Overview.

Cyclosporiasis is an intestinal infection caused by Cyclospora cayetanensis, a coccidian protozoan parasite transmitted exclusively by the faecal-oral route via contaminated fresh produce or water, with no known animal reservoir. The United States is currently experiencing its largest recorded cyclosporiasis season: more than 6,700 confirmed or probable cases had been reported to CDC by mid-July 2026, against roughly 2,700 for the whole of 2025, and the agency is separately reviewing over 5,100 additional reports to determine whether they belong to the same surge.^1,2

The rise includes an outbreak of 1,644 infections and 94 hospitalisations linked to shredded iceberg lettuce supplied by Taylor Farms de Mexico and served at Taco Bell locations in five states, which prompted a 17 July 2026 recall. ³

The much larger domestic surge, 1,645 lab-confirmed cases across 34 states (most recent CDC Health Alert Network notice) has no identified single source, and is best described as a seasonal variation of a chronic food-safety vulnerability that has produced outbreaks in the United States almost every year since the mid-1990s. ⁴

Epidemiology

The current outbreak

Cyclosporiasis has been nationally notifiable in the United States since January 1999, following large multistate outbreaks in 1996 and 1997. By 2015 it was reportable in 44 jurisdictions covering 42 states, the District of Columbia and New York City.

CDC designates 1st May to 31st August as the annual “cyclosporiasis season,” reflecting both the temperature dependence of oocyst sporulation (22–32°C) and the seasonal concentration of fresh imported produce consumption.^5,6

The 2026 season is exceptional in scale. Domestically acquired, laboratory-confirmed cases reported since 1 May 2026 (1,645, across 34 states) are more than six times the 249 cases reported over the equivalent period in 2025. No deaths were reported. CDC surveillance discovered a further 440 travel-associated cases.^4,7

The Taco Bell/Taylor Farms de Mexico cluster is the only one, within this surge, with a firmly identified food source. FDA and CDC traceback and epidemiological analysis linked illnesses in Indiana, Kentucky, Michigan, Ohio and West Virginia to shredded iceberg lettuce from a single supplier. Taylor Farms de Mexico voluntarily withdrew, then formally recalled, all iceberg lettuce sourced from central Mexico on 17 July 2026.

The CDC states explicitly that the true number of illnesses is likely higher than reported figures given cyclosporiasis’s typical under-diagnosis, and that the outbreak may extend to states without yet-confirmed cases.^1,9

Three decades of recurring US outbreaks

Cyclospora emerged as a recognised US food-borne pathogen in the mid-1990s, beginning with a large 1996 multistate outbreak traced to Guatemalan raspberries.

Since then, US outbreaks have recurred in most years, typically clustering in spring and summer and typically implicating imported fresh produce that is eaten raw and difficult to wash thoroughly: raspberries, basil, cilantro, mesclun, snow peas, sugar snap peas, cabbage, parsley, broccoli, green onions, blackberries, watercress, mango and prepackaged vegetable and salad trays have all been implicated across outbreaks since 1995.^10,11,12

Prior events include a 2018 outbreak exceeding 2,299 cases across 33 states (about a third linked to prepackaged vegetable trays and fast-food salads), a 2019 multistate outbreak linked to fresh basil that reached over 2,400 cases across the US and Canada, and a 2022 Florida outbreak linked to contaminated lettuce in salad kits that affected more than 500 people. Only a handful of US outbreaks over the past two decades have exceeded 1,000 cases; 2026 is on course to be the largest on record.^12,13

Why outbreaks keep recurring. Public Health opinion attributes the rising frequency over the past decade partly to improved clinician awareness and diagnostic testing, and partly to environmental conditions, including warmer temperatures that favour oocyst sporulation and survival. Climate changes might be expanding the window and geographic range for outbreaks.

Because no universally deployed molecular typing tool existed for C. cayetanensis until relatively recently (see Microbiology, below), many temporally clustered cases historically could not be conclusively linked to a single source, meaning the true count of discrete outbreaks within any given season has likely been under-estimated for most of the parasite’s history as a notifiable US disease.^6,14

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Increasing antibiotic resistance is one of the most important public health threats of our time. In England alone, the number of antibiotic-resistant bloodstream infections rose by 9.3% in a single year, from 18,740 cases in 2023 to 20,484 in 2024, while estimated deaths from resistant infections increased from 2,041 to 2,379 over the same period.

Those affected are often elderly, often from the most deprived communities.

The UK Health Security Agency (UKHSA) now documents close to 400 new drug-resistant infections every week in England ¹. Globally, more than one million people have died each year as a direct result of antimicrobial resistance (AMR) since 1990, and the situation is getting worse. Modelling published in The Lancet in 2024 predicts that, without intervention, AMR deaths could reach 1.91 million annually by 2050, a near 70% increase on current figures ².

And there is worse news: resistance to carbapenems, a class of antibiotics that has long served as medicine’s final line of defence, is increasing.

The Carbapenem Problem

Carbapenems - a group that includes meropenem, imipenem and ertapenem - occupy a critical position in the antibiotic arsenal. They are broad-spectrum beta-lactam antibiotics, reserved for severe or multidrug-resistant infections where other agents have failed. When a bacterium becomes resistant to carbapenems, doctors are left with very limited, often more toxic alternatives. In many cases, there is no good option at all.

