Just one heatwave away, dengue virus could be ready to stay!
By Rada Rusu
This post is part of a series in diverse mediums focusing on the theme “How do we envision equity in global health?”. These submissions are by McGill students who were part of the course, Fundamentals of Global Health, in Fall 2023.
In 2010, the WHO declared dengue to be one of the fastest growing mosquito-borne diseases globally (1). Over the past 50 years, dengue incidence has surged 30-fold, making it one of the most critical mosquito-borne diseases worldwide (2, 3). But do Canadians need to worry about this neglected tropical disease? The answer is yes.
The dengue virus, transmitted by the Aedes aegypti and Aedes albopictus mosquitoes, is a flavivirus causing febrile illness (4, 5). Symptoms range from fever, fatigue, and maculopapular rashes to more severe manifestations like dengue shock syndrome, potentially leading to death (4, 5). The virus is endemic to humid, tropical locations, such as Thailand, Singapore, Cuba, and Brazil, and usually follows a seasonal pattern of disease transmission, in coordination with local rainy seasons (4, 5).
Recently, however, dengue has been spreading to new areas within the United States and Europe, and explosive outbreaks are occurring, with the highest number of global dengue cases reported in 2019 (4). There have been many examples of dengue spreading outside of traditionally endemic regions. Just this year, the ECDC has said that the A. albopictus mosquito has been established in 13 European Economic Area Countries (6), where outbreaks have started to occur, including in Paris (7). Not to mention, the unusual reporting of a locally-acquired case in California this year (8). Lastly, the devastating and unpredictable outbreak in Bangladesh this summer, depicts the impacts of climate change, shifting seasonal patterns, and extreme weather events on the transmission of the dengue virus (9). One study even estimated that dengue fever will affect 60% of the world’s population by 2080 (10).
Climate change has been attributed to the emergence of new serotypes and expanding transmission boundaries, along with globalization, urbanization, and the increase of international trade and travel (6). Given Canada’s climate and geographic location, many may not consider neglected tropical diseases (NTDs) to be a risk, however, Canada is by no means immune. Currently, the Government of Canada reports that there are about 200-300 dengue cases every year due to travellers returning from endemic countries [9]. Yet, one review explains that more cases have been documented by provincial public health laboratories [10]. A study conducted in Ontario from 2008-2020, found that dengue and chikungunya laboratory-confirmed cases predominantly remained at around 100-280 cases per year. However, in 2019 cases peaked at 715 (11), more cases than what was reported federally by the Public Health Agency of Canada (PHAC).
PHAC does not classify dengue as a notifiable disease, and even in countries where dengue is notifiable, actual case counts are underreported. This is usually due to misdiagnoses as other febrile illnesses or due to asymptomatic cases (5). Here in Canada, dengue has not been classified as a notifiable disease based on the premise of low case counts and disease burden, as well as little chance of local disease transmission (12). But it is easy to imagine the extent of current underreporting, due to lack of awareness and passive surveillance of dengue infections.
To this day, there have been no reports of any locally transmitted cases [12], but this could be possible in the future. As the climate crisis continues to persevere, the right environment is forming to allow for locally transmitted cases. 2023 has been named the hottest year on record by the World Meteorological Organization (WMO)(13). Given that dengue transmission requires warm temperatures, high humidity, and increased precipitation, longer and hotter summers could create conditions to facilitate and accelerate the lifecycles of A. aegypti and A. albopictus mosquitoes. The warming temperatures, creates a suitable environment for shorter mosquito breeding cycles, and faster viral replication [6, 14], thereby increasing the risk for locally transmitted cases. Just this summer alone, we have already started to see the effects of climate change here in Canada, with multiple forest fires, tornadoes, and intense flash flooding. It is only a matter of time until these mosquitoes permanently establish here.
In fact, this could be occurring already, with reports of these mosquitos in Southwestern Canada (14). One study found that both A. albopictus and A. aegypti appeared to have emerged and established in the city of Windsor in 2016. This was the most northern reporting of A. aegypti (15). It seems that mosquito viral hosts establishing in Canada is slowly becoming a reality. That means that dengue could be on our doorsteps a little sooner than anticipated.
Effective disease surveillance, education and awareness, and vector control programs, are key components needed for managing mosquito-borne outbreaks (5, 16). Surveillance systems, in particular, can provide the data needed to understand the burden of disease, as well as prepare for vector control and intervention measures (5). However, post-pandemic, our healthcare systems are not yet ready for another infectious disease emergency. If a dengue outbreak were to occur, containing and managing the spread of the virus, especially one with a different mode of transmission, would be difficult. Additionally, there are only a few approved efficacious compounds available for the prevention or treatment of dengue infection (8). Vector control methods exist, such as Wolbachia, but have their limitations; many are outdated, with little effectivity (17, 18). Lastly, there are many diagnostic challenges (19).
