Imagine falling ill with a fever typically associated with tropical paradises while vacationing in a scorching desert resort – that's the alarming reality uncovered in this study of dengue virus cases among Israeli travelers. Dengue fever, caused by the dengue virus (DENV), has skyrocketed in prevalence over the last 20 years, affecting millions worldwide. This surge isn't random; it's largely fueled by factors like shifting climate patterns, which expand mosquito habitats, and our increasingly interconnected world through travel and trade. While we're used to hearing about dengue outbreaks in places like Southeast Asia and the Americas, it's now popping up in unexpected spots, including parts of Europe where it hasn't been common before.
But here's where it gets controversial: Could our love for global adventures be unknowingly spreading these diseases far beyond their traditional boundaries, turning holiday hotspots into hidden health threats?
In this report, we detail four confirmed cases of dengue fever in individuals who recently traveled back to Israel after stays in Sharm El-Sheikh, a popular beach destination in Egypt's Sinai Peninsula. What makes this particularly intriguing is that Sharm El-Sheikh isn't known for dengue transmission, and the arid, dry climate of the Sinai region is generally thought to be inhospitable for the primary carriers of DENV – Aedes mosquitoes, which thrive in more humid environments. For beginners wondering about dengue, it's a viral infection transmitted by these mosquitoes, leading to symptoms like high fever, severe headaches, muscle aches, and sometimes a rash. In severe cases, it can cause life-threatening complications, such as dengue hemorrhagic fever. Think of it like a mosquito-borne version of the flu, but with the potential for much more serious outcomes if not managed promptly.
These four cases, documented between April and June 2024, involved unrelated travelers whose trips didn't overlap, and they stayed in different accommodations spread 3 to 25 kilometers apart. Each patient presented with classic dengue symptoms and was admitted to the hospital for supportive treatment, such as fluids and rest, before making a full recovery. Interestingly, one patient showed signs of meningeal irritation – that's inflammation around the brain and spinal cord – but tests of their cerebrospinal fluid came back normal, except for the detection of DENV serotype 2 (DENV-2) RNA via a sensitive lab technique called quantitative real-time PCR, with a cycle threshold of 32.5. All samples were gathered within a week of symptoms starting, and further blood tests using multiplex quantitative real-time PCR confirmed the presence of DENV-2. In some instances, additional markers like the nonstructural protein 1 antigen and antibodies (IgM and IgG) were also positive, providing a clearer picture of the infection.
To dig deeper into where this virus might have originated, our team conducted full-genome sequencing of the DENV-2 samples. We used specialized primers designed for whole-genome capture, prepared the sequencing libraries with a tool called Nextera-XT, and ran the analysis on an Illumina NovaSeq machine. By aligning the sequences to a reference DENV-2 genome (available in GenBank under accession number NC_001474.2), we created consensus sequences, which we then submitted to GenBank for public access. This research received ethical approval from the Sheba Medical Center Institutional Review Board (approval number SMC-6190-19), ensuring patient privacy and consent were upheld.
And this is the part most people miss: The genomic data revealed key insights, even though one sample (from patient number 4) had low virus levels, possibly due to a high cycle threshold of 34, and was excluded from the full analysis. By comparing our sequences to a global dataset of 1,492 DENV-2 strains, we found that the Israeli cases grouped together within the Cosmopolitan genotype – a widespread variant of the virus. The three viable sequences formed their own tight cluster, indicating they likely stem from a shared common ancestor and differed by only 32 mutations from the closest global strain. Surprisingly, the most similar sequences were from Pakistan, not from nearby regions. The single publicly available sequence from the nearby United Arab Emirates in 2023 fell into a different branch of the Cosmopolitan lineage, clustering with strains from countries like China, India, and Bangladesh.
These discoveries point to four DENV-2 infections in tourists from Sharm El-Sheikh, an arid area in Egypt's Sinai Peninsula that was previously seen as unsuitable for Aedes mosquitoes and free of dengue reports. Through genetic analysis, we see evidence of a small outbreak, with the virus most akin to strains circulating in Pakistan. Beyond that one UAE sequence from 2023, which clusters elsewhere, there are no recent genetic data from Sinai, highlighting a significant gap in monitoring efforts. This aligns with broader reports of DENV-2 spreading along the Red Sea coast and recent infections in Florence, Italy, showing how travel can bridge continents.
