The World Health Organization warned Wednesday that dengue fever and other diseases caused by mosquito- borne viruses are spreading faster and more widely due to climate change, raising fears of a worldwide outbreak.

World Health Organization experts sounded the alarm about rising cases of dengue fever and chikungunya, and said they expected the Zika virus to spread again in the world.

These three diseases are spread by arthropod viruses (viruses transmitted by arthropods), which are transmitted to humans by mosquitoes of the genus Aedes, called tiger mosquitoes.

"Climate change has played a major role in facilitating the spread of mosquito vectors," Raman Velayudhan, coordinator of the WHO's Dengue Fever and Virus Initiative, told a news conference.

With his colleague Diana Rojas-Alvarez, who is in charge of controlling chikungunya and Zika viruses, Velayudan called for swift action to curb the spread of mosquitoes, in the face of the risk of the disease spreading outside the areas of historical transmission.

Velayudhan urged countries to "exercise caution" in detecting the spread of the disease "to avoid any major outbreak".

Dengue remains endemic in 100 countries, but poses a threat to 29 others.

Velayudhan said the number of cases has skyrocketed in recent years, from nearly half a million in 2000 to 5.2 million in 2019, the worst year on record.

Cases were not properly reported during the Covid pandemic, but numbers remained high.

Meanwhile, infections of chikungunya, which have so far been reported in 115 countries since it was discovered in the 1950s, are on the rise in the Americas region, Rojas-Alvarez said.

Since January, about 135,000 cases have been reported in this region, compared to 50,000 in the first half of 2022.

Perhaps the most worrisome thing is the geographical expansion of these two diseases, from the Americas in the south to the northern hemisphere, including some European countries.

"With climate change, mosquitoes have multiplied and the spread of these diseases has expanded ... in latitude and longitude," Rojas-Alvarez said, describing the situation as "alarming".

And she warned that this strong outbreak in the Americas "could be an indication of what the next summer season might be like in the northern hemisphere."

Both diseases often cause mild symptoms (fever, body aches, and rash).

Most people who contract chikungunya only feel symptoms for a week, but 40% feel the effects for months or even years.

Rojas warned Alvarez that chikungunya could lead to permanent disability.