Health officials warn US doctors about dengue fever as cases rise worldwide

FILE – This 2003 photo provided by the Centers for Disease Control and Prevention shows a female Aedes albopictus mosquito taking a blood meal from a human host. Dengue, a tropical disease caused by a virus, is transmitted by Aedes mosquitoes, a type of insect found in warm climates whose geographic range is expanding due to climate change, experts say. (James Gathany/Centers for Disease Control and Prevention via AP, File)

NEW YORK (AP) — U.S. health officials warned doctors on Tuesday to be on the lookout for dengue cases as the tropical disease breaks international records.

The mosquito-borne virus is spreading worldwide, aided by climate change. In just six months, countries in the Americas have already broken annual records for dengue cases.

The World Health Organization declared a state of emergency in December and Puerto Rico declared a public health emergency in March.

Dengue remains less common in the Americas, but there have been three times as many cases in the 50 states so far this year as at the same time last year. Most infections have been transmitted by travelers abroad, but authorities warn that domestic mosquitoes pose a growing dengue threat.

In a health alert on Tuesday, the U.S. Centers for Disease Control and Prevention advised doctors to monitor symptoms, ask questions about patients’ recent travel destinations and, if necessary, order dengue testing.

Dengue fever (pronounced “DEHN’-gay”) is caused by a virus transmitted by a type of warm-weather mosquito whose geographic range is expanding due to climate change, experts say.

Many infected people do not become ill, but some suffer from headaches, fever and flu-like symptoms. In severe cases, severe bleeding, shock and death can occur.

Repeated infections can be particularly dangerous.

There are four types of the dengue virus, referred to simply as 1, 2, 3 and 4. When someone is infected with dengue for the first time, their body makes antibodies against that type for life. If the person becomes infected with a different type of dengue, the antibodies from the first infection may not be able to neutralize the second type – and may actually help the second type of virus to enter immune cells and multiply.

This is a cause for concern in Puerto Rico, where dengue fever has been widespread over the past two decades. Last month, the island reported its first dengue death of the year.

“We are currently seeing an increase in cases of dengue 2 and dengue 3, for which the population has very little immunity,” said Dr. Gabriela Paz-Bailey, the Puerto Rico-based chief of the CDC’s dengue division.

There is no widely available medication to treat dengue infections.

Vaccines are a tricky business because it has been difficult to develop a shot that protects against all four types of dengue. U.S. authorities recommended a vaccine from Sanofi Pasteur in 2021. The three-dose vaccine is designed to protect against all four types of dengue and is recommended only for children ages 9 to 16 who have a laboratory history of previous dengue infection and who live in an area – such as Puerto Rico – where dengue is common.

Because of these limitations and other problems, the vaccine has not been widely used. As of late last month, only about 140 children in Puerto Rico had been vaccinated since the shot became available there in 2022, and Sanofi Pasteur has notified the CDC that it will stop producing the vaccine.

Another vaccine from Tokyo-based pharmaceutical company Takeda is not currently approved in the United States. Others are in development.

Last year, more than 6.6 million infections were reported by around 80 countries worldwide. In the first four months of this year, 7.9 million cases and 4,000 deaths were reported, according to the World Health Organization. The pandemic was particularly severe in America.

In the US, the numbers were far lower – there were about 3,000 cases in US states and territories last year. However, it was the worst in a decade and included more infections caused locally by native mosquitoes. Most of the cases were in Puerto Rico, but about 180 cases were in three US states – Florida, Texas and California.

There have been nearly 1,500 locally transmitted cases in the United States so far this year, almost all of them in Puerto Rico.

Most cases in the mainland United States continue to affect people who became infected while traveling abroad.

It is “a traveler’s nightmare” and is a growing cause for concern internationally, says Dr. Lulu Bravo, who researches pediatric tropical diseases at the University of the Philippines Manila and has worked with Takeda on its vaccine.

“If there is an outbreak in a country, tourists may not want to come anymore,” Bravo said.

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The Associated Press Health and Science Department receives support from the Science and Educational Media Group of the Howard Hughes Medical Institute. All content is the responsibility of the AP.