This study aimed to explore the epidemiological patterns of the 2024 dengue fever outbreak in Iran and to clarify the characteristics of infected individuals. Our results indicated that dengue fever affected all age and gender groups; however, it was most prevalent among young men. At the onset of the outbreak in May 2024, most cases were imported. However, as the disease continued to spread in southern regions of the country, the majority of cases shifted to a local transmission pattern, primarily in Chabahar, located in southeast Iran.
Initially, dengue fever was introduced into the country by young men who had traveled to neighboring countries, notably the United Arab Emirates and Pakistan, mainly for business purposes. Once the virus entered Iran, local transmission became more common, especially in the southern regions where A. aegypti was already established. As a result, the proportion of women and other age groups affected by dengue fever increased since local transmission can occur in all demographics, and travel history was no longer a risk factor for local infections. This scenario helps explain the changes observed in the distribution of dengue fever considering age, sex, occupation, and travel history during the 2024 outbreak in Iran.
In recent years, the geographic patterns of dengue fever have altered worldwide. Iran’s climate and geography are particularly conducive to the spread of Aedes spp. and DENV. At the onset of the outbreak, it was widely recognized that increased international travel—especially to endemic areas—has been a significant factor in the spread of dengue fever in Iran [26]. It is crucial to adopt preventive measures to avert outbreaks within Iran’s borders, considering its proximity to dengue-endemic countries. This underscores the importance of enhanced border control and disease screening, particularly for febrile passengers at border crossings, which must be implemented through intersectoral cooperation to effectively combat the spread of the disease [27, 28].
The impact of climate change on this scenario is significant and should not be overlooked. Climate change creates favorable conditions for mosquito breeding and survival. Rising global temperatures have contributed to the growth of mosquito populations, allowing them to expand into new regions. This has led to an increase in dengue-endemic areas and a larger at-risk population [20, 29]. The presence of disease vectors in the southern and northern regions of Iran, particularly those adjacent to the sea with hot and humid climates, poses a significant risk for local dengue transmission [15]. Furthermore, stagnant water in containers, discarded tires, and other receptacles provide ideal breeding grounds for Aedes mosquitoes, which are often found in marginalized communities. Therefore, it is crucial to urgently improve environmental conditions and eliminate sites where mosquitoes can lay eggs and develop larvae to effectively control outbreaks [30]. Additionally, the use of insecticides or biological interventions, such as genetically modified mosquitoes, is recommended to manage the Aedes mosquito population and combat the transmission of DENV to at-risk individuals [31].
To protect against mosquito bites, it is important to adopt human preventive strategies that involve communication to inform the general population. Individuals living in endemic areas should wear light-colored clothing that covers the body well. To further prevent bites, they should use screens on windows and doors, apply mosquito repellent creams during outdoor activities, and utilize insecticide-treated bed nets while sleeping, along with other protective measures [32].
Our findings indicated that suspected cases of dengue fever typically present with a triad of fever, myalgia, and headache, accompanied by epidemiological evidence. Despite the rapid spread and significant pathogenicity of DENV, most cases were mild and could be managed on an outpatient basis, eventually leading to full recovery. Clinicians working in endemic areas should consider dengue fever when patients exhibit the above triad of symptoms along with relevant epidemiological history, and they should take appropriate diagnostic and therapeutic actions.
Diagnosing dengue fever can be challenging, as it requires distinguishing it from other febrile illnesses and identifying early severe warning signs [33, 34]. These warning signs include abdominal pain or tenderness, persistent vomiting, clinical fluid imbalance, mucosal bleeding, lethargy or restlessness, hepatomegaly, and the simultaneous presence of thrombocytopenia and increased hematocrit. Clinical manifestations of fluid imbalance may include increased hematocrit, pleural effusion, ascites, hypoproteinemia, and albuminuria. These signs strongly suggest plasma leakage into the interstitial space and the onset of dengue shock syndrome [35, 36]. Additionally, thrombocytopenia and prolonged coagulation tests indicate dengue hemorrhagic fever and are associated with a poor prognosis [37].
Dengue fever currently lacks a specific antiviral treatment. Instead, it is mainly managed through supportive care, which involves monitoring fluid levels, replacing electrolytes, and using antipyretics and analgesics to alleviate fever and pain. In cases of dengue hemorrhagic fever or dengue shock syndrome, it is essential to evaluate the need for vasoconstrictors, blood products, and ventilatory support [38]. Additionally, if complications such as encephalopathy, hepatitis, liver failure, cardiac issues, acute renal failure, or respiratory failure arise, specific treatments for each of them should be considered [18, 22, 36].
During the 2024 dengue fever outbreak in Iran, only one patient, a homeless individual suffering from dengue shock syndrome, passed away after an extended hospitalization. The fatality rate for dengue fever can vary depending on the severity of the disease, ranging from 1% to as high as 15% in cases of hemorrhagic dengue fever. However, early diagnosis and prompt treatment can reduce the fatality rate by preventing the progression of the disease into more severe forms, such as dengue hemorrhagic fever and dengue shock syndrome [39].
The epidemiological patterns of the 2024 dengue fever outbreak in Iran share both similarities and distinctions with those of neighboring countries. Pakistan, an endemic region for dengue fever, reported more than 58,000 cases in 2024 [40], with a significant proportion originating from Balochistan—a province bordering Iran [41]. This geographical overlap underscores the need for bilateral cooperation to enhance surveillance at border crossings to mitigate imported cases. Pakistan’s cases peak during the monsoon season (July–November) [42], aligning with the second wave of the outbreak observed in Iran. Both countries also reported higher incidence among young and middle-aged men [43], a trend echoed in Afghanistan [44]. The case-fatality rates across these nations remained low (~ 0.1%). Minor regional variations in fatality rate were likely attributable to differences in diagnostic capacity, patient demographics and comorbidities, and virulence of strains [40, 44]. However, critical differences exist in the epidemiological trajectories of Iran and Pakistan. Dengue is endemic in Pakistan for several years [45]. Meanwhile, Iran historically recorded only imported cases until the 2024 outbreak [17]. We provided the first evidence of local transmission in Chabahar (Sistan and Baluchestan province) and Bandar-e Lengeh (Hormozgan province).
Afghanistan documented the first case of dengue fever in 2019, with subsequent outbreaks. The trend of disease in Afghanistan shows a monsoonal transmission pattern concentrated in Nangarhar province near Pakistan. This epidemiological profile indicates that similar climatic conditions, established vector populations, as well as cross-border spread create risks for both imported and local transmission [44]. A parallel pattern emerged in Oman, where only imported cases were reported prior to 2019, followed by sustained local transmission thereafter [46, 47]. Additionally, Saudi Arabia reports substantial annual case numbers [48, 49]. Official statistics from other countries, including Iraq, United Arab Emirates, Turkey, Azerbaijan, Qatar, Kuwait, Bahrain, Armenia, and Turkmenistan, remain limited [40]. This epidemiological pattern highlights the varying degrees of dengue risk across the Middle East. In this area, some countries remain unaffected while others face management challenges of imported/locally transmitted cases.
This study has several limitations, so the generalizability of its findings should be interpreted with caution. First, some patients were of non-Iranian nationality, which may have complicated data collection, especially in terms of symptom reporting due to language barriers. Second, routine laboratory tests, such as complete blood counts (CBC), liver enzyme tests, and coagulation tests, were not conducted for all patients because of financial constraints. These assessments were limited to hospitalized patients, and the results can be found in the article text and the additional file. Third, due to the challenges in gathering data on hospitalized patients nationwide, we did not address the clinical course of these patients during hospitalization in our study.