Mosquitoes in Cambodia: Dengue, Malaria and Bite Prevention

Prepared by the NovAsia Editorial Team

Mosquitoes in Cambodia are more than a seasonal nuisance. For people living in Phnom Penh, the main practical concern is dengue: it is spread largely by day-biting mosquitoes, occurs throughout the year and often becomes more common during the rainy season. Malaria follows a different pattern. Its remaining risk is concentrated mainly in particular rural and forested areas, while transmission in Phnom Penh and central Siem Reap is considered absent or negligible.

That distinction matters. The right precautions depend on the exact itinerary, the time of year, the condition of the home and how much time a person spends outdoors. A family living in a central Phnom Penh condominium needs a different plan from someone sleeping in a forest village near a remote border area.

Which mosquito-borne infections occur in Cambodia

A general instruction to “avoid mosquito bites” covers several diseases with different vectors, locations and times of exposure. Mosquitoes that transmit dengue and chikungunya are mainly active during the day. Malaria vectors bite more often from dusk through the night. Japanese encephalitis is more closely associated with rural and agricultural settings, rice-growing areas, livestock and extended outdoor exposure.

Dengue is endemic across Cambodia. The US Centers for Disease Control and Prevention describes it as the mosquito-borne viral infection travellers are most likely to encounter in the country. Large outbreaks do not occur every year, but cases continue between peaks. Dengue is not a “jungle disease”: Aedes mosquitoes breed close to people and can use small containers of water around homes, schools, offices and building sites.

Chikungunya also occurs in Cambodia, including in urban areas. Its early symptoms can overlap with dengue, although joint pain may persist for longer in some people. Fever, rash and body aches are not enough to distinguish the two without medical assessment.

Malaria has a much narrower geography. The remaining risk is concentrated primarily in some remote rural and forested locations. CDC guidance treats transmission in Phnom Penh, the city of Siem Reap and the main Angkor Wat temple complex as absent or negligible. Urban residents still need mosquito protection, but dengue—not malaria—is usually the more relevant reason.

Japanese encephalitis is considered endemic in Cambodia. Transmission can occur throughout the year and commonly rises during the May-to-October rainy season. Risk is generally low for a short urban visit, but it becomes more relevant for long-term residents, people who travel regularly to villages, and those who spend substantial time outdoors or sleep in places without effective screens or air conditioning.

Zika has also been identified in Cambodia. Most infections are mild or asymptomatic, but infection during pregnancy can harm fetal development. Anyone who is pregnant, planning a pregnancy or travelling with a pregnant partner should obtain current, individual advice from a clinician familiar with travel medicine.

This article is general information, not a medical consultation. Decisions about vaccination or antimalarial medication depend on the exact route, length of stay, age, pregnancy, medical history and current medicines.

When mosquito numbers tend to rise

Mosquitoes are present in Cambodia throughout the year. Their numbers depend on rainfall, temperature, drainage and the amount of standing water around buildings. During the rainy season, flowerpot saucers, buckets, uncovered tanks, discarded containers, construction materials, blocked gutters and air-conditioning trays can all become breeding sites.

A single downpour does not always produce more mosquitoes immediately. Eggs and larvae need time to develop. The practical problem appears when water remains for several days. Heavy rain can wash some larvae away, but it also creates new water-holding containers, so the rule “more rain always means more mosquitoes the next day” is too simplistic.

The dry season is not risk-free. Households may store more water, and permanent breeding sites can remain active. In a condominium, the source may be on a roof, in a car park, beside a pump room or on a neighbouring property rather than inside the apartment itself.

Dengue activity commonly increases during the rainy season, but infection remains possible in drier months. Evening bite counts are also a poor proxy for dengue risk because Aedes mosquitoes are active by day. Exposure may occur at school, at work, in a café, in a shaded garden or on a terrace.

National surveillance can indicate whether a season is becoming more active, but it cannot predict the risk in a particular building. Local water management, screens, drainage and mosquito-control practices still matter.

How to choose an effective repellent

Repellent performance depends on the active ingredient, concentration and correct application. Labels such as “tropical”, “natural” or “family” do not by themselves demonstrate reliable protection.

Well-established active ingredients used in travel-health guidance include:

• DEET;
• picaridin, also called icaridin;
• IR3535;
• oil of lemon eucalyptus or its active component PMD;
• 2-undecanone.

In Cambodian shops and pharmacies, DEET, picaridin and icaridin are the names people are most likely to see. Check the percentage and the protection period stated on the product rather than choosing by brand alone.

For prolonged protection, UK travel-health guidance commonly recommends a product containing 50% DEET. Picaridin at around 20% can be a practical alternative for people who do not tolerate DEET. Higher concentrations generally extend the period of protection; they do not make the product “more poisonous to mosquitoes”.

Reapply according to the label, especially after swimming, heavy sweating or towel-drying. When sunscreen and repellent are both needed, apply sunscreen first and repellent afterwards. Combination products can be inconvenient because sunscreen often needs to be renewed more frequently than repellent.