Among Gram-negative bacteria, pathogens including Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii and Pseudomonas aeruginosa, resistance to carbapenems has increased more than any other antibiotic class between 1990 and 2021, with attributable deaths rising by 89,200 over that period ². Carbapenem-resistant A. baumannii and carbapenem-resistant Enterobacterales are classified by the World Health Organization (WHO) as critical priority 1 pathogens, the highest category of concern, reserved for organisms where new active antibiotics are most urgently needed ³.

Carbapenem resistance can arise through several mechanisms, but the most clinically and epidemiologically important involves the production of carbapenemase enzymes. These are proteins that chemically hydrolyse the carbapenem molecule, rendering it inactive. The most transferable and globally distributed carbapenemase genes include KPC (Klebsiella pneumoniae carbapenemase), NDM (New Delhi metallo-beta-lactamase), OXA-48 and VIM (Verona integron-encoding metallo-beta-lactamase). What makes these genes particularly problematic is their capacity to move between bacteria through a process known as horizontal gene transfer.

Horizontal Gene Transfer

Unlike vertical transmission, where a parent bacterium passes genes to its offspring, horizontal gene transfer (HGT) allows resistance genes to move laterally between entirely different bacterial species. The primary vehicle for carbapenemase gene transfer is the plasmid: a small, circular piece of DNA that sits in the bacterium’s cytoplasm separate from the main chromosome and can be readily copied and passed to neighbouring organisms through a process called conjugation. Plasmids are frequently mobile genetic elements; some can transfer themselves to bacteria of entirely different genera, or even different phyla.

Research published in The Lancet Microbe in 2023 demonstrated just how actively this process occurs in real-world bacterial communities within hospital sewage. Using CRISPR-tagged plasmids, the study tracked the transfer of NDM-5-positive plasmids across multiple bacterial phyla within a hospital wastewater treatment system, the first culture-independent evidence of interphylum gene transfer in such an environment ⁴.

Plasmids and transposons also carry integrons, genetic structures that can capture and accumulate multiple resistance genes, creating bacteria resistant to several antibiotic classes simultaneously.

Crucially, horizontal gene transfer does not require contact between clinical pathogens. It can occur among the broader microbial communities that inhabit wastewater, river sediments and agricultural soil. At this is point we have to consider the problem of sewage pollution.

The UK’s Sewage Problem

The United Kingdom’s waterways are in a dire state. Routine sewage overflows, inadequate wastewater treatment and agricultural runoff have created conditions in which antibiotic-resistant bacteria and resistance genes are accumulating in rivers, lakes and coastal waters. Every water body in England currently fails the Water Framework Directive standards for ecological quality - a systemic failure with direct implications for AMR.

A 2024 study led by the University of York, conducted in partnership with Surfers Against Sewage, tested 23 designated inland bathing sites across England, Wales and Scotland. Antimicrobial resistance genes were detected at all sites but one; the most heavily contaminated - the River Dart in Devon - harboured 53 of the 71 resistance genes tested for. Among those detected were genes conferring resistance to last-resort antibiotics ⁵.

In February 2026, research from Index Microbiology found that 97% of water samples taken from Oxford’s rivers tested positive for bacteria producing extended-spectrum beta-lactamases (ESBLs), a key step on the pathway towards carbapenem resistance ⁶. A 2019 analysis of the River Thames catchment found that large portions of the river system are chronically exposed to antibiotic concentrations sufficient to promote resistance gene selection, even after wastewater treatment, with 64% of the catchment at risk of selection for macrolide resistance and 74% for fluoroquinolones resistance ⁷.

Hospital effluent is a particularly concentrated source. Studies of hospital wastewater in Wales, conducted under the PATH-SAFE programme, found the ‘big five’ carbapenemase gene variants distributed across NHS sites, along with concentrations of antibiotics exceeding thresholds associated with resistance emergence ⁸. When this effluent passes through wastewater treatment plants (WWTPs), treatment reduces but does not eliminate resistance genes. The treated water, along with sewage sludge subsequently applied to agricultural land, then disperses resistant organisms and genetic material into the wider environment.

Animal Agriculture and One Health

Human sewage is not the only source of risk; animal agriculture contributes substantially to antibiotic resistance. Antibiotics used in livestock, including those related to classes used in human medicine, are excreted in manure which can then enter watercourses through runoff. A nationwide wastewater study published in Nature Communications in January 2026 found aminoglycoside resistance genes present at concentrations 50% higher in sewage than in clinical samples, a discrepancy attributed to inputs from poultry, aquaculture and other agricultural sources ⁹.

Studies of rural English rivers, including the Eden in Cumbria and the Coquet in Northumberland, have confirmed that diffuse agricultural pollution, mediated by soil saturation and surface runoff, measurably increases the abundance of resistance genes in river microbiomes¹⁰. In Northern Ireland, veterinary antibiotics have been found downstream of farm sites, consistent with farm runoff as a direct source. This runoff, along with the disposal of treated and untreated human sewage, is implicated in the heavy pollution of Lough Neagh, a water source which supplies approximately 40% of Northern Ireland’s drinking water.

This interplay between human medicine, veterinary practice and environmental contamination is why AMR is increasingly approached from a One Health perspective, recognising that human, animal and environmental health are inseparably linked. The carbapenemase genes accumulating in the rivers of the United Kingdom do not distinguish between clinical and non-clinical bacteria. Through horizontal gene transfer, antibiotic resistance can transfer from environmental organisms to pathogens that subsequently cause human infection.

