In a new analysis, researchers report that only four of 7,600 patients who tested negative for dengue were positive for chikungunya virus by reverse-transcription polymerase chain reaction, or RT-PCR. The patients came from a broader cross-sectional sample of 8,000 febrile individuals in the greater Yogyakarta area. The same study identified 400 dengue-PCR-positive cases, reinforcing dengue’s dominant position among acute febrile illnesses in the region. Yet the four chikungunya infections may say as much about the limitations of disease surveillance as they do about the virus’s actual prevalence.

Chikungunya is transmitted primarily by Aedes mosquitoes, including Aedes aegypti and Aedes albopictus, the same vectors responsible for spreading dengue and several other arboviruses. Infection can cause sudden fever, severe joint pain, headache, rash and muscle pain. The overlapping symptoms create a major diagnostic problem: without laboratory confirmation, clinicians may have little practical way to distinguish chikungunya from dengue during the first days of illness. In regions where dengue is common and testing resources are constrained, a patient with chikungunya can easily be counted as having dengue, another febrile disease or no specific infection at all.

The Yogyakarta findings are therefore not equivalent to proof that chikungunya is nearly absent from Java. RT-PCR detects viral genetic material, but only during a relatively narrow period when virus is circulating in the bloodstream. Chikungunya typically produces a brief viraemic phase lasting several days around the onset of symptoms. A patient tested after that window may still have had chikungunya but return a negative molecular result. A single cross-sectional sampling event can consequently underestimate the number of people infected over a longer period, particularly when patients arrive at clinics at different stages of illness.

The test also focuses on current infection rather than accumulated exposure. Serological studies, which measure antibodies produced after infection, can reveal whether people were infected weeks, months or years earlier. But these tests have their own technical complications. Antibodies against chikungunya may cross-react with related alphaviruses, potentially producing results that are difficult to interpret without carefully validated assays. The authors say a random sample of the original 8,000 clinical specimens is now being examined to estimate past chikungunya exposure and the proportion of people who may have developed protective immunity.

That distinction could determine whether Java is facing a hidden reservoir of immunity or a largely susceptible population. If many infections have gone unnoticed, the island’s communities may have accumulated substantial protection, including through infections that caused mild or no symptoms. Such immunity could help explain why few acute cases were detected. Conversely, if chikungunya has genuinely circulated at low levels, many people may remain vulnerable, creating the conditions for a large outbreak if a virus variant is introduced or mosquito transmission intensifies.

Indonesia’s wider epidemiological record offers no simple answer. Bali is a recognised chikungunya transmission hotspot, and outbreaks during 2021 and 2022 reached a reported incidence of 20.6 cases per 100,000 people. Java lies close to Bali and has dense populations, extensive movement of people and abundant mosquito habitat, yet published surveillance data paint a much patchier picture. In other Indonesian regions, evidence is similarly inconsistent. A study of asymptomatic adults in North and South Sulawesi found chikungunya IgG antibodies in more than half of participants, suggesting widespread previous exposure. By contrast, chikungunya was rarely detected in hospital-based sampling conducted across Ambon, Banjarmasin and Batam.

The apparent volatility of national case reports further complicates interpretation. Indonesia recorded 2,974 chikungunya cases in 2022, followed by 6,049 cases across 29 provinces in 2023, then only 571 cases in seven provinces in 2024. Such dramatic changes could reflect real shifts in transmission, but they could also result from differences in diagnostic capacity, reporting practices, access to care and the number of provinces actively conducting surveillance. Passive hospital-based systems tend to capture people who develop noticeable symptoms and seek medical attention, while people with mild or asymptomatic infections remain outside the reporting network.

The uncertainty has become more consequential because chikungunya vaccination is moving from theory into public-health policy. Two vaccines have reached licensure: IXCHIQ, a live-attenuated vaccine, and Vimkunya, a virus-like-particle vaccine. IXCHIQ contains a weakened form of the virus designed to stimulate immunity without causing typical disease, whereas Vimkunya presents viral structural components to the immune system without using a complete replicating virus. Both approaches aim to prepare immune defences before exposure, but their use must be weighed against the local risk of infection and the population’s age, health status and prior immunity.

Safety concerns have complicated that calculation. Post-marketing surveillance of IXCHIQ identified serious adverse events, predominantly among older adults. In 2025, use in that age group was temporarily restricted, and the vaccine was voluntarily withdrawn from the United States market in January 2026, although it remains available elsewhere. It is also being supported through an access programme for low- and middle-income countries and a pilot vaccination programme in Brazil. For Java, policymakers must therefore compare the expected number of chikungunya cases prevented with the vaccine’s potential risks, while recognising that neither the true infection rate nor the age distribution of previous exposure is yet well defined.

Those unknowns make the four positive PCR results more than a curious statistical footnote. On one interpretation, they indicate that chikungunya transmission in Yogyakarta is genuinely uncommon, and that large-scale vaccination might offer limited benefit. On another, they represent only the visible tip of a much larger iceberg hidden by late testing, asymptomatic disease and misdiagnosis as dengue. A third possibility is that past transmission has generated enough population immunity to suppress current cases without eliminating the threat of future outbreaks. Distinguishing among these scenarios will require repeated molecular surveillance, better timing of specimen collection, carefully designed antibody studies and monitoring that extends beyond hospitals.

