Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne viral illness that can cause high fever, a dangerous drop in blood platelets, and in severe cases, organ failure or death. First identified in central China in 2009, the disease has since been confirmed in South Korea, Japan, and Vietnam, with modeling studies suggesting it could spread further as tick habitats expand under climate change. The virus behind it, now formally called Dabie bandavirus, primarily reaches people through the bite of an infected tick, though less common routes including contact with infected blood and even bites from sick pets have been documented.
What Causes SFTS and How Does It Spread
SFTS is caused by Dabie bandavirus (DBV), a member of the Phenuiviridae family of viruses.{1PubMed Central. Genetic variants of Dabie bandavirus: classification and biological/clinical implications} The primary vector is the Asian longhorned tick, Haemaphysalis longicornis. Research in China found that these ticks can pick up the virus by feeding on infected animals, pass it through their own life stages, and transmit it to new hosts during later feedings.{2PubMed Central. Haemaphysalis longicornis Ticks as Reservoir and Vector of Severe Fever with Thrombocytopenia Syndrome Virus in China} The overall infection rate in wild ticks tends to be low, but because people in rural and agricultural areas encounter ticks frequently, even a small percentage of infected ticks can sustain regular human cases.
Tick bites are not the only route. A systematic review of individual case data found that person-to-person transmission, particularly through contact with blood or body fluids, was the most commonly reported secondary route. Exposure to a patient’s bodily fluids significantly raised the odds of infection.{3PubMed. Transmission of Severe Fever with Thrombocytopenia Syndrome (SFTS) to humans: A systematic review of individual participant data and meta-analysis} Healthcare workers, family caregivers, and funeral attendants handling bodies of SFTS patients have all been documented as secondary cases in outbreak investigations. This makes infection-control practices in hospitals a real concern in areas where SFTS circulates.
Companion animals have also entered the picture. In South Korea, a veterinary technician contracted SFTS after being bitten by an infected dog, with molecular sequencing confirming the dog as the source.{4Emerging Infectious Diseases. Severe Fever with Thrombocytopenia Syndrome Acquired through Dog Bite, South Korea} Cat-to-human transmission has been reported in Japan as well.{5PubMed. A Case of Cat-to-Human Transmission of Severe Fever with Thrombocytopenia Syndrome Virus} These animal cases remain uncommon, but they are a reminder that pets roaming tick-infested areas can bring the virus home in ways people do not expect.
Signs and Symptoms
The illness typically begins with a sudden high fever, often after an incubation period of about one to two weeks following a tick bite. The hallmark early findings are fever, a sharp drop in platelets (the cells that help blood clot), and low white blood cell counts.{6PubMed. Identification of severe fever with thrombocytopenia syndrome virus in ticks collected from patients} Patients commonly experience fatigue, muscle pain, nausea, vomiting, diarrhea, and loss of appetite. Some develop swollen lymph nodes. The fever can persist for over a week, and in mild cases the illness resolves with supportive care as blood counts gradually recover.
What makes SFTS especially concerning is how the virus manipulates the immune system. One of its key proteins acts as what researchers describe as a “master manipulator” of host defenses: it suppresses interferon signaling (one of the body’s first antiviral alarms), rewires inflammatory pathways, and creates conditions that favor viral survival.{7PubMed. Severe fever with thrombocytopenia syndrome virus NSs: a multifaceted viral protein in host-virus interactions} This immune evasion helps explain why some patients deteriorate rapidly despite apparently normal early presentations.
When SFTS Turns Severe
The most feared complication is involvement of the central nervous system. In a retrospective study of 109 SFTS patients, roughly a quarter developed encephalitis or encephalopathy, and the in-hospital death rate among those patients was about 43%, compared to around 13% for patients without brain involvement.{8PubMed Central. Clinical feature of severe fever with thrombocytopenia syndrome (SFTS)-associated encephalitis/encephalopathy: a retrospective study} Symptoms of neurological involvement can include confusion, seizures, involuntary tremors, and altered consciousness. In one reported case, a 69-year-old woman presented with persistent involuntary shaking of the mouth area and limbs as her first noticeable symptom.{9PubMed Central. Severe fever with thrombocytopenia syndrome with central nervous system symptom onset: a case report and literature review}
Research suggests the virus may directly invade the brain. Studies have detected viral genetic material in cerebrospinal fluid along with elevated levels of inflammatory signaling molecules, pointing to a combination of direct viral damage and an overwhelming inflammatory response as the mechanism behind brain injury.{10PubMed. Severe fever with thrombocytopenia syndrome-associated encephalopathy/encephalitis} Beyond the brain, severe cases can involve multi-organ dysfunction, hemorrhaging, acute liver injury, and kidney failure.