The Politics of Antimicrobial Resistance

Antibiotic resistance is not a politically neutral crisis. UKHSA data consistently demonstrate that people in the most deprived communities bear a disproportionate burden. In 2022, individuals from the most deprived 10% of the population were more than twice as likely to carry carbapenemase-producing Gram-negative bacteria than those from the least deprived 10% - rates of 6.8 compared to 2.8 per 100,000 ¹¹. Resistant infections are substantially more common in areas of poverty, where overcrowding, poorer housing conditions, reduced access to timely healthcare and higher baseline rates of comorbidity combine to increase both vulnerability and exposure.

The communities most likely to swim in polluted rivers, to live near water company sewage overflow points or to work in agricultural settings with high antibiotic use are rarely those with the most political or economic power to demand regulatory action. This is an environmental justice failure as much as a scientific one.

The UK Response

The UK published a new five-year National Action Plan (NAP) for antimicrobial resistance in 2024, setting targets including a 5% reduction in total antimicrobial use in humans by 2029 relative to 2019 levels, and strengthened One Health surveillance ¹². There has been progress: overall NHS antibiotic use in 2024 was 2% below the pre-pandemic 2019 baseline. But the trend remains concerning, with resistant bloodstream infections continuing to rise and the surveillance gap between human and animal sectors still inadequately closed. The National Audit Office and Public Accounts Committee both highlighted in early 2025 that further action is urgently required.

On the environmental front, antibiotics discharged into rivers and waterways remain largely unregulated. No environmental quality standards currently exist in England for antibiotic concentrations in surface water, a gap that researchers in the field have called untenable given the evidence of resistance selection at concentrations which are routinely exceeded ⁷. Wastewater surveillance for AMR, pioneered during the COVID-19 pandemic, is now being extended; Wales is among the early adopters of national hospital wastewater screening for carbapenemase genes. But upgrading wastewater treatment infrastructure to reliably remove resistance genes remains a longer-term, expensive ambition. It is an upgrade that the water companies have not convincingly prioritised in the past.

Conclusion

The spread of carbapenem resistance represents a significant risk to medicine and to health. Procedures that depend on reliable antimicrobials, such as major surgery, cancer chemotherapy, organ transplantation, the care of premature infants, become more dangerous when bacterial infections that were once treatable can no longer be controlled.

The sewage crisis contaminating Britain’s rivers isa significant factor. Environmental reservoirs of resistance genes, amplified by HGT in microbial communities and dispersed by failing water infrastructure and agricultural runoff, represent a source of developing resistance that clinical antibiotic stewardship alone cannot address. Reducing medical use of antibiotics, though desirable, will have little effect unless all the other factors are addressed.

Tackling this will require enforced reductions in agricultural antibiotic use, no more antibiotic prescriptions for viral chest infections, the development and dissemination of vaccines for bacterial infections, enforceable regulation of antibiotic discharges into waterways, investment in wastewater treatment capable of removing resistance genes, and a recognition that the communities most harmed by environmental AMR are those already least supported by the systems meant to protect them. The science is clear. The politics is hazy. The effects of profiteering are disastrous.

References

1. UK Health Security Agency. Nearly 400 antibiotic-resistant infections each week in 2024 [Internet]. London: UKHSA; 2025 [cited 2026 Mar 14].

2. GBD 2021 Antimicrobial Resistance Collaborators. Global burden of bacterial antimicrobial resistance 1990–2021: a systematic analysis with forecasts to 2050. Lancet. 2024;404(10459):1129–61.

3. World Health Organization. WHO Bacterial Priority Pathogens List, 2024: bacterial pathogens of public health importance to guide research, development and strategies to prevent and control antimicrobial resistance. Geneva: WHO; 2024.

4. Prof Qiu E Yang, Xiaodan Ma, Lingshuang Zeng, Qinqin Wang, Minchun Li, Lin Teng, Mingzhen He, Chen Liu, Mengshi Zhao, Mengzhu Wang, Deng Hui, Jonas Stenløkke Madsen, Hanpeng Liao , Prof Timothy R Walsh, Prof Shungui Zhou. Interphylum dissemination of NDM-5-positive plasmids in hospital wastewater from Fuzhou, China: a single-centre, culture-independent, plasmid transmission study. Lancet Microbe. 2024;5(1):e13–e23.

5. University of York. UK inland bathing sites polluted by chemicals and antibiotic-resistant genes [Internet]. York: University of York; 2024 [cited 2026 Mar 14].

6. Morley R. Antibiotic-resistant bacteria in Oxford rivers [Internet]. Oxford: Index Microbiology/Oxford Daily News; 2026 Feb [cited 2026 Mar 14].

7. Singer A, Quiying Xu, Keller VDJ. Translating antibiotic prescribing into antibiotic resistance in the environment: a hazard characterisation case study. PLoS One. 2019;14(9):e0221568.

8. Reshma Silvester, William B. Perry, Gordon Webster, Laura Rushton, Amy Baldwin, Daniel A. Pass, Neil Andrew Byrnes, Kata Farkas, Margaret Heginbothom, Noel Craine, Gareth Cross, Peter Kille, Barbara Kasprzyk-Hordern, Andrew J. Weightman, Davey L. Jones. Metagenomic profiling of hospital wastewater: a comprehensive national scale analysis of antimicrobial resistance genes and opportunistic pathogens. J Infect. June 2025.

