Research and analysis

Travel-associated infections in England, Wales and Northern Ireland: January to June 2024

Updated 3 December 2024

Applies to England, Northern Ireland and Wales

Background

This report, produced by the Travel Health and International Health Regulations (TH and IHR) team in the Clinical and Emerging Infections Directorate, UK Health Security Agency (UKHSA), summarises case numbers of selected travel-associated infections reported in England, Wales and Northern Ireland (EWNI) from January to June 2024.

The data presented in this report are provisional; more detailed reports are produced on an annual basis and can be found here. 

Detailed information is included on the trends of chikungunya, dengue, rickettsial infections and Zika during the first half of 2024. An infection summary and key findings are provided for cholera, Japanese encephalitis and yellow fever. Data presented here is collated from a variety of sources and may be subject to limitations in completeness due to various factors, including underreporting.

Detailed reports and data are available elsewhere for imported malaria cases in the UK and travel-associated enteric fever cases in EWNI.

Data sources

Data for cases of chikungunya, dengue, Japanese encephalitis, rickettsial infections, yellow fever and Zika was obtained from the Rare and Imported Pathogens Laboratory (RIPL), UKHSA Porton (1).

Case definitions used for these infections are:

• confirmed: molecular detection (PCR, other molecular amplification test or sequencing) and/or positive virus isolation and/or seroconversion between acute and convalescent samples and/or four-fold rise in antibody titre
• probable: IgM and IgG positive and compatible clinical syndrome

Data for confirmed cholera cases was obtained from the UKHSA Gastrointestinal Bacteria Reference Unit (GBRU). A confirmed case is a person with Vibrio cholerae serogroup O1 or O139 confirmed by the GBRU (2).

For all cases, specimen collection date was used where available to conduct analysis. In cases where this information was not available, laboratory receipt date was used. Case numbers presented in this report include both confirmed and probable cases, collated from multiple sources, including confirmed cases from GBRU, and both confirmed and probable cases from RIPL.

Geographical areas were assigned based on the patient’s residential postcode; if the patient postcode was missing, the sending laboratory postcode was used.

World regions of travel were assigned based on the United Nations world region classifications (3).

Chikungunya

Chikungunya is a mosquito-borne infection transmitted by the bite of an infected female Aedes mosquito and is caused by a virus from the Flaviviridae family. It is characterised by a sudden onset of fever usually accompanied by joint pain (arthralgia); however, symptoms vary in severity. Serious complications are uncommon, but, rarely, in older people the disease can contribute to the cause of death, particularly if there is other underlying illness. Chikungunya mainly occurs in Africa, Asia and specifically in Southern Asia, although cases have been reported in parts of Europe and North America (4).

In EWNI, there were 24 chikungunya cases reported between January and June 2024. Of these, 9 (38%) were confirmed and 15 (62%) were probable cases. This represents a 71% increase compared to the same period in 2023, which saw 14 cases (2 confirmed and 12 probable) (Figure 1).

Figure 1. Number of chikungunya cases by month, January to June 2023 and 2024

Of the cases reported so far in 2024, sex was known in 23 out of 24 cases and age was known for all cases. Of these, 12 cases (52%) were female (aged 14 to 62 years, median=45) and 11 (48%) were male (aged 26 to 70, median=48) (Figure 2).

Figure 2. Number of chikungunya cases by age group and sex, January to June 2024 (n=23)

There were 23 cases reported in England, one case in Wales and zero cases in Northern Ireland. The largest proportion of English cases were reported in London (43%) (Table 1).

Table 1. Number of chikungunya cases in England, Wales and Northern Ireland by geographical distribution, January to June 2024

Geographical area (UKHSA)	Number of cases
London	10
South West	4
East of England	3
South East	3
West Midlands	2
North East	1
England total	23
Wales	1
Northern Ireland	0
EWNI Total	24

In 2024, travel history was known for 23 out of 24 cases, with the majority of these reporting travel to Southern Asia (12, 52%), followed by South-Eastern Asia (6, 26%) and South America (5, 22%). The most frequently reported countries of travel were India and Brazil (Table 2).

