By Anastasia Moloney
BOGOTA, Aug 28 (Thomson Reuters Foundation) - Central America is grappling with its worst outbreak of dengue fever in decades - and scientists say the disease is likely to spread and become more frequent in the future due to climate change.
Worst hit is Honduras where about 109 deaths from the mosquito-borne disease have been recorded, many among children, making this year's dengue fever outbreak the deadliest on record in the Central America nation, the United Nations noted.
Also hard hit in Central America are Nicaragua, El Salvador, and Guatemala, with other Latin American nations such as Brazil, Paraguay, Colombia and Belize also affected, according to the Pan American Health Organization (PAHO).
Across Latin America and the Caribbean, dengue cases are rising. At least 2 million people have caught the disease so far this year and more than 720 have died, according to PAHO, the regional arm of the World Health Organization.
"We have seen dengue cases in the Americas double each decade since the 1980s and this year is particularly severe," said Rachel Lowe, a London School of Hygiene and Tropical Medicine professor who researches the impact of environmental change on infectious diseases.
The dengue virus is spread by biting Aedes aegypti mosquitoes - the same species that carries other diseases such as chikungunya, Zika and yellow fever.
While no single dengue outbreak can be linked directly to climate change, scientists say warming temperatures, changing weather conditions and more extreme weather from torrential rains to drought can fuel outbreaks.
"Climate change is altering the climate patterns we expect. These shifting rainfall patterns can change the timing and intensity of outbreaks," Lowe said.
"One thing we have seen from my research is certainly that warmer temperatures and rainfall can increase the risk of dengue outbreaks," she told the Thomson Reuters Foundation.
As climate change strengthens, dengue and other mosquito-borne diseases are expected to expand into new communities living in highland regions.
"As the temperature warms, mosquitoes can survive at higher altitudes and then people who haven't previously been exposed to different infections, and don't have immunity to the diseases, are more susceptible," Lowe said.
People living in densely populated slum areas with no running water or proper sewage and rubbish collection systems are particularly at risk of catching dengue, she said.
During heavy rainfall, slums often flood because drains are non-existent or blocked, leaving puddles of stagnant water outside people's homes where mosquitoes can breed.
During periods of rain and drought, slum dwellers often store water in buckets and collect rain water in roof-top tanks. Water also collects in discarded tyres and among rubbish. All are ideal breeding grounds for mosquitoes, Lowe said.
"Drought conditions can also increase the probability of dengue outbreaks mainly due to the way that people store water in response to water shortages," she said.
"If those water storage containers are not well maintained and are not covered, they create additional breeding sites."
Lowe said research she is carrying out in Brazil's Amazon, "shows that both extreme rainfall and drought could increase the probability risks of dengue outbreaks".
Research from Barbados, published last year, also showed drought, followed by wet and warm conditions, provides "optimum conditions" for an outbreak to occur, Lowe said.
MORE BIG OUTBREAKS
Colin Carlson, who models which temperatures best spur mosquito-borne disease transmission, said there is a consensus among scientists like himself that outbreaks are likely to become more frequent and occur in new areas.
"We are going to see more big outbreaks and we are going to see them in new places," said Carlson, from Washington-based Georgetown University's biology department.
Warmer temperatures - up to a certain point - favour mosquitoes, which do "a really good job of transmitting" disease when temperatures reach around 29 degrees Celsius (84 Fahrenheit), Carlson said.
"In the next 10 to 20 years, there is absolutely going to be an expansion of Aedes aegypti-borne disease into new places, facilitated by warming temperatures," Carlson said, adding that places in the United States, including Florida, are at risk.
"More and more areas, not just in the Americas, but in the world .. are moving into the right thermal window," Carlson said.
A 2018 study published in the Proceedings of the National Academy of Sciences (PNAS), showed that combating global warming could have a significant impact on lowering the incidence and spread of dengue fever in Latin America.
"If we could keep global temperatures at the 2 degree Celsuis target (3.6 Fahrenheit) ... that should prevent about 3 million dengue cases in Latin America and the Caribbean every year," Carlson said.