The transmission of Dengue Fever within Iran has been demonstrated for the first time in June 2024, according to a press release issued by the World Health Organization on 22 July 2024. The Ministry of Health and Medical Education of Iran reported to cases of the disease had been confirmed by Polymerase Chain Reaction testing at the Pasteur Institute in Bandar Abbas, both in patients from the city of Bandar-Lengheh in Hormozgan Province who had never travelled outside of Iran, and who can therefore be confirmed to have acquired the infection within the country. By 17 July 2024 twelve cases had been confirmed in Bandar-Lengheh among people who had no history of travel outside the country.
This development is not entirely unexpected, as the number of imported cases within Iran has remained steady at about 20 per year between 2017 and 2023, and the Aedes aegypti and Aedes albopictus Mosquitoes, which act as vectors for the disease, are both present in Sistan and Balouchistan, Hormozgan, Bushehr, Khuzastan, and Gilan provinces. In 2024 the number of cases in the country has risen sharply, with 137 reported between 15 May and 10 July.
Dengue is a viral infection transmitted to humans through the bite of infected Mosquitoes and is found in tropical and sub-tropical climates worldwide, mostly in urban and semi-urban areas. The primary vectors that transmit the disease are Aedes aegypti Mosquitoes and, to a lesser extent, Aedes albopictus. These mosquitoes are also vectors of Chikungunya, Yellow Fever and Zika viruses. Dengue is widespread throughout the tropics, with local variations in risk influenced by climate parameters as well as social and environmental factors.
Infection with the Dengue Virus can cause a wide spectrum of disease. Ranging from subclinical disease (people may not know they are even infected) to severe flu-like symptoms in those infected. Although less common, some people develop Severe Dengue, which can be any number of complications associated with severe bleeding, organ impairment and/or plasma leakage. Severe Dengue has a higher risk of death when not managed appropriately. Severe Dengue was first recognised in the 1950s during Dengue epidemics in the Philippines and Thailand. Today, Severe Dengue affects most Asian and Latin American countries and has become a leading cause of hospitalisation and death among children and adults in these regions.
Dengue is caused by a Virus of the Flaviviridae family of positive-strand RNA Viruses and there are four distinct, but closely related, serotypes of the Virus that cause Dengue (Dengue Fever Virus-1, Dengue Fever Virus-2, Dengue Fever Virus-3 and Dengue Fever Virus-4). Recovery from infection is believed to provide lifelong immunity against that serotype. However, cross-immunity to the other serotypes after recovery is only partial, and temporary. Subsequent infections (secondary infection) by other serotypes increase the risk of developing Severe Dengue.
Dengue has distinct epidemiological patterns, associated with the four serotypes of the Virus. These can co-circulate within a region, and indeed many countries are hyper-endemic for all four serotypes. Dengue has an alarming impact on both human health and the global and national economies. Dengue Fever Virus is frequently transported from one place to another by infected travellers; when susceptible vectors are present in these new areas, there is the potential for local transmission to be established.
The incidence of Dengue has grown dramatically around the world in recent decades. A vast majority of cases are asymptomatic or mild and self-managed, and hence the actual numbers of dengue cases are under-reported. Many cases are also misdiagnosed as other febrile illnesses.
One modelling estimate indicates 390 million Dengue Virus infections per year, of which 96 million manifest clinically (with any severity of disease). Another study on the prevalence of dengue estimates that 3.9 billion people are at risk of infection with dengue viruses. Despite a risk of infection existing in 129 countries, 70% of the actual burden is in Asia.
The number of dengue cases reported to the World Health Organization increased over 8 fold over the last two decades, from 505 430 cases in 2000, to over 2.4 million in 2010, and 5.2 million in 2019. Reported deaths between the year 2000 and 2015 increased from 960 to 4032, affecting mostly younger age group. The total number of cases seemingly decreased during years 2020 and 2021, as well as for reported deaths. However, the COVID-19 pandemic might have also hampered case reporting in several countries.
The overall alarming increase in case numbers over the last two decades is partly explained by a change in national practices to record and report Dengue to the Ministries of Health, and to the World Health Organization. But it also represents government recognition of the burden, and therefore the pertinence to report Dengue disease burden.
Before 1970, only 9 countries had experienced Severe Dengue epidemics. The disease is now endemic in more than 100 countries in the World Health Organization regions of Africa, the Americas, the Eastern Mediterranean, South-East Asia and the Western Pacific. The Americas, South-East Asia and Western Pacific regions are the most seriously affected, with Asia representing about 70% of the global burden of disease.
Not only is the number of cases increasing as the disease spreads to new areas including Europe, but explosive outbreaks are occurring. The threat of a possible outbreak of Dengue now exists in Europe; local transmission was reported for the first time in France and Croatia in 2010 and imported cases were detected in 3 other European countries. In 2012, an outbreak of Dengue on the Madeira islands of Portugal resulted in over 2000 cases and imported cases were detected in mainland Portugal and 10 other countries in Europe. Autochthonous cases are now observed on an annual basis in few European countries.
Iran forms part of the World Health Organization's Eastern Mediterranean Region, which is considered to be at high risk to Dengue Fever epidemics, with many countries having fragile healthcare systems due to conflict and political instability, while other countries where healthcare systems are considered to be stronger are sufferering increased rains due to climate change, leading to a proliferation of the Aedes aegypti and Aedes albopictus Mosquitoes which act as vectors for the disease.
Iran is particularly threatened by the presence of both types of Mosquito and a climate favourable to the spread of the disease, as well as a large numbers of visitors from countries where the disease is endemic. The discovery that the disease is being transmitted in the country at this time is particularly alarming as it comes shortly before the annual Arba'in Pilgrimage, which this year will take place in August, with potentially millions of Shiite Muslims from around the world visiting the Shrine of Husayn ibn Ali in the city of Karbala in central Iran.
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