Research and analysis

Global high consequence infectious disease events: summary December 2024

Updated 3 April 2025

Interpreting this report

The report provides updates on known, high consequence infectious disease (HCID) events around the world as monitored by UK Health Security Agency’s (UKHSA) epidemic intelligence activities.

The report is divided into 2 sections covering all the defined HCID pathogens. The first section contains contact and airborne HCIDs that have been specified for the HCID programme by NHS England. The second section contains additional HCIDs that are important for situational awareness.

Each section contains information on known pathogens and includes descriptions of recent events. If an undiagnosed disease event occurs that could be interpreted as a potential HCID, a third section will be added to the report.

Events found during routine scanning activities that occur in endemic areas will briefly be noted in the report. Active surveillance, other than daily epidemic intelligence activities, of events in endemic areas will not be conducted (for example, actively searching government websites or other sources for data on case numbers).

The target audience for this report is any healthcare professional who may be involved in HCID identification, treatment and management.

Risk rating

Included for each disease is a current risk rating based on the probability of introduction to the UK and potential impact on the UK public. Past UK experience and the global occurrence of travel-associated cases are also considered. Currently, all diseases are classified into one of 3 categories: Low, very low and exceptionally low to negligible.

Incidents of significance of primary HCIDs

Contact HCIDs

Crimean-Congo haemorrhagic fever (CCHF)

Geographical risk areas	Endemic in Africa, the Balkans, the Middle East and western and south-central Asia. Cases have also been reported in Russia and Georgia. Spain has previously reported locally acquired cases (first reported in 2016, with the latest case reported in 2024). Portugal reported its first human case in August 2024 with symptom onset in July 2024.
Sources and routes of infection	• bite from, or crushing of, an infected tick  • contact with the blood, tissues or body fluids of infected humans or animals
UK experience to date	Two cases have been reported in individuals who have travelled to the UK from Afghanistan in 2012 and Bulgaria in 2014.
Risk rating	Low – rarely reported in travellers.
Recent cases or outbreaks	During December 2024, 21 new cases of CCHF and one associated death was reported in Afghanistan. Between 1 January and 28 December 2024, Afghanistan reported 1,221 suspected cases of CCHF and 95 associated deaths equating to a case fatality rate (CFR) of 7.8%.

Ebola disease (EBOD)

Geographical risk areas	Map of Ebola disease in Africa
Sources and routes of infection	• contact with blood, tissues or body fluids of infected animals, or consumption of raw or undercooked infected animal tissue • contact with infected human blood or body fluids
UK experience to date	Four confirmed cases (one lab-acquired in the UK in 1976, 3 healthcare workers associated with West African epidemic 2014 to 2015).
Risk rating	Very low – other than during the West Africa outbreak, exported cases are extremely rare.
Recent cases or outbreaks	No confirmed or suspected human cases were reported in December 2024.

Lassa fever

Geographical risk areas	Endemic in sub-Saharan West Africa.
Sources and routes of infection	• contact with excreta, or materials contaminated with excreta from an infected rodent  • inhalation of aerosols of excreta from an infected rodent  • contact with infected human blood or body fluids
UK experience to date	Three travel-related Lassa fever cases reported in 2022. Prior to this, 8 imported Lassa fever cases had been reported since 1980, all in travellers from West Africa.
Risk rating	Low – overall, Lassa fever is the most common imported viral haemorrhagic fever (VHF) but importations to the UK are still rare.
Recent cases or outbreaks	Between 1 January and 29 December 2024, Nigeria reported 11,407 Lassa fever cases (1,309 confirmed; 10,098 suspected; 23 probable). 214 deaths were reported amongst confirmed cases (case fatality rate (CFR) of 16.3%). This is a lower CFR compared to the same period in 2023 (17.9%). Confirmed cases have been reported from 28 out of 36 states. 955 cases (192 confirmed cases) were reported during December 2024.

Marburg virus disease (MARD)

Geographical risk areas	Sporadic outbreaks have previously been reported in Central and Eastern Africa. Outbreaks were reported for the first time in Guinea (in 2021), Ghana (in 2022), Equatorial Guinea and Tanzania (in 2023) and Rwanda (in 2024).
Sources and routes of infection	• exposure in mines or caves inhabited by Rousettus bat colonies • contact with infected human blood or body fluids
UK experience to date	No reported cases in the UK.
Risk rating	Very low – globally, 5 travel-related exported MARD cases have previously been reported in the literature.
Recent cases or outbreaks	On 20 December 2024, the Ministry of Health of Rwanda declared an end to the MARD outbreak which started on 27 September 2024. The WHO summary for this outbreak can be found here.

