Dengue is a seasonal, mosquito-borne disease commonly found in hot, wet regions of the tropics and subtropics during the rainy months.

Add to the mix inadequate or unprepared health services and the circulation of a virus, and you have the ingredients for an outbreak of epidemic proportions -- and one that is likely to spread.

The 'break-bone' fever and climate crisis

Dengue-carrying mosquitoes thrive in urban areas and lay their eggs in shallow pools of water, in household containers, buckets, even upturned bottle caps. But environmental changes can affect how quickly viruses replicate in mosquitoes and how long they live, increasing the risk to humans.

"As the average temperature increases the survival of mosquitoes and the actual replication of the pathogen with mosquitoes becomes more efficient," said Dr. Rabindra Abeyasinghe, Coordinator of Malaria, Other Vectorborne and Parasitic Diseases, at the WHO's Regional Office for the Western Pacific. "So the mosquitoes only need to survive for shorter periods of time."

Erratic weather makes it harder to predict outbreaks

"Climate change is altering weather patterns across the globe. Seasonality is changing, we're having less predictable extreme events," said Dr. Rachel Lowe of the London School of Hygiene and Tropical Medicine.

Lowe said that these changing patterns can cause the dengue season to shift "making it harder to know when and where an epidemic might occur."

Abeyasinghe said it is one thing to have an intensive monsoon season where it rains steadily for a few weeks, but quite another to have showers that "are scattered over a number of months, creating multiple opportunities for mosquito breeding and prolongs the survival of mosquitoes as opposed to a short, monsoon season."

Modern lifestyles are also to blame

But climate is just one factor in dengue's spread. We travel around a lot more than 50 years ago and it's not just souvenirs that we bring back from trips abroad.

"People are able to travel across the globe within a few hours and that certainly facilitates the spread of dengue and can allow the virus to establish in places where it wasn't before," Lowe said.

Even global trade can contribute to allowing invasive mosquito species to establish in new places as the insects and their eggs can be transported in tires, shipping containers, and even hitch a ride on planes. Some airlines, particularly in Australia and New Zealand, spray commercial planes to kill any mosquitoes on board before passengers disembark.

There is a growing chorus among experts saying it's time policy makers start to prepare for the consequences of climate change and its affect on the spread of infectious diseases.

Rezza said lessons should be learned from outbreaks of West Nile virus in North America and chikungunya in the Caribbean and Italy to "highlight the importance of assessing future vector-borne disease risks and preparing contingencies for future outbreaks."

Stopping the dengue menace

It's called Wolbachia and scientists at the program inject it into mosquito eggs to make them dengue-resistant and then release the eggs or the fully-grown mosquitoes into communities where dengue is prevalent.

"In each country we are working on, we've got a growing body of evidence that this seems to be a practical and effective way of stopping dengue," said Peter Ryan, Director of Business Development for The World Mosquito Program.

In ongoing field trials in 10 countries around the world, the team has found that mosquitoes passed the Wolbachia bacteria on from generation to generation -- meaning those mosquitoes did not transmit dengue.

The program has been a success in northern Queensland, Australia, where the first trials were held in 2011.

"We've seen almost complete elimination of dengue from areas in northern Queensland where we have now successfully implemented Wolbachia. That's 300,000 people living in areas that had suffered from the scourge of dengue almost every year from the 1980s onwards and we have seen a complete collapse now."

Trials in Vietnam and Indonesia are also delivering positive results.

"The challenge is, how do we scale this quickly to make it an affordable intervention," Ryan said. Their aim is to lower the cost of the program to about $1 for every person it helps, so it can be rolled out in some of the world's poorest nations. Field trials are expected to end in about 18 months.

Progress is being made on the climate front too. Lowe's team is looking at how countries with dengue can set up early warning systems to predict future abnormal climate conditions and help prepare for potential outbreaks.

"We can no longer rely on seasonal averages or average conditions to decide when dengue is going to peak," Lowe said.

"We need to be thinking about how each place is linked up with other endemic areas, we need to be thinking about the climate conditions and unexpected extreme climactic events, which can change the time intensity of outbreaks."

Until scientists find an affordable way to stop dengue from spreading, the WHO is focusing on educating people about the disease -- and preventing more deaths.

"What we are encouraging countries to do is focus on better management of patients," Abeyasinghe said. "Because if you manage the patient and you prevent the deaths, what we basically do is we turn dengue into a sort of normal flu-like thing. Which comes and goes."