A Bold Look at Dengue Viral Footprints in Travelers from Sinai
Dengue virus (DENV) remains the most widespread arbovirus worldwide, with incidence rising tenfold over the last two decades due to climate change and global travel. While transmission is well documented in Southeast Asia and the Americas, autochthonous outbreaks are increasingly reported in nonendemic regions, including parts of Europe.
This study presents four confirmed dengue fever cases in travelers who returned to Israel after visiting Sharm El-Sheikh, a desert resort city on the southern Sinai Peninsula, during April–June 2024. Notably, Sharm El-Sheikh had not previously been recognized as a dengue transmission area. The Sinai’s arid climate is traditionally considered unfavorable for Aedes mosquitoes, the primary DENV vectors.
The four cases were unrelated, with nonoverlapping travel dates and accommodations 3–25 km apart. Symptoms were typical of dengue: fever, headache, myalgia, and rash. All patients were hospitalized for supportive care and recovered. One patient showed meningeal irritation; cerebrospinal fluid tests were normal, though dengue virus serotype 2 (DENV-2) RNA was detected by quantitative real-time PCR (cycle threshold 32.5). Samples were collected within a week of symptom onset. Serum testing confirmed DENV-2 by multiplex real-time PCR, with some cases also showing nonstructural protein 1 antigen and IgM/IgG positivity.
To determine where these DENV-2 infections originated, whole-genome sequencing was conducted on the virus from the travelers. DENV-2 genomes were amplified using dedicated whole-genome primers, libraries prepared with Nextera-XT, and sequencing performed on an Illumina NovaSeq platform. Consensus genomes were created by mapping to the DENV-2 reference sequence NC_001474.2 and were deposited in GenBank. The study received approval from the Sheba Medical Center Institutional Review Board (SMC-6190-19).
Among the samples, three yielded sufficient DENV-2 genome coverage; one (patient 4) was excluded due to a high cycle threshold (34) limiting genome recovery.
Phylogenetic analysis, incorporating 1,492 global DENV-2 sequences, placed the Israeli samples firmly within the Cosmopolitan genotype. The three sequences formed a tight cluster with a shared ancestor, differing by 32 mutations from the nearest global strain. The most closely related sequences originated from Pakistan. In contrast, a publicly available sequence from the United Arab Emirates (2023), geographically near Sinai, clustered with a different Cosmopolitan lineage that also includes strains from China, India, and Bangladesh.
What do these findings suggest? The data indicate four linked DENV-2 infections in travelers from Sharm El-Sheikh, a city previously deemed unsuitable for Aedes mosquitoes and without prior dengue reports. The clustered genomes imply a single local outbreak with origins most closely related to Pakistani strains. The broader regional context shows a lack of recent Sinai-specific sequence data, highlighting a major gap in surveillance. These results align with other reports of DENV-2 movement along the Red Sea region and recent dengue cases in Florence, Italy.
Over the past two decades, Aedes aegypti populations have expanded along Egypt’s Red Sea coast, correlating with dengue outbreaks. However, there is no entomologic data available for Sinai itself. Although an arid climate challenges mosquito survival, the clustering of cases within a resort area hints at local adaptation, potentially supported by urban microhabitats. Maritime and air travel likely drive repeated introductions of Aedes mosquitoes and DENV into the Red Sea region, with daily ferries from Hurghada to Sharm El-Sheikh possibly playing a key role in ongoing transmission. Genetic data from prior outbreaks in Jizan (Saudi Arabia) and strains circulating in Saudi Arabia (1992–2014) suggest multiple introductions linked to imported DENV-2 variants related to strains from Malaysia, Singapore, Korea, and China. Additional analyses of Saudi Arabia strains further implicate connections to countries with large numbers of Hajj and Umrah pilgrims (Indonesia, Pakistan, and India). In our study, the closest relatives are recent Pakistani sequences. Yet, the scarcity of Egyptian and neighboring-region sequences limits precise tracing of origin, circulation, and distribution, and observed viral diversity points to undersampling and undetected cases.
This report of four cases over three months in different Sharm El-Sheikh localities suggests sustained DENV-2 transmission and underscores the need for enhanced vector surveillance and control. The genetic data help address regional reporting gaps and contribute to understanding dengue’s molecular epidemiology and origins in this part of the world.
Authorship and affiliations: Zuckerman, Lustig, Friedman, Kushnir, Indenbaum, and Schwartz are with Sheba Medical Center, Ramat-Gan, Israel; Lustig, Choshen, Halutz, and Schwartz with Tel Aviv University; Choshen and Shoykhet with Meir Medical Center; Azulay with the Infectious Disease Institute, Soroka University Medical Center, Beersheba. The article notes that the conclusions do not necessarily reflect the official positions of the U.S. Department of Health and Human Services, the CDC, or the authors’ institutions. Acknowledgments and references follow, with related studies cited to place these findings in a broader context.
But here’s where it gets controversial: if dengue is establishing itself in regions once considered low-risk, should travel advisories, border screening, and routine genomic surveillance be re-evaluated even in arid zones? And this is the part most people miss: local microhabitats and human movement patterns can enable transmission in places thought resistant to vector establishment. Do travelers returning from such destinations deserve routine testing during outbreaks, even when symptoms are mild or nonspecific?
What’s your take? Is the Sinai a new frontier for dengue risk, or an early sign of broader gaps in regional surveillance? Share your views in the comments: should public health policies adapt faster to genomic evidence of pathogen movement, even when conventional wisdom about vectors and climates challenges seems to lag?
