Research and analysis

Infectious disease surveillance and monitoring for animal and human health: summary December 2023

Updated 25 April 2024

1. Interpreting this report

The UK Health Security Agency’s (UKHSA) Emerging Infections and Zoonoses (EIZ) team uses an integrated horizon scanning approach, which combines information on both human and animal health, to identify and assess outbreaks and incidents of new and emerging infectious diseases globally. For further information about the EIZ team’s horizon scanning process, please see our Epidemic intelligence activities.

This summary provides an overview of incidents (new and updated) of public health significance, which are under close monitoring. The incidents are divided into 2 sections: Notable incidents of public health significance and Other incidents of interest. For each notable incident of public health significance, an incident assessment is provided, based on the EIZ team’s interpretation of the available information.

The report also includes a section that focuses on Novel pathogens and diseases and a final Publications of interest section, which contains new publications relevant to emerging infections.

Historically, these reports included summaries for high consequence infectious diseases (HCID). Epidemiological updates for diseases classified as an HCID will now only be published in UKHSA’s HCID monthly summary, unless they are considered a notable incident of public health significance, in which case a more detailed summary will be provided in this report.

For more information, or to sign up to the distribution list to receive an email alert when new reports are published, please contact epiintel@ukhsa.gov.uk

2. Notable incidents of public health significance

2.1 Summary of incidents

Disease or infection	Location	New or update since the last report
Measles	European Region	New
Zika virus	Thailand	New

2.2 Measles – European Region

Event summary

On 14 December 2023, the World Health Organization (WHO) reported more than a 50-fold increase in measles cases from the WHO European Region countries. Between January and December 2023, a total of 58,114 measles cases were reported in the WHO European Region, compared to 941 cases in the whole of 2022. The WHO stated that an increase in case numbers during 2023 was largely due to a reduction in vaccination coverage, particularly between 2020 and 2022 when the COVID-19 pandemic disrupted immunisation campaigns. This resulted in an accumulation of children with an incomplete immunisation status, with approximately 1.8 million infants in the WHO European Region missing their vaccinations during this period.

Within European Union and European Economic Area (EU/EEA) countries, 2,361 measles cases and 3 deaths were reported across 23 countries between 1 January and 31 December 2023. Countries reporting the most cases included Romania (1,755 cases), Austria (186 cases), France (118 cases), Germany (82 cases) and Belgium (69 cases).

In England, between 1 January and 31 December 2023, the UK Health Security Agency (UKHSA) reported 368 measles cases; a near 7-fold increase compared to 2022 (when 53 cases were reported). The West Midlands (160 cases, 44%) and London (122 cases, 33%) regions reported the most cases in 2023. Children under 10 years old accounted for 63% of cases in 2023 (232 cases). Measles activity increased markedly at the end of 2023 with 157 new cases reported in December, compared to 45 cases reported in November.

2.3 Incident assessment

In 2023, the majority of EU/EEA countries reported sporadic cases of measles after a period of low measles activity during the global COVID-19 pandemic. The overall number of measles cases in the EU/EEA has been increasing since June 2023, which is likely due to suboptimal vaccination rates in reporting countries. Notably, Romania declared a measles epidemic on 5 December 2023, where vaccination coverage for the second dose of measles, mumps and rubella (MMR) vaccine is 62%; below the 95% vaccination coverage recommended by the WHO to maintain herd immunity. An assessment by the European Centre for Disease Prevention and Control (ECDC) stated that more measles cases should be expected in the coming months given suboptimal MMR vaccination coverage in the majority of EU/EEA countries.

In the UK, the increase in measles cases observed in England in 2023 has been mainly  in children under the age of 10 years old, reflecting the decline in MMR vaccination coverage observed during the last decade, and exacerbated by the COVID-19 pandemic. Based on historic and current levels of vaccine coverage, observed measles cases and modelling, the UKHSA assesses the risk of widespread measles transmission leading to an epidemic across the UK as low.

2.4 Zika virus - Thailand

Event summary

Thailand has been experiencing an ongoing Zika virus outbreak. So far in 2023, and as of 22 December 2023, a total of 742 cases (including 1 death) have been reported across 36 provinces. This is substantially greater than 190 cases reported nationally in 2022. In 2023, the central and northern regions of Thailand are most affected, recording 292 and 139 cases, respectively. The highest proportion of cases (22.9%) have been in the 25 to 34 years age group.

