Infectious disease surveillance and monitoring for animal and human health: summary February 2024
Updated 1 August 2024
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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.
Epidemiological updates for diseases classified as a high consequence infectious disease (HCID) are 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
Notable incidents of public health significance
Summary of incidents
| Disease or infection | Location | New or update since the last report |
|---|---|---|
| Dengue | Region of the Americas | New |
| Western equine encephalitis | Argentina and Uruguay | New |
Dengue: Region of the Americas
Event summary
Since the beginning of 2024, the Region of the Americas has reported a 249% increase in the number of dengue cases compared to the equivalent 2023 period (535,640 cases; accessed 8 April 2024), and a 354% increase compared to the previous 5-year average (413,109 cases; accessed 8 April 2024) according to the World Health Organization (WHO). Between epidemiological weeks 1 and 8 of 2024, 1,874,021 dengue cases (658,215 confirmed cases), and 422 deaths (case fatality rate of 0.023%) were reported in the Region of the Americas. The number of cases reported in 2024 has also surpassed the peak reported during epidemiological week 15 in 2023 (Figure 1).
Since the beginning of 2024, and up to epidemiological week 8 of 2024, the countries reporting the highest number of dengue cases include Brazil (1,017,278 cases; 687 deaths), Paraguay (154,391 cases; 62 deaths) and Argentina (57,461 cases; 37 deaths). Additionally, Mexico’s Ministry of Health reported 6,173 dengue cases nationally, representing a 468% increase in reported cases compared to the equivalent period in 2023, when 1,086 cases were reported.
Figure 1. Dengue: cumulative and average case numbers by reporting week and year in the Region of the Americas, as of February 2024 Pan American Health Organization and the World Health Organization (accessed 19 March 2024)
Incident assessment
Dengue epidemics in the Region of the Americas occur cyclically every 3 to 5 years. In 2023, the region reported the highest number of dengue cases globally. The number of cases reported in 2024 has surpassed those reported during the equivalent period in 2023. This increase may be due to the El Niño weather patterns and the rainy season in the southern Region of the Americas creating warmer and wetter conditions suitable for the proliferation of the Aedes aegypti mosquitoes, and thus prolonging the dengue season. Additionally, improvements in surveillance following the COVID-19 pandemic may have resulted in an overall increase in case detection and reporting.
Transmission of dengue virus in the UK is dependent on the presence of infected humans and of competent mosquito vectors required for dengue transmission. There is no current evidence of established populations of competent vectors in the UK. All human cases reported in the UK have been acquired as a result of travelling to endemic areas; the majority to South and South East Asia, the Caribbean, Eastern Africa and South and Central America. Given the small number of travel-associated infections imported into the UK annually, established processes for the diagnosis of cases and previous experience of managing cases, and the absence of competent mosquito populations in the UK required for the dengue virus transmission, the risk to the UK public is assessed as very low.
Western equine encephalitis: Argentina and Uruguay
Event summary
On 30 January 2024, Uruguay’s International Health Regulations National Focal Point (IHR NFP) reported a confirmed human case of western equine encephalitis (WEE), the first human case in Uruguay since 2009. The case was reported in the Department of San Jose, a department where WEE is known to circulate and which had also reported the greatest number of equine cases in 2024 nationally. The case, a 42 year old male, developed symptoms in early January 2024 and was hospitalised for treatment. Samples from the case tested positive for WEE on 20 January 2024. The case has fully recovered.
Since the first case was reported, and as of 27 February 2024, Uruguay’s Ministry of Public Health has reported 4 confirmed and 23 suspected human cases of WEE. Of the confirmed cases, 2 cases have been reported in San Jose, and one case each in Maldonado and Montevideo departments.
Argentina has also been experiencing an ongoing outbreak of WEE. On 20 December 2023, Argentina’s IHR NFP reported the first human case of WEE since 1996. Between December 2023 and 29 February 2024, 395 human cases (including 91 confirmed and 22 probable cases) and 7 deaths have been reported from 15 provinces. Of these cases, 59% have been reported in individuals aged 50 to 69 years old, and 86% of cases have been males. The province of Buenos Aires has reported the most cases (227 cases) and deaths (3 deaths).
Incident assessment
WEE virus typically circulates in the western regions of Canada and the United States, and the southern region of South America. Since November 2023, Argentina and Uruguay have reported an increase in both equine and human WEE cases residing in rural areas. The mosquito vector, Culex tarsalis, becomes infected after taking a blood meal from infected passerine birds, rodents or bats, which are considered viral reservoirs.
