This year, Latin America has recorded the highest number of dengue cases in history, according to the World Health Organization (WHO). This mosquito-borne disease has surged across the region with nearly 3 million cases reported. This figure is more than 20 percent higher than the previous record in 2015.

In an article published by NPR, Brazil leads the list with over 2 million reported cases followed by countries in Central America, including Belize, Honduras and Nicaragua.

WHO describes Dengue fever as a flu-like illness with symptoms such as bad headaches, vomiting, pain in muscles and joints. It occasionally develops into a potentially lethal complication called severe dengue which can cause blood vessels to leak and organs to fail. This year, more than 1,300 people have died from dengue in Latin America. Hospitals across the continent are running short of manpower and facilities to keep up with the number of patients who need care.

The reasons behind the surge range from climatic to viral causes.

Leah Katzelnick, an epidemiologist at the University of California, Berkeley working on dengue in Nicaragua, admits that climate definitely plays a role.

The mosquito species Aedes aegypti which carries the dengue virus lays its eggs in any pool of clean water. Due to the weather disturbances that hit the region this year, "you're just fighting against everything," Katzelnick says. The mosquitoes will breed anywhere as long as there's stagnant water: in a puddle on the lid of a trash barrel or even discarded tires.

This notion is supported by Raman Velayudhan, a mosquito specialist working at WHO, who said climate conditions such as warmer temperatures, high humidity and abnormal rains have contributed to this year's surge. He added that drought also played a huge role in the increase of cases. "If you have less rainfall, people hoard water," he says, which can create places where mosquitoes can breed.

Another reason cited by experts is the emergence of Zika virus.

The Pan American Health Organization (PAHO) reported that rates of dengue dropped to fewer than 600,000 cases per year in the two years following the proliferation of Zika throughout the Latin American region in 2016, the lowest number in the decade.

Gabriela Paz-Bailey, senior epidemiologist at the Center for Disease Control and Prevention's Dengue Branch in Puerto Rico, said that it is possible that the Zika outbreak in the Americas provided some short-term protection against dengue since Zika and dengue are closely related viruses.

Moreover, researchers believe that the antibodies created by the immune system to fight Zika also protect against dengue. However, this immune system response fades after a few years which may have primed in 2019 causing a big dengue surge.

Paz-Bailey added that the nature of Latin American cities could also be a factor. "Increased urbanization provides the right environment for these mosquitoes, in areas with large populations and poor sanitation. And that just provides breeding sites for the mosquitoes next to people."

The WHO also cited economic factors such as changing land use patterns and increased international travel and trade which have brought people into more frequent contact with dengue carrying mosquitos.

For Maurício Nogueira, a virologist in Sao Paulo, the 2019 figures are alarming. But he said the caseload spikes but then comes back down every three to five years because people who recover from dengue are immune to it for a couple of years which leads to lesser dengue virus circulating for mosquitoes to pick up and pass on, thus, lesser dengue cases in Latin America for the next couple of years.