2.5 Incident assessment

Zika virus is transmitted primarily by the Aedes mosquito and can also be spread by sexual contact and during pregnancy from the mother to the foetus. There is evidence that Zika virus has circulated at a low but sustained level in Thailand since approximately 2002. Most transmission occurs during the rainy season (July to October), when mosquito populations are at their greatest. There is currently no vaccine against Zika virus and although most cases are asymptomatic, some can develop mild symptoms including fever, headache, joint and muscle pain. In pregnancy, infection with Zika virus can lead to birth defects known as congenital Zika syndrome and other congenital anomalies and neurological problems such as Guillain-Barré syndrome; a rare condition affecting the nervous system.

There have been no recorded locally transmitted cases of Zika virus in the UK, due to the absence of the competent vector. The number of travel associated Zika cases peaked in 2016 with 275 cases, before decreasing in subsequent years. In 2022, 8 travel associated Zika virus cases were reported in the UK, of which 5 had a history of travel to Thailand. The UK National Travel Health Network and Centre recommends that pregnant women should consider postponing non-essential travel to countries associated with a high risk of Zika virus exposure until after the pregnancy. When travelling to areas with Zika virus, travellers should take measures to prevent nuisance mosquito biting by using insect repellent, wearing loose clothing which covers arms and legs and sleeping under mosquito nets treated with insecticide.

In 2017, the probability and impact of human infection with Zika virus infection in the UK was assessed as very low. Given the continued absence of competent vectors necessary for Zika transmission in the UK, this risk rating remains valid.

3. Other incidents of interest

3.1 Summary of other incidents

Disease/infection	Location
Anthrax	multi-country
Avian Influenza A(H5N6)	China
Avian Influenza A(H9N2)	China
Chikungunya	multi-country
Cholera	multi-country
Dengue	multi-country
Diphtheria	multi-country
Hepatitis A	Slovakia
Mpox (Clade II only)	multi-country
Plague (Bubonic)	Madagascar
Polio	multi-country
Western equine encephalitis	Argentina
Yellow fever	African region

3.2 Anthrax

On 12 December 2023, the WHO reported a total of 1,166 suspected and 37 confirmed cases of anthrax across Kenya, Malawi, Uganda, Zambia and Zimbabwe.

Zambia is experiencing its largest anthrax outbreak since 2011. Between 1 January and 20 November 2023, a total of 684 suspected anthrax cases, including 4 deaths, were reported in Zambia. The Sinazongwe District, located in the Southern Province, has reported 42% of all cases and is considered the outbreak epicentre. The most affected areas include Southern (370 cases), Western (88 cases) and Lusaka (82 cases) provinces. The WHO assesses the risk of the outbreak spreading within Zambia and at a regional level as high, due to the unrestricted movement of animals between provinces and frequent movement of people between neighbouring countries.

3.3 Avian Influenza A(H5N6)

On 22 December 2023, the Hong Kong Centre for Health Protection reported a fatal human case of avian influenza A(H5N6) in Mainland China. The case was a 33-year-old female living in Bazhong City, Sichuan Province. The case had exposure to poultry at a market prior to developing symptoms on 20 October 2023. She was admitted to hospital on 22 October 2023 where she died on 14 November 2023. From 2014 to date, 88 human cases of avian influenza A(H5N6) have been reported in Mainland China. One case has been reported from Laos.

3.4 Avian Influenza A(H9N2)

On 27 December 2023, the Hong Kong Centre for Health Protection reported 2 cases of avian influenza A(H9N2) from the same village in Sichuan Province, China. The first case, a 1-year old male, developed mild symptoms on 14 November 2023. A sample was collected on the same day as a part of routine surveillance and was confirmed positive on 18 November 2023. The second case, a 74 year old female, was identified during contact tracing follow-up of the first case. She had an onset of mild illness on 5 November 2023. A sample collected on 18 November 2023 was confirmed positive for avian influenza A(H9N2) on the same day. Both cases were exposed to backyard poultry infected with avian influenza A(H9) viruses. Whilst epidemiolocal investigations suggest separate spillover events from infected poultry, human-to-human transmission cannot be excluded. Since 1998, 130 human cases of avian influenza A(H9N2), including 2 deaths, have been confirmed globally, of which China has reported 117 cases. No human cases have been reported in EU/EEA countries.