9. Paul D, Dutta B, Gupta A, Bhattacharya S. Hospital superbugs are circulating through urban sewage. Nat Commun. 2025

10. Katie Robins, Greg O'Donnell, Anke Neumann, Wiebke Schmidt, Alwyn Hart, David W. Graham. Antimicrobial resistance in rural rivers: comparative study of the Coquet (Northumberland) and Eden (Cumbria) river catchments. Sci Total Environ. 2024;Volume 928, 10 June 2024, 172348.

11. UK Health Security Agency. English surveillance programme for antimicrobial utilisation and resistance (ESPAUR) report 2022 [Internet]. London: UKHSA; 2022

12. UK Government. UK 2024 to 2029 antimicrobial resistance national action plan [Internet]. London: HM Government; 2024 [cited 2026 Mar 14].

Integrons are bacterial genetic mechanisms that enable the rapid adaptation and evolution of bacteria by capturing, storing, rearranging, and expressing gene cassettes.

Integrons are primarily found in bacteria, where they serve as genetic platforms for capturing and expressing mobile genes. Approximately 15–17% of all sequenced bacterial genomes contain these elements.

National Institutes of Health (NIH) | (.gov) +4

They are typically found in two distinct genetic contexts:

• Bacterial Chromosomes: Many integrons are sedentary components of the host chromosome. These “chromosomal integrons” (sometimes called super-integrons) can be very large, carrying hundreds of gene cassettes that contribute to general bacterial adaptation and evolution.

• Mobile Genetic Elements (MGEs): Integrons are frequently found on plasmids and transposons. These “mobile integrons” (MIs) are much smaller, typically carrying fewer than ten cassettes, and are the primary drivers for spreading antibiotic resistance in clinical settings.

• Wikipedia +4

Environmental Distribution

Beyond clinical isolates, integrons are ubiquitously distributed in diverse natural habitats, including:

• Aquatic Environments: Freshwater (rivers, lakes, and hot springs) and marine environments (deep-sea sediments and aquatic biofilms).

• Terrestrial Environments: Forest, desert, and Antarctic soils.

• Human-Impacted Sites: Wastewater treatment plants, hospital effluents, and agricultural areas treated with manure.

• Biological Surfaces: On the surfaces of plants and in the symbionts of eukaryotes

• Gene Cassettes: These are small, mobile, circular DNA elements, often carrying a single, promoterless antibiotic resistance gene.

• Transposons, or "jumping genes," are DNA sequences that move (transpose) from one location to another within a genome.

An AI-designed vaccine targeting the entire sarbecovirus family, the coronavirus subgroup responsible for both the 2003 SARS outbreak and COVID-19, has passed its first human clinical trial, researchers at the University of Cambridge have announced.

The vaccine, pEVAC-PS, was developed by Cambridge spin-out DIOSynVax using an AI platform that analysed global genetic sequence data across all known sarbecoviruses and identified the conserved molecular features shared by the entire family. Rather than targeting a specific strain, it encodes a synthetic “super-antigen” representing a common factor of a virus group and is explicitly designed to remain effective even as new variants emerge.

In a phase I dose-escalation trial involving 39 healthy volunteers at NIHR facilities in Cambridge and Southampton, pEVAC-PS was safe and well-tolerated at all doses. The team detected cross-reactive antibody responses against multiple sarbecoviruses, including SARS-CoV-2, SARS, and related bat coronaviruses.

There are caveats: the trial was designed for safety rather than efficacy, neutralising antibody responses were not robust, and pre-existing coronavirus immunity in most participants complicates interpretation. A larger Phase II trial is planned. The same AI platform is being developed for influenza and haemorrhagic fever viruses, including Ebola, fostering hope for future vaccines.

There are further advantages over current vaccination systems. The delivery system used involves a needle-free microfluidic jet and the thermostable DNA platform requires no ultra-cold storage. The DNA vaccine’s thermostability and needle-free delivery are genuine advantages for low-resource settings. But pEVAC-PS is a commercialised spin-out product developed with UK public funding. Without explicit access commitments now, history gives us every reason to ask whether the populations most vulnerable to pandemic coronaviruses will benefit, or whether this will follow the familiar pattern of innovation for affluent markets first.

Full trial data: Munro et al., Journal of Infection, 2026

Since its discovery in 1976, Ebola virus has caused more than 40 confirmed outbreaks across sub-Saharan Africa, sixteen of them in the Democratic Republic of Congo (DRC). Health systems in the region have developed protocols, trained responders, and, since 2019, relied on a licensed vaccine to reduce transmission among those most at risk. That vaccine, rVSV-ZEBOV (Ervebo), has been a critical tool. It works against the Zaire strain, which has driven virtually every major DRC outbreak. But the 2026 outbreak is different.

On 15 May 2026, the DRC Ministry of Health declared an Ebola outbreak in Ituri Province in the north-eastern part of the country. The causative agent is Bundibugyo virus (BDBV), a rare Ebola species for which there is no approved vaccine and no approved treatment. Within 24 hours, cases had crossed the border into Uganda. Within 48 hours, a confirmed case was identified in Kinshasa, the DRC’s capital, some 1,700 kilometres from the epicentre. On 17 May 2026, the World Health Organisation (WHO) declared the outbreak a Public Health Emergency of International Concern (PHEIC).

