severe fever with thrombocytopenia syndrome (SFTS)



Overview

Definition

Fever with thrombocytopenia syndrome (SFTS) is an acute infectious disease caused primarily by infection with the fever with thrombocytopenia syndrome virus (a novel Bunyavirus, or SFTS virus), which is transmitted primarily by ticks.

Incidence

Confirmed cases have been reported in five countries worldwide, all in Asia, i.e., China, Korea, Japan, Myanmar, and Vietnam [2].

Cases are mainly distributed in rural areas in mountainous and hilly regions, in a disseminated state, and regionally relatively concentrated, mainly in seven provinces: Henan, Mountain, Anhui, Hubei, Liaoning, Zhejiang and Jiangsu [6].

The disease can develop throughout the year, with obvious seasonality, the epidemic season is from April to October, and the peak incidence is from May to July [6].

The current reported case fatality rate is 10%, and it can be transmitted from person to person[2] .

The incidence rate is slightly higher in females than in males, and the case-fatality rate is higher in males than in females, and the incidence rate and case-fatality rate of the disease tends to increase with increasing age[7].

The national incidence of SFTS was 0.041/100,000 people in 2011, rising to 0.188/100,000 people in 2021; the average annual incidence is 0.125/100,000 people[7].

Etiology

Pathogenesis

It is mainly caused by SFTS viral infection, and there are three basic conditions that lead to epidemics.

Source of infection

Vector ticks and host animals such as goats and cattle.

SFTS patients can also be a source of infection. Blood, secretions and excretions of SFTS patients are infectious.

Transmission route

Vector transmission: mainly through tick bites, the main vector is the longhorned blood tick.

Human-to-human transmission: direct contact with blood, secretions and excretions of patients can cause infection.

Susceptible population

The population is generally susceptible.

Risk factors

The following groups are at high risk of developing the disease.

Farmers involved in agricultural activities, tea picking, living in rural hilly or forested areas.

Farmers living in endemic areas, especially in forested or hilly areas and working in the fields.

People living in endemic areas, exposed to ticks or in contact with host animals [6].

Symptoms

Main symptoms

Most patients with SFTS have an incubation period of 5-15 days and can be categorized into the following three phases depending on the progression of the disease.

Fever stage

Most of the patients start the disease acutely, which is mainly manifested as unexplained fever, body temperature is usually around 38℃, accompanied by chills, fatigue, poor appetite, muscle aches and pains, etc. There may also be gastrointestinal symptoms such as nausea, vomiting and diarrhea.

Physical examination by the doctor may reveal enlarged superficial lymph nodes in the neck and groin with tenderness, enlarged liver and spleen, and epigastric tenderness.

Extreme stage

There may be clinical manifestations of the fever stage, and a few patients may have consciousness disorder, gastrointestinal bleeding, pulmonary hemorrhage and other manifestations.

Critically ill patients may have shock, respiratory failure, diffuse intravascular coagulation, etc., which may cause death.

Recovery period

The disease is mostly self-limiting, the duration of the disease is about 2 weeks, most patients have a good prognosis.

Some patients have a poorer prognosis, such as patients with chronic underlying diseases (diabetes, hypertension, etc.), high viral load, neurological symptoms, and obvious bleeding tendency.

Consultation

Department of Medicine

Department of Infectious Diseases

Patients with a history of tick bite or close contact with a confirmed infected person are advised to seek medical treatment promptly if they develop symptoms such as fever, chills, malaise, muscle aches and pains.

Hematology

When symptoms such as skin petechiae, ecchymosis, or subcutaneous bleeding occur, prompt medical attention is recommended.

Emergency Medicine

When symptoms such as high fever convulsions, profuse vomiting of blood, convulsions, impaired consciousness, shock, etc. occur, it is recommended to consult a doctor immediately.

Preparation for medical treatment

Preparation for medical consultation: registration, preparation of documents, common problems

Tips for seeking medical treatment

Patients with high fever can be cooled down physically before going to the doctor.

Wear clothes that are easy to put on and take off so that the doctor can conduct a physical examination.

Preparation Checklist

Symptom list

Pay particular attention to the time of onset of symptoms, special manifestations, etc.

Is there a fever? How long has the fever been present? What is the highest temperature?

Are there chills and muscle aches?

Are there skin petechiae or ecchymosis?

Is there nausea, vomiting, diarrhea, vomiting blood, black stool?

Are there any headaches, convulsions, or disorders of consciousness?

When did the above symptoms appear?

List of medical history

Is there a history of close contact with a person with SFTS?

Is there any history of tick bite?

Is there any history of sojourn in forests, mountains, or hilly areas?

Checklist

Examination results in the last six months, which can be brought to the doctor’s office

Laboratory tests: blood test, urine test, blood biochemistry, etc.

Medication list

Medication in the last 3 months, if available in boxes or packages, bring with you to the doctor’s office

Antiviral drugs: ribavirin, etc.

Antipyretic and analgesic drugs: acetaminophen, ibuprofen, etc.

Diagnosis

Diagnosis is based on

History of the disease

History of working, living or traveling in forests, mountains and hills during the epidemic season.

Tick bite within 2 weeks prior to onset of illness.

Clinical manifestations

There may be fever, skin petechiae, nausea, vomiting, diarrhea, vomiting blood, black stools, impaired consciousness, and convulsions.