Cases who travelled to India reported travelling to a number of regions including Karnataka, Punjab, Tamil Nadu and Telangana states. As of 30 June 2024, India reported 72,461 confirmed and suspected chikungunya cases in 2024, with Karnataka state reporting the majority (44%) of cases (5) Of the cases in EWNI who reported travel to Brazil, 2 stated the region of travel and both travelled to Minas Gerais. In 2024, as of 1 July, Brazil reported 233,226 cases of chikungunya and 134 associated deaths, with Minas Gerais reporting the highest number of cases and highest case incidence per 100,000 population (6).

Table 2. Number of chikungunya cases by country of travel, January to June 2024

Country of travel	Number of cases
India	7
Brazil	5
Indonesia	4
Maldives	4
Philippines	2
Sri Lanka	1
Not stated	1
Total	24

Dengue

Dengue is a mosquito-borne infection transmitted by the bite of an infected female Aedes mosquito. It is caused by a virus from the Flaviviridae family and has 4 main serotypes: DEN-1, DEN-2, DEN-3 and DEN-4.

Illness is characterised by an abrupt onset of fever often accompanied by severe headache and pain behind the eyes, muscle pain, joint pains, nausea, vomiting, abdominal pain and loss of appetite. However, symptoms can range from mild or non-existent to severe.

Severe dengue is rare in travellers (7). Dengue is endemic in over 100 countries across Africa, the Americas, the Eastern Mediterranean, South-East Asia and the Western Pacific. with sporadic autochthonous cases occurring in France, Italy and Spain within Europe (7), 8). Since the beginning of 2024, the World Health Organization (WHO) has reported a substantial rise in dengue cases and deaths globally. By April 2024, over 7.6 million cases, including over 3,000 deaths, were recorded. The increase is particularly notable in the Americas, where cases have exceeded 7 million, surpassing previous annual high of 4.6 million cases in 2023 (9). 

In EWNI, there were 473 dengue cases reported between January and June 2024. Of these, 421 (89%) were confirmed cases and 52 (11%) were probable cases. This represents a 201% increase compared to the same period in 2023, which saw 157 cases (150 confirmed and 7 probable) (Figure 3) and marks the highest number of cases reported for the first and second quarters since dengue surveillance commenced in 2009.

Figure 3. Number of dengue cases by month, January to June 2023 and 2024

Of the cases reported so far in 2024, age and sex were known for all cases. Of these, 238 cases (51%) were female (aged 4 to 87 years, median=42) and 235 (49%) were male (aged 0 to 85, median=45) (Figure 4).

Figure 4. Number of dengue cases by age group and sex, January to June 2024 (n=473)

There were 459 cases reported in England, 11 cases in Wales and 4 cases in Northern Ireland. The largest proportion of English cases were reported in London (40%) (Table 3).

Table 3. Number of dengue cases in England, Wales and Northern Ireland by geographical distribution, January to June 2024

Geographical area (UKHSA)	Number of cases
London	183
South East	87
South West	51
East of England	42
North West	29
Yorkshire and Humber	25
East Midlands	18
West Midlands	17
North East	6
England Total	458
Wales	12
Northern Ireland	4
EWNI Total	473

In 2024, travel history was known for 441 out of 473 cases, with the majority of these reporting travel to Barbados (125, 28%), followed by Brazil (67, 15%) and Indonesia (54, 12%) (Table 4). This aligns with reported local outbreaks in these regions. According to the Pan American Health Organization (PAHO), Barbados and Brazil have experienced notable increases in dengue cases, reflecting a broader regional trend in the Americas, where the number of cases recorded during the first half of 2024 exceeded the highest historical number of cases reported for any year (10). Indonesia also reported a significant rise by 1 July 2024, with nearly 150,000 cases – approximately 3 times higher than the same period in 2023 (11). These trends are consistent with the cases observed among travellers returning to EWNI.

Notably, one EWNI case reported travel to Malaysia and then France, with symptoms emerging after returning to the UK from France. Although autochthonous dengue has been reported sporadically in Europe, 2023 saw significant outbreaks in France and Italy (8).