3.5 Chikungunya

Between January and 31 December 2023, approximately 500,000 chikungunya cases were reported globally. Most chikungunya cases were reported from South and Central American countries. Brazil accounted for 264,767 cases and 114 deaths, followed by Paraguay (140,905 cases and 297 deaths), Argentina (1,746 cases and no deaths) and Bolivia (1,455 cases and no deaths).

Outside of the Americas, other notable outbreaks were reported from India (93,465 cases), the Philippines (2,561 cases) and Thailand (1,422 cases). In 2023, the Philippines have reported a surge in cases compared to 2022 (600 cases) and 2021 (92 cases).

3.6 Cholera

In 2023, and as of 15 December 2023, over 667,000 cholera cases and 4,000 deaths (case fatality rate of 0.6%) have been reported from 30 countries. The WHO states that the overall capacity to respond to multiple and large number of outbreaks remains strained due to a lack of resources, including shortages of vaccines and supplies, as well as overstretched public health and medical personnel. The WHO continues to assess the risk of cholera at the global level as very high.

As of 15 December 2023, the countries reporting the highest number of cholera cases, globally, in 2023 include:

• Afghanistan (215,210 cases and 99 deaths since 1 January 2023)
• Syrian Arab Republic (180,288 cases and 7 deaths since 1 January 2023)
• Haiti (76,556 cases and 1,156 deaths since October 2022)

Since the previous monthly summary report, Togo has reported a new outbreak of cholera, bringing the total number of countries reporting cholera cases in the African Region during 2023 to 17.

In the Greater Horn of Africa, the WHO reported a concerning rise in cholera cases in Sudan, over a larger geographical distribution. Between 15 April and 8 December 2023, 6,739 cases and 200 deaths were reported from 18 states. The outbreak has intensified with over 2,500 cases reported in the first 3 weeks of December 2023.

Between January and December 2023, Somalia reported 16,989 cholera cases and 43 deaths. Since mid-November 2023, approximately 400 new cases have been reported per week. Most cases have been reported from the southwest region of the country, including areas bordering Kenya and Ethiopia. 

Ethiopia has also been experiencing increased transmission and reported approximately 400 cholera cases between 15 November and 10 December 2023. The country has reported a total of 29,399 cases and 428 deaths since the outbreak began in August 2022. The WHO stated that the combination of heavy rainfall, floods and mass population displacement in November and December has likely intensified the spread of cholera in Ethiopia.

As of 31 December 2023, the Zambian Ministry of Health (MoH) reported 3,905 cholera cases and 116 deaths across the country since January 2023, of which Lusaka city is the epicentre of the outbreak. According to the Zambian MoH, the country has been experiencing frequent cholera outbreaks due to poor water and sanitation services. Zambia experienced its largest cholera outbreak between 2017 and 2018, during which more than 6,000 cases and 50 deaths were reported.

Between 22 and 31 December 2023, the Africa Centers for Disease Control and Prevention (Africa CDC) reported 1,155 new cholera cases and 16 deaths in Zimbabwe, bringing the total number of cases 13,569, including 295 deaths, during 2023. Cases have been reported from 46 out of 64 districts. The cholera epidemic has strained the existing healthcare capacity, particularly in remote areas, and can be largely attributed to inadequate access to clean water and poor sanitation.

3.7 Dengue

On 21 December 2023, the WHO assessed the global risk of dengue as high. Several factors are associated with an increased risk of the dengue transmission including the changing distribution of vectors, the El Niño weather pattern and increased rainfall and temperatures.

In 2023, the WHO Region of the Americas was the most affected region. During 2023, the WHO Pan American Health Organization reported a total of 4,570,260 dengue cases and 2,379 deaths. This is a 63% increase compared to 2022 (2,812,204 cases) and is higher than the average yearly number of total cases reported in the prior 5 years (2,820,284 cases). In 2023, most cases within the WHO Region of the Americas were reported from:

• Brazil (3,089,019 cases and 1,179 deaths)
• Mexico (277,963 cases and 203 deaths)
• Nicaragua (181,096 cases and 4 deaths).

