Research and analysis

Outbreaks under monitoring: week 40 (week ending 5 October 2025)

Updated 9 October 2025

Disease or pathogen	Chikungunya
Location	Global
Status	Situation update
Reporting date	3 October 2025
Summary	On 3 October 2025, the World Health Organization (WHO) reported a resurgence of chikungunya in several countries, including countries that have not recorded a notable increase in number of cases over recent years. According to the WHO, 445,271 chikungunya cases (including suspected and confirmed cases, both locally acquired and imported), and 155 deaths have been reported from 40 countries between 1 January and 30 September 2025. The highest number of cases have been reported in the Region of the Americas (328,920 cases and 115 deaths) and the European Region (56,456 cases and 40 deaths). In the European Region, France and Italy have reported active chikungunya outbreaks in 2025. In France, between 1 May and 29 September 2025, 633 locally acquired cases of chikungunya [in French] have been reported. The number of locally acquired cases recorded in 2025 is the highest since 2010. For the first time ever, locally acquired cases were reported in the departments of Grand Est, Bourgogne-Franche-Comte and Nouvelle-Aquitaine. The WHO states the increased incidence in 2025 is linked to the chikungunya outbreak in Reunion and the rest of the Indian Ocean region. In Italy, between 1 January and 30 September 2025, 364 confirmed cases [in Italian] (including 323 locally acquired and 41 travel associated cases) and no deaths have been reported. The number of locally acquired cases reported in 2025 is the highest since 2017 [in Italian]. In Reunion, between 1 January and 14 September 2025, 54,517 confirmed cases and 40 deaths have been reported. A decline in newly reported cases has been observed since 26 April 2025. The WHO states that the variation in case trends among reporting countries makes it difficult to classify the current picture as a global increase in chikungunya cases. However, the risk of further geographical spread of chikungunya to new areas remains noteworthy in the event of limited population immunity, favourable climate conditions for vector establishment, increased human movements and trades and gaps in public health systems. In the United Kingdom (UK), an increase in travel-associated chikungunya cases has been reported in 2025. Most cases reported travel to Sri Lanka, India and Mauritius. No locally acquired cases of chikungunya have ever been reported in the UK.
Further information	Chikungunya: transmission, epidemiology and guidance Chikungunya: epidemiology in England, Wales and Northern Ireland NaTHNaC: Chikungunya

Disease or pathogen	Ebola virus disease
Location	Democratic Republic of the Congo (DRC)
Status	Situation update
Reporting date	4 September to 3 October 2025
Summary	On 4 September 2025, the DRC’s Ministry of Health reported an outbreak [in French] of Ebola virus disease (EVD) in Bulape health zone, Kasai province. As of 30 September 2025, 64 EVD cases (53 confirmed and 11 probable cases) including 42 deaths (31 confirmed and 11 probable cases) have been reported in Bulape health zone. According to the WHO, a decrease in newly reported cases has been observed in recent weeks and since 30 September 2025, no new EVD cases have been reported. The Emergency Response Coordination Centre of the European Commission reported that as of 3 October 2025, EUR 1,800,000 emergency humanitarian aid funding has been provided by humanitarian partners to strengthen the ongoing response to the outbreak. The WHO assesses the public health risk of this outbreak as high at the national level, moderate at the regional level and low at the global level. Imported cases of Ebola disease are very rare in the UK. Four confirmed cases, and no deaths, have been previously reported in the UK. The last reported confirmed case was in 2014
Further information	Ebola: overview, history, origins and transmission Ebola virus disease: clinical management and guidance Ebola and Marburg haemorrhagic fevers: outbreaks and case locations NaTHNaC country information page: Democratic Republic of the Congo.

Disease or pathogen	Legionella
Location	France
Status	Situation update
Reporting date	3 October 2025
Summary	On 23 September 2025, the Auvergne-Rhone-Alpes Regional Health Agency reported a cluster of Legionnaires’ disease cases [in French] in Albertville, Savoie department, France. Between 16 September and 3 October 2025, 50 confirmed cases [in French] and 2 deaths were reported. This is an increase of 4 cases since the last report on 26 September 2025. Investigations are still ongoing to identify the source of exposure. In the UK, Legionnaires’ disease cases follow a seasonal pattern, with a peak number typically reported between June and October. Between 2017 and 2023, 3,276 cases of Legionnaires’ disease were reported in the UK. In 2023, 212 of 604 confirmed Legionella exposures (35.1%) were related to travel abroad.
Further information	Legionnaires’ disease: guidance, data and analysis NaTHNaC country information page: France

For more information on the background and methods used in this report, see Outbreaks under monitoring: background and methodology.