Table 4. Number of dengue cases by country of travel, January to June 2024

Country of travel	Number of cases
Barbados	125
Brazil	67
Indonesia	54
Thailand	54
India	30
Argentina	15
Mexico	14
Singapore	9
Malaysia	8
Sri Lanka	7
Other Caribbean	25
Eastern Africa	13
Western Asia	9
Other Central America	6
Other Southern Asia	6
Other South America	6
Middle Africa	6
Other South-Eastern Asia	5
Eastern Asia	5
Northern Africa	3
Oceania	3
Western Africa	3
Northern America	2
Western Europe	1
Not stated	37
Total*	513

*some cases travelled to more than 1 country/region; all countries/regions are included here so the total may be higher than the actual number of cases.

Rickettsial infections

Rickettsial infections are a group of bacterial infections of the genera Orientia and Rickettsia, which are transmitted by different arthropod vectors, including ticks, mites, lice and fleas, to animals such as humans, dogs, cats and cattle. In general, the incubation period is between 6 to 14 days post infection and symptoms vary but may include fever, myalgia, headache, dry cough and rash (12), 13), 14).

Human rickettsial infections are classified into 3 main groups: spotted fever group, typhus group and scrub typhus group. Spotted fever group infections are caused by over 30 Rickettsia species such as Rickettsia africae, Rickettsia conorii sp., and Rickettsia rickettsii. They are transmitted by ticks and have a specific geographical distribution. Typhus group infections are composed of 2 organisms; Rickettsia typhi is transmitted to humans through flea faeces mostly in Asia, Africa and the Western Pacific. R. prowazekii is transmitted to humans through louse faeces and is associated with high density living with associated poor hygiene. Scrub typhus infections are mainly caused by Orientia tsutsugamushi and transmitted through the bite of infected mite larvae. They are most commonly found in Asia and the Western Pacific, but are now also endemic in South America and Africa, and cause an estimated 1 million cases per year (13), 14).

In EWNI, there were 23 cases of rickettsial infections reported between January and June 2024. Of these, 9 (39%) were confirmed cases and 14 (61%) were probable cases. This represents a 15% increase compared to the same period in 2023 (n=20) (Figure 5). Of the reported cases, there were 8 cases (35%) in the spotted fever group, 8 cases (35%) in the typhus group and 7 cases (30%) in the scrub typhus group.

Figure 5. Number of cases with rickettsial infections by month, January to June 2023 and 2024

Of the cases reported so far in 2024, age and sex were known for all cases. Of these, 10 cases (43%) were female (aged 12 to 80 years, median=38) and 13 (57%) were male (aged 29 to 75, median=52) (Figure 6).

Figure 6. Number of cases with rickettsial infections by age group and sex, January to June 2024 (n=23)

There were 21 cases reported in England, one case in Wales and one case in Northern Ireland. The largest proportion of English cases were reported in London (43%) (Table 5).

Table 5. Number of cases with rickettsial infections in England, Wales and Northern Ireland by geographical distribution, January to June 2024

Geographical area (UKHSA)	Number of cases
London	9
South East	5
East Midlands	2
North East	2
Yorkshire and Humber	2
East of England	1
England total	21
Wales	1
Northern Ireland	1
EWNI Total	23

Between January and June 2024, travel history was known for 22 out of 23 cases, with some cases travelling to more than one country. Of these, the majority of spotted fever cases reported travel to Southern Africa (4, 50%). Scrub typhus cases are tested only when travel to Southern Asia or South-Eastern Asia is reported, and of the cases so far in 2024, 3 cases (38%) travelled to Southern Asia and 2 cases (25%) travelled to South-Eastern Asia. The majority of typhus group cases reported travel South-Eastern Asia (3, 38%).

For all cases of rickettsial infection, the most frequently reported country of travel was South Africa, followed by India (Table 6).

Table 6. Number of cases with rickettsial infections by country of travel and rickettsial group, January to June 2024

Country of travel	Scrub typhus	Spotted fever	Typhus group	Total number of cases
Australia	1	-	-	1
Bangladesh	1	-	-	1
Egypt	-	-	1	1
Ethiopia	-	-	1	1
Hong Kong	1	-	1	2
India	1	1	1	3
Indonesia	1	-	1	2
Mauritius	1	-	-	1
Mozambique	-	1	-	1
Sierra Leone	-	-	1	1
Singapore	1	-	-	1
South Africa	-	4	-	4
Sri Lanka	1	-	-	1
Thailand	1	-	-	1
Vietnam	-	-	2	2
Zimbabwe	-	1	-	1
Africa unspecified	-	1	-	1
Asia unspecified	-	1	-	1
Not stated	-	-	1	1
Total*	9	9	9	27

*some cases travelled to more than 1 country; all countries are included here so the total may be higher than the actual number of cases.

