Research and analysis

Outbreaks under monitoring: week 38 (week ending 21 September 2025)

Updated 25 September 2025

Disease or pathogen	Chikungunya
Location	France
Reporting date	17 September 2025
Summary	Between 1 May and 15 September 2025, 479 locally acquired cases of chikungunya were recorded in mainland France. This is an increase of 178 cases since the last report on 3 September 2025. On 17 September 2025, Sante Publique France reported that several metropolitan regions in France are experiencing an increased circulation of arboviruses. The reported number of locally acquired chikungunya cases in France is the highest since 2010. 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 country information page: France

Disease or pathogen	Ebola virus disease
Location	Democratic Republic of the Congo (DRC)
Reporting date	4 to 18 September 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. This is the sixteenth EVD outbreak reported in the DRC. According to the World Health Organization (WHO), 48 EVD cases (including 38 confirmed) and 31 deaths have been reported from Bulape, Kasai province as of 17 September 2025. The first 2 EVD cases to recover in the current outbreak were discharged on 15 September 2025. As of 16 September 2025, 523  healthcare workers in Bulape and contacts of confirmed cases have been vaccinated. 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 (EBOD) are very rare in the UK. Four confirmed cases of EBOD, and no deaths, have been previously reported in the UK. The last reported confirmed case of EBOD in the UK 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	Nipah virus (NiV) infection
Location	Bangladesh
Reporting date	18 September 2025
Summary	On 18 September 2025, the WHO reported that 4 confirmed fatal NiV cases were recorded in Bangladesh between 1 January and 29 August 2025. According to the WHO, the cases had symptom onset dates between 25 January and 3 August 2025. No epidemiological link was identified between the cases. Three of the cases had a history of consuming raw date palm sap while the fourth case’s source of infection is still being investigated. The NiV cases who consumed raw date palm sap were reported during the expected season for NiV outbreaks (December to May), while the fourth case presented outside of this seasonal pattern. Since the first Nipah virus outbreak in Bangladesh in 2001 and as of 18 September 2025, 347 NiV cases have been reported. No NiV cases (including travel-associated) have ever been reported in the UK.
Further information	Nipah virus: epidemiology, outbreaks and guidance WHO Nipah virus collection NaTHNaC country information page: Bangladesh

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