The question is especially urgent on Java, a densely populated and economically important island where an outbreak could spread rapidly through communities with abundant Aedes mosquitoes. Better data would allow health authorities to estimate the number needed to vaccinate, identify groups most likely to benefit and determine whether vaccination is cost-effective. It would also clarify whether apparent changes in national case counts reflect genuine epidemic dynamics or fluctuations in detection. Until that evidence is available, the low number of chikungunya infections found in Yogyakarta should be treated neither as reassurance nor as a warning of an imminent outbreak, but as a signal that one of Indonesia’s most important mosquito-borne diseases remains poorly measured.

Leveraging machine learning techniques, the team synthesized extensive epidemiological data concerning chikungunya infections with environmental and socioeconomic variables, such as the distribution of Aedes aegypti and Aedes albopictus mosquitoes, regional temperature profiles conducive to viral transmission, annual precipitation rates, habitat suitability indices, and national Gross Domestic Product (GDP) indicators. This multifactorial approach enabled an unprecedented projection of the disease’s geographic reach beyond traditional tropical and subtropical zones, emphasizing that the threat posed by chikungunya extends far into previously unsuspected regions.

The model estimated that globally, approximately 14.4 million individuals face an annual risk of contracting chikungunya under current conditions. However, accounting for possible geographic expansion of risk zones and emerging case reports, that figure could escalate dramatically to nearly 35 million people at risk each year. India alone represents a significant fraction of this burden, with 5.1 million individuals currently identified at risk and a potential increase to 12.1 million under future spread scenarios.

Importantly, this research illuminated that India, Brazil, and Indonesia emerge as the top three countries most vulnerable to enduring, severe consequences from chikungunya infection. These nations are expected to endure nearly half (48%) of the global health impact from the virus. Unlike many infectious diseases where acute morbidity and mortality dominate, chikungunya’s primary burden arises from chronic sequelae. Approximately 50% of those infected develop persistent disability, chiefly manifested as debilitating joint pain that can persist for months or even years after the initial febrile illness.

The clinical presentation of chikungunya typically includes sudden onset of high fever exceeding 39℃, accompanied by severe polyarthralgia disproportionately affecting hand, wrist, ankle, and foot joints. While acute symptoms generally subside within weeks, the pain and stiffness can transition to a protracted chronic syndrome that significantly reduces quality of life. Fatalities are infrequent but have been documented, predominantly in elderly or immunocompromised individuals.

This novel modeling study contrasted previous attempts to quantify chikungunya’s burden, which largely depended on underreported surveillance and outbreak data, often failing to capture asymptomatic or mildly symptomatic cases, thereby underestimating true incidence. Instead, the force of infection concept, which integrates not only infection counts but also transmission dynamics and vector ecology, was harnessed to estimate realistic infection probabilities in populations at risk.

Findings indicated that while the average annual risk of infection per susceptible person hovered around 1.2–1.3%, certain hotspots exhibited notably higher rates. For example, in Gabon, Central Africa, up to 11% of residents living in at-risk areas might contract the virus annually, signaling substantial localized epidemics that could overwhelm healthcare infrastructures.

Age-stratified analyses revealed differential vulnerabilities along the lifespan. Middle-aged adults, particularly those between 40 and 60 years old, accounted for the majority of chronic disability burden, emphasizing this group’s high risk for long-term morbidity. In contrast, children under 10 and the elderly over 80 were most susceptible to acute manifestations of chikungunya infection, underscoring the nuanced interplay between age and disease outcomes.

The expanding global footprint of vector species capable of transmitting chikungunya poses significant challenges for public health preparedness. Aedes aegypti and Aedes albopictus mosquitoes, commonly known as yellow fever and tiger mosquitoes, have been recorded in more than 114 countries since the virus’s resurgence in 2004. Their adaptation to temperate climates, urban landscapes, and varying precipitation patterns facilitates the virus’s potential entry into new territories.

Researchers caution that their model reflects a long-term average and does not incorporate extreme weather anomalies or evolving climatic trends, which could alter vector populations and transmission dynamics unpredictably. Consequently, continuous surveillance and adaptive response frameworks remain paramount to mitigate emerging chikungunya threats.

The absence of specific antiviral therapies against chikungunya compounds the urgency for effective prevention interventions. To date, supportive care addressing symptoms represents the primary clinical management strategy. Encouragingly, two vaccines, identified as Ixchiq® and Vimkunya®, have received approval for use in various countries, including Brazil. The researchers advocate for leveraging their detailed risk maps to strategically target vaccine deployment, prioritizing age groups and regions identified as most vulnerable.

Co-author Hyolim Kang emphasized the paradigm shift from considering chikungunya a geographically confined threat to recognizing its potential as a pervasive global health hazard. Sushant Sahastrabuddhe from the International Vaccine Institute highlighted the study’s real-time utility, underscoring the imperative that scientific insights must translate to actionable public health measures swiftly.

Ultimately, this pioneering force of infection mapping and spatial modeling study charts a path for stakeholders—from governments to global health agencies like the WHO—to anticipate and curtail chikungunya’s expanding impact. Through informed resource allocation and proactive immunization campaigns, the global community moves closer to mitigating the substantial and lingering human costs wrought by this resurging virus.

Subject of Research:
Global and national burden of chikungunya virus infection and its long-term impacts

Article Title:
Global, regional, and national burden of chikungunya: force of infection mapping and spatial modelling study

News Publication Date:
1-Oct-2025

Keywords:
Health and medicine, Diseases and disorders, Infectious diseases