Research and analysis

Outbreaks under monitoring: week 3 (week ending 18 January 2026)

Updated 22 January 2026

Disease or pathogen	Mpox (clade Ib)
Location	Madagascar, Mayotte (overseas department of France), and Spain.
Status	New
Reporting date	17 December 2025 to 15 January 2026
Summary	On 31 December 2025, health authorities in Madagascar declared an outbreak of mpox (in Malagasy) following the country’s first detection on 17 December 2025. Clade Ib mpox infection was confirmed amongst cases by Institut Pasteur de Madagascar on 13 January 2026. As of 15 January 2026, 290 mpox cases (in French) have been reported across 18 regions, including 78 confirmed cases. Most cases have been reported in Boeny (180 cases, of which 61 are confirmed). On 8 January 2026, the Regional Health Agency of Mayotte (in French) reported a travel-associated case of mpox in an individual who had recently travelled to Madagascar. This represents Mayotte’s first detection of mpox. Between August 2024 and 15 January 2026, the European Centre for Disease Prevention and Control reported 45 clade Ib mpox cases in Spain, 34 of which have been among specific Gay, Bisexual and other Men who have Sex with Men (GBMSM) sexual networks. Prior to October 2025, cases had predominantly been associated with travel to clade I mpox affected countries, however there is increasing evidence of local transmission of clade Ib mpox among GBMSM sexual networks in several European countries. In the UK, clade Ib and clade IIb mpox cases have been reported. As of 31 December 2025, 21 clade Ib mpox cases have been reported. 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: Madagascar, Mayotte and Spain.

Disease or pathogen	Argentine Haemorrhagic fever (Junin virus)
Location	Argentina
Status	New
Reporting date	16 January 2026
Summary	On 16 January 2026, media reported (in Spanish) a confirmed case of Argentine haemorrhagic fever (AHF) in Casilda Municipality, Santa Fe, Argentina. Local health authorities implemented epidemiological investigations and control measures. AHF is endemic across Buenos Aires, Cordoba, Sante Fe and La Pampa provinces in Argentina. Most cases are reported during the harvest season in Argentina, which occurs between April and July. There have been no known cases of AHF reported in the UK to date.
Further information	- Argentine Haemorrhagic fever: origins, reservoirs, transmission and guidelines - Viral haemorrhagic fever: ACDP algorithm and guidance on management of patients - NaTHNaC country information page: Argentina

Disease or pathogen	Nipah virus
Location	India
Status	New
Reporting date	13 January 2026
Summary	On 13 January 2026, 2 confirmed cases of Nipah virus (NiV) were reported in Kolkata, West Bengal State, India. Both cases are healthcare workers and were confirmed by the All India Institute of Medical Sciences Kalyani and the National Institute of Virology Pune using RT-PCR. The cases were hospitalised in intensive care in Barasat, and have been receiving Remdesivir. Epidemiological investigations are ongoing to determine the source of infection. A national joint outbreak response team comprising the Union Health Ministry and the State Government was deployed for the testing and tracing of contacts. Media reported that 190 samples collected from identified contacts tested negative for NiV. Prior to the current outbreak, previous outbreaks of NiV infection in West Bengal State were reported in 2001 and 2007. The current outbreak represents the first in West Bengal in 19 years. Between 2018 and 2025, outbreaks have been reported almost annually in Kerala State in south India. There have been no known cases of NiV reported in the UK to date.
Further information	- Nipah virus: epidemiology, outbreaks and guidance - WHO Nipah virus collection - NaTHNaC country information page: India