Research and analysis

Outbreaks under monitoring: week 42 (week ending 19 October 2025)

Updated 23 October 2025

Disease or pathogen	Chikungunya
Location	France and the United States
Status	Situation update
Reporting date	14 to 16 October 2025
Summary	In France, 729 locally acquired cases of chikungunya [in French] have been reported between 1 May and 13 October 2025. 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, Centre-Val de Loire and Nouvelle-Aquitaine. The World Health Organization (WHO) states the increased incidence in 2025 is linked to the chikungunya outbreak in Reunion and the rest of the Indian Ocean region.  In the United States, the New York Department of Health reported a confirmed chikungunya case in Nassau County, New York. This is the first locally acquired chikungunya case reported in the United States since 2019. On 15 October 2025, media reported that the case started to experience symptoms in August 2025 after travelling out of the region, however they had not travelled outside of the country. Health officials reported that the case was likely bitten by an infected mosquito. The virus has not been detected in local mosquito pools, and there is no evidence of ongoing transmission. In the 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 and the United States

Disease or pathogen	Ebola virus disease
Location	Democratic Republic of the Congo (DRC)
Status	Situation update
Reporting date	4 September to 7 October 2025
Summary	On 4 September 2025, the DRC’s Ministry of Health (MoH) declared an outbreak [in French] of Ebola virus disease (EVD) in Bulape health zone, Kasai Province. As of 19 October 2025, 64 EVD cases (53 confirmed and 11 probable cases) including 45 deaths (34 confirmed and 11 probable deaths) have been reported in Bulape health zone. This is an increase of 2 deaths among previously confirmed cases since the last report. A total of 19 patients have recovered and since been discharged from an Ebola treatment centre. On 19 October 2025, the last EVD patient was discharged from hospital following recovery, triggering a 42-day countdown to declaration of the outbreak being over pending no further cases. 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 previously been 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	Middle East respiratory syndrome
Location	Saudi Arabia
Status	New incident
Reporting date	3 September to 10 October 2025
Summary	Between 1 January and 6 October 2025, 12 Middle East respiratory syndrome (MERS) cases were reported in Saudi Arabia. The latest case was reported in August 2025. The UK has previously reported imported cases of MERS. 5 cases and 2 deaths were reported between 2012 and 2018 with 3 of these cases classed as imported cases and 2 cases were secondary cases in close family members.
Further information	MERS-CoV: clinical management and guidance NaTHNaC country information page: Saudi Arabia

Disease or pathogen	Mpox (clade I)
Location	Multi-region (United States and Europe)
Status	New incident
Reporting date	14 to 16 October 2025
Summary	During epidemiological week 41 of 2025 (13 to 19 October 2025), the first clade I  mpox cases with no travel history to a region where clade I mpox is known to be in circulation was reported in the United States and in Europe. On 14 October 2025, the  first case of clade I mpox in the City of Long Beach, California, was confirmed. This is the seventh clade I mpox case in the United States, and the first without known travel history.  The city Health Department is reviewing the cases potential source of exposure and is conducting contact tracing. On 16 October 2025, the Los Angeles County Department of Public Health reported a new confirmed case of clade I mpox in an adult that had no recent travel History. A public health advisory was issued by the California Department of Public Health (CDPH) on 17 October 2025 stating that 3 cases of clade I mpox had been detected with no recent history of international travel. The clade subtype was not specified. These cases were not stated to be epidemiologically linked. All 3 cases were detected within the gay, bisexual, and other men who have sex with men (GBMSM) community.  CDPH states that the overall public health risk of clade I mpox to the population in California and the US continues to be low. On 10 October 2025, a confirmed clade Ib mpox case was reported in Madrid, Spain. The individual was a male who had symptom onset on 3 October 2025 and reported having sex with two men who did not have signs or symptoms of mpox. The case reported no recent international travel history. Laboratory and clade type confirmation was received on 16 October 2025 [in Spanish]. This is the first autochthonous transmission of clade I mpox in Spain, and the first reported clade Ib mpox case within the GBMSM community in the EU/EEA. The European Centre for Disease Prevention and Control states that given the low probability of infection and the very low impact of an infection, the risk to the GBMSM community is estimated to be low.   In the UK, clade Ib and clade IIb mpox cases have been reported. As of 16 October 2025, 16 clade Ib mpox cases have been reported, all in England. Most of the cases have direct or indirect travel links to countries where clade Ib mpox is circulating.
Further information	Mpox: guidance Mpox clade Ib and clade IIb outbreak: epidemiological overview NaTHNaC country information page: United States

Disease or pathogen	Rift Valley fever
Location	Mauritania and Senegal
Status	Situtation update
Reporting date	26 September to 17 October 2025
Summary	On 26 September 2025, Senegal’s Ministry of Health and Public Hygiene reported an outbreak [in French] of Rift Valley fever (RVF) in the Saint-Louis region. As of 15 October 2025, 245 RVF cases [in French], including 21 deaths, have been reported. Most cases have been reported in Saint-Louis region (197 cases). This is an increase of 98 cases and 2 deaths since the last report [in French]. The last reported human RVF outbreak in Senegal was in Saint-Louis region in 2020 and resulted in 9 cases. On 27 September 2025, Mauritania’s MoH [in Arabic] reported a fatal RVF case in Rosso City. The MoH states that the case had returned from an unspecified neighbouring country. Ten contacts of the fatal case were initially identified. Between 1 January and 14 October 2025, 89 RVF cases (29 confirmed) and 12 deaths have been reported across 13 regions of Mauritania. This is an increase of 81 cases (including confirmed cases) and 6 deaths since previous media reports valid for 8 October 2025, with geographical expansion to 10 more regions. Genomic analysis suggests that the current RVF outbreak in Senegal is directly linked to the previous outbreaks in Senegal (Fatick in 2020 and Matam in 2022) and Mauritania (2020). No known human RVF cases have been reported in the UK.
Further information	Viral haemorrhagic fevers: origins, reservoirs, transmission and guidelines NaTHNaC country information page: Senegal