Research and analysis

Outbreaks under monitoring: week 36 (week ending 7 September 2025)

Updated 11 September 2025

Disease or pathogen	Chikungunya
Location	France
Reporting date	3 September 2025
Summary	Between 1 May and 2 September 2025, 301 locally acquired cases of chikungunya were recorded in mainland France. This is an increase of 73 cases since the last report on 27 August 2025. 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	Cholera
Location	Global
Reporting date	26 August 2025
Summary	On 29 August 2025, the World Health Organization (WHO) reported a deterioration in the global cholera situation that is being driven by conflict and other humanitarian crises. According to the WHO, 409,222 cholera and acute watery diarrhoea cases and 4,738 deaths (case fatality rate (CFR) of 1.2%) have been reported from 31 countries between 1 January and 17 August 2025. The highest number of cases have been registered in the Eastern Mediterranean region (230,991 cases and 943 deaths, CFR of 0.4%) and the highest number of deaths were reported in the African region (172,750 and 3,763 deaths, CFR of 2.2%). The number of fatalities recorded in 2025 is 46% higher when compared to the equivalent 2024 period (3,248 deaths reported globally from 28 countries). The WHO reported a resurgence of cholera in Chad and the Republic of the Congo, and a geographical expansion of cholera outbreaks in the Democratic Republic of the Congo (DRC), South Sudan, and Sudan. The last locally acquired cholera case in England and Wales was reported in 1893. Cholera is occasionally reported in returning UK travellers.
Further information	Cholera: guidance, data and analysis Travel-associated infections reports Green Book: Cholera Gastrointestinal infections: guidance for public health management NaTHNaC Topics in Brief: Cholera

Disease or pathogen	Ebola virus disease
Location	Democratic Republic of the Congo (DRC)
Reporting date	4 to 8 September 2025
Summary	On 4 September 2025, the DRC’s Ministry of Health (MoH) reported an outbreak of Ebola virus disease (EVD) in Kasai Province. This is the sixteenth EVD outbreak reported in the DRC. According to the WHO country office in the DRC, 28 EVD cases (including 5 confirmed) and 15 deaths (CFR of 53.6%) have been reported as of 5 September 2025. Suspected cases have been reported in Bulape and Mweka health zones. Further media reports have since indicated that 33 suspected cases and 16 deaths have been reported. The presumed index case, a pregnant woman, presented to Bulape General Reference Hospital on 20 August 2025 with symptoms of high fever, bloody diarrhoea, haemorrhage and extreme weakness. She died on 25 August 2025 from multiple organ failure. Two health-care workers that had contact with this first case also developed similar symptoms and died. The WHO states that approximately 80% of the suspected cases are aged 15 years and older. In response to the outbreak, frontline responders from the DRC MoH and WHO have arrived Bulape health zone and delivered the first batch of emergency health supplies. The WHO has shipped 12 tonnes of medical supplies and equipment from its emergency preparedness and response hub in Nairobi, Kenya to the DRC. Vaccination of frontline responders that may be deployed to the affected area has begun in Kinshasa. Monoclonal antibodies are available at the national level for deployment to Bulape and Mweka. Genomic analysis suggests that this outbreak is likely a zoonotic spillover event and is not directly linked to the previous outbreak in Luebo (2007) and Mweka (2008 to 2009). The WHO assess 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 EVD 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	Severe fever with thrombocytopaenia syndrome
Location	Japan and South Korea
Reporting date	2 to 3 September 2025
Summary	On 3 September 2025, media reported that 153 Severe Fever with Thrombocytopenia Syndrome (SFTS) cases have been recorded in South Korea between 1 January and 31 August 2025. This compares to 89 SFTS cases reported during the same period in 2024. In Japan, between 1 January and 24 August 2025, 142 SFTS cases have been reported. Kochi Prefecture reported the highest number of cases (14 cases). The number of SFTS cases reported in 2025 is higher than the number reported in 2024 (120 cases). No known SFTS cases have been reported in the UK.
Further information	Severe fever with thrombocytopaenia syndrome (SFTS): epidemiology, outbreaks and guidance NaTHNaC country information page: Japan and South Korea

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