On Tuesday, U.S. health officials cautioned clinicians to be on the lookout for dengue cases as the tropical disease set new international records.
The virus, transmitted by mosquitos, has been spreading globally, aided by climate change. In just six months, countries in the Americas have shattered calendar-year records for dengue cases.
The World Health Organization declared an emergency in December, while Puerto Rico declared a public health emergency in March.
Dengue fever is still uncommon in the continental United States, but there have been three times as many cases in the 50 states this year as at the same time last year. Most infections occurred while traveling abroad, and experts say no sign of a new outbreak exists.
However, they also caution that local mosquitos are a threat.
The Centers for Disease Control and Prevention issued a health advisory on Tuesday, advising clinicians to be aware of the symptoms, ask questions about where patients have recently visited, and conduct dengue testing when necessary.
According to researchers, dengue (pronounced DEHN’-gay) is caused by a virus transmitted by a warm-weather mosquito that is expanding its geographic range due to climate change.
Many infected persons do not become ill; some develop headaches, fevers, and flu-like symptoms. Severe cases can result in significant bleeding, shock, and death.
Repeated infections can be quite harmful.
There are four kinds of dengue virus, denoted 1, 2, 3, and 4. When someone becomes infected for the first time, their body produces antibodies against that type for the rest of their lives. Suppose they become infected with another variety of dengue. In that case, the antibodies from the first infection may fail to neutralize the second type, allowing the virus to enter and reproduce in immune cells.
This is a source of concern in Puerto Rico, where type 1 diabetes has been prevalent for the past two decades. Last month, the island recorded its first dengue death of the year.
Given these limitations and other concerns, it has not been extensively adopted. As of late last month, only approximately 140 children had been vaccinated in Puerto Rico since injections became available there in 2022. Sanofi Pasteur has informed the CDC that it will discontinue producing the vaccine.
A separate vaccination developed by the Tokyo-based pharmaceutical company Takeda is not currently licensed in the United States. Others are under development.
Last year, almost 80 nations reported more than 6.6 million illnesses. The World Health Organization reports 7.9 million illnesses and 4,000 deaths in the year’s first four months. It has been especially intense throughout the Americas, including Brazil and Peru.
The numbers have been significantly more modest in the United States, with approximately 3,000 cases reported last year in states and territories. However, it was the worst in a decade, with more local diseases caused by native mosquitoes. The majority were in Puerto Rico, while approximately 180 were in three U.S. states: Florida, Texas, and California.
So far this year, there have been approximately 1,500 locally acquired U.S. cases, almost entirely in Puerto Rico.
Most cases in the continental United States are still caused by people infected while traveling elsewhere.
It is “a traveler’s nightmare” and an increasing international worry, according to Dr. Lulu Bravo, a pediatric tropical disease researcher at the University of the Philippines Manila who collaborated with Takeda on the vaccine.
“When you have an outbreak in a country, tourists might not want to come,” Mr. Bravo explained.