Equines and humans act as terminal hosts for WEE and therefore do not contribute to secondary transmission of the virus. Where WEE is circulating in animal populations, then sporadic human cases are not unexpected. While most cases result in asymptomatic or moderate symptoms, some individuals can develop severe disease which can be fatal, resulting in a mortality rate of 3% to 4%. The risk of WEE in the Region of the Americas has been assessed by the WHO as moderate. Transmission risk within the wider UK population is negligible as mosquito vectors implicated in WEE transmission are not found in the UK.
Other incidents of interest
Summary of other incidents
| Disease or infection | Location |
|---|---|
| Avian Influenza A(H9N2) | China |
| Borealpox (formerly Alaskapox) | United States |
| Cholera | multi-country |
| Dengue | multi-country |
| Diphtheria | multi-country |
| Measles | multi-country |
| Oropouche virus | multi-country |
| Polio | multi-country |
| Yellow fever | multi-country |
| Zika virus | Brazil |
Avian influenza A(H9N2)
On 23 February 2024, the Hong Kong Centre for Health Protection of the Department of Health confirmed a human case of avian influenza A(H9N2) in a 22 month old female, who developed symptoms on 15 February 2024. The case had a recent travel history to Zhongshan, Mainland China. No recent contact with poultry was reported. Since December 2015, 95 cases of human infection with avian influenza A(H9N2), including 2 deaths, have been reported from the Western Pacific Region including China (93 cases) and Cambodia (2 cases).
Borealpox (formerly Alaskapox)
The Borealpox virus, formerly known as Alaskapox virus, was first discovered in the Fairbanks area, Alaska State, in the United States during 2015. Until December 2023, all 6 cases reported from this area had self-resolving illnesses. On 11 February 2024, the State of Alaska reported a fatal case of Borealpox in the Kenai Peninsula. The case, who was immunocompromised following cancer treatment, presented with symptoms including pox-like lesions in September 2023, and succumbed to the disease in January 2024. Although the case exposure remains unclear, it is understood that scratches from a stray cat which hunted rodents around the cases home may have been a possible route of transmission.
Cholera
During February 2024, 37,269 new cholera cases and 322 associated deaths were reported from 20 countries across 3 WHO regions; representing a 12% decrease in cases since the previous month. Most cases were reported in the Eastern Mediterranean Region (19,049 cases and 22 deaths across 5 countries), followed by the African Region (18,218 cases and 300 deaths across 14 countries). To note, in January 2024, the cholera vaccine global stockpile was depleted, and its replenishment is awaited.
Following the declaration of a cholera outbreak in Comoros on 2 February 2024, the WHO have reported 132 confirmed cholera cases and 6 deaths as of 28 February 2024. This is the first cholera outbreak in Comoros since 2008, which began following the arrival of a case from Tanzania.
The cholera outbreaks in Zambia (since October 2023) and Zimbabwe (since February 2023) remain active. In February 2024, Zambia reported 4,904 cholera cases and 118 deaths, while Zimbabwe reported 4,785 cases and 75 deaths. Although the number of new cholera cases has been on a downward trend since January 2024, the number of cases remains high.
Dengue
Between 1 January and 17 February 2024, the Africa Centres for Disease Control and Prevention (Africa CDC) reported 3,593 dengue cases (1,283 confirmed cases) and 2 deaths across 4 African Union member states including: Ethiopia (1,561 cases), Mali (925 cases), Mauritius (1,098 cases) and Sao Tome and Principe (9 cases). In 2023, 280,411 dengue cases and 808 deaths were reported in 18 African Union member states.
On 25 February 2024, media reported 4,787 dengue cases between 1 January and 10 February 2024 in Costa Rica. This represents a 1,260% increase in cases compared to the 352 dengue cases reported during the equivalent 2023 period. Most cases have been reported from the Central North (1,228 cases), Central Pacific (832 cases) and the Central South (762 cases) regions.
As of 11 February 2024, Sante Publique France has reported 6,627 confirmed and 12,885 suspected dengue cases in French Guiana since the start of 2023. Of the confirmed cases, 3,929 cases were reported between 1 January and 11 February 2024. This is the largest dengue epidemic in French Guiana in 20 years.
Diphtheria
Between 1 January and 17 February 2024, the Africa CDC reported 2,243 diphtheria cases and 22 deaths in Nigeria and 98 cases in Chad. The WHO reported 1,184 diphtheria cases and 5 deaths in Guinea between 1 January and 4 February 2024, bringing the total to 3,445 cases and 83 deaths since the start of the outbreak on 4 July 2023. In 2023, 27,346 diphtheria cases and 797 deaths were reported across 6 African Union member states.