Between 1 January and 24 December 2023, Sri Lanka’s Ministry of Health reported 87,029 dengue cases nationally. This compares to 74,769 cases reported in 2022. Colombo district is the epicentre of this outbreak reporting 18,357 cases, followed by Gampaha (15,946 cases) and Kandy (9,043 cases). Since October 2023, the weekly number of dengue cases reported in the country has consistently increased. 3,375 dengue cases were reported in week 51 of 2023, which was 38% higher than in the previous week (2,348 cases). Other Asian countries reporting a notable increase in dengue cases compared to previous years include:

• Bangladesh (308,167 cases and 1,598 deaths)
• the Philippines (167,335 cases and 557 deaths)
• Vietnam (149,557 cases and 36 deaths)
• Thailand (136,665 cases and 147 deaths)

On 31 December 2023, the Africa CDC reported 270,133 dengue cases and 768 associated deaths across 15 African Union Member States. Burkina Faso has reported most cases (237,291 cases and 701 deaths) from all 13 regions within the country. In November 2023, the WHO stated that Burkina Faso is experiencing an overwhelmed healthcare system due to the number of dengue cases. Additionally, the lack of public health resources and issues around national security have impeded an effective response, exacerbating the outbreak further.

3.8 Diphtheria

Since the beginning of 2023, and as of 12 December 2023, the ECDC has reported 131 diphtheria cases in EU/EEA countries. Since the previous emerging infections monthly summary report, 12 additional cases of diphtheria were reported: 11 in Germany (90 cases in total during 2023) and one case in Slovenia (4 cases in total during 2023). No new deaths were reported.

As of 24 December 2023, a total of 22,293 cases of diphtheria, including 598 deaths, were reported across 33 states in Nigeria. Most cases were reported in Kano (14,126 cases), Yobe (2,238 cases) and Katsina (1,734 cases). 67.6% of confirmed cases were among children aged between 1 and 14 years old. Only 25.2% of confirmed cases reported being fully vaccinated.

3.9 Hepatitis A

As of 13 December 2023, a total of 1,789 cases of viral hepatitis A have been reported in Slovakia since the beginning of 2023. The Košice region has reported the most cases (1,160 cases) followed by the Prešov region (548 cases). A high proportion of cases are among children aged between 5 to 9 years old (41.9%) and 1 to 4 years old (19.9%) and are predominantly from the Roma communities. A vaccination campaign is ongoing in affected areas.

Another notable outbreak of viral hepatitis A has been reported from Costa Rica. On 12 December 2023, media reported 2,070 cases nationally since January 2023. This compares to 118 cases reported during the equivalent 2022 period.

3.10 Mpox (Clade II only)

As of 31 December 2023, 93,030 confirmed mpox cases and 176 deaths have been reported from 117 countries to the WHO. Most cases have been reported from the United States of America (31,246 cases), Brazil (10,967 cases) and Spain (7,752 cases). In December 2023, Cambodia reported its first ever mpox case.

On 20 December 2023, media reported the first fatal mpox case in Pakistan. The case was a 40 year old male from Islamabad and was also infected with HIV. Since the first confirmed case was reported in April 2023, Pakistan has registered 7 cases, including 6 recoveries and 1 death.

Incidents in countries that have reported Clade I mpox are not included here as this is considered a HCID.

3.11 Plague (Bubonic)

On 8 December 2023, media reported a fatal case of plague in a 42 year old resident in the Ivato-Centre commune of Ambositra District, Madagascar. The type of plague was not specified. On 16 December 2023, media reported 2 additional fatal cases of bubonic plague, in an 8 year old from the Ivato-Centre commune, and a 7 year old in the neighbouring Antoetra commune. Plague is endemic in Madagascar and between 200 and 400 cases are reported each year by the Ministry of Public Health, of which most cases are classified as bubonic.

3.12 Polio

Wild polio virus type 1 (WPV1)

Between 1 January and 26 December 2023, 12 cases of WPV1 were reported to the Global Polio Eradication Initiative from Afghanistan (6 cases) and Pakistan (6 cases). This is a reduction from the 22 cases reported in 2022. WPV1 is endemic in both countries.

Circulating vaccine derived polio virus (cVDPV)

In 2023, a total of 133 cases of cVDPV1 have been reported from 3 countries:

• the Democratic Republic of the Congo (DRC) (105 cases)
• Madagascar (24 cases)
• Mozambique (4 cases)

This is a decrease compared to the 193 cases reported during 2022.

Additionally in 2023, 371 cVDPV2 cases have been reported across 21 countries, with the DRC (118 cases), Nigeria (81 cases) and Chad (54 cases) reporting the most cases. This is a decrease compared to 689 cases reported in 2022.

