July 28th 2021
Pathogen of the month: Dengue virus
written by Chandana Balasubramanian
Halfway through every Hollywood disaster movie, when all hell breaks loose, a few rogue scientists are brought in. This handful of experts would have predicted the disease outbreak or catastrophe years, or sometimes decades, before. But their advice would have fallen on deaf ears – until it was almost too late.
Meanwhile, in real life, a large and vocal group of researchers and public health organizations are sounding the alarm about Dengue as a pandemic-level threat in the near future.
The relatively good news is that Dengue, a vector-borne illness, is not transmissible between humans. So, we can prevent a full-blown Dengue pandemic if the global community of public health officials:
- Train frontline health professionals on early and accurate detection and treatment,
- Implement protective and preventive measures to mitigate Dengue risk, and
- Consistently track Dengue cases and outbreaks using robust databases like WHO and GIDEON (Global Infectious Disease and Epidemiology Online Network).
But why is Dengue such a colossal threat? Why is prevention important?
Dengue cases on the rise
Currently, Dengue cases are estimated to be anywhere from 5 – 100 million. This wide range is because many cases stay unreported, or the symptoms of Dengue are confused for other diseases. But the number of Dengue cases is expected to boom in the next few decades, with 60% growth by 2080 .
The latest study on the spread of Dengue is by Aliaga-Samanez et al. from Spain . The study is the first high-resolution analysis of how the risk of Dengue transmission has been changing geographically since the late 20th century. The study uses robust databases like the World Health Organization (WHO) , and the Global Infectious Disease and Epidemiology Online Network (GIDEON)  to track and map global Dengue cases since the 1900s.
All Dengue experts agree that the number of Dengue cases is rising fast and spreading wide across the globe. WHO estimates that about half the world’s population is now at risk . Aliaga-Samanez et al. identified that the Dengue virus (DENV) has been making a home in previously low-risk areas, potentially due to global warming and deforestation. The authors also report that while the Aedes mosquito is responsible for Dengue transmission, DENV can be spread by primates and could adapt to be transmissible by other vectors.
Tracking the geographical spread of the Dengue virus by different vectors is complex. According to the primary researcher Alisa Samanez, using the GIDEON database – “one of the most complete data sources worldwide on zoonoses” – to build their own database was a significant factor to track a zoonotic disease like Dengue.
Reported Dengue cases in different regions, 1980 – 2020
Dengue mosquitoes spread their wings worldwide
While Dengue cases are primarily found in the tropical regions of Asia, Africa, and the Americas, this is rapidly changing. The study from Spain determined that other regions now at risk are South-East China, Papua New Guinea, North Australia, South USA, parts of Columbia, Venezuela, Madagascar, and even Japan and South and Central Europe. The study predicts that Dengue could spread to Argentina and South-West Asia, from Pakistan and the Arabian Peninsula.
Ideally, public health officials in these regions will begin training their healthcare professionals to diagnose and treat Dengue early and raise awareness among their populations.
For example, initially, Egypt’s Ministry of Health dismissed reports of Dengue fever in certain regions. But eventually, they reviewed published reports of Dengue outbreaks in studies that used GIDEON’s clinical tools. This prompted them to develop a training program for their health workers for the early detection and treatment of Dengue .
Two significant factors accelerating the spread of Dengue worldwide are the 2.9 trillion U.S dollar global travel and tourism industry and climate change.
Many studies indicate that international travelers are at considerable risk for Dengue spread. Ratnam et al. from Australia concluded that Dengue infections in international travelers occur frequently and may be associated with substantial morbidity .
What is worrisome is that while Dengue is not directly contagious between humans, it is transmittable from an infected human to an infection-free Aedes mosquito. So, if a Dengue-infected individual travels to another country during the viremic or infection-spreading period, a native Aedes mosquito may bite the individual and become infected . This newly infected mosquito can infect other individuals.
Additionally, climate change is a contributor because rising temperatures in previously colder environments are fertile grounds for mosquitoes to thrive. Higher temperatures also shorten the cycle of a mosquito picking up a Dengue infection and transmitting it.
Why is Dengue dangerous?
According to WHO, severe Dengue is a leading cause of serious illness, hospitalization, and death among children and adults in some Asian and Latin American countries . Severe Dengue involves severe bleeding, liver, heart, and other organ impairment, and plasma leakage.
Many Dengue infections are mild with flu-like symptoms, but a lack of awareness and early detection could lead to severe Dengue. And since the incubation period varies from four to ten days, it may be overlooked or misdiagnosed until it becomes severe. Additionally, because there are four different types of the Dengue virus, individuals once affected by Dengue can be re-infected up to four times.
The Dengue vaccine is only available in certain countries and, as per WHO, is restricted to those aged 9 to 45 and individuals previously infected by DENV. Hopefully, we get a better alternative. But until then, we need to raise awareness about early detection and treatment on the frontlines and track outbreaks closely.
If we have learned anything from the COVID-19 pandemic, it is this: the best disaster control is early detection and prevention. According to Aliaga-Samanez et al., Dengue is poised to be the next pandemic. Only through global collaboration, rigorous tracking, and preventive public health programs can we banish health catastrophes like a Dengue pandemic to the world of fiction – away from our collective reality.
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|||World Health Organization, “Global strategy for Dengue prevention and control, 2012-2020,” World Health Organization, Genève, Switzerland, 2012.|
|||A. A.-S. e. al., “Worldwide dynamic biogeography of zoonotic and anthroponotic Dengue,” PLoS Negl. Trop. Dis., vol. 15, no. 6, p. e0009496, 2021.|
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|||Department of Tropical Medicine, Ain Shams University, Cairo, Egypt, “Dengue fever, Correspondence to Nadia A Abdelkader, MD,” Egypt J Intern Med, vol. 30, pp. 47-48, 2018.|
|||F. Irani Ratnam, “Dengue Fever and International Travel,” Journal of Travel Medicine, vol. 20, no. 6, p. 384–393, 2013.|
|||J. P. Messina, “The current and future global distribution and population at risk of Dengue,” Nature Microbiology, vol. 4, p. 1508–1515, 2019.|