Climate change is pushing ‘alarming’ spread of dengue, chikungunya and zika

Climate change is driving the spread of mosquito-borne arboviruses – dengue, chikungunya and Zika – to new regions, leading the world to new 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 trend may be repeated in the northern hemisphere in the summer.

“We are concerned that mosquitoes and these diseases are increasing with climate change, in altitude and latitude, so now we are seeing transmission where we haven’t seen it before,” said technical lead Dr Diana Rojas Alvarez. from the WHO for zika and chikungunya.

In South America, these new areas of transmission are further south on the continent, while in the northern hemisphere cases have been reported in southern Europe.

Major cities in Argentina and Bolivia issued dengue health alerts this year, while Colombia, Uruguay, Bolivia, Peru and Paraguay reported cases in new geographic areas, including those located at higher altitudes.

Diseases such as dengue fever, chikungunya and Zika are prevalent in tropical and subtropical regions of the world. They are transmitted by mosquitoes belonging to the type of the genus Aedes which reproduce in water, therefore an increase in precipitation, as well as a greater quantity of stored water during droughts, encourage increased reproduction.

Dengue fever accounts for by far the highest number of arbovirus cases in humans, and the number of cases has more than doubled between 2021 and 2022, from 1.2 million to 2.8 million cases, the The WHO announced last month.

In 2000, half a million cases of dengue fever were reported worldwide, but in 2019, 5.2 million cases were recorded, said Dr Raman Velayudhan, WHO unit chief for the program global fight against neglected tropical diseases.

“In 2022, we had an increase in dengue fever in many parts of the world. In the Americas region, they have recorded 2.8 million cases with over 1,200 deaths. The geographical spread of dengue is expanding,” he added.

“It’s really concerning because it shows that climate change has played a key role in facilitating the spread of the vector, mosquitoes, in the south. In 2023, we already have more than 441,000 cases in the American region and more than 100 deaths from dengue fever.

Chikungunya Alert

There has also been an increase in chikungunya cases, Velayudha reported.

“Currently, we have about 135,000 (chikungunya) cases as of March 31 in the Americas, compared to about 50,000 cases in the first half of 2022,” he said.

“If we want to compare the number of weekly cases, the average weekly cases reported in the Americas range from two to 3,000 (in 2022) and this year we had a record number of almost 35,000 cases in a single week” , Alvarez said. underline.

In February, WHO’s agency for the Americas, the Pan American Health Organization (PAHO), issues an epidemiological alert warning member states to “intensify actions to prepare health care services, including diagnosis and proper case management, to deal with possible outbreaks of chikungunya and other arbovirus diseases, in order 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 reported each year in 89 countries and territories.

Calling the current distribution of disease-causing mosquitoes “alarming”, Alvarez said that wherever mosquitoes are present, people will be at risk. 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 could happen in the northern part of South America, Central America and the Caribbean. We must also be ready to detect some cases in spring and summer in Europe and the northern hemisphere, also in Southeast Asia, because the arbovirus season starts later there.

Vaccines in preparation

For dengue, there are currently an authorized vaccine in about 20 countries, Velayudhan said. “It is effective in people who have had dengue fever before.”

Two other vaccines are in the works, in various stages of trials.

“The second vaccine developed by Takeda is currently being evaluated by our committee. We hope that a recommendation will arrive towards the end of this year. We also have a third vaccine which is currently completing its studies and which could probably be recommended to WHO in 2024,” he explained.

Two antiviral drugs to fight dengue have completed phase one safety trials. “We also hope that the pandemic has provided an opportunity to have several studies on antivirals, and some of these antivirals may be beneficial for dengue and chikungunya and other arboviruses.”

Similarly, three chikungunya vaccines are currently in development, completing phase three trials. “They ask for different approvals in countries. So hopefully we will have chikungunya vaccines soon,” Alvarez said.

She added that for Zika, there had been 45 candidate vaccines underway, but none had gone beyond phase one trials due to lack of funding.

“However, advances in specific chikungunya treatments to prevent congenital Zika syndrome and other neurological complications continue. There are phase two trials of monoclonal antibodies and potential treatments to prevent complications,” he said. she stated.

Picture credits: James Gathany/PHIL, CDC, public domain.