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Five diseases, two mosquito species, and very different levels of risk depending on where you are. Here is what is actually true — and what to do if symptoms appear.
Thailand is a tropical country. Mosquitoes are part of life here — and most bites amount to nothing more than a brief irritation. But a small number carry diseases that can be serious, or in some cases fatal if not treated promptly.
The five diseases covered in this guide are not equally distributed across Thailand, nor equally dangerous for all visitors. Dengue is nationwide and year-round; malaria is confined to specific border regions; Japanese encephalitis only poses a real risk in rural settings near rice paddies. Understanding which disease is where — and which mosquito carries it — determines what protection you actually need.
This guide covers each disease in turn — the mosquito, the symptoms, the risk areas, and exactly when to go to hospital — followed by a full prevention section. For a closer look at traditional and natural repellents that sit alongside these measures, see our companion article on natural mosquito repellents in Thailand.
The most important distinction is bite time. Dengue, chikungunya and Zika are carried by day-biting mosquitoes. Malaria and Japanese encephalitis are carried by night-biting mosquitoes. Different protection strategies apply.
| Disease | Mosquito | Bites | Risk in Bangkok | Vaccine | Severity |
|---|---|---|---|---|---|
| Aedes aegypti | Day | High | Yes | ||
| Aedes aegypti & Aedes albopictus | Day | Moderate | No | ||
| Aedes aegypti | Day | Low | No | ||
| Anopheles mosquito | Night | Very Low | No | ||
| Culex tritaeniorhynchus | Night | Negligible | Yes |
Breakbone Fever
ไข้เลือดออก
Mosquito
Aedes aegypti
Bites
Daytime
Incubation
4–10 days
Pregnancy
Pregnancy: CautionRisk Areas
Nationwide — Bangkok, Chiang Mai, all cities and resorts
Lower risk: None. Dengue is present across all of Thailand.
Season
Year-round; peak rainy season (May–October)
Paracetamol and oral fluids only. DO NOT take aspirin or ibuprofen — both increase bleeding risk. Hospital monitoring is required if platelet count drops. No specific antiviral exists.
Qdenga (TAK-003) available at private hospitals in Thailand. Can be given regardless of prior dengue infection. Dengvaxia available for previously infected patients only.
DEET or OLE repellent, long-sleeved clothing especially in mornings and late afternoons, eliminate standing water around your home — flower pots, air-conditioner trays and uncovered containers all breed Aedes aegypti.
Children, older adults, and anyone who has had dengue before are at higher risk of severe disease. A second infection with a different serotype is often more dangerous than the first, not less.
Check your home for standing water weekly — this species breeds in teaspoon-sized amounts. If you develop a sudden high fever in Thailand, assume dengue until a blood test says otherwise, and avoid aspirin or ibuprofen from the first symptom.
Key fact: Dengue has four serotypes (DENV 1–4). Recovering from one provides no cross-protection against the others. Second and subsequent infections are often significantly more severe.
Bending Disease
ไข้ชิคุนกุนยา
Mosquito
Aedes aegypti & Aedes albopictus
Bites
Daytime
Incubation
2–12 days
Pregnancy
Pregnancy: Low RiskRisk Areas
Sporadic outbreaks countrywide
Lower risk: No region is consistently low risk during an outbreak.
Season
Year-round; outbreaks are unpredictable
No specific antiviral treatment. Rest, fluids, and paracetamol for fever. NSAIDs (not aspirin) may relieve joint pain once the fever has resolved. Symptoms typically improve within a week; joint pain may persist for months.
No vaccine is currently available.
Identical to dengue prevention — both share the Aedes aegypti mosquito as the primary vector. Repellent and long sleeves during daytime hours.
Newborns infected around the time of birth, adults over 65, and people with existing joint conditions or diabetes are more likely to develop severe or prolonged symptoms.
If joint pain lingers for weeks after the fever has gone, tell your doctor it followed a mosquito-borne illness — this is a recognised pattern and there are ways to manage it, though it can take time to resolve.
Key fact: The name derives from the Makonde word for 'to become contorted' — describing the hunched posture caused by severe joint pain. Arthralgia can persist for months or years in some patients, making chikungunya more debilitating than dengue despite rarely being fatal.
The Silent Risk
ไวรัสซิกา
Mosquito
Aedes aegypti
Bites
Daytime
Incubation
3–14 days
Pregnancy
Pregnancy: Critical — See DoctorRisk Areas
Sporadic cases across Thailand; no sustained high-risk zone
Lower risk: Zika risk is low in most areas but cannot be eliminated in Thailand.
Season
Year-round; 80% of infections produce no symptoms at all
Symptomatic relief only: rest, fluids, paracetamol. Avoid aspirin and NSAIDs until dengue is ruled out. Sexual transmission is possible — men should use condoms for at least 3 months after infection.
No vaccine is currently available.
Pregnant women or those trying to conceive should take maximum mosquito precautions: DEET repellent, long sleeves, air-conditioned accommodation. Consult your obstetrician immediately if you suspect any exposure.
Pregnant women, and their unborn children, carry almost all of Zika's serious risk. Partners of pregnant women also need to take precautions, since Zika can be sexually transmitted.
If you are pregnant, or planning to conceive, and you develop a fever, rash or red eyes in Thailand, contact your obstetrician the same day rather than waiting to see if it passes. Male partners should use condoms for at least three months after any possible exposure.
Key fact: Zika is mild or invisible for most adults — but infection during pregnancy can cause microcephaly (underdeveloped brain) and other permanent neurological defects in the unborn child. This is not a risk to dismiss.
The Jungle Fever
มาลาเรีย
Mosquito
Anopheles mosquito
Bites
Night
Incubation
7–30 days (can be longer for P. vivax)
Pregnancy
Pregnancy: Critical — See DoctorRisk Areas
Rural, forested border provinces: the Thai–Myanmar border (Tak, Mae Hong Son), Thai–Cambodia border (Sa Kaeo, Trat, Chanthaburi), Kanchanaburi, forested parts of Chiang Rai, and several southern border provinces (Yala, Narathiwat, Songkhla, Satun). Risk is concentrated in forest and forest-fringe areas within these provinces, not the provinces as a whole.
Lower risk: Bangkok, Chiang Mai city, Phuket and Koh Samui are very low risk — official travel-health guidance does not routinely recommend antimalarial tablets for these destinations, though basic bite avoidance is still sensible everywhere in Thailand.
Season
Year-round in endemic border areas, with transmission peaking during and shortly after the rainy season (roughly May–October) and a smaller second peak around December
Artemisinin-based combination therapy (ACT). Seek immediate medical care — Plasmodium falciparum malaria can be fatal within 24–48 hours if untreated. Do not self-treat without a confirmed diagnosis.
No licensed malaria vaccine available in Thailand. Antimalarial prophylaxis (Malarone, doxycycline or mefloquine) is recommended before travel to high-risk areas — start as directed by a travel health clinic.
Antimalarial prophylaxis is recommended before visiting forested border areas — discuss options with a travel health clinic, since resistance patterns affect which drug is suitable. Use permethrin-treated clothing and mosquito nets. Apply DEET or Picaridin repellent from dusk onwards. Sleep in screened or air-conditioned rooms.
Travellers heading into forested border areas without prophylaxis carry by far the highest risk. Pregnant women and young children are more likely to develop severe malaria if infected, and P. falciparum resistance to some standard drugs has been confirmed near the Myanmar and Cambodia borders, which affects which prophylaxis is appropriate.
If your trip is limited to Bangkok, Chiang Mai city, Phuket or the main islands, antimalarial tablets are not routinely needed. If it includes trekking, forest stays or overnight travel near a land border, get specific advice from a travel health clinic or GP before you go — risk varies by district, not just by province.
Key fact: Malaria risk in Thailand is real but narrow: it is concentrated in specific forested border districts, not spread evenly across the country. Bangkok, Chiang Mai city, Phuket and Koh Samui carry very low risk and tablets are not routinely advised there — but 'low risk' is not the same as 'no risk', and border-area travel plans should always be checked individually.
JE
ไข้สมองอักเสบ
Mosquito
Culex tritaeniorhynchus
Bites
Night
Incubation
5–15 days
Pregnancy
Pregnancy: High RiskRisk Areas
Rural Thailand — particularly near rice paddies, irrigation systems and pig farming areas. Highest risk: northern and northeastern provinces
Lower risk: Urban Bangkok and all major cities carry negligible JE risk
Season
Peak: rainy season (May–October) — especially August and September
No specific antiviral treatment exists. Intensive supportive care only. Severe JE carries a 20–30% fatality rate; 30–50% of survivors experience permanent neurological damage.
YES — Ixiaro vaccine. 2 doses given 28 days apart. Highly effective and strongly recommended for anyone spending extended time in rural Thailand. Available at international travel clinics and private hospitals.
Vaccination is the most effective protection. Use insect repellent after dusk, sleep under treated nets, and avoid outdoor activity at night near rural water sources or agricultural land.
Children under 15 and people staying long-term or repeatedly in rural, agricultural areas carry the most risk. Short city-based trips carry negligible risk and vaccination is not routinely recommended for those itineraries.
If you are relocating to or spending extended periods in a rural province — particularly near rice paddies or livestock farming — discuss Ixiaro vaccination with a travel health clinic well before the rainy season, since the two doses need to be spaced a month apart.
Key fact: JE is rare but catastrophic when severe. The Ixiaro vaccine is highly effective and widely available in Thailand — anyone living or spending significant time in rural, agricultural parts of the country should discuss vaccination with a doctor rather than skip it.
Use this table as a quick reference before planning a trip within Thailand. Risk levels reflect general guidance — local outbreaks can change conditions. Always check current advisories before travel to border regions.
| Location | Dengue | Malaria | Chikungunya | Zika | JE |
|---|---|---|---|---|---|
| Bangkok | High | Very Low | Moderate | Low | Negligible |
| Chiang Mai city | Moderate | Very Low | Low | Low | Negligible |
| Phuket / Koh Samui | Moderate | Very Low | Low | Low | Negligible |
| Thai–Myanmar border | High | High | Low | Low | Low |
| Thai–Cambodia border | High | High | Low | Low | Low |
| Rural / rice paddy areas | Moderate | Variable | Low | Low | Moderate |
No single measure is enough on its own. The mosquitoes behind these diseases bite at different times of day, so effective prevention combines several layers — most of them free or low-cost — rather than relying on repellent alone.
Loose, long-sleeved clothing and long trousers cut down bites from both day- and night-biting species. Aedes mosquitoes (dengue, chikungunya, Zika) are most active in the two to three hours after dawn and before dusk; Anopheles and Culex mosquitoes (malaria, Japanese encephalitis) bite mainly from dusk to dawn. Knowing which window matters for your location helps you dress and plan accordingly.
Air-conditioned or well-screened rooms are one of the most effective, lowest-effort protections available. Check window and door screens for gaps, especially in older or rural accommodation, and close them before dusk if you are in a higher-risk area.
A permethrin-treated mosquito net is standard advice for sleeping in rural or border areas without reliable screening or air-conditioning. A simple electric fan also helps — mosquitoes are weak fliers and struggle to land in moving air, which is a genuinely useful low-cost measure indoors and on balconies.
Aedes aegypti — the dengue, chikungunya and Zika mosquito — breeds in small amounts of clean, stagnant water around the home: plant saucers, air-conditioner drip trays, buckets, uncovered water storage and discarded containers. Checking and emptying these weekly is one of the few prevention steps that protects your neighbours as well as you.
DEET, picaridin and oil of lemon eucalyptus (OLE/PMD) are the repellents with the strongest evidence behind them, and are widely available in Thai pharmacies and supermarkets. Apply to exposed skin after sunscreen, and reapply according to the product's instructions — protection times vary by concentration and product.
If your plans include trekking, camping or overnight stays near forested border areas, factor mosquito-borne disease risk into your planning the same way you would altitude or water safety — check current guidance and consider antimalarial prophylaxis before you go, rather than after symptoms appear.
Any of the following symptoms after mosquito bites in Thailand require immediate hospital assessment. Do not wait to see if they improve.
Bumrungrad International
Bangkok
24hr ER — largest international hospital in Southeast Asia
Samitivej Hospitals
Bangkok / Chiang Mai
4 Bangkok campuses; specialist tropical medicine
Bangkok Hospital Group
Nationwide
35+ hospitals including resorts and border towns
When you see a doctor for a fever in Thailand — or after you get home — say exactly where you travelled and when, including any rural, forested or border areas. Mosquito- borne diseases share overlapping symptoms, and travel history is often what points a clinician toward the right test. This matters just as much after you leave Thailand: some incubation periods run to several weeks, so a fever that starts after you've returned home can still be mosquito-related. Tell your GP or A&E that you have recently been in Thailand, even if the trip feels like it was a while ago.
If you've been diagnosed with dengue, wait until you've fully recovered and your doctor confirms it's safe before flying or continuing onward travel — dehydration and altitude can both worsen recovery. For malaria, some species can relapse weeks or months later, so mention any past Thailand travel to a doctor if unexplained fever develops even long after your trip has ended.
Part of the Mosquito Health Cluster
Alongside DEET, picaridin and OLE, Thailand has centuries of traditional and plant-based approaches to keeping mosquitoes away — from phlai oil to lemongrass and neem. Our companion guide rates 17 traditional remedies by scientific evidence, covers where to buy them, and explains what still works and what doesn't.
These methods are a genuinely useful addition to daily prevention — particularly around the home — but they complement, rather than replace, the evidence-based protection above in areas where malaria, dengue or Japanese encephalitis risk is real. Where risk is elevated, use them alongside DEET, picaridin, screening and — for malaria — prescribed prophylaxis, not instead of them.
THAIBK Digital
Published 23rd July 2026
Health guidance for expats, long-stay visitors and travelling families in Thailand. Cross-referenced with the CDC Yellow Book country guidance for Thailand and UK TravelHealthPro country information for Thailand. This article is guidance, not medical advice — always confirm current recommendations and antimalarial choices with a travel health clinic or GP before you travel, especially to rural or border areas.