Brazil has a Dengue emergency, portending a health crisis for the Americas

Brazil is experiencing an enormous outbreak of dengue fever, the sometimes fatal mosquito-borne disease, and public health experts say it is a harbinger of a coming surge in cases in the Americas, including Puerto Rico.

Brazil’s Health Ministry warns that it expects more than 4.2 million cases this year, outstripping the 4.1 million cases the Pan American Health Organization recorded for all 42 countries in the region last year.

Brazil was due for a bad dengue year – numbers of cases of the virus typically rise and fall on a roughly four-year cycle – but experts say a number of factors, including El Niño and climate change, have significantly amplified the problem this year.

“The record heat in the country and the above-average rainfall since last year, even before the summer, have increased the number of mosquito breeding sites in Brazil, even in regions that had few cases of the disease,” Brazilian Health Minister Nísia Trindade said.

Dengue case numbers have already soared in Argentina, Uruguay and Paraguay in the last few months.

“When we see waves in one country, we will generally see waves in other countries; that’s how interconnected we are,” said Dr. Albert Ko, an expert on dengue in Brazil and a professor of public health at Yale University.

The World Health Organization has warned that dengue is rapidly becoming an urgent global health problem, with a record number of cases last year and outbreaks in places, such as France, that have historically never reported the disease.

In the United States, Dr. Gabriela Paz-Bailey, chief of the dengue branch at the division of vector-borne diseases at the Centers for Disease Control and Prevention, said that she expected high rates of dengue infection in Puerto Rico this year and that there would be more cases in the continental United States as well, especially in Florida, as well as in Texas, Arizona and Southern California.

Dengue is spread by Aedes aegypti, a species of mosquito that is becoming established in new regions, including warmer, wetter parts of the United States, where it had never been seen until the past few years.

Cases in the United States are still expected to be relatively few this year – in the hundreds, not millions – because of the prevalence of air conditioning and window screens.

This article originally appeared in The New York Times.