Climate Change Pushing an ‘Alarming’ Spread of Dengue, Chikungunya and Zika Climate and Health 06/04/2023 • Megha Kaveri Share this:Click to share on Twitter (Opens in new window)Click to share on LinkedIn (Opens in new window)Click to share on Facebook (Opens in new window)Click to print (Opens in new window) The Aedes aegypti mosquito is the carrier of dengue, zika and chikungunya. Climate change is driving the spread of mosquito-borne arboviruses – dengue, chikungunya and Zika – into new areas, thus leading the world to newer crises, the World Health Organization (WHO) warned this week. Several countries in the Americas region have reported an increase in dengue, zika and chikungunya cases and that the pattern might repeat in the northern hemisphere in the summer. “It worries us that the mosquito and these diseases have been increasing with climate change, by altitude and by latitude, so now we are seeing transmission where we didn’t see it before,” said Dr Diana Rojas Alvarez, the WHO technical lead for zika and chikungunya. In South America, these new transmission areas are further south on the continent whereas, in the northern hemisphere, cases have been reported in the south of Europe. Major cities in Argentina and Bolivia have issued dengue health alerts this year, while Colombia, Uruguay, Bolivia, Peru and Paraguay have reported cases in new geographical areas, including those at higher altitudes. Diseases like dengue, chikungunya and Zika are prominent in the tropical and subtropical regions of the world. They are transmitted by mosquitoes belonging to the Aedes genus type that breed in water, so an increase in rainfall, as well as more stored water during droughts, encourage increased breeding. Dengue accounts for by far the most arbovirus cases in humans, and the caseload more than doubled between 2021 and 2022, from 1.2 million to 2.8 million cases, the WHO reported last month. In 2000, there were half a million dengue cases being reported globally, but 2019 recorded 5.2 million cases, said Dr Raman Velayudhan, the WHO unit head for the global program on control of neglected tropical diseases. “In 2022, we had an increase of dengue in many parts of the world. In the Americas region, they recorded 2.8 million cases with more than 1200 deaths. The geographic spread of dengue is expanding,” he added. “This is really worrying because this shows that climate change has played a key role in facilitating the spread of the vector, the mosquitoes, down south. In 2023, we already have more than 441,000 cases in the American region and more than 100 deaths due to dengue.” Chikungunya alert There has also been a leap in chikungunya cases, Velayudha reported. “Currently we have around 135,000 cases (of chikungunya) as of 31 March in the Americas, compared with about 50,000 cases during the first semester of 2022,” he said. “If we want to compare the number of weekly cases, the average weekly cases that are reported in the Americas are from two to 3000 [in 2022] and this year we had a record number of almost 35,000 cases in just one week,” Alvarez pointed out. In February, the WHO’s Americas body, the Pan American Health Organization (PAHO), issued an epidemiological alert warning member states to “intensify actions to prepare health care services, including the diagnosis and proper management of cases, to face possible outbreaks of chikungunya and other arbovirus diseases, to minimize deaths and complications from these diseases”. Although the number of Zika cases has been declining since 2017, around 40,000 cases are still being reported annually from 89 countries and territories. Terming the current distribution of disease-causing mosquitoes “alarming”, Alvarez said that wherever the mosquitoes are present, the population would be exposed. She added that when people travel after being exposed to these mosquitoes, the risk of transmission is multiplied. “The current situation in the southern hemisphere could be an anticipation of what might happen in the northern part of South America, Central America, and the Caribbean. We should also be prepared to detect some cases during spring and summer in Europe and in the northern hemisphere, also in Southeast Asia, because the arbovirus season starts later there.” Vaccines in the pipeline For dengue, there is currently one vaccine licensed in around 20 countries, Velayudhan said. “It is effective in people who’ve had dengue once.” There are two more vaccines in the pipeline, in various stages of trials. “The second vaccine developed by Takeda is currently under evaluation by our committee. We hope a recommendation may come towards the end of this year. We also have a third vaccine which is completing its studies right now and probably may come in for a recommendation to WHO in 2024,” he explained. Two antiviral drugs to combat dengue have completed phase one safety trials. “We also hope the pandemic has given an opportunity to have several studies on antivirals, and some of these antivirals may be beneficial to dengue and chikungunya and other arboviruses.” Similarly, there are three vaccines against chikungunya that are currently in the pipeline, completing phase three trials. “They are applying for different approvals in the countries. So hopefully we will have chikungunya vaccines coming up soon,” Alvarez said. She added that for Zika, there had been 45 vaccine candidates in the pipeline but none had gone further than phase one trials due to lack of funding. “However, the advancements with specific treatments for chikungunya to prevent Zika congenital syndrome and other neurological complications is ongoing. There are some phase two trials on monoclonal antibodies and potential treatments to prevent complications,” she said. Image Credits: James Gathany/ PHIL, CDC, Public Domain. Share this:Click to share on Twitter (Opens in new window)Click to share on LinkedIn (Opens in new window)Click to share on Facebook (Opens in new window)Click to print (Opens in new window) Combat the infodemic in health information and support health policy reporting from the global South. Our growing network of journalists in Africa, Asia, Geneva and New York connect the dots between regional realities and the big global debates, with evidence-based, open access news and analysis. To make a personal or organisational contribution click here on PayPal.