The global dengue epidemic and a resurgence of Zika loom over Easter travel

Fifty years ago, dengue was only a public health issue in a few remote tropical areas. The virus has since spread to over 100 countries, making it a global concern. Nowadays, the many tourists vacationing in these regions raise the risk of spreading the disease upon their return home. The presence of the tiger mosquito (Aedes albopictus) in Spain since 2004 has further raised concerns as it can transmit the virus and lead to local outbreaks.

“In a world that’s going through a global transformation, the way we travel will also change forever,” said Manuel Linares Rufo, president of the Fundación iO, an organization specializing in tropical and travel medicine. Taking care of your own health and that of others is crucial. “A straightforward example highlighting the upcoming changes is what to do upon your return. In the past, it was a time for relaxation. Now, after visiting dengue-prone areas, stay vigilant for a week. Avoid tiger mosquito bites to prevent potential local outbreaks in your area.”

The arrival of infected travelers in Spain provides a way to monitor the progression of the disease. In September 2022, a rise in dengue cases was observed in tropical regions after a severe outbreak in Cuba during the pandemic. The previous year, dengue had reached epidemic levels in many warm regions worldwide.

“The incidence of dengue continues to skyrocket throughout the world, but especially in the Americas,” said Marta Díaz, head of the imported pathology and international health unit of Madrid’s Carlos III Hospital. “January and February were unusually busy months for us, even though cases usually drop at the beginning of the year. It has been quite remarkable.”

A recent report from the European Center for Disease Prevention and Control (ECDC), covering data from November 2023 to January 2024, highlights high incidences of dengue globally. “In January 2024, over half a million dengue cases and over 100 dengue-related deaths were reported globally.” America is the hardest-hit continent, with over 550,000 cases in January, triple the count from the same month in 2023. Most countries in the region, with exceptions like Chile and Uruguay, report over 100 cases per 100,000 people.

The outbreak’s severity prompted Brazil to initiate the world’s first public health vaccination campaign against the disease. The vaccine, named Qdenga, is manufactured by the Japanese pharmaceutical company Takeda and has been approved in Europe since late 2022. “The vaccine is given in two doses, three months apart. The first shot provides good protection after 14 days and lasts for several months,” said Natividad Tolosa of the Spanish Association of Vaccinology (AEV), at an informational event on dengue held in Barcelona by the National Association of Health Reporters (ANIS).

The available data shows that the vaccine is slightly over 61% effective. It demonstrates higher efficacy against serotypes 1 and 2, but lower against 3 and 4, all present in American countries. This vaccine has been newly introduced in Spain for travelers going to high-incidence areas with a risk of severe symptoms based on their medical backgrounds.

Dengue infection can be asymptomatic, but typically shows up with flu-like symptoms and a rash. Around 1 in 20 cases can progress to a severe or hemorrhagic condition, which has a high mortality rate. The virus is transmitted through mosquito bites, not person-to-person contact. In tropical regions, Aedes aegypti is the main mosquito species responsible for infections, being a more effective carrier compared to the tiger mosquito (Aedes albopictus).

After dengue, chikungunya is the most imported disease in Spain. It’s transmitted by mosquitoes and causes intense joint pain (chikungunya means “doubled over” in Tanzania). The virus has been circulating in countries like Brazil, Paraguay, Mali, Burkina Faso and India. In January 2024, there were around 10,000 global cases with no reported deaths. Chikungunya incidence remains stable compared to 2023.

A significant shift in trend is underway with the spread of Zika, another virus transmitted by mosquitoes. Zika’s spread was minimal after the major American outbreak in 2015-2016. “Reported cases of Zika are increasing, especially in countries like Thailand — a hotspot for Spanish travelers — where it surged by nearly 300%,” said Marta Díaz.

Nerea Irigoyen is a researcher specializing in the Zika virus and group leader in the Department of Pathology at the University of Cambridge. “Incidences have been minimal after the major epidemic eight years ago, which can be attributed to natural immunity developed by the population. However, this immunity wanes over time. Studies indicate a faster decline than anticipated, raising the possibility of an uptick in cases,” said Irigoyen. Zika is a virus that generally causes similar but milder symptoms than dengue and chikungunya. “Zika poses a significant risk during pregnancy, leading to microcephaly and brain damage in the unborn baby. It is sexually transmitted.”

To prevent transmission of dengue, chikungunya and Zika through mosquito bites, use repellents and mosquito nets, wear long sleeves and pants, and sleep in air-conditioned rooms. Avoid sleeping with windows open so mosquitos don’t get in.

Measles is another infectious disease that is on the rise in many parts of the world, including Europe. “It’s not related to tropical diseases, but the rise in cases underscores the importance of maintaining vaccination rates above 95% to prevent outbreaks initiated by imported cases,” said Manuel Linares.

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