Who Faces the Greatest Risk
Older age is the single most consistent risk factor for dying from SFTS. Multiple studies have confirmed this independently. One analysis found the average age of patients who died was about 70, compared to roughly 64 among survivors.{11Scientific Reports. A nomogram to predict mortality in patients with severe fever with thrombocytopenia syndrome} Beyond age, markers of disease severity at admission predict outcomes. Higher viral loads, multi-organ dysfunction, prolonged clotting times, and elevated D-dimer levels have all been independently linked to fatal outcomes.{11Scientific Reports. A nomogram to predict mortality in patients with severe fever with thrombocytopenia syndrome} Another study identified the need for blood-pressure-supporting medications and higher acute illness severity scores as independent predictors of death.{12PubMed Central. Risk Factors for Death in Patients with Severe Fever with Thrombocytopenia Syndrome}
A long delay between the start of symptoms and diagnosis also increases the risk of a fatal outcome.{13PubMed Central. Transmission and mortality risk assessment of severe fever with thrombocytopenia syndrome in China: results from 11-years’ study} This is a practical problem. SFTS symptoms overlap with many other febrile illnesses, and patients in rural areas may not seek care quickly or may be initially misdiagnosed. Early recognition and testing can make the difference between supportive care that works and a case that spirals out of control.
How SFTS Is Diagnosed
The gold standard for confirming SFTS during the acute phase is detecting viral RNA in the blood using real-time RT-PCR.{14PubMed Central. Detection of SFTS virus RNA and antibodies in severe fever with thrombocytopenia syndrome surveillance cases in endemic areas of China} This test is highly reliable in the first week of illness when the virus is circulating at high levels. However, some patients with strong clinical suspicion test negative on PCR, possibly because they present later in the disease course when viral levels have dropped. For these cases, antibody testing for SFTS-specific IgM can help confirm or exclude the diagnosis.{14PubMed Central. Detection of SFTS virus RNA and antibodies in severe fever with thrombocytopenia syndrome surveillance cases in endemic areas of China}
One challenge in endemic areas is that many rural clinics lack sophisticated lab equipment. Researchers have been developing simpler, portable diagnostic tools. One promising approach uses a rapid nucleic acid amplification system paired with a lateral flow strip (similar in concept to a home pregnancy test) that has shown results consistent with standard PCR in clinical samples.{15PubMed Central. Rapid and portable bunyavirus SFTSV RNA testing utilizing catalytic hairpin assembly coupled with lateral flow immunoassay} If this technology matures, it could bring early diagnosis to places where it matters most.
Diagnostic tools for animals are also advancing. RT-PCR and antibody tests adapted for cats and dogs have proven useful for identifying SFTS-suspected companion animals, which matters for tracing outbreaks and protecting veterinary workers.{16PLOS ONE. Diagnostic system for the detection of severe fever with thrombocytopenia syndrome virus RNA from suspected infected animals}
Treatment Options
There is currently no approved antiviral specifically for SFTS. Treatment relies overwhelmingly on supportive care: fluids, platelet transfusions when counts drop dangerously low, management of bleeding, and intensive-care support for patients who develop organ failure. That said, one drug has shown enough promise to change clinical practice in some regions.
Favipiravir (also known as T-705), a broad-spectrum antiviral originally developed for influenza, has been the most studied candidate. In a clinical trial of 145 patients, those receiving favipiravir showed faster viral clearance and less disease progression compared to patients receiving standard supportive care alone.{17PubMed Central. Antiviral Treatment Options for Severe Fever with Thrombocytopenia Syndrome Infections} A separate trial reported that among patients treated with favipiravir, the death rate was about 10%, compared to roughly 18% in the control group. The benefit was clearest in patients who started treatment earlier and had lower viral loads; the treated group also experienced fewer hemorrhagic signs and faster recovery of lab abnormalities.{18Signal Transduction and Targeted Therapy. Clinical effect and antiviral mechanism of T-705 in treating severe fever with thrombocytopenia syndrome} For patients with very high viral loads, however, favipiravir did not significantly reduce deaths, suggesting that early intervention before the virus overwhelms the system is critical.
Favipiravir is not universally available, and larger confirmatory trials are still needed before it becomes a standard recommendation everywhere SFTS occurs. Other experimental approaches, including monoclonal antibodies and convalescent plasma, are at earlier stages of investigation.
Prevention Measures
Because there is no approved vaccine and no reliably curative antiviral, prevention remains the frontline strategy. For individuals, this boils down to avoiding tick bites and managing exposure in healthcare settings.
- Tick avoidance: Wear long sleeves and pants tucked into socks when walking through grass, brush, or woodland. Light-colored clothing makes ticks easier to spot. Apply insect repellents containing DEET or permethrin to skin and clothing, respectively.
- Post-exposure checks: After spending time outdoors in tick-prone areas, do a full-body tick check. Pay attention to the scalp, behind the ears, underarms, and groin. Remove attached ticks promptly with fine-tipped tweezers, pulling straight up without twisting.
- Pet management: Dogs and cats can carry infected ticks into the home and, as documented in South Korea and Japan, can themselves become infected and transmit the virus. Using veterinary tick-prevention products on pets is a practical household measure.
- Healthcare precautions: Clinicians and caregivers should use standard contact and droplet precautions when handling SFTS patients, especially avoiding unprotected contact with blood and bodily fluids.