As of 16 May, there were 246 suspected cases and 80 suspected deaths across at least three health zones in Ituri, alongside three laboratory-confirmed cases in Uganda and Kinshasa. These numbers almost certainly understate the true incidence. A high positivity rate in initial testing, eight confirmed positives from just thirteen samples, points to a much larger undetected outbreak.

What is Bundibugyo virus?

The genus Orthoebolavirus contains six recognised species. Four are known to cause disease in humans: Zaire, Sudan, Tai Forest, and Bundibugyo. Zaire has been responsible for the most catastrophic outbreaks, including the 2013–2016 West African epidemic that infected nearly 30,000 people and killed over 11,000. Sudan has caused nine outbreaks since 1976, most recently in Uganda in January 2025. Tai Forest has infected only a single confirmed human case, in 1994.

Bundibugyo virus was first characterised as a distinct species in 2007–2008, when an outbreak struck Bundibugyo District in western Uganda, a region that borders the DRC. That outbreak produced 131 reported cases and 42 deaths. A second outbreak occurred in 2012, in Province Orientale in the DRC, resulting in 38 laboratory-confirmed cases and 13 deaths. Molecular analysis of the 2012 outbreak suggested the possibility of multiple independent spillover events from an animal reservoir, rather than a single introduction with subsequent human-to-human spread.

The 2026 outbreak is therefore only the third documented Bundibugyo event in human history and, by a considerable margin, the largest. It has already surpassed both previous outbreaks combined in suspected case count, and has demonstrated rapid cross-border spread within weeks of its presumed index case.

In clinical presentation, Bundibugyo infection closely resembles Ebola Zaire. Onset is typically sudden, with fever, fatigue, muscle pain, headache, and sore throat - flu-like symptoms - in the early phase, progressing to vomiting, diarrhoea, rash, and haemorrhagic features - internal and external bleeding - in severe disease. The incubation period runs from 2 to 21 days, averaging 8–10 days. One notable difference: the case fatality rate (CFR) for Bundibugyo is estimated at 30–40%, somewhat lower than the 70–90% seen in untreated Zaire outbreaks.

The diagnostic blind spot: how the outbreak grew unseen

A notable feature of this outbreak is how long the virus spread before anyone knew what it was. The earliest known case is a nurse who developed symptoms on 24 April 2026 and died at the Evangelical Medical Centre in Bunia, Ituri’s provincial capital. Yet the outbreak was not declared until 15 May - three weeks later.

The reason lies in a critical diagnostic gap. Field testing for Ebola in the DRC relies heavily on the GeneXpert platform, which is designed to detect Ebola Zaire, the strain responsible for almost all previous DRC outbreaks. When samples from the affected health zones were tested in Bunia, they returned negative. It was only when samples were sent to the National Institute of Biomedical Research (INRB) in Kinshasa, where multi-species Ebola assays are available, that the Bundibugyo strain was identified.

Decades of Zaire-centric outbreaks have shaped surveillance infrastructure, diagnostic capacity, and response protocols around a single viral species. When a different species arrives, with identical clinical features but a different genome, diagnosis can be missed. The result is unchecked community transmission during the period when containment is most achievable.

The head of epidemiology and global health at INRB, Placide Mbala, has been explicit: a rapid field-deployable test capable of detecting Bundibugyo virus is urgently needed. This is an immediate requirement for which no solution is currently available.

Why containment is especially difficult

Ebola outbreaks are always hard to contain. This one more so.

Firstly, there is no vaccine. The rVSV-ZEBOV vaccine, deployed with considerable success in the 2018–2020 DRC outbreak, is specific to Ebola Zaire. It offers no protection against Bundibugyo virus. A ring vaccination strategy, the primary tool that helped control the last major DRC outbreak, is simply not available here. The absence of both vaccine and licensed drug therapy means the entire response burden falls on isolation, contact tracing, infection prevention and control (IPC), and safe burial practices.

Ring vaccination, sometimes called reactive or targeted vaccination, is a strategy in which, rather than vaccinating entire populations, you rapidly identify and vaccinate the social and geographic ‘ring’ of people most at risk around each confirmed case: household contacts, close community contacts, and the healthcare workers who treated them. The logic is to build a protective barrier around the virus before it can reach the wider population, cutting off transmission chains at source.

This strategy, deployed with rVSV-ZEBOV, proved effective during the 2018–2020 North Kivu and Ituri epidemic, which, despite lasting nearly two years in a conflict zone, was ultimately contained without becoming a global catastrophe. By the end of that outbreak, more than 303,000 doses had been administered. Clinical evidence from Guinea’s 2015 Ebola Ça Suffit! trial demonstrated that rVSV-ZEBOV achieved approximately 100% efficacy in vaccinated contacts, giving responders a genuinely powerful and precisely targeted tool.

None of that is available now. With no licensed vaccine for Bundibugyo virus, outbreak control reverts entirely to the pre-vaccine toolkit: early detection, isolation of cases, exhaustive contact tracing, rigorous infection prevention and control (IPC) in health facilities, and safe and dignified burial practices to prevent transmission from deceased individuals. Each of these interventions is demanding under ideal circumstances; in a conflict-affected, resource-constrained setting with a three-week diagnostic delay already embedded, the challenge is huge.