Measles
Between 18 and 24 February 2024, 1,190 suspected measles cases and 5 deaths were reported in Afghanistan. This is the highest number of suspected cases reported in a week since epidemiological week 26 (25 June to 1 July) of 2022 (1,574 cases). Cumulatively, since 1 January 2024, 7,197 measles cases and 29 deaths have been reported nationally. There has been an increasing trend of suspected measles cases since the third week of November 2023. This increase may be attributed to increased community transmission exacerbated by the winter season and low immunisation coverage. During 2023, a total of 25,876 suspected measles cases and 64 deaths were reported.
According to the Africa CDC, 5,697 measles cases (261 confirmed cases) and 108 deaths have been reported across 10 African Union member states in 2024, up to 17 February 2024. Most cases have been reported from the Democratic Republic of the Congo (DRC) (2,364 cases, 45 deaths), Somalia (1,662 cases) and Zambia (470 cases).
The Peru Ministry of Health have reported 2 confirmed measles cases since the beginning of 2024. The first case had recent travel history to Spain and Italy. The second case was in an unvaccinated 10 month old infant with no recent travel history. This is the first autochthonous measles case to be reported in Peru since 2000. A further 34 cases are under investigation.
In 2024, various states across the United States have been reporting an increase in cases of measles. As of 29 February 2024, the United States Centers for Disease Control and Prevention have reported 41 cases of measles across 15 states. During 2023, 58 measles cases were reported in 20 states.
Oropouche virus
Oropouche virus (OROV) is endemic to the Amazon region of northern Brazil. In 2024, up to 25 February 2024, 2,104 confirmed cases of OROV were reported in Brazil, of which 1,821 cases were from the State of Amazonas. This is an increase from 773 confirmed samples reported in 2023.
In Peru, between epidemiological weeks 1 and 8, 146 cases were reported from the departments of Loreto, Ucayali and Madre de Dios, all of which border northern Brazil. This is the highest number of cases reported to date in Peru; between 2016 and 2022, 94 cases of OROV were reported.
Polio
Circulating vaccine derived polio virus (cVDPV)
During February 2024, the Global Polio Eradication Initiative (GPEI) reported 3 cases of cVDPV1 in the DRC. In 2023, 133 cases were reported across 3 countries: the DRC (105 cases), Madagascar (24 cases), Mozambique (4 cases).
During February 2024, the GPEI reported 29 cases of cVDPV2 from Guinea (12 cases), Nigeria (12 cases), Chad (3 cases), Niger (one case) and Yemen (one case). All of the cases had a symptom onset during 2023. A total of 373 cases were reported across 22 countries in 2023, with most cases reported from the DRC (118 cases), Nigeria (82 cases) and Guinea (46 cases).
Yellow fever
The Africa CDC reported 91 yellow fever cases between 1 January and 17 February 2024. South Sudan reported 64 cases and 6 deaths, the Republic of the Congo reported 22 cases (no deaths) and Gabon reported 5 cases (no deaths). During 2023, 2,951 yellow fever cases and 45 deaths were reported across 8 African Union member states.
Zika virus
In 2024, up to 25 February 2024, the Region of the Americas has reported 1,021 cases of Zika virus infection (accessed 11 March 2024) of which 48 cases have been confirmed. Countries reporting the most cases include Brazil (867 cases), Bolivia (65 cases) and Colombia (49 cases). This compares to 6,489 Zika cases (including 805 confirmed cases) reported during the equivalent period in 2023.
Publications of interest
Crimean-Congo haemorrhagic fever (CCHF)
In October 2023, French officials reported the detection of CCHF virus in Hyalomma marginatum ticks collected from cattle in the eastern Pyrénées. Whilst H. marginatum have established populations in southern France, this was the first time the presence of the virus in tick populations had been confirmed in France. As of February 2024, no autochthonous human cases have ever been reported in France.
Dengue
During a first-in-human safety study, it was found that a recombinant dengue monoclonal antibody (VIS513) did not elicit any serious adverse effects and was well tolerated in healthy adults. The antibody can neutralize all 4 dengue serotypes.
Malaria
Results of a phase 3 trial in over 4,800 children across Mali, Tanzania, Burkina Faso and Kenya showed that the R21/Matrix-M malaria vaccine was well tolerated and provided high efficacy (up to 75%) against malaria. The authors concluded that the vaccine, which is already licensed in several African countries, has the potential to assist in reducing the burden of Malaria in sub-Saharan Africa.
Mpox
A study investigating the changes in the clinical symptoms associated with mpox between 1970 and 2023 found patient symptoms have become more diverse over time. The prevalence of non-specific symptoms such as fever, lymphadenopathy, headache, cough and sore throat have decreased, whilst rash was consistently the most common symptom over the study period.
During 2023, the DRC reported the highest annual number of monkeypox virus (MPXV) cases on record; with cases being reported in new geographic areas for the first time. Sexual transmission of Clade I MPXV was also reported in 2023, which has continued into 2024. A study published in February 2024 reported a novel Clade I sub-lineage from cases in South Kivu Province. Amongst 10 mpox patients in the Kamituga health zone, 8 patients were sex works. All cases were classified as Clade I but were distinct from all other Clade I sequences from the DRC, suggesting the outbreak resulted from a separate MPXV introduction. Genomic analysis also suggests at least 2 independent, ongoing MPXV outbreaks in the country, with the Kamituga outbreak in the east being unrelated to the outbreak in Kinshasa in the west.
A deletion in the genome of the novel MPXV led to failure of the Clade I specific reverse transcription polymerase chain reaction (RT-PCR). A deletion at the same site is also seen in Clade II MPXV, which was the basis of the clade differentiation using the PCR. Therefore, the authors of the study conclude this tool can no longer be used to rapidly differentiate Clade I and II MPXV infection if viruses from this new lineage spread internationally.
Poliovirus
Novel oral poliovirus vaccine type 2 (nOPV2) was created to improve the genetic stability of Sabin oral poliovirus vaccine (OPV) and reduce the emergence of circulating vaccine-derived polioviruses. Results from a recent phase 3 trial provide evidence that nOPV2 is safe and immunogenic amongst infants and young children, providing support for nOPV2 licensure and WHO prequalification. When delivered through outbreak response campaigns, it is expected that nOPV2 will interrupt viral transmission while reducing the risk of further paralytic outbreaks, even in OPV2-naive populations, compared with Sabin OPV2.
Yellow fever
A fractional dose of 17DD yellow fever vaccine, containing one-fifth of the standard dose, was used during a mass vaccination campaign in the DRC among children aged 2 years and older and non-pregnant adults in 2016. One year after vaccination, 97% of participants were seropositive, while 95% of participants remained seropositive after 5 years. The authors conclude the results of the study support the use of fractional-dose vaccination for outbreak prevention with the potential for sustained immunity.
Zika virus
Zika virus (ZIKV) infection during pregnancy can result in congenital Zika syndrome, which is a distinct pattern of birth defects including severe developmental malformations. Using a marmoset pregnancy model, the authors investigated the administration of Zika purified inactivated virus (ZPIV). The vaccine prevented vertical transmission of ZIKV by eliciting a neutralizing antibody response comparable to when elicited by pre-pregnancy vaccination, without causing adverse effects. These results provide further insight into the safety and efficacy of ZPIV use during pregnancy.
Novel pathogens and diseases
Mammarenavirus vellosense
A recently published study investigating Junin virus, a New World Clade B arenavirus, in samples from rodents taken between 1993 and 2019 in Argentina describes 13 novel New World arenavirus Clade C genomes. Two of these genomes displayed enough genetic diversity to be considered a new species (proposed name Mammarenavirus vellosense). The authors conclude the risk for human infection is currently unknown.
Novel Oropouche virus (OROV) lineage
A study investigating OROV in the Amazon region of Brazil found that recent outbreaks (between 2002 and 2024) resulted from sustained transmission and dissemination of a novel OROV reassortant lineage. The novel lineage has been associated with a recent increase in OROV cases in large urban areas. The study highlights the ongoing risk of transmission and establishment of OROV into new geographical areas outside of the Amazon region.
Further reading
Antimicrobial resistance
Avian influenza A(H9N2)
Lassa fever
Malaria
Ancient genomes illuminate Eastern Arabian population history and adaptation against malaria
Related resources
High consequence infectious diseases monthly summaries
National flu and COVID-19 surveillance reports
Avian influenza (influenza A H5N1): technical briefings
Avian influenza (bird flu) in Europe, Russia and the UK reports
Bird flu (avian influenza): latest situation in England updates
Human Animal Infections and Risk Surveillance (HAIRS) group risk assessments and statements
Animal and Plant Health Agency (APHA) monitoring of disease in livestock and poultry monthly reports
Authors of this report
UKHSA’s Emerging Infections and Zoonoses team. You can contact us at: epiintel@ukhsa.gov.uk