Airborne HCIDs

Avian influenza A(H7N9) virus

Geographical risk areas	All reported human infections have been acquired in China.
Sources and routes of infection	• close contact with infected birds or their environments  • close contact with infected humans (no sustained human-to-human transmission)
UK experience to date	No known cases in the UK.
Risk rating	Very low (UKHSA risk assessment).
Recent cases or outbreaks	No confirmed or suspected human cases were reported in December 2024.

Avian influenza A(H5N1) virus

Geographical risk areas	Human cases have been predominantly reported in Southeast Asia, but also in Egypt, Iraq, Pakistan, Turkey and Nigeria. Since 2022, human cases of clade 2.3.4.4b have been reported in Spain, the US, and the UK, Ecuador and Chile. Since October 2023, 11 human cases of clade 2.3.2.1c have been reported in Cambodia.
Sources and routes of infection	• Close contact with infected animals (notably birds) or their environments • Close contact with infected humans is a theoretical risk although there is currently no evidence of any human-to-human transmission having occurred).
UK experience to date	Since December 2021, 7 detections were reported in the UK, one in 2022, 4 in 2023 and one in 2024.
Risk rating	Very low (UKHSA risk assessment).
Recent cases or outbreaks	Between 1 January and 31 December 2024, a total of 66 confirmed human cases of avian influenza A(H5) or A(H5N1) have been reported in the US. 7 probable cases were also reported during 2024. Probable cases were cases that were unable to be confirmed at US CDC laboratories. During December 2024, 10 cases were reported in the US in the states of California (8 cases), Iowa (one), Wisconsin (one). During 2024, 10 US states reported cases: California, Colorado, Iowa, Louisiana, Michigan, Missouri, Oregon, Texas, Washington and Wisconsin. The probable cases were reported from Arizona, California, Delaware and Washington. Of the 66 confirmed cases reported in the US, 40 cases were associated with the dairy cattle industry, 23 cases with the poultry industry or poultry culling operations, 1 case with non-agricultural animal exposure and 2 cases with unidentified exposure source/s. Notably, on 18 December 2024, the US CDC confirmed the first severe case of avian influenza A(H5N1) infection in a human. The individual had backyard exposure to sick and dead birds. A technical summary from genetic sequencing for this case was published which showed some changes to virus receptor binding motifs. This virus belonged to clade 2.3.4.4b, genotype D1.1 which is different to genotype B3.13 currently associated with dairy cattle infections. For further information see the US Centres for Disease Control and Prevention H5 Bird Flu: Current Situation webpage.

Middle East respiratory syndrome (MERS-CoV)

Geographical risk areas	MERS has been concentrated in countries from the Arabian Peninsula, with the majority of cases having occurred in the Kingdom of Saudi Arabia. Other previously affected countries in the region include Yemen, Oman, United Arab Emirates, Qatar, Bahrain, Kuwait, Jordan, Lebanon and Iran. MERS is transmitted from camels and has been detected in camels from the Arabian Peninsula and also parts of North, West and Eastern Africa.
Sources and routes of infection	• Transmission through the air •Direct contact with contaminated environment • Direct contact with camels or consumption of raw camel milk • Working in or exposure to healthcare settings where outbreaks are occurring airborne particles
UK experience to date	Five cases in total – 3 imported cases (2012, 2013 and 2018), 2 secondary cases in close family members of the case in 2013, 3 deaths.
Risk rating	Very low (UKHSA risk assessment).
Recent cases or outbreaks	No confirmed or suspected human cases were reported in December 2024.

Mpox (Clade I only)