Secondly, the outbreak is occurring in a highly insecure environment. Ituri Province has been the scene of sustained inter-communal violence and militia activity for years. Armed groups, including those affiliated with the Islamic State, operate in and around the affected health zones.

This directly impedes response efforts: it restricts the movement of health workers, disrupts community engagement, damages trust in health authorities, and can render entire areas inaccessible. The 2018–2020 DRC Ebola outbreak in North Kivu and Ituri - also complicated by conflict - ultimately lasted nearly two years and became the second-largest Ebola outbreak in history.

Thirdly, population mobility in the region is high. Ituri shares porous borders with Uganda and South Sudan. Mining activity in Mongwalu creates significant cross-border movement of workers. Urban centres such as Bunia serve as transit hubs. These are precisely the conditions under which outbreaks amplify geographically. Confirmed cases in Kampala, Uganda’s capital, and in Kinshasa demonstrate that the virus is already using established mobility networks to spread.

Fourth, healthcare-associated transmission appears to be occurring. At least four of the eight laboratory-confirmed cases in DRC are healthcare workers, suggesting nosocomial spread. At least four healthcare worker deaths compatible with viral haemorrhagic fever have been reported from affected areas. This pattern, seen repeatedly in Ebola outbreaks, reflects the extreme IPC demands of managing viral haemorrhagic fever patients and the catastrophic consequences of inadequate protective equipment or training.

The WHO declaration and the global response

On 17 May 2026, WHO Director-General Tedros Adhanom Ghebreyesus declared the outbreak a Public Health Emergency of International Concern under the International Health Regulations (2005). The PHEIC designation, the WHO’s highest alert level, indicates that the event is extraordinary, constitutes a public health risk through international spread, and requires coordinated global action.

WHO explicitly noted that the outbreak does not meet the criteria for a ‘pandemic emergency’ but that countries sharing land borders with the DRC are at high risk of further spread. States have been advised to activate national emergency management mechanisms, strengthen cross-border surveillance, implement screening at major transit points, and prepare health facility IPC capacity.

Africa CDC convened an urgent high-level regional coordination meeting on 15–16 May, bringing together health authorities from DRC, Uganda, and South Sudan alongside WHO, UNICEF, Médecins Sans Frontières (MSF), the Gates Foundation, the Wellcome Trust, pharmaceutical partners including Gilead Sciences, Merck, Regeneron, BioNTech, and Moderna, and multilateral funders including the World Bank and the African Development Bank. MSF has announced preparations for a large-scale operational response in Ituri.

The involvement of vaccine and therapeutics manufacturers at this early stage reflects both the urgency of the situation and the current void: no approved product exists for Bundibugyo virus, and there is the question of how rapidly candidate interventions might be evaluated and deployed.

An outbreak that was always going to hit hardest here

The communities bearing the burden of this outbreak, in one of the world’s poorest and most conflict-affected regions, have been rendered vulnerable by forces that long predate this virus. Decades of extractive colonialism, post-independence political instability, and ongoing conflict over the region’s mineral wealth have left Ituri’s health infrastructure chronically underfunded and repeatedly disrupted.

The informal health facilities and gaps in IPC capacity that WHO identifies as outbreak amplifiers are not accidents; they are the product of sustained underinvestment and institutional neglect.

The diagnostic blind spot described above, Zaire-centric surveillance infrastructure failing to detect a different species, is also, in part, a resource allocation story. Comprehensive multi-species diagnostic capacity requires sustained funding that has not been consistently available. The same applies to research pipelines for Bundibugyo-specific vaccines and therapeutics; because previous Bundibugyo outbreaks were small and geographically contained, they generated insufficient commercial interest to drive product development.

It is also worth noting the timing. The outbreak is unfolding against the backdrop of significant reductions in global health funding, including cuts to USAID programming, which have reduced both surveillance capacity and community health infrastructure across Central and East Africa. A global health security architecture already under financial strain is being tested at a time when the potential consequences are most severe.

What does this mean for the UK?

The direct risk to the UK from this outbreak, based on current evidence, remains low. Ebola is not airborne. It spreads through direct contact with the bodily fluids of symptomatic individuals. There is no documented sustained transmission of any Ebola species outside Africa; even during the 2013–2016 West African epidemic only a handful of cases were exported to Europe, almost all among repatriated healthcare workers.

The UK Health Security Agency (UKHSA) maintains standing protocols for viral haemorrhagic fever (VHF) in returning travellers. NHS England High Consequence Infectious Disease (HCID) units — currently designated at Royal Free London, Royal Victoria Infirmary Newcastle, and Sheffield Teaching Hospitals — are equipped and staffed to manage suspected Ebola cases under negative-pressure isolation with full barrier precautions.

However, the absence of a Bundibugyo-specific vaccine or antiviral introduces an additional dimension of clinical uncertainty. In the event of an imported case, the two licensed Ebola therapeutics, atoltivimab/maftivimab/odesivimab (Inmazeb) and ansuvimab (Ebanga) - monoclonal antibodies which target Ebola Zaire glycoprotein used to gain access to target cells, are unlikely to be effective against Bundibugyo virus. Treatment would necessarily be supportive, as in the affected DRC communities. Clinicians should be aware of this in the unlikely event that a returning traveller from eastern DRC or Uganda presents with a febrile illness and relevant exposure history.