A few glimmers of hope do exist! Firstly, there are some surveillance efforts through the GeoSentinel Project, a global network with the goal of surveillance and study of travel-related illnesses, including dengue. CanTravNet is the Canadian network affiliated with the GeoSentinel and commonly liaises with PHAC (20). Surveillance is already occurring at the provincial and national levels, albeit passively and when there are suspected cases (14). Additionally, there is a wealth of dengue knowledge, research, and expertise from across the Global South to lean on.
Considering the probable underreporting and the inevitable resurgence of NTDs in North America due to climate change, it may be time to consider adding dengue to the list of notifiable diseases. The last time dengue was under evaluation to become a notifiable disease was in 2009. This was also when the Committee to Advise on Tropical Medicine and Travel (CATMAT) made their last Advisory Committee Statement about dengue fever, with no other statements made since then (12). We know that a dengue outbreak is possible in Canada, and we know that the globe is warming. Instead of hoping dengue doesn’t ever reach our shores, let’s be proactive and ensure both our surveillance and healthcare systems are ready to take on an outbreak. In her Nature publication, Ainsworth called out that “Physicians need to be alert to the reality that NTDs can be acquired as local infections — and not just during foreign travel.”(6), but I think this call extends beyond physicians. It’s also a call to our health agencies, policymakers, and the public. It is critical to ensure Canada plays its part as a global citizen, by strengthening our NTD surveillance and listing dengue as a notifiable disease. Actively reinforcing our surveillance system are essential steps to protect our most vulnerable, and sound the alarm to our neighbours (21). The US and EU made dengue a notifiable disease in 2010, it is time for Canada to do the same.
References
1. WHO. Dengue: the fastest growing mosquito-borne disease in the world. WHO News. 2010.
2. Ebi KL, Nealon J. Dengue in a changing climate. Environ Res. 2016;151:115-23.
3. World Health Organization. South-East Asia Region. Dengue Bulletin. 2021. Report No.: 0250-8362.
4. WHO. Dengue and severe dengue. WHO News. 2023.
5. Bhatt S, Gething PW, Brady OJ, Messina JP, Farlow AW, Moyes CL, et al. The global distribution and burden of dengue. Nature. 2013;496(7446):504-7.
6. Ainsworth; C. Tropical diseases move north. 2023.
7. Zatta M, Brichler S, Vindrios W, Melica G, Gallien S. Autochthonous Dengue Outbreak, Paris Region, France, September–October 2023. Emerging Infectious Disease journal. 2023;29(12):2538.
8. Nolen; S. What to Know About Dengue Fever as Cases Spread to New Places. The New York Times. 2023.
9. World Health Organization. Dengue in Bangladesh. Disease Outbreak News. 2023.
10. Bhatia S, Bansal D, Patil S, Pandya S, Ilyas QM, Imran S. A Retrospective Study of Climate Change Affecting Dengue: Evidences, Challenges and Future Directions. Frontiers in Public Health. 2022;10.
11. Harish V, Buajitti E, Burrows H, Posen J, Bogoch II, Corbeil A, et al. Geographic clustering of travel-acquired infections in Ontario, Canada, 2008–2020. PLOS Global Public Health. 2023;3(3):e0001608.
12. Committee to Advise on Tropical Medicine and Travel (CATMAT). Statement on Dengue. 49 ed2009.
13. 2023 shatters climate records, with major impacts [press release]. 2023.
14. Ng V, Rees EE, Lindsay LR, Drebot MA, Brownstone T, Sadeghieh T, et al. Could exotic mosquito-borne diseases emerge in Canada with climate change? Can Commun Dis Rep. 2019;45(4):98-107.
15. Giordano BV, Gasparotto A, Liang P, Nelder MP, Russell C, Hunter FF. Discovery of an Aedes (Stegomyia) albopictus population and first records of Aedes (Stegomyia) aegypti in Canada. Medical and Veterinary Entomology. 2020;34(1):10-6.
16. Bouri N, Sell TK, Franco C, Adalja AA, Henderson DA, Hynes NA. Return of epidemic dengue in the United States: implications for the public health practitioner. Public Health Rep. 2012;127(3):259-66.
17. Bowman LR, Donegan S, McCall PJ. Is Dengue Vector Control Deficient in Effectiveness or Evidence?: Systematic Review and Meta-analysis. PLOS Neglected Tropical Diseases. 2016;10(3):e0004551.
18. Dorigatti I, McCormack C, Nedjati-Gilani G, Ferguson NM. Using <em>Wolbachia</em> for Dengue Control: Insights from Modelling. Trends in Parasitology. 2018;34(2):102-13.
19. Wong P-F, Wong L-P, AbuBakar S. Diagnosis of severe dengue: Challenges, needs and opportunities. Journal of Infection and Public Health. 2020;13(2):193-8.
20. GeoSentinel. CanTravNet 2012 [Available from: https://geosentinel.org/sites/cantravnet.
21. Beatty ME, Stone A, Fitzsimons DW, Hanna JN, Lam SK, Vong S, et al. Best Practices in Dengue Surveillance: A Report from the Asia-Pacific and Americas Dengue Prevention Boards. PLOS Neglected Tropical Diseases. 2010;4(11):e890.