Zika

Zika virus is viral infection transmitted by the bite of an infected female Aedes mosquito. It is caused by a virus from the Flaviviridae family. Less commonly, transmission can occur through sexual contact, congenitally from a pregnant woman to her foetus and though blood transfusion (15).

The majority of people with Zika infection do not develop symptoms. Those that do often have mild symptoms which can include fever, headache, malaise, joint and muscle pain, a rash, itching, conjunctivitis and swollen joints (16).

Serious complications are uncommon, however an infection with Zika is a cause of congenital Zika Syndrome (characterised by microcephaly and other congenital anomalies) and neurological complications such as Guillain-Barré Syndrome.

During 2015 to 2016, there was a large outbreak of Zika virus infection in the Americas and the Caribbean, leading to the first imported Zika cases in the UK. As of May 2024, 92 countries across Africa, Europe, the Americas, South-East Asia and the Western Pacific have reported autochthonous Zika cases (17).

In EWNI, there were 8 Zika virus cases reported between January and June 2024, all were confirmed cases. This represents a 700% increase compared to the same period in 2023 (n=1) (Figure 7).

Figure 7. Number of Zika virus cases by month, January to June 2023 and 2024

Of the cases reported so far in 2024, age and sex were known for all cases. Of these, 5 cases (62%) were female (aged 23 to 41 years, median=31) and 3 (38%) were male (aged 26 to 42, median=35) (Figure 8).

Figure 8. Number of Zika virus cases by age group and sex, January to June 2024 (n=8)

There were 7 cases reported in England, 1 case in Wales and zero cases in Northern Ireland. The largest proportion of English cases were reported in London (71%) (Table 7).

Table 7. Number of Zika virus cases in England, Wales and Northern Ireland by geographical distribution, January to June 2024

Geographical area (UKHSA)	Number of cases
London	5
Yorkshire and Humber	1
South East	1
England total	7
Wales	1
Northern Ireland	0
EWNI Total	8

In 2024, travel history was known for all cases, with the majority of these reporting travel to South-Eastern Asia (91%). The most frequently reported countries of travel were Thailand (5 cases) and Singapore (2 cases) (Table 8). Thailand has seen an ongoing Zika transmission into 2024, with 148 confirmed cases reported so far, following the high levels of transmission from 2023, when 777 cases were reported in Thailand (18).

Table 8. Number of Zika virus cases by country of travel, January to June 2024

Country of travel	Number of cases
Thailand	5
Singapore	2
Malaysia	1
Indonesia	1
Vietnam	1
Seychelles	1
Total*	11

*some cases travelled to more than 1 country; all countries are included here so the total may be higher than the actual number of cases.

Other travel-associated infections

Cholera (Vibrio cholerae serogroup O1 or O139)

Cholera is caused by infection of 1 of 2 serogroups of the Vibrio cholerae bacteria, serogroups O1 and O139.

Cholera is an acute diarrhoeal disease caused by ingestion of contaminated food or water. A vaccine is available but is only recommended for some travellers. Cases of cholera may be asymptomatic or have mild symptoms, including acute, profuse watery diarrhoea (‘rice water stools’) and vomiting, leading to dehydration. Some infections may progress to severe disease, and in extreme cases may result in death if untreated (19). In 2022, cases were reported in 44 countries. The disease occurs mainly in Africa and Asia, but sporadic cases have also been reported in other regions (20).

There was one confirmed case of cholera reported in EWNI between January and June 2024. The case was a male between 20 to 29 years old who reported travel to Pakistan prior to onset of illness.