Geographical risk areas	Central and East African countries including Burundi, Cameroon, Central African Republic, Democratic Republic of the Congo, Gabon, Kenya, Republic of the Congo, Rwanda, and Uganda.
Sources and routes of infection	• close contact with an infected animal (in an endemic country) or an infected person • contact with clothing or linens (such as bedding or towels) used by an infected person • direct contact with mpox skin lesions or scabs • coughing or sneezing of an individual with an mpox rash • consumption of contaminated bushmeat
UK experience to date	Five cases in total – 3 imported cases (2024) and 2 secondary cases in household members of a case from 2024.
Risk rating	The importation risk of clade I mpox into the UK is considered medium. The risk of potential spread in the UK and risk of acquisition in the UK is considered low to medium. Travel-associated cases of clade I mpox have been reported from Belgium, Canada, Germany, India, Oman, Pakistan, Sweden, Thailand, United States. Secondary transmission of cases within household contacts has been reported in the UK, Germany and Belgium.
Recent cases or outbreaks	In endemic countries where clade I mpox is know to circulate access to subclade specific PCR or sequencing may be limited. Therefore, we report below all reported mpox cases from these countries, regardless of whether the samples have undergone specific subclade testing. A comprehensive list of mpox clade I affected countries is available from the UKHSA. Burundi declared an mpox outbreak on 25 July 2024. As of 22 December 2024, 2,861 confirmed cases and 1 death have been reported from 45 out of 49 health districts. The Central African Republic reported 573 cases of mpox (89 confirmed) and 3 deaths (CFR of 3.1%) between 1 January and 8 December 2024. Clade Ia mpox was detected in confirmed cases. Between 1 January and 15 December 2024, the Democratic Republic of the Congo (DRC) reported 59,120 mpox cases (13,056 confirmed), including 1,308 deaths (CFR of 2.2%), from all 26 provinces. Of which,  7,475 cases (1,653 confirmed) and 80 cases were reported during December 2024. During 2023, the DRC reported its highest annual number of mpox cases (14,434 cases, including 728 deaths). Kenya officially reported its first confirmed case of clade Ib mpox on 31 July 2024. During December 2024, it reported 8 new cases of mpox, and as of 30 December 2024 recorded a  cumulative total of 31 confirmed cases and 1 death (CFR of 3.2%) across 12 counties. The mpox death was reported in an individual with HIV co-infection. Uganda first identified 2 confirmed cases of clade Ib mpox on 15 July 2024. During December 2024, it reported 525 new cases (519 confirmed), and as of 29 December 2024 recorded a cumulative total of 1,309 cases (1,303 confirmed) and 6 deaths (CFR of 0.5 %) across 60 districts. Rwanda declared an outbreak of clade Ib mpox on 26 July 2024. During December 2024, it reported 1,260 new cases (30 confirmed), and as of 29 December 2024 recorded a cumulative total of 5,618 cases (82 confirmed). Zambia reported its first clade Ib mpox case during November 2024. During December 2024, 2 new cases were reported within the same household, with the clade type not reported, bringing the total case count to 3 cases. During December 2024, 4 countries outside of the African Region reported travel-associated cases of clade I mpox. Of these, 3 countries reported their first-ever detections (Belgium, Oman and Pakistan) and one country reported its second travel-associated case (Germany). The cases reported from Pakistan and Oman had a travel history to the United Arab Emirates (UAE). The UAE has not reported any cases of clade Ib mpox during 2024.

Nipah virus

Geographical risk areas	South East Asia, predominantly in Bangladesh and India. Cases have also been reported in Malaysia and Singapore.
Sources and routes of infection	• direct or indirect exposure to infected bats • consumption of contaminated raw date palm sap • close contact with infected pigs or humans
UK experience to date	No known cases in the UK.
Risk rating	Exceptionally low to negligible – no travel-related infections in the literature.
Recent cases or outbreaks	No confirmed or suspected human cases were reported in December 2024.

Pneumonic plague (Yersinia pestis)

Geographical risk areas	Predominantly sub-Saharan Africa but also Asia, North Africa, South America, Western USA. Endemic in Madagascar, Peru, and the DRC.
Sources and routes of infection	• flea bites  • close contact with infected animals  • close contact with human cases of pneumonic plague
UK experience to date	Last outbreak in the UK was in 1918.
Risk rating	Exceptionally low to negligible
Recent cases or outbreaks	No confirmed or suspected human cases were reported in December 2024.

Severe acute respiratory syndrome (SARS)

Geographical risk areas	Currently none. Two historical outbreaks originating from China in 2002 and 2004.
Sources and routes of infection	• airborne particles  • direct contact with contaminated environment
UK experience to date	Four imported SARS cases related to the 2002 outbreak.
Risk rating	Exceptionally low to negligible
Recent cases or outbreaks	No confirmed or suspected human cases reported globally since 2004.

