Vector-borne infectious diseases, particularly mosquito-borne, pose a substantial threat to populations throughout South and Southeast Asia. Outbreaks have affected this region several times during the early years of the 21st century, notably through outbreaks of Chikungunya and Dengue. These diseases are believed to be highly prevalent at endemic levels in the region as well. With a changing global climate, the impacts of changes in ambient temperatures and precipitation levels on mosquito populations are important for understanding the effects on risk of mosquito-borne disease outbreaks [1].

Chikungunya is a re-emerging arbovirus that causes significant morbidity and some mortality. In Asia, chikungunya was generally associated with the Aedes (Stegomyia) aegypti mosquito in a mosquito-human-mosquito life cycle. Global climate change leading to warmer temperatures and changes in rainfall patterns allow mosquito vectors to thrive at altitudes and at locations where they previously have not, ultimately leading to a spread of mosquito-borne diseases. While mutations to the chikungunya virus are responsible for some portion of the re-emergence, chikungunya epidemiology is closely tied with weather patterns in Southeast Asia. Extrapolation of this regional pattern, combined with known climate factors impacting the spread of malaria and dengue, summate to a dark picture of climate change and the spread of this disease from south Asia and Africa into Europe and North America [2].

Re-emergence of Chikungunya and climate change

Understanding why chikungunya has re-emerged on a global scale may offer some clues to future prevention of such large epidemics. An increasing percentage of the world’s population is living in cities. A. aegypti thrives in urban areas, while A. albopictus lives in both urban and rural settings. With such anthropophilic mosquitoes, human activity is linked to their survival and may even promote breeding. It is intriguing that increased populations of Aedes mosquitoes and related chikungunya infection can be seen during periods of drought, as well as following heavy rains. Climate change is pushing weather patterns to these extremes. Recent trends show increased periods of drought in the tropics, as well as increased rainfall in temperate areas, with episodes of heavier precipitation in both regions. The chikungunya re-emergence is complex and multifactorial, but it appears, in part, to follow the weather patterns that are associated with global climate change. On a larger scale, climate change increases the global habitat available to mosquitoes by increasing average temperatures and periods of heavy precipitation. In rainy periods, mosquito reproduction relies on small pools and ponds. During an epidemic in central Thailand, chikungunya infection followed periods of heavy rainfall by approximately six weeks. During drought conditions, people maintain water stores for long periods of time and are less likely to replenish or clean storage containers on a regular basis. These water conservation practices during drought lead to increased mosquito breeding, and have been implicated in the outbreak of disease.³¹ For example, the outbreak that Kenya experienced in 2004 occurred after long periods of drought, which were the driest since 1998. As drought and heavy rainfall events increase with climate change and disease vectors spread, chikungunya prevalence is likely to increase, with the possibility of becoming endemic worldwide [2].

Chikungunya outbreak in Bangladesh

Bangladesh documented the first outbreak of the disease in the year 2008 at Rajshahi and Chapainawabganj, the border-districts with India. Since then, the disease has behaved as a re-emergent disease in the country with outbreaks occurring in 2011 at the sub-district of Dohar, Dhaka and again, in 2012 in the village of Palpapara of Tangail district. Dhaka, the capital of Bangladesh, experienced the latest outbreak of Chikungunya fever in the monsoon season of 2017. This epidemic was widely covered by the country’s mainstream media. A government organization, Institute of Epidemiology, Disease Control and Research (IEDCR), actively monitored the epidemic. Based on their newsletter on Chikungunya virus, the epidemic peaked between early May and late July of 2017. Their newsletter also reported that 12060 out of 13814 people with CHIKV-related symptoms had visited three of the most prominent public hospitals along with IEDCR itself for clinical aid. Moreover, there was no alert of any other arbovirus-related diseases in the country at that time [3].

Surveillance for chikungunya in Bangladesh is patchy, with very little information available on the geographic spread of the disease, particularly outside Dhaka. In that respect, Bangladesh is representative of many low-income countries, and innovations that can aid surveillance and intervention planning in the absence of strong reporting systems would be beneficial [4].

References

1. Servadio JL, Rosenthal SR, Carlson L, Bauer C. Climate patterns and mosquito-borne disease outbreaks in South and Southeast Asia. J Infect Public Health. 2018;11(4):566-71. doi: 10.1016/j.jiph.2017.12.006.
2. Meason B, Paterson R. Chikungunya, climate change, and human rights. Health Hum Rights. 2014;16(1):105-12. doi,
3. Shourav AH, Mahbub MM, Yasmin M, Ahsan CR, Nessa J. Seroepidemiology of Chikungunya Fever in Dhaka, Bangladesh: A Crosssectional Study. Bangladesh Journal of Microbiology. 2021;38(2):79-85. doi,
4. Mahmud AS, Kabir MI, Engø-Monsen K, Tahmina S, Riaz BK, Hossain MA, et al. Megacities as drivers of national outbreaks: The 2017 chikungunya outbreak in Dhaka, Bangladesh. PLoS Negl Trop Dis. 2021;15(2):e0009106. doi: 10.1371/journal.pntd.0009106.