Examination may include superficial lymph node swelling and pain, epigastric tenderness, hepatosplenomegaly, and relatively slow pulse.

Laboratory Tests

Blood test

The total number of leukocytes can be reduced, mostly (1~3)×109/L, and in severe cases, it can be lower than 1×109/L. The proportion of neutrophils and lymphocytes is mostly normal.

The total number of platelets can be seen to decrease, mostly (30~60)×109/L, and in severe cases, it can be lower than 30×109/L.

Urine routine

Proteinuria (+~+++) can be seen in some patients, and a few of them may have positive urinary occult blood and hematuria.

Blood biochemical examination

There may be elevation of glutamic oxaloacetic transaminase, glutamic alanine transaminase, creatine kinase isoenzyme, lactate dehydrogenase, etc., and decrease of blood sodium, and individual patients may have elevation of urea nitrogen.

Pathogenetic examination

Nucleic acid test: SFTS virus infection can be diagnosed if the serum is positive for specific nucleic acids.

Virus isolation: SFTS can be diagnosed if SFTS virus is isolated from serum specimens of patients in the acute phase.

Serologic tests

Serum-specific IgG antibodies: A positive test for IgG antibodies to SFTS virus or a more than 4-fold increase in titer in the recovery phase compared to the acute phase confirms recent infection.

Serum-specific IgM antibodies: early positivity helps diagnosis, and IgM antibodies are usually undetectable 4 months after infection.

Diagnostic criteria

Clinical diagnosis can be made on the basis of epidemiologic history (history of working, living, or traveling in hilly, forested, or mountainous areas during the epidemic season; history of tick bite 2 weeks prior to the onset of the disease), clinical manifestations such as fever, and lowered platelets and white blood cells in laboratory tests.

Confirmation of the diagnosis requires one of the following three things.

Positive nucleic acid test for SFTS virus;

SFTS virus is isolated from the case specimen;

A positive test for SFTS virus IgM or a fourfold or greater increase in IgG antibody recovery titer compared to the acute phase.

Differential diagnosis

Anaplasmosis

The two are similar in terms of season of onset, vector of transmission, susceptible population, and clinical manifestations. Differential diagnosis of anaplasmosis and SFTS can be made by pathogenetic examination.

Renal syndrome hemorrhagic fever

Both are caused by Bunyaviridae virus infection, and their epidemiologic history and clinical manifestations are similar. Differential diagnosis can be made by laboratory findings, with elevated leukocyte counts seen in routine blood tests for Renal Syndrome Hemorrhagic Fever and decreased leukocyte counts seen in routine blood tests for SFTS.

Dengue fever

Dengue fever is caused by dengue virus infection and SFTS is caused by SFTS virus infection.

Dengue fever is caused by dengue virus infection and SFTS is caused by SFTS virus infection, and the differential diagnosis can be made by pathogenetic examination.

Treatment

Aim of treatment: to relieve symptoms, control the development of the disease and reduce the death rate.

Treatment principle: There is no specific treatment for this disease, mainly symptomatic supportive treatment, and single room isolation for patients with hemorrhagic manifestations as far as possible.

Symptomatic supportive treatment

Bed rest, diet mainly consists of fluids or semi-fluids, drink more water.

Patients who cannot eat or are in serious condition need to replenish calories in time to ensure water, electrolyte and acid-base balance.

Those with high fever can be physically cooled down, such as ice packs, if necessary, use drugs to reduce fever.

Patients with bleeding manifestations should be isolated in a single room as much as possible.

Medication

Patients with high fever can be cooled down with medications such as acetaminophen and ibuprofen if necessary.

Obvious bleeding phenomenon or platelet count <30×109/L, platelet and plasma transfusion can be given.

Neutrophil count <1×109/L, can be given to use granulocyte colony-stimulating factor.

If there is a combination of bacterial and fungal infections, sensitive anti-infective drugs such as cefotaxime and fluconazole may be used.

There is no specific antiviral drug, and ribavirin can be chosen for treatment, and some studies have shown that it can inhibit viral replication in in vitro experiments, and it needs to be used under the guidance of a doctor.

Prognosis

Cure

The disease is self-limiting and most patients have a favorable prognosis.

The prognosis is poorer for patients with chronic underlying diseases, neurological symptoms, and obvious bleeding tendencies, and may be life-threatening in the absence of timely treatment.

Hazards

SFTS is contagious and human-to-human transmission exists and may be transmitted to others.

There may be gastrointestinal bleeding, shock, diffuse intravascular coagulation and other manifestations, which may be life-threatening.

Daily

Daily management

Diet should be mainly fluids and semi-fluids, and nutrition should be comprehensive and balanced.

Pay attention to rest and avoid exertion.

Avoid traveling to forests, mountains, hills and other areas where ticks are abundant.

Prevention

Avoid traveling to areas where SFTS is prevalent.

When working in the field, wear brightly colored protective clothing and avoid sitting or lying in the grass or woods for too long.

If you find any ticks attached to your body surface, you need to use tweezers to remove them promptly, with the help of a doctor if necessary.

Repellents such as mosquito repellents and ketamine can be used appropriately.

Medical personnel need to be well protected, such as wearing masks, hats, long-sleeved overalls, and avoiding direct contact with the patient’s blood and body fluids.