Incidents of significance of additional HCIDs

Argentine haemorrhagic fever (Junin virus)

Geographical risk areas	Argentina (central). Endemic to the provinces of Buenos Aires, Córdoba, Santa Fe and La Pampa.
Sources and routes of infection	• direct contact with infected rodents  • inhalation of infectious rodent fluids and excreta  • person-to-person transmission has been documented
UK experience to date	No known cases in the UK.
Risk rating	Exceptionally low to negligible – one travel-related case was identified in Belgium in 2020.
Recent cases or outbreaks	Between 1 January 2024 and 29 December 2024, 23 confirmed of Argentine haemorrhagic fever (AHF) were reported in Argentina. During 2024, the most affected district was San Nicolas which had 19 confirmed AHF cases. The number of confirmed cases is higher compared to 2023 (7 confirmed cases) and similar to 2022 (27 confirmed cases).

Bolivian haemorrhagic fever (Machupo virus)

Geographical risk areas	Bolivia – cases have been identified in the departments of Beni (Mamoré, Iténez and Yucuma provinces) and Cochabamba (Cercado province).
Sources and routes of infection	• direct contact with infected rodents  • inhalation of infectious rodent fluids and excreta  • person-to-person transmission has been documented
UK experience to date	No known cases in the UK.
Risk rating	Exceptionally low to negligible – travel-related cases have never been reported.
Recent cases or outbreaks	No confirmed or suspected human cases were reported in December 2024.

Lujo virus disease

Geographical risk areas	A single case acquired in Zambia led to a cluster in South Africa in 2008.
Sources and routes of infection	• presumed rodent contact (excreta, or materials contaminated with excreta of infected rodent)  • person to person via body fluids
UK experience to date	No known cases in the UK.
Risk rating	Exceptionally low to negligible – a single travel-related case has been reported. No cases have been reported anywhere since 2008.
Recent cases or outbreaks	No cases have been reported anywhere since 2008.

Severe fever with thrombocytopenia syndrome (SFTS)

Geographical risk areas	Mainly reported from China (south-eastern), Japan and Korea. Cases have also been reported in Taiwan, Thailand, Myanmar and Vietnam. Serological evidence of SFTS in Pakistan.
Sources and routes of infection	• presumed to be tick exposure  • person-to-person transmission described in household and hospital contacts, via contact with blood or bloodstained body fluids
UK experience to date	No known cases in the UK.
Risk rating	Exceptionally low to negligible – not known to have occurred in travellers.
Recent cases or outbreaks	Between January and 26 December 2024, the Korea Disease Control and Prevention Agency reported 169 SFTS cases. 1 case during December 2024. This is a lower number of reported cases compared to the 5 year average (2019 – 2023) (205 cases). Between January and 29 December 2024, Japan’s National Institute of Infectious Diseases reported 120 SFTS cases. During December 2024, 3 SFTS cases were reported.

Andes virus (Hantavirus)

Geographical risk areas	Chile and Southern Argentina.
Sources and routes of infection	• rodent contact (excreta, or materials contaminated with excreta from an infected rodent) • person-to-person transmission described in household and hospital contacts
UK experience to date	No known cases in the UK.
Risk rating	Very low – rare cases in travellers have been reported.
Recent cases or outbreaks	On 13 December 2024, the Department of Health in Ñuble region of Chile, reported a new confirmed case of hantavirus with cardiopulmonary syndrome. The exact type was not reported. This brings the total case count in 2024 to 5 cases. During 2023, 7 cases of hantavirus infection and 1 death were reported Ñuble region, Chile. During December 2024, the Buenos Aires Provincial Department of Health reported 3 confirmed cases of hantavirus (the type was not reported). The cumulative total at the end of December 2024 is 69 cases (11 confirmed, 58 were under investigation) and 2 deaths..

Avian influenza A(H5N6) virus

Geographical risk areas	Mostly China. New strain reported in Greece in March 2017, and subsequently found in Western Europe in birds.
Sources and routes of infection	Close contact with infected birds or their environments.
UK experience to date	No known cases in the UK.
Risk rating	Very low – not known to have occurred in travellers (UKHSA risk assessment).
Recent cases or outbreaks	No confirmed or suspected human cases were reported in December 2024.

Avian influenza A(H7N7) virus

Geographical risk areas	Sporadic occurrence in birds across mainland Europe and the UK. A human case was reported in Ireland in 1996, 89 cases were reported in the Netherlands in 2003, and 3 human cases were reported in Italy in 2013.
Sources and routes of infection	• close contact with infected birds or their environments  • close contact with infected humans (no sustained human-to-human transmission reported)
UK experience to date	No known cases in the UK.
Risk rating	Very low – human cases are rare, and severe disease even rarer.
Recent cases or outbreaks	No confirmed or suspected human cases were reported in December 2024.

Authors of this report

Emerging Infections and Zoonoses Team, UKHSA