Over the past couple of decades, populations of Aedes aegypti mosquitoes – the main dengue vectors – have grown in Egypt, particularly near the Red Sea. This expansion has coincided with dengue outbreaks, yet we lack specific entomological data for Sinai. While the dry climate poses challenges for mosquito survival, the fact that these cases clustered in one resort area suggests the mosquitoes might be adapting to local conditions, perhaps aided by urban water sources or micro-environments that retain moisture, like artificial ponds or irrigation systems. For those new to this, Aedes aegypti are known for laying eggs in stagnant water, so even in deserts, human activities can create niches for them.
But here's where it gets controversial again: Maritime and air travel could be repeatedly introducing Aedes aegypti and DENV into the Red Sea area, with some experts arguing that ocean transport plays a bigger role than air travel in spreading these vectors and viruses. The pattern of DENV-2 outbreaks in Red Sea ports supports this idea, with ferries running daily between Hurghada – where dengue has recently appeared – and Sharm El-Sheikh being a potential hotspot. Genetic evidence from a 2019 outbreak in Jizan, Saudi Arabia, and older Saudi strains from 1992 to 2014 points to multiple viral introductions, linked to a DENV-2 variant similar to those from Malaysia, Singapore, Korea, and China. Further studies of Saudi Arabian strains from that period show strong genetic ties to viruses from countries sending large numbers of pilgrims for Hajj and Umrah, such as Indonesia, Pakistan, and India. Indeed, our phylogenetic analysis reveals that the Israeli dengue sequences are closest to modern Pakistani strains. Yet, the limited number of sequences from Egypt and its neighbors makes it hard to pinpoint the exact origins, circulation routes, and spread patterns of the virus, with the genetic differences hinting at underreporting and possibly many undetected cases.
This cluster of four cases over three months across different Sharm El-Sheikh locations signals ongoing DENV-2 transmission, stressing the need for stronger mosquito surveillance and control measures. It serves as a wake-up call for public health officials worldwide. By sharing this genetic information, we aim to fill in blanks in regional dengue reporting and better understand the virus's molecular epidemiology and roots.
Dr. Zuckerman heads the Bioinformatics and Genomics Center at Israel's Central Virology Laboratory under the Ministry of Health and is also connected to Tel Aviv University's School of Public Health. Her research emphasizes genomic monitoring, molecular epidemiology, and how bioinformatics can unravel the mysteries of viral diseases.
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Suggested citation: Zuckerman NS, Choshen G, Lustig Y, Shoykhet A, Friedman K, Kushnir T, et al. Molecular evidence of dengue virus serotype 2 in travelers returning to Israel from the Sinai Peninsula. Emerg Infect Dis. 2025 Nov [date cited]. https://doi.org/10.3201/eid3111.250991
These authors contributed equally to this article.
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.
Disclaimer: Early release articles are not considered as final versions. Any changes will be reflected in the online version in the month the article is officially released.
Author affiliations: Sheba Medical Center, Ramat-Gan, Israel (N.S. Zuckerman, Y. Lustig, K. Friedman, T. Kushnir, V. Indenbaum, E. Schwartz); Tel-Aviv University, Tel Aviv, Israel (G. Choshen, Y. Lustig, O. Halutz, E. Schwartz); Meir Medical Center, Kfar-Saba, Israel (G. Choshen, A. Shoykhet); Infectious Disease Institute, Soroka University Medical Center, Beer Sheba, Israel (H. Azulay)
What do you think – is the rise in global travel making us more vulnerable to diseases like dengue, or should we focus on tightening mosquito control measures instead? Do you agree that arid regions like Sinai could become dengue hotspots due to human activities, or is this just an overblown concern? Share your thoughts in the comments; I'd love to hear differing opinions!
