Scrub typhus is a bacterial infection passed on by the bite of tiny mite larvae, called chiggers, that live in grass, scrub and the edges of farmland in Thailand. It causes a high fever one to three weeks later, often with a painless black scab where the chigger fed, and it is curable when a doctor treats it early.
Few visitors have heard of it, yet it is one of the classic causes of fever after a trek, a rafting trip or a homestay in the countryside. The disease is not spread from person to person and there is no vaccine, so prevention comes down to clothing, repellent and checking your skin afterwards. This page explains the risk and the signs. It is general information, not medical advice; a doctor decides on tests and treatment.
Scrub typhus at a glance
- Cause
- Orientia bacteria, carried by chiggers (larval mites)
- Thai names
- Scrub typhus, or khai rak sat yai (ไข้รากสาดใหญ่)
- Where
- Grass, scrub, bushes and farmland near forest (DDC)
- When
- All year; most common from the rainy season into the early cool season (DDC)
- Time to symptoms
- 6-20 days, on average 10 (DDC)
- Vaccine
- None (CDC, DDC)
- Treatment
- Antibiotics chosen by a doctor, as early as possible
How you catch it: chiggers in grass and scrub
Chiggers are the larvae of a mite, too small to notice. They live on grass and low bushes and get onto people who walk, sit or work there, and the bite usually goes unnoticed. Some carry the bacteria, which they pick up from their usual hosts: according to Thailand's Department of Disease Control (DDC), rodents and tree shrews.
The US Centers for Disease Control and Prevention (CDC) describes the mites as "encountered in high grass and brush". Its Yellow Book, the CDC's guide for travel doctors, says more than a million cases occur each year across the region where the disease is found, which includes Southeast Asia, China, the Indian subcontinent, Indonesia, Japan and eastern Australia. Most of those infected are farmers. Travelers who catch it usually do so after time in rural areas or outdoor activities such as camping, hiking and rafting.
Where and when the risk is higher in Thailand
The DDC says scrub typhus is found mainly in agricultural areas and in all seasons, but is most common from the rainy season to the early cool season. We found no official list of the provinces with the most cases, so we do not rank regions here.
For a visitor, the activity matters more than the map. These are the situations that bring you into chigger habitat:
- trekking through grassland and forest edges, for example on multi-day hikes in the north covered in our northern Thailand itinerary;
- camping, or sitting and lying on the grass at viewpoints and campsites;
- homestays and volunteer work on farms, rice fields and plantations;
- jungle walks and river trips in parks such as Khao Sok.
City breaks, beach resorts and temple visits carry very little risk. You do not need to avoid the countryside; you need to dress for it.
The eschar: the black scab that gives it away
The one sign that points clearly to scrub typhus is the eschar. The DDC describes it as a painless, round black sore "like a cigarette burn", usually where clothing is tight or skin folds meet: the groin, the waistband, under the underwear or in the armpit. Because it does not hurt or itch, many people never notice it.
Not everyone gets one. The CDC notes that not all infections produce an eschar, so its absence does not rule the disease out. If you get a fever after a trip to the countryside, check your whole body in good light, or ask someone to check your back, and show the doctor anything that looks like a small burn.
A painless black spot plus a fever after a trek needs a doctor today. Do not wait to see if the fever settles; the CDC says untreated scrub typhus can be fatal, while early treatment works well.
Symptoms, and why it is mistaken for dengue
The illness starts with fever, headache and aching muscles. The CDC lists swollen lymph nodes and a cough or other breathing symptoms, which affect about two thirds of patients, and in severe cases inflammation of the brain. The DDC adds that a fine red rash on the body may follow after four to five days of fever.
All of this looks like other fevers common in the same places and the same season. Dengue causes fever, aches and a rash and peaks in the rainy months, and leptospirosis follows contact with floodwater and mud, often on the same rural trips. Only a doctor, with blood tests where needed, can tell them apart, and your account of where you have been is a large part of that.
The time gap matters too. The DDC gives 6 to 20 days from the bite to symptoms, so the fever can start after you have left the countryside, or after you have flown home. If you get a fever up to about three weeks after a trip, tell the doctor you were in rural Thailand.
Seeing a doctor and what happens next
The DDC's advice is to see a doctor at once if fever follows time in fields, scrub or forest, and to mention where you went. Mention the words "scrub typhus" and any black spot you have found. Go straight to an emergency department, or call 1669 for an ambulance (see our emergency numbers), if someone with a fever becomes short of breath, confused or very drowsy.
Treatment is with antibiotics, and the choice is the doctor's. The CDC says treatment "should never be withheld pending confirmatory testing", so a doctor may start it before the results are back, and that early treatment saves lives. The CDC also says antibiotics are not recommended as prevention after a possible bite, so do not take tablets "just in case". Our guide to hospitals in Thailand explains where to go and how payment works, and travel insurance should cover a stay if you need one.
Preventing chigger bites
There is no vaccine, so the advice from the DDC and the CDC is about not getting bitten:
- Cover up: long trousers and long sleeves in grass and scrub, so that arms and legs are covered.
- Use repellent on exposed skin and on clothing. Our article on avoiding mosquito bites covers the products sold in Thailand; the same habits help against chiggers.
- Do not sit or lie directly on the ground or grass; use a mat or a groundsheet, and keep to cleared paths where you can.
- After the walk, shower and wash your hair, check your body (especially the groin, waist and armpits) and wash your clothes straight away.
The vaccinations guide covers the shots that do exist for rural travel, such as Japanese encephalitis; scrub typhus is not among them.
Frequently asked questions
Is scrub typhus common in Thailand?
It is a well-known disease in rural Thailand, mainly among farmers, and the CDC estimates more than a million cases a year across its range in Asia and the Pacific. Travelers are infected far less often, usually after trekking, camping, rafting or farm stays.
How long after a chigger bite do symptoms start?
The DDC gives 6 to 20 days, on average about 10. That means the fever can begin after you have left the area or returned home. Tell the doctor about any countryside trip in the previous three weeks.
Is there a vaccine against scrub typhus?
No. Both the CDC and the DDC say there is no vaccine. Protection comes from long clothing, repellent on skin and clothes, not sitting on bare grass, and checking your body and washing after a trek.
Can scrub typhus be cured?
Yes. It is treated with antibiotics, and the CDC says early treatment saves lives. The doctor chooses the medicine and may start it before tests confirm the diagnosis. Without treatment the disease can become serious, so do not delay.
Sources
- CDC Yellow Book – Rickettsial diseases, including scrub typhus (23 April 2025) (checked October 2026)
- Department of Disease Control – Scrub typhus (Thai, updated 10 August 2022) (checked October 2026)
- CDC – Travelers' health: Thailand (checked October 2026)