Dengue fever outbreaks around the world

That’s three times higher than the same period in 2023, highlighting the danger of the pandemic, the WHO said. The increase was most pronounced in the Americas, where the number of cases surpassed 7 million at the end of April.

Genesis Polanco Marte, 9, arrived at a hospital emergency room in the United States with a fever, body aches and dehydration. He was pale and lethargic, and he kept getting upset as a pediatrician stroked his hair and spoke to him in Spanish. Tests showed that Marte was one of 10 million people infected with dengue fever — an unprecedented outbreak that scientists say is being driven by climate change.

The disease is common in Southeast Asia but is often overlooked in Western countries. Higher global temperatures have accelerated the life cycle and range of the mosquito that carries the virus. According to statistics, one in 800 people contracted dengue fever in the first six months of the year.

The surge of patients has overwhelmed hospitals from Brazil to Bangladesh, recalling the worst days of the Covid-19 pandemic. Puerto Rico declared a public health emergency in the spring, with more cases than last year. Health officials are bracing for the virus to spread to temperate regions, including South America.

“The dengue storm is coming. It’s active in Puerto Rico, but it’s going to get worse soon,” said Grayson Brown, executive director of the Puerto Rico Pest Control Unit.

Last week, the US Centers for Disease Control and Prevention (CDC) warned of a rise in dengue fever and urged doctors to be vigilant about the disease. But while cases have surged to record levels, it remains one of the most neglected diseases, according to the WHO. Three out of four cases have mild or no symptoms, making it difficult to track.

There are four strains of dengue virus, corresponding to four serotypes, so previous natural infections do not provide immunity for the future. Another thing that makes dengue dangerous is the serious complications that occur when a person is infected with two strains of the virus consecutively.

There is currently no specific treatment for dengue fever. Severe cases can result in plasma leakage from veins, internal bleeding, multiple organ failure, and death.

Experts see the Puerto Rico crisis as a warning sign for the rest of the world and the United States. It shows how quickly an outbreak can move through communities with weak health infrastructure as global temperatures rise. Research suggests that without drastic action, about 2 billion people could be at risk of dengue in the next 50 years.

Climate change is a threat

Puerto Rico public health officials are bracing for a surge in cases as the island enters its hot, rainy season. In mid-June, the region reported more than 1,500 cases and at least two deaths.

Hot and stormy weather is ideal for the Aedes aegypti mosquito, the intermediate host of dengue fever. Unlike malaria mosquitoes, which only need to bite a human once before laying eggs, the Aedes aegypti mosquito moves from person to person, increasing the chance of spreading disease with each bite.

In Puerto Rico’s crowded urban areas, most families cannot afford air conditioning, so they stay cool by opening windows and doors without mosquito screens.

Meanwhile, global warming is creating a serious outbreak. Greenhouse gas emissions, mainly from burning fossil fuels, have increased average temperatures in the region since 1950, according to the National Climate Information Center. The change benefits the Aedes aegypti mosquito. Scientists have found that warmer conditions can cause the insect to reproduce more quickly, bite more people, and lay more eggs. Temperatures also make dengue viruses more infectious, allowing them to multiply rapidly in their hosts.

Officials are concerned that high temperatures could create conditions for outbreaks in the United States. “Even one case in an area where dengue is not common is a huge resource drain, creating public concern,” said Gabriela Paz-Bailey, director of the CDC’s dengue branch in Puerto Rico.

In tropical regions across Latin America, Africa and Asia, dengue is endemic mainly during the summer months. However, warmer weather is allowing the disease to spread year-round. Meanwhile, climate change is allowing the virus to penetrate temperate regions and highland communities. Nepal, which had no dengue cases before 2004, has seen more than 50,000 cases in the past year.

In Vietnam, in the first three months of this year, Hanoi recorded 513 cases of dengue fever, three times higher than the same period last year.

Vaccination is difficult

In fact, dengue viruses have many serotypes, unusual mechanisms of causing severe disease, making treatment and prevention particularly difficult. Infection with one strain of the virus can generate antibodies against the pathogen in the future. But the same antibodies bind to viruses of another serotype, allowing them to invade and cause more severe disease.

Dengvaxia is the only vaccine licensed in the United States that protects children against all four strains of dengue fever. However, vaccination is conditional on the child having had the disease before.

In Puerto Rico, few people have heard of Dengvaxia. The vaccination process has been slow, and many parents are unaware of the dangers of dengue. After the pandemic, they are tired of hearing about the vaccine.

According to the CDC, only 145 children in Puerto Rico have started vaccination since Dengvaxia went into effect in 2022, a tiny number compared to the 140,000 children who are eligible.

Now, access to a vaccine is even more limited. Months before Puerto Rico declared a public health emergency, Sanofi announced that it had stopped manufacturing Dengvaxia because of low demand. The last doses are set to expire in August 2026.

In May, countries including Argentina, Brazil, Colombia and Indonesia approved a second vaccine, Qdenga. Developed by Japan’s Takeda, the vaccine is recommended by the WHO for children aged 6 to 16, requires only two doses and can be used regardless of previous infection. However, the company withdrew its application from the Food and Drug Administration in July 2023 due to data collection issues.

The US National Institutes of Health (NHS) is developing a third vaccine, which is expected to be at least a year away.

In Vietnam, in May, the Drug Administration of Vietnam, Ministry of Health, approved the Qdenga dengue vaccine. The vaccine is more than 80% effective, for children from 4 years old. The vaccination schedule is two doses, three months apart.