The World Health Organization rates dengue as the most dominant mosquito-borne viral disease in the world as its incident rates have increased 30-fold in the past 50 years.

And new research shows how climate change, bringing hotter and wetter weather, is creating a more ideal home for these disease-spreading pests.

Dengue is carried by the Aedes aegypti and Aedes albopictus mosquitos. The illness can cause severe fevers, headaches, and bone and joint pain. Symptoms usually increase in intensity with every subsequent infection in the same person.

There are no vaccines for it and the best preventative measures appear to be avoiding being bit by an infected mosquito.

Dengue is now endemic to 100 countries, causing up to 50 million infections a year and 22,000 deaths, mainly among children.

In the United States, cases of dengue have historically happened in the warmest locations, such as south Texas, Florida, Hawaii, and Puerto Rico.

In 2005, there was a large outbreak break along the Texas-Mexico border, but it caused no deaths. Upon investigation, researchers found an “abundant” winter population of Aedes mosquitoes, living and breeding in water inside old tires and buckets in Brownsville and Matamoros.

But new findings have determined dengue is now endemic to China, the most populous country in the world. That nation had an outbreak in 2014 that infected more than 40,000 people.

Read More: Get the Facts on Dengue Fever »

Dengue Exposure Year Round in China

New research published in the American Journal of Tropical Medicine and Hygiene shows that dengue can persist in parts of southern China long past the seasonal incubation period.

Previously, the consensus was that dengue was transported into China from elsewhere, as it had historically

“We now have compelling evidence that dengue can persist in China — in some cases up to six to eight years,” lead investigator Rubing Chen, Ph.D., an evolutionary virologist at the University of Texas Medical Branch, Galveston, said in a press release. “Further, we found a surprisingly complex and diverse mix of viral subtypes represented in China, a factor that can mean greater risk of epidemic dengue in the future.”

The researchers say China faces a substantial threat of dengue infections because of its hot, humid climate and large populations in its southern region. 

Using genetic testing, the researchers were able to identify more than 70 different variations of the four types of the virus that cause dengue.

“Even within the same year, a person can catch dengue more than once if distantly related variants are circulating in the same region,” Chen said. “That's why we become concerned about public health when many variants are found, as was the case in our study.”

Read More: Scientists Genetically Engineer ‘Dead End’ Mosquitos to Fight Dengue »

Climate Change Encouraging Dengue Spread

Delhi, India is currently in the midst of the worst dengue outbreak since 1996, with more than 10,000 confirmed cases and more than 40 reported deaths. Hospitals in the capital city are reportedly at maximum capacity.

Humidity is one of the biggest environmental drivers of dengue and other vector-borne diseases as mosquito populations thrive in wet and moist conditions.

With climate change and population growth factored in, some experts estimate that 50 to 60 percent of the Earth’s population in 2085 will be at risk of dengue.

Without climate change, that number would fall to 35 percent, according to a study published in The Lancet.

“On the assumption that other factors affecting dengue fever transmission remain the same, we forecast that climate change will contribute to a substantial increase in the number of people and proportion of global population at risk of dengue fever,” the study authors wrote in their conclusion.

Read More: Climate Change Could Be Devastating to Global Human Health »

El Niño to Accelerate Dengue

The El Niño that’s building in the Pacific is expected to be one of the warmest and wettest weather events in the past 20 years.

It’s also expected to spur the spread of dengue throughout areas around the equator.

The last strong El Niño in 1997-1998 directly affected dengue transmission with a reported 3.5 million people infected in Southeast Asia.

Studying these patterns, an international team of researchers found that the two- to five-year infection cycles were related directly to the increase in oceanic temperatures.

They published their findings earlier this month in the journal Proceedings of the National Academy of Sciences