WHO counts 445,271 chikungunya cases in 40 countries over nine months

Between 1 January and 30 September 2025, 40 countries reported a combined 445,271 suspected and confirmed cases of chikungunya virus disease and 155 deaths, the World Health Organization said in a Disease Outbreak News notice published on 3 October [s1]. Of those, 263,592 were suspected cases and 181,679 were laboratory-confirmed [s1].

The notice is unusual for what it declines to say. WHO writes that some regions are seeing significant increases compared with 2024 while others are reporting lower case numbers, and that this uneven distribution "makes it challenging to characterize the situation as a global rise" [s1]. The data, it says, suggest localised resurgence or emergence in specific geographic areas rather than a single worldwide wave [s1].

Where the cases actually are

The Region of the Americas reported the most: 228,591 suspected cases from 14 countries as of 20 September, including 100,329 confirmed cases and 115 deaths [s1]. Brazil accounts for nearly 96 percent of the region's reported cases and deaths, with 96,159 confirmed cases and 111 deaths [s1]. Bolivia reported 5,372 cases, 73 percent of them laboratory-confirmed, and four deaths, with 99 percent of cases in the department of Santa Cruz [s1]. Cuba reported 34 cases, all PCR-confirmed, across five provinces [s1].

The European Region ranks second — an artefact of how WHO assigns French overseas departments. A total of 56,456 cases and 40 deaths were reported from four countries in the region [s1]. Almost all of that is La Réunion in the Indian Ocean, where 54,517 confirmed cases and 40 deaths had been reported as of 14 September [s1]. It was the island's first autochthonous chikungunya transmission since 2014 [s1]. New cases have declined steadily since the week of 26 April, indicating the outbreak is waning [s1]. In Mayotte, 1,255 locally acquired cases including 39 hospitalisations had been reported as of 18 September [s1].

Continental Europe recorded local transmission in two countries. France reported 479 locally acquired cases across 54 clusters, 40 of them still active as of 15 September; Italy reported 205 locally acquired cases across four clusters, three still active [s1]. WHO notes that France reported only one chikungunya case in all of 2024 [s1].

The Western Pacific reported 21,299 cases from 16 countries and areas [s1]. China's Guangdong Province accounted for 16,452 locally transmitted, all laboratory-confirmed, cases as of 27 September — the largest documented chikungunya outbreak in the country to date [s1]. Foshan City alone reported 10,032 [s1]. WHO records no severe cases or deaths among them [s1].

South-East Asia reported more than 34,628 suspected and confirmed cases, primarily from India and Bangladesh [s1]. India reported 30,876 suspected and 1,741 confirmed cases in the first quarter alone [s1]. Thailand reported 1,128 cases through 14 September [s1].

Africa reported the least: 2,197 suspected and 108 confirmed cases from four countries — Comoros, Kenya, Mauritius and Senegal [s1]. Mauritius recorded the most, 1,583 cases between 15 March and 4 August, of which 1,543 were local, with no deaths [s1].

The countries going the other way

Two of the region-level numbers move in the opposite direction, and they are the reason WHO hedges. The Philippines reported 628 cases as of 16 August, a 78 percent decrease from the 2,886 reported in the same period of 2024 [s1]. Malaysia reported 40 cases against 63 in the same period last year, with all three of its clusters contained within two weeks of detection [s1].

Indonesia moved the other way, reporting 3,608 confirmed cases across 19 provinces as of 31 July against 1,399 in the same period of 2024 [s1].

What links La Réunion to Europe

The Indian Ocean epidemic and the European clusters are not independent events. WHO attributes the larger number and earlier onset of chikungunya cases in France this year to the La Réunion and broader Indian Ocean epidemic, driven by a viral strain highly adapted to the Aedes albopictus mosquito [s1].

Sequencing work published in June puts a name to that adaptation. Analysis of 173 genomes from the Réunion epidemic found a monophyletic clade carrying mutations linked to Ae. albopictus adaptation, including E1-A226V [s2]. The virus re-emerged on the island in August 2024, 18 years after the first major outbreak, and Bayesian inference suggested only brief cryptic circulation before detection [s2]. The same lineage was detected on Mayotte in March 2025 [s2].

WHO's notice makes the general version of the point: transmission efficiency is enhanced for chikungunya lineages carrying the E1 226V mutation in Ae. albopictus, the species established across much of southern Europe [s1].

What is not available

There is no specific antiviral treatment for chikungunya [s1]. Clinical management is supportive — fever and joint pain control, hydration, rest — and WHO advises paracetamol or acetaminophen for pain relief until dengue is ruled out, because non-steroidal anti-inflammatory drugs can increase bleeding risk [s1].

Two chikungunya vaccines have received regulatory approvals or recommendations for use in at-risk populations in several countries, but WHO states they are not yet widely available nor in widespread use [s1]. WHO and external expert advisors are reviewing vaccine trial and post-marketing data against current global epidemiology to inform possible recommendations for use [s1]. No such recommendation exists as of the notice's publication.

The number to be careful with

The 445,271 figure combines suspected and confirmed cases reported through different national systems with different testing capacity, and the date of last report varies by country [s1]. Some of the regional totals are current only to July or August. WHO states plainly that countries differ in their ability to detect and report chikungunya, and that many outbreaks are identified only retrospectively [s1].

That cuts both ways. It means the global total is not a precise count, and it means the true burden in the least-surveilled places is likely higher than the table shows — Africa's 2,197 suspected and 108 confirmed cases across four countries being the most conspicuous candidate.

What to watch

WHO's stated concern is introduction into places that have never had local transmission. Before 2025, 119 countries and territories had reported current or previous autochthonous chikungunya transmission; a further 27 have established, competent Aedes aegypti populations but no documented local transmission yet [s1]. Additional countries have established Ae. albopictus populations [s1].

The Réunion outbreak is receding and the Guangdong outbreak is being counted in a system that has recorded no deaths from it. Neither of those closes the question the notice raises, which is whether a lineage adapted to a mosquito with a far wider temperate range than Ae. aegypti changes where chikungunya can establish.

Sources

• Disease Outbreak News: Chikungunya virus disease – Global situation — World Health Organization, 3 October 2025
• Genomic insights into the re-emergence of chikungunya virus on Réunion Island, France, 2024 to 2025 — Eurosurveillance, 1 June 2025