On the vaccine front, researchers are pursuing several platforms including live-attenuated vaccines, DNA vaccines, viral vector vaccines, protein subunit vaccines, and mRNA vaccines.{19PubMed Central. Current Progress of Severe Fever with Thrombocytopenia Syndrome Virus (SFTSV) Vaccine Development} None have reached late-stage clinical trials in humans yet, but the diversity of approaches increases the chances that at least one will eventually succeed. For now, personal protection against ticks remains the most effective way to avoid SFTS.
Where SFTS Has Been Found and Where It May Spread
The first documented cases emerged in Henan Province, China, in 2009. South Korea confirmed its first cases in 2012, Japan in 2013, and Vietnam in 2017.{20The Lancet Regional Health – Western Pacific. Global epidemiology of severe fever with thrombocytopenia syndrome virus in human and animals: a systematic review and meta-analysis} The disease remains concentrated in East and Southeast Asia, but the tick vector has a wider footprint. Modeling studies have predicted high receptivity to the Asian longhorned tick in northeastern United States, New Zealand, parts of Australia, and several Pacific islands.{21PubMed Central. Mapping the global potential transmission hotspots for severe fever with thrombocytopenia syndrome by machine learning methods} The tick has already been confirmed in the eastern United States, though no locally acquired human SFTS cases have been reported there to date.
Climate change is projected to make things worse. Warming temperatures are expected to expand the range of Haemaphysalis longicornis into northern and northwestern China, while potentially reducing its suitability in some central and eastern areas.{22PubMed. Projecting spatiotemporal dynamics of severe fever with thrombocytopenia syndrome in the mainland of China} One study modeling conditions in a high-incidence Chinese province estimated that by 2028, SFTS case counts could increase by roughly 23% compared to 2023 levels, and that eight counties that have never reported a case are expected to see their first ones.{23One Health. Environmental, climatic, and social risk factors of severe fever with thrombocytopenia syndrome and the implications of climate change} Broader projections suggest that as tick populations grow and spread, both the number of SFTS cases and the costs of tick control will rise.{24PubMed Central. The impact of climate change on ecology of tick associated with tick-borne diseases}
The Problem of Co-Infections
In areas where SFTS circulates, the same ticks can carry other pathogens simultaneously. A study in Zhejiang Province, China, one of the country’s hardest-hit regions, found that multiple tick-borne pathogens were circulating in the same ecological areas and detected antibodies against other tick-borne infections in SFTS patients.{25One Health. Coinfection patterns and associations of tick-borne pathogens in natural foci of severe fever with thrombocytopenia syndrome: A One Health approach} Previous research has suggested that bacterial co-infections may increase the risk of death in SFTS patients.
One co-infection that has received specific attention is scrub typhus, caused by a bacterium also transmitted by mites and ticks in parts of Asia. In one study, about 5% of patients initially suspected of having SFTS turned out to be co-infected with scrub typhus, and a similar proportion of scrub typhus patients had concurrent SFTS. The authors recommended that in areas where both diseases are common, clinicians should test for co-infection and consider empirical antibiotic treatment with doxycycline for SFTS patients until scrub typhus is ruled out.{26PubMed Central. Coinfection of Severe Fever with Thrombocytopenia Syndrome and Scrub Typhus in Patients with Tick-Borne Illness} This is a useful point because SFTS itself does not respond to antibiotics, but scrub typhus does, and missing a treatable co-infection in someone who is already critically ill could be the difference between recovery and death.
Recovery and Long-Term Effects
For those who survive the acute illness, SFTS is not always a clean recovery. A large longitudinal study of nearly 1,200 survivors found that about 63% developed persistent sequelae. The most common complaints were memory problems, joint pain, hair loss, and declining vision, each affecting roughly a third of survivors.{27PLOS Neglected Tropical Diseases. Long-term clinical sequelae in severe fever with thrombocytopenia syndrome: A longitudinal cohort study} These are not trivial symptoms. Memory impairment and joint pain, in particular, can significantly affect daily life and work capacity, and they appear to persist for years rather than weeks.
Lab abnormalities can linger as well. A cross-sectional study of recovered patients found that certain blood markers related to platelet size and red blood cell characteristics remained abnormal in anywhere from 13% to 70% of individuals after recovery.{28PubMed Central. The holistic rehabilitation from acute severe fever with thrombocytopenia syndrome virus infection to 10 years after recovery: A cross-sectional study} In a small fraction of survivors, lab abnormalities including low platelets and elevated markers of tissue damage persisted for ten years or more.{27PLOS Neglected Tropical Diseases. Long-term clinical sequelae in severe fever with thrombocytopenia syndrome: A longitudinal cohort study}
The picture is not entirely grim. Survivors do appear to develop lasting immunity. A study measuring antibody responses in recovered patients found that neutralizing antibodies and virus-specific immune memory cells were still detectable up to nearly seven years after infection.{29PubMed Central. Sustained humoral immunity in the patients recovered from severe fever with thrombocytopenia syndrome} This suggests that reinfection with the same virus strain is unlikely for many years, though how well this immunity holds against different genetic variants of the virus remains an open question. For most survivors, the practical worry is less about catching SFTS again and more about managing the lingering effects of the first bout.