The probability of such an event remains very low. Nonetheless, this outbreak is a reminder that the UK’s imported VHF preparedness must account not only for the most common Ebola strain, but for the full range of viral haemorrhagic fever pathogens - a lesson that was underlined, but not fully implemented, after previous Sudan virus and Marburg alerts.

Conclusion

The 2026 Bundibugyo Ebola outbreak in the DRC is the most significant Ebola event since the 2018–2020 North Kivu epidemic. It is the first WHO PHEIC for Ebola in six years, the largest documented Bundibugyo outbreak on record, and the first to demonstrate rapid multi-country spread within days of its identification. The outbreak exposes critical gaps: diagnostic infrastructure calibrated for a single strain, a vaccine availability that does not cover rare Ebola species, and a global response system under growing resource pressure.

The communities at the centre of this outbreak are once again facing the severest consequences. The international response, now formalised under PHEIC, must be sustained, well-resourced, and attentive to the structural conditions that made this crisis possible. For the global health community, this outbreak is both a test and a reckoning.

References

1. World Health Organization. Epidemic of Ebola Disease caused by Bundibugyo virus in the Democratic Republic of the Congo and Uganda determined a public health emergency of international concern. WHO statement, 17 May 2026.. Available at: https://www.who.int/news/item/17-05-2026-epidemic-of-ebola-disease-in-the-democratic-republic-of-the-congo-and-uganda-determined-a-public-health-emergency-of-international-concern

2. CNN. Latest Ebola outbreak an emergency of international concern, WHO declares. CNN, 17 May 2026.. Available at: https://www.cnn.com/2026/05/16/africa/congo-uganda-ebola-international-concern-intl-hnk

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4. Africa CDC. Africa CDC calls for urgent regional coordination following Ebola Virus Disease outbreak in Ituri Province, DRC, and imported Ebola Bundibugyo case reported by Uganda. Africa CDC statement, 15 May 2026.. Available at: https://africacdc.org/news-item/africa-cdc-calls-for-urgent-regional-coordination-following-ebola-virus-disease-outbreak-in-ituri-province-drc-and-imported-ebola-bundibugyo-case-reported-by-uganda/

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In late April 2026, passengers and crew aboard the MV Hondius, a Dutch-flagged expedition cruise ship returning from Antarctica and remote South Atlantic islands, began to fall gravely ill. Fever, pneumonia, and acute respiratory distress syndrome progressed rapidly. Three people died. Further confirmed or suspected cases of hantavirus infection were identified, with the Andes strain confirmed by PCR.

The ship, carrying 147 people from 23 countries, found itself marooned: Cape Verde lacked the capacity to manage an evacuation, and the president of the Canary Islands refused to allow the vessel to dock, citing fears of a local outbreak and the scarring memory of COVID-19. Spain’s central government eventually overruled him.

The Hondius saga is now, simultaneously, a clinical story, a public health story, and a story about how disease and inequality are inseparable — even at sea.

The leading investigative hypothesis is that the index cases, a Dutch couple, were exposed to infected rodent material during a birdwatching excursion to a landfill in Ushuaia, southern Argentina, before the voyage departed on 1 April 2026.

What is hantavirus, and why does the Andes strain matter?

Hantaviruses are a genus of single-stranded RNA viruses with a particular tropism for vascular endothelium. They are carried principally by rodents, which act as lifelong reservoirs without themselves becoming ill. Human infection is almost always acquired by inhaling aerosolised particles from infected rodent excreta. Most hantaviruses cause dead-end infections in humans: an individual gets sick, but the chain of transmission stops there. There is no person-to-person transmission.

The Andes virus, found predominantly in southern South America and carried by the long-tailed colilargo mouse (Oligoryzomys longicaudatus), is the single known exception. It is the only hantavirus strain for which human-to-human transmission has been documented. Transmission requires close, prolonged contact - household members, intimate partners, healthcare workers without adequate protection - and appears most likely during the early prodromal phase of illness.

Two principal disease syndromes result from hantavirus infection. Hantavirus Pulmonary Syndrome (HPS), the dominant pattern in the Americas, causes massive capillary leak into the pulmonary vasculature, producing non-cardiogenic pulmonary oedema and cardiogenic shock, with case fatality rates of 35–50% for the Andes strain. Haemorrhagic Fever with Renal Syndrome (HFRS), more common in Europe and Asia and caused by strains such as Puumala and Hantaan, primarily targets the kidney and carries lower but still significant mortality.

The pathophysiology: an immune system that becomes the enemy

Hantavirus pathology is immunopathological in nature. The virus does not destroy the endothelial cells it infects. Instead, it replicates within them while suppressing the early interferon response, buying time for widespread vascular spread before adaptive immunity can respond. When the immune response does engage, it is excessive and poorly regulated. A dense infiltrate of CD8+ cytotoxic T lymphocytes accumulates in affected tissues; the vigour of this response correlates with disease severity.

The result is a dysregulated cytokine storm — high TNF-α, IL-6, and interferon-γ — which destabilises the vascular endothelium through VE-cadherin disassembly (loosening the grip between endothelial cells and threatening barrier continuity) and elevated Vascular Endothelial Growth Factor (VEGF) signalling (increases vascular permeability). Capillary leak follows, flooding the lungs in HPS and the renal interstitium in HFRS. As the subsequent pulmonary oedema is due to increased capillary permeability, attempts to treat using a diuretic will not provide any benefit and can only decrease an already compromised circulating fluid volume.

