Bold opening statement: A silent dengue outbreak may be closer than imagined, now reported in travelers returning to Israel from Sharm El-Sheikh, Sinai, with genetic evidence linking cases to a broader regional network.
A recent study documents four confirmed dengue virus serotype 2 (DENV-2) infections in travelers who visited Sharm El-Sheikh, a desert resort city in South Sinai, Egypt, between April and June 2024. Notably, Sharm El-Sheikh had not previously been identified as a dengue transmission area, and its arid climate has been considered unfavorable for the primary vector, Aedes mosquitoes. All four cases were unrelated, with overlapping but nonidentical travel itineraries and accommodations located 3–25 kilometers apart. The patients exhibited typical dengue symptoms—fever, headache, myalgia, and rash—and all required hospitalization with supportive care, followed by recovery. One patient showed signs of meningeal irritation, but cerebrospinal fluid analysis was normal. Dengue virus RNA consistent with DENV-2 was detected by quantitative real-time PCR in serum samples collected within a week of symptom onset (cycle threshold around 32.5). Additional serology showed DENV-2 by multiplex real-time PCR, with some cases also positive for nonstructural protein 1 antigen and IgM/IgG antibodies.
To determine the origin of these DENV-2 infections, whole-genome sequencing was performed on the viral samples. The researchers used targeted whole-genome primers for DENV and prepared libraries with Nextera-XT, sequencing on an Illumina NovaSeq platform. Consensus genomes were generated by mapping reads to the DENV-2 reference genome NC_001474.2, and the resulting sequences were deposited in GenBank. Sample usage was approved by the Sheba Medical Center Institutional Review Board (approval no. SMC-6190-19).
Sequencing results showed adequate genome coverage for three samples; one sample (patient 4) was excluded due to a high cycle threshold, which likely reflected low viral load. Phylogenetic analysis, using 1,492 global DENV-2 sequences, placed the Israeli samples within the Cosmopolitan genotype. The three sequences formed a tight cluster, sharing a recent common ancestor and differing by 32 mutations from the nearest global strain. The closest related sequences originated from Pakistan. A public sequence from the United Arab Emirates in 2023, geographically near Sinai, clustered separately within another Cosmopolitan lineage that includes strains from China, India, and Bangladesh.
These findings describe four DENV-2 infections among travelers returning from Sharm El-Sheikh, Egypt, a site previously deemed unsuitable for Aedes transmission and with no prior dengue reports. The genomic data indicate a single outbreak cluster most closely related to Pakistani strains. Except for the UAE 2023 sequence, which clusters in a different lineage, Sinai-specific regional sequences are scarce, highlighting a substantial surveillance gap. The results align with reports of DENV-2 dissemination along the Red Sea and with recent dengue cases reported in Florence, Italy.
Over the past two decades, Aedes aegypti populations have expanded along the Red Sea coast of Egypt, correlating with dengue outbreaks; however, there is no entomological data for Sinai. The arid climate can challenge mosquito survival, yet the clustering of cases within a resort area suggests local adaptation potentially supported by urban microhabitats. Maritime and air travel likely drive repeated introductions of vectors and the virus into the Red Sea region, with daily ferries from Hurghada to Sharm El-Sheikh being particularly relevant. Historical data from Jizan, Saudi Arabia (1992–2014) also imply multiple introductions of DENV-2 linked to travel and migration patterns involving pilgrims from Indonesia, Pakistan, and India. The Israeli sequences appear closest to recent Pakistan strains, but limited regional sampling constrains precise origin inferences. The observed diversity suggests more undetected cases and undersampling in the region.
The report, spanning three months and multiple locations within Sharm El-Sheikh, implies sustained DENV-2 transmission and underscores the need for heightened vector surveillance and control measures. The genetic analyses contribute to filling regional gaps in DENV sequence reporting and enhance understanding of molecular epidemiology and viral origins in the area.
Author context: Dr. Zuckerman leads the Bioinformatics and Genomics Center at Israel’s Central Virology Laboratory, with affiliations to Tel Aviv University. Her research emphasizes genomic surveillance and bioinformatics in viral pathogen studies.
Controversial take and discussion prompts:
- If a tourist hotspot can harbor a sustained dengue outbreak in an arid environment, should travel advisories and vector-control strategies shift to focus on microhabitats within popular resorts rather than broad regional climates?
- Do these findings challenge assumptions about mosquito habitat constraints in desert regions and call for more aggressive surveillance of vectors in nontraditional settings?
- Given the limited regional sequence data, how much confidence can be placed in tracing DENV-2 origins to Pakistan, and what are the implications for cross-border surveillance and public health collaboration?
Would readers like to see a brief explainer on how whole-genome sequencing clarifies outbreak origins, or a map showing connections between Sinai, Pakistan, UAE, and other cited regions to visualize transmission pathways?
