Dengue cases in the Americas have reached an all-time high
Infections with the mosquito-borne virus are surging worldwide
![Mosquito control worker in Brazil](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2019/11/111919_ac_dengue_feat.jpg?fit=1028%2C579&ssl=1)
A worker collects Aedes aegypti mosquito larva in Salvador, Brazil, in July. Ridding homes and neighborhoods of pools of standing water, where mosquitoes breed, can help to stop the spread of dengue.
Joa Souza/Shutterstock
The Americas set a gloomy record in 2019: the most dengue cases ever reported. More than 2.7 million cases of the mosquito-borne disease have struck the region, largely in Brazil, the Pan American Health Organization reported on November 13.
Dengue is one of the top 10 threats to global health, according to the World Health Organization, with cases of the viral disease climbing rapidly around the world in recent decades. An estimated 390 million dengue infections occur each year, which can be mild or cause flulike symptoms and headaches. Less commonly, dengue can lead to a severe, life-threatening illness. South Asian countries including Pakistan, Bangladesh and Nepal have also been slammed with large dengue outbreaks this year (SN: 10/7/19).
The last record-breaking year for the Americas was 2015, when there were more than 2.4 million cases. After that, cases dropped slightly in 2016 and then precipitously in 2017 and 2018, coming in below 600,000 each of those years. “Dengue is endemic in the Americas, with cycles of the epidemics that are repeated every three to five years,” says Jose Luis San Martin, an advisor on dengue and other mosquito-borne diseases for PAHO in Washington D.C. “During those two years there was an accumulation of a large number of people susceptible to the disease.”
That may seem like too short a time for so many people to be vulnerable again to dengue, transmitted by the bite of an Aedes aegypti mosquito. But dengue outbreaks are complicated by the fact that there are four different types of the virus. Infection with one type provokes the development of antibodies that provide lifelong immunity to that type. Those antibodies can initially protect against other types, but that effect is temporary, lasting roughly one to three years.