US Doctors Advised to Stay Alert as Global Dengue Cases Escalate

U.S. health officials have alerted doctors to be vigilant for dengue cases as the disease sets international records. The virus, spread by mosquitoes, has surged globally, exacerbated by climate change. In just six months, countries in the Americas have surpassed previous annual records for dengue cases. The World Health Organization declared an emergency in December, and Puerto Rico followed with a public health emergency in March.

In the continental United States, dengue remains less common. However, this year has seen three times more cases than the same period last year. Most infections were contracted abroad by travelers, with no evidence of a current outbreak. Nevertheless, local mosquitoes still pose a threat. The Centers for Disease Control and Prevention (CDC) advised doctors to recognize symptoms, inquire about patients' recent travels, and consider dengue tests when necessary.

Dengue Virus and Its Impact

Dengue is caused by a virus spread by warm-weather mosquitoes, which are expanding their range due to climate change. Many infected individuals do not exhibit symptoms, but some experience headaches, fever, and flu-like symptoms. Severe cases can lead to serious bleeding, shock, and death. Repeated infections are particularly dangerous due to the presence of four types of dengue virus: 1, 2, 3, and 4.

When first infected, the body develops antibodies against that specific type for life. However, if infected with another type later on, these antibodies may fail to neutralize the new infection and can even aid the virus in entering immune cells and replicating. This is a significant concern in Puerto Rico, which has been widely exposed to type 1 over the past two decades.

Vaccination Efforts and Challenges

There is no widely available treatment for dengue infections. Vaccines have proven challenging to develop. In 2021, U.S. officials recommended a vaccine made by Sanofi Pasteur. This three-dose vaccine protects against all four dengue types and is recommended only for children aged 9 to 16 who have previously been infected with dengue and live in areas where it is common, such as Puerto Rico.

Due to these restrictions and other issues, the vaccine has not been widely used. As of late last month, only about 140 children had been vaccinated in Puerto Rico since it became available there in 2022. Sanofi Pasteur has informed the CDC that it will stop producing this vaccine. Another vaccine made by Tokyo-based Takeda is not currently licensed in the U.S., though others are under development.

Global and Local Statistics

Last year saw over 6.6 million reported infections across approximately 80 countries. In the first four months of this year alone, there have been 7.9 million cases and 4,000 deaths reported globally according to the World Health Organization. The Americas have been particularly affected, including Brazil and Peru.

In the United States last year, around 3,000 cases were reported in states and territories—the highest number in a decade—including more locally acquired infections due to native mosquitoes. Most cases occurred in Puerto Rico; however, about 180 were reported in Florida, Texas, and California combined.

This year has seen nearly 1,500 locally-acquired cases in the U.S., almost all of them in Puerto Rico. Most cases in the continental U.S. continue to be from travelers who were infected internationally.

"It's a traveler's nightmare" and an increasing global concern," said Dr. Lulu Bravo from the University of the Philippines Manila who studies pediatric tropical diseases and has collaborated with Takeda on its vaccine development efforts.

"When you have an outbreak in a country," Bravo added, "tourists might not want to come."