an infected mosquito.

Patients often experience a fever, headaches, muscle and joint pain, nausea and vomiting, a rash, and fatigue.

As the disease progresses, some also suffer from respiratory distress, bleeding from the nose and gums, accompanied by a rapid drop in blood pressure leading to shock.

This last symptom is potentially fatal.

Roughly five percent of infections result in serious complications. And hospital care reduces fatality rates to less than one percent in most affected countries.

But outbreaks, which tend to have seasonal patterns, can cause extreme stress on health systems.

Why is it becomming more widespread?

Dengue is a climate-sensitive disease, Professor Cameron Simmons, director of the Institute of Vector-Borne Disease at Monash University, tells RNZ.

It's spread by common biting mosquitoes (various Aedes species) which "love to live where people live".

A combination of climate change and increased urbanisation will lead to more outbreaks, says Simmons, who is also the global delivery director of the World Mosquito Programme.

South-East Asia, Latin American, and the Western Pacific have had outbreaks for decades.

But the disease travels to new places via infected people, where conditions such as natural disasters, use and storage of water, as well as climate, influence whether the mosquito will then happily live and breed there.

"It's a neglected tropical disease. Partly because the countries it impacts are low or middle income. It doesn't kill a lot of people, but it makes people sick and puts them in hospital."

What's the situation in Samoa?

The recent surge in Samoa, with a population of 220,000, was troubling because of its impact on the health system as well as patients and their families, Simmons said.

The country's Ministry of Health declared the outbreak on April 19, after more than 80 cases were reported in the first two weeks of the month.

Since November, 2023, more than 250 lab-confirmed cases have been recorded, with the North-West Upolu and Apia urban areas being the most affected.

The ministry was encouraging people to clean up and remove all stagnant water sources. And to protect themselves from bites by wearing loose clothing covering as much of their body as possible, using mosquito nets and repellent lotions or sprays,

The ministry is planning a mass cleanup of potential mosquito breeding sites, as well as the spraying of "hot spot areas". RNZ has asked for further details.

A recent editorial in the Samoa Observer saysd: "Dengue fever just does not put stress and burden on individuals or families. If an outbreak is declared that would mean additional stress on the already stressed public health system. It would impact schools, workplaces and above all the economy."

Travelling to Samoa?

While the Ministry of Foreign Affairs hasn't issued a specifical travel advisory for Samoa, SafeTravel notes the outbreak and asks people to read up on dengue before travelling.

"New Zealanders travelling or living in Samoa should have comprehensive medical and travel insurance policies in place that include provision for medical evacuation by air," according to the site.

Samoa's Health Ministry says children under the age of 10 and adults over 60 are most at risk of severe illness.

Associate professor of immunology at University of Otago Wellington and associate Pacific dean at the Division of Health Sciences Dianne Sika-Paotonu tells RNZ, travellers from New Zealand should read up on the disease.

"Take appropriate precautions and avoid getting bitten by mosquitoes, but also be on the lookout for any sign of illness.

"Mosquitoes will lay their eggs in or near pools of water. Removing areas of still or standing water from around the home and covering areas where water can pool, will help stop mosquitoes from laying their eggs."

Treatment and prevention

There's no specific treatment for dengue fever but medical care can help manage the severity of the illness.

In terms of prevention: there are two existing vaccines for dengue available overseas, but not in New Zealand.

One is an expensive two-shot regimen and the other can only be given to people who have already had a dengue infection.

A more promising approach appears to be targeting the mosquitoes themselves.

For years, Simmons has been researching and implementing projects that aim to counter outbreaks by rendering mosquitos unable to carry the dengue virus.

The World Mosquito Project cultivates and releases mosquitos that have been infected with a bacterium, naturally occurring in many insects - but not the main carriers of dengue - called Wolbachia.

The bacterium appears to block the mosquitos from transmitting dengue.

"The beauty is we can deploy our infected mosquitos into the community and over time, [the bacterium] stays in the population, as it gets inherited."

Fiji, Vanuatu, and Kiribati recently joined 11 other countries who have participated in the project.

Simmons said the programme was open to "a conversation around whether our approach is a good fit for Samoa", he says.

"Fow now, [Samoa] is stuck with the old method of cleaning up households and spraying some insecticides."

-RNZ.