Japanese encephalitis

Japanese encephalitis (JE) is a vaccine preventable mosquito-borne infection transmitted by the bite of Culex species mosquitoes. It is a flavivirus from the Flaviviridae family and is transmitted via mosquitoes to humans from pigs and water birds. Japanese encephalitis is found in 24 countries in South-Eastern Asia and the Pacific, mainly in settings where humans live in close proximity to pigs and water birds. A vaccine is available; however this is only advised for travellers at increased risk of infection. Most people with JE do not develop symptoms but for those who do symptoms may include fever and headache or vomiting in children. Less than 1% of people develop severe disease, which is characterised by encephalitic symptoms such as disorientation, seizures, coma and paralysis and approximately 30% of these cases are fatal. For cases who survive, approximately 30% suffer long term cognitive, behavioural or neurological complications (21), (22).

In EWNI there were no cases of Japanese encephalitis reported between January and June 2024. The most recently reported case was in 2023.

Yellow fever

Yellow fever is a vaccine preventable mosquito-borne infection transmitted by the bite of multiple species of infected mosquitoes, including Aedes and Haemogogus species. Yellow fever virus is a flavivirus from the Flaviviridae family. Yellow fever is endemic in all or parts of 47 countries in Africa and Central and South America.

The incubation period ranges from 3 to 6 days. Many people do not develop symptoms but for those who do, these may include fever, headache, nausea or vomiting, muscle pain (often with backache), and loss of appetite. Most people will make a full recovery after 3 to 4 days; however, a small number (approximately 15%) will progress to a second phase of the infection and go on to develop jaundice, abdominal pain, renal failure and haemorrhage (bleeding). Up to half of infections in cases who develop severe symptoms may result in death. Yellow fever is rare in international travellers as there is a safe and effective vaccine available. Although the vaccine is safe, there have been reports of rare adverse events associated with its use (23).

In EWNI there were no cases of yellow fever reported between January and June 2024. The most recently reported case in EWNI was in 2018.

References

1. UKHSA. ‘Rare and Imported Pathogens Laboratory (RIPL): user manual’ (updated 27 March 2024)

2. UKHSA. ‘Bacteriology reference department user manual’ (updated 7 February 2024)

3. UNSD. ‘Methodology’

4. WHO. ‘Chikungunya’ (updated 8 December 2022)

5. NCVBDC. ‘Chikungunya Situation in India’

6. Brazil Ministry of Health. ‘Arbovirus Case Update’

7.  WHO. ‘Dengue and severe dengue’ (updated 17 March 2023)

8. ECDC. ‘Autochthonous vectorial transmission of dengue virus in mainland EU/EEA, 2010-present’ (updated 11 June 2024)

9. WHO. ‘Dengue - Global situation’ (updated 30 May 2024)

10. PAHO. ‘Epidemiological Update - Increase in dengue cases in the Region of the Americas - 18 June 2024’ (updated 18 June 2024)

11. WHO. ‘Indonesia takes decisive, pioneering action to strengthen multisource collaborative surveillance for dengue’ (updated 30 July 2024)

12. Premaratna R (2022). ‘Rickettsial illnesses, a leading cause of acute febrile illness’. Clinical Medicine Journal: volume 22, issue 1

13. Blanton LS (2019). ‘The Rickettsioses: A Practical Update’. Infectious Disease Clinics of North America: volume 33, issue 1

14. Warrell CE, Osborne J, Nabarro L, Gibney B, Carter DP, Warner J, Houlihan CF, Brooks TJG, Rampling T (2023) ‘Imported rickettsial infections to the United Kingdom, 2015–2020’. Journal of Infection: volume 86, issue 5

15. WHO. ‘Zika virus factsheet’ (updated 8 December 2022)

16. UKHSA. ‘Zika virus: symptoms and complications guidance’ (updated 2 August 2017)

17. WHO. ‘Zika epidemiology update - May 2024’ (updated 3 June 2024)

18. Bureau of Epidemiology (Thailand). ‘Zika virus’

19. WHO. ‘Cholera vaccines: WHO position paper – August 2017’ (updated 25 August 2017)

20. WHO. ‘Cholera Annual Report 2022’. Weekly Epidemiological Record: volume 98 (38), pages 431 to 452

21. WHO. ‘Japanese encephalitis’ (updated 9 May 2019)

22. Yun SI, Lee YM (2013). ‘Japanese encephalitis: the virus and vaccines’. Human Vaccines & Immunotherapuetics: volume 10, issue 2

23. WHO. ‘Yellow fever’ (updated 31 May 2023)