Mosquito-borne virus Chikungunya expands as climate change fuels spread

A mosquito-borne virus that can leave people debilitated for years is spreading rapidly across the globe, with cases now reported in nearly every region except Antarctica. Health officials warn that climate change is accelerating the spread of chikungunya, a disease closely related to Zika and dengue.

More than 240,000 cases have been reported worldwide so far this year, according to The New York Times.

Latin America accounts for the vast majority, with about 200,000 cases, while China recently reported its first 8,000 infections. Authorities there have responded with aggressive public health measures reminiscent of the early Covid-19 response.

Although chikungunya has not yet established itself in the United States or Canada, local transmission has been documented in France, Italy and Mexico, where the virus is endemic.

The World Health Organization (W.H.O.) warns that current transmission patterns resemble a global outbreak two decades ago, when around 500,000 people were infected, many left with chronic health problems.

“Fatality levels are low, but we really care about chikungunya because it leaves people with months or potentially years of debilitating pain,” said Scott Weaver, scientific director of the Galveston National Laboratory in Texas. “That has not only an individual toll but also a social one, with strain on health care systems, economic impact, the demand on caregivers, a lot of things.”

A painful and prolonged illness

Transmitted by Aedes aegypti and Aedes albopictus mosquitoes, chikungunya typically causes fever, rash and severe joint pain within a week of infection. Unlike dengue and Zika, which often cause mild or asymptomatic cases, chikungunya sickens most people it infects.

“You have people who were working, with no disabilities, and from one day to the next, they cannot even type on a phone, they can’t hold a pen, a woman cannot even hold a knife to be able to cook for her family,” said Dr. Diana Rojas Alvarez, who leads chikungunya work at the W.H.O. “It really impacts quality of life and also the economy of the country.”

Though rarely fatal, the disease can kill young children and the elderly. In up to 40 percent of cases, patients suffer chronic joint pain that lasts months or years. Between 2005 and 2007, more than two-thirds of all disabilities reported in India — including those caused by cancer, arthritis and diabetes — were linked to a massive chikungunya outbreak.

Climate change and global spread

The W.H.O. estimates that 5.6 billion people now live in areas where chikungunya-carrying mosquitoes can survive. A warming climate, heavier rains and extreme weather events are providing more breeding grounds for the insects, while rapid urbanization in parts of Asia and Latin America creates conditions for outbreaks.

The Aedes albopictus mosquito has recently established itself in European cities including Amsterdam and Geneva. In South America, Aedes aegypti thrives in poor urban neighborhoods with unreliable water supplies.

“In the U.S. I don’t think we’re going to see massive outbreaks of chikungunya,” Weaver said. “But in places like China and the Southern Cone of South America, the warming temperatures are going to have a big impact because people don’t stay inside with air-conditioners in their houses or their workplaces. They don’t even like to screen their windows in many parts of Asia and South America.”

Vaccines and prevention

Two vaccines exist but are available in limited quantities, mostly for travelers from wealthy countries. Bavarian Nordic’s newly approved shot costs about $270 in the United States, pricing it out of reach for countries such as Paraguay, which has faced large outbreaks. Brazil’s Butantan Institute is working on a cheaper version.

Neither vaccine currently has a W.H.O. recommendation for widespread use, partly because chikungunya outbreaks erupt and subside too quickly to conduct large-scale clinical trials.

For now, the most effective strategy remains preventing mosquito bites and reducing breeding sites, such as stagnant water. China has mobilized local health workers to inspect homes in an effort to suppress transmission.

A long history, renewed urgency

Chikungunya was first identified in Tanzania in the 1950s and caused sporadic outbreaks for decades. Its global profile rose after a 2004 outbreak in Kenya spread to the Indian Ocean island of La Réunion, infecting a third of the population. From there, the virus traveled to South Asia, the Caribbean and South America, where it continues to circulate.

With climate change expanding mosquito habitats and surveillance systems weakened by reduced international funding, health experts fear chikungunya could trigger more frequent and severe outbreaks in the years ahead.

By Sabina Mammadli