3.13 Western Equine Encephalitis

On 20 December 2023, the WHO was notified by Argentina’s MoH of the first human case of WEE in the country since 1996. The case developed symptoms on 19 November 2023, which included headache, dizziness and fever. They were subsequently hospitalised on 24 November 2023, requiring intensive care treatment before being discharged on 20 December 2023. The case is a rural worker, in an area where horses had previously tested positive for WEE. Including this case, and as of 31 December 2023, Argentina’s MoH has reported 63 human cases, of which 12 cases are confirmed, including 1 death. The 12 confirmed cases are distributed across Buenos Aires (5 cases), Entre Ríos (1 case) and Santa Fe (6 cases). The age range of cases is from 9 months to 72 years old. Most cases are males aged between 30 and 70 years old. All cases required hospitalisation; 7 of which have been discharged.

3.14 Yellow fever

Between January and 24 December 2023, the Africa CDC reported 2,917 yellow fever cases and 39 deaths. This is an increase of 87 cases since the previous monthly report. The top 3 reporting countries include Nigeria (1,819 cases and 21 deaths), Republic of the Congo (389 cases and 2 deaths) and Central African Republic (349 cases and 6 deaths).

On 24 December 2024, South Sudan’s MoH confirmed a yellow fever outbreak in Yambio County, Western Equatoria State. This had previously been reported in the media as an undiagnosed viral haemorrhagic fever incident, resulting in 10 cases including 5 deaths. The MoH, with support from the WHO and partners, activated its Public Health Emergency Operation Centre to coordinate a response including field investigations, active case searching and a yellow fever vaccination campaign in Yambio and surrounding counties.

4. Publications of interest

4.1 Crimean-Congo haemorrhagic fever (CCHF)

CCHF is a widespread tick-borne viral infection. A study commissioned by the ECDC updated a 2015 model for predicting potential CCHF risk areas in Europe whilst accounting for recent cases and vector distribution. The new model indicates more regions which are ecologically suitable for CCHF, extending into northern Europe. Several subnational regions show increased ecological suitability for CCHF, particularly pockets throughout France, Italy, Spain, the Balkans and the Caucasus.

4.2 Dengue

In October 2023, a cluster of 3 locally acquired cases of dengue were detected in the Val de Marne department neighbouring Paris, France. This marks the northernmost transmission of dengue in Europe to date. A recent study outlined the epidemiological and microbiological investigations implemented during these incidents and highlights the need for early case detection and response to contain dengue in Europe. This is particularly pertinent given the upcoming 2024 Summer Olympic and Paralympic Games, when millions of visitors are expected to visit the Greater Paris area.

In 2023, the Chad Ministry of Public Health and Prevention declared its first known dengue outbreak in the Abeche, Quaddai province, with a total of 2,037 cases reported across 4 provinces. Sequencing of samples and phylogenetic analysis confirmed DENV-1, genotype 2, in circulation.

4.3 West Nile virus (WNV)

A recent study aimed to assess WNV presence in Switzerland where no locally acquired human cases have ever been reported. In 2022, WNV was detected in mosquitoes from 8 out of 12 sampling sites for the first time. Whole genome sequencing revealed a lineage 2 virus linked to strains in Northern Italy. This study highlights the value of entomological surveillance in early detection and prevention of human infections of WNV.

5. Novel pathogens and diseases

5.1 Novel Norovirus variant

A recent study conducted by the US Centre for Disease Control reported a novel norovirus GII.4 variant detected in human stool samples obtained from the United States, South Africa and the UK from 2017 to 2022. The authors state that identifying such variants early is essential for assessing pandemic risks and guiding vaccine development.

6. Further reading

6.1 Tick borne encephalitis

High habitat richness reduces the risk of tick-borne encephalitis in Europe: A multi-scale study

6.2 Japanese encephalitis

Potential for emergence of Japanese encephalitis in the European Union

7. Related resources

1. High consequence infectious diseases monthly summaries

2. National flu and COVID-19 surveillance reports

3. Avian influenza (influenza A H5N1): technical briefings

4. Avian influenza (bird flu) in Europe, Russia and the UK reports

5. Bird flu (avian influenza): latest situation in England updates

6. Human Animal Infections and Risk Surveillance (HAIRS) group risk assessments and statements

7. Animal and Plant Health Agency (APHA) monitoring of disease in livestock and poultry monthly reports

8. Authors of this report

UKHSA’s Emerging Infections and Zoonoses team epiintel@ukhsa.gov.uk