Thrombocytopenia is almost universal, driven by platelet consumption, immune-mediated destruction, and direct viral binding via β3 integrin receptors, the receptors that hantavirus binds to to gain cellular access, and the occupation of which by the virus enhances the VEGF effect and further forces capillary leaking. Compensated disseminated intravascular coagulation can also emerge, with petechiae, haematuria, and occasionally more serious haemorrhagic complications.

In HPS specifically, a distinctive haemodynamic profile with low cardiac output, high systemic vascular resistance and relative bradycardia reflects direct cytokine-mediated myocardial depression rather than distributive shock. This pattern can mislead clinicians unfamiliar with the syndrome.

Could this become the next pandemic?

The question has circulated widely since the Hondius outbreak broke in early May 2026. The WHO has assessed the global public health risk as low, and epidemiologists are not anticipating a COVID-like scenario.

SARS-CoV-2 achieved global reach because it spread efficiently in the presymptomatic and asymptomatic phases: infected individuals who felt entirely well were seeding communities for days before their illness was apparent. Hantavirus does not do this. Individuals are not infectious before symptoms appear, and symptoms are severe enough to incapacitate quickly. The virus’s lethality constrains its spread.

Even in the Hondius outbreak, a confined ship with over 150 people in sustained close contact, an almost ideal scenario for respiratory pathogen spread, transmission remained limited to individuals with the most direct exposure. The R value estimated during the 2018–2019 Epuyen outbreak in Argentina, the largest documented Andes outbreak, was 2.12 before control measures, falling to 0.96 after their implementation. These figures reflect superspreader-driven dynamics in a tightly clustered community context, not a baseline biological constant, and should not be extrapolated to general population settings.

Continued vigilance, however, is necessary because of gaps in knowledge. Hantaviruses have been comparatively under-studied compared to other viruses. The mechanism by which the Andes virus acquired human-to-human transmissibility is not fully understood. No approved vaccine exists for any Americas-affecting hantavirus strain. And rising rodent populations in endemic regions, potentially linked to climate-driven shifts in habitat and food availability, may increase the frequency of zoonotic spillover events that could, in theory, provide further opportunities for adaptive evolution - and for human-to-human transmission.

At present, there is no specific treatment for hantavirus infection though access to intensive care does improve outcomes.

Who bears the burden?

The Hondius outbreak occurred aboard a luxury expedition cruise ship carrying passengers from wealthy nations on a voyage to Antarctica, but hantavirus is fundamentally a disease of poverty and marginalisation.

In endemic regions of South America, hantavirus disproportionately affects agricultural workers, forestry workers, and those living in rural housing with inadequate rodent exclusion. In Argentina, where the Andes strain is most prevalent, cases cluster among low-income rural communities with limited access to healthcare, poor housing stock, and occupational exposures that cannot be easily avoided. The 25.7% case fatality rate recorded across the Americas in 2025 reflects, in part, the absence of ECMO infrastructure in communities where cases actually occur. Survival from severe HPS in a well-resourced intensive care unit is better than survival in a rural district hospital.

In the UK context, hantavirus remains rare but is present. The predominant strains are Seoul virus (carried by brown rats) and Puumala virus (carried by bank voles). Cases are most commonly associated with occupational exposure - agricultural workers, sewer workers, laboratory staff, and increasingly, pet rat owners and hobbyist rat breeders. The UKHSA monitors cases and issues guidance on safe handling of potentially contaminated environments. Critically, rodent infestation in substandard housing represents a structural exposure risk that no amount of individual health messaging can adequately address without improvement in housing conditions.

For healthcare workers, awareness of hantavirus is important because of the importance in avoiding diagnostic delay. The prodromal syndrome is non-specific - fever, myalgia, headache, nausea, abdominal pain, very much like a flu or Covid presentation - and in the UK context, a clinician who has not considered hantavirus may pursue an extensive differential workup before the diagnosis is made. Occupational and exposure history, including contact with rodents or rodent-contaminated environments, should be routine.

Clinical and public health takeaways

• Consider the exposure history. In any febrile illness with rapid respiratory deterioration, ask about rodent contact, rural environments, or travel to South America.

• Thrombocytopenia plus haemoconcentration is a useful early marker of capillary leak syndrome; combined with an appropriate exposure history, it should prompt hantavirus testing.

• The haemodynamic profile of HPS - low output, high resistance, relative bradycardia - is distinct from septic shock and requires a different management approach.

• ECMO capability. Referral to an ECMO-capable centre for severe HPS should be considered early.

• Infection control in suspected cases should include respiratory precautions given the theoretical risk of aerosol transmission, particularly for the Andes strain.

• Housing and occupational policy are hantavirus prevention. Individual advice is necessary but insufficient without structural intervention in the conditions that drive rodent exposure.

Key references

WHO Disease Outbreak News — Hantavirus cluster linked to cruise ship travel, Multi-country (May 2026)

Superspreaders and person-to-person transmission of Andes virus in Argentina — NEJM (2020)

Person-to-person transmission of Andes virus — NCBI PMC

Human-to-human transmission of Andes virus modelled in Syrian hamsters — Emerging Infectious Diseases (2023)

WHO Hantavirus Fact Sheet

MV Hondius hantavirus outbreak — Wikipedia (live updates)

UKHSA guidance on hantavirus in the UK