Apply repellent to exposed skin and, where the label permits, to the outside of clothing. Do not spray it under clothes, onto broken skin, directly onto the face or close to the eyes. For facial use, spray or pour a small amount onto the hands first and then apply carefully.

An adult should apply repellent to a child. Avoid the child’s hands because children may rub their eyes or put their fingers in their mouths. Age restrictions vary by ingredient and product registration, so the product label takes priority.

CDC advises against applying insect repellent directly to the skin of infants younger than two months. Protect a pram or carrier with a securely fitted mosquito net and use lightweight clothing that covers the skin. For older babies and children, confirm the permitted age and formulation on the label and seek paediatric advice where appropriate.

Products registered by a competent authority and used according to instructions may be suitable during pregnancy and breastfeeding, but pregnancy requires a wider risk discussion. Repellent choice does not replace advice about dengue, Zika, malaria or the itinerary itself.

Wristbands, ultrasonic devices and essential oils generally provide shorter or less predictable protection. They should not be treated as a substitute for a proven repellent.

Clothing, screens and protection while sleeping

Repellent works best as one layer in a wider system. For evenings, waterside areas or trips into the provinces, loose trousers, a lightweight long-sleeved shirt, socks and closed shoes reduce exposed skin. Very thin fabric may not stop a bite when it lies tightly against the body.

Clothing and mosquito nets can be treated with permethrin when the product is specifically designed for fabrics. Permethrin is not applied to the skin as a normal repellent. Factory-treated clothing is a simpler option for people who do not want to handle treatment products themselves.

A mosquito net is especially important in rural accommodation, rooms without reliable screens or air conditioning, and when sleeping outdoors. In a malaria-risk area, an insecticide-treated net is preferable.

Before sleeping, check that the net has no holes, reaches fully around the bed and is tucked beneath the mattress. The body should not press against the fabric because mosquitoes may bite through it.

In city apartments, properly fitted window and door screens are often more practical than a bed net. Screens help only if there are no gaps, balcony doors are not left open and mosquitoes are not entering from corridors or shared spaces.

Plug-in vaporisers may reduce mosquito activity in a room, but they should not be the only protective measure. Mosquito coils produce smoke that can irritate the respiratory tract. Use them only as directed, with particular caution around children, people with asthma and pets.

Air conditioning lowers room temperature and allows windows to remain closed, so fewer mosquitoes may enter. It does not kill mosquitoes reliably or protect people in lifts, lobbies, restaurants, schools or gardens. A fan can make it harder for mosquitoes to land, but only within the airflow.

What to inspect in an apartment and building

Mosquito control begins during the property viewing. Look beyond the number of mosquitoes present at that moment and ask whether the property creates persistent breeding sites.

Inspect the balcony, kitchen, bathrooms and air-conditioning area. Check for:

• water in plant saucers;
• open buckets and containers;
• blocked gutters;
• air-conditioner drainage trays;
• rarely used floor drains;
• decorative bowls or water features;
• uncovered storage tanks;
• puddles in the car park or on the roof.

A large pond is not necessary. A forgotten cup, small tray or bucket that repeatedly fills with rainwater can be enough.

Ask building management how often the roof and drains are checked, who removes standing water, whether larval control is used and how complaints are handled. “We fog once a month” is not a complete mosquito-control plan. Spraying adult mosquitoes has limited value if breeding sites remain.

A maintained swimming pool is not automatically a major risk. Circulation and correct chemical treatment usually make it less suitable for mosquitoes than a small stagnant container. Problems arise around neglected pools, idle fountains, plant areas and technical trays.

After moving in, empty and scrub small containers at least weekly. Topping up the water is not enough because eggs may remain attached above the water line. Containers needed for household use should be tightly covered.

A high floor may reduce exposure to some mosquitoes close to ground level, but it does not create a mosquito-free zone. Mosquitoes enter high-rise buildings through lifts, stairwells, corridors, open doors and service shafts. Balcony plants on the twentieth floor can still support breeding.

A practical urban system combines intact screens, closed doors and windows, removal of standing water, repellent outdoors, suitable clothing for prolonged exposure and competent management of common areas.

Malaria: when extra precautions may be necessary

People staying only in Phnom Penh or central Siem Reap are not usually advised to take antimalarial medicine solely because they are in those cities. The situation changes for travel to remote rural and especially forested areas.

Malaria recommendations can change, and resistance patterns matter. Do not choose a drug from an old forum post, a friend’s leftover supply or a general map that does not show the exact route.

A clinician may recommend prophylaxis for some itineraries. The choice depends on the area, duration, age, body weight, pregnancy, medical conditions and interactions with other medicines.

Different antimalarial medicines start at different times before travel and continue for different periods afterwards. Do not shorten a prescribed course. Tablets also do not replace repellent, clothing and a mosquito net.

Before travelling beyond the cities, clarify:

1. Whether the route includes forested areas.
2. Where you will sleep.
3. Whether screens or air conditioning are available.
4. How long it would take to reach a clinic.
5. Whether preventive medicine is advised.
6. Where a malaria test could be obtained if fever develops.

A fever during or after travel to a malaria-risk area requires prompt medical assessment. Tell the clinician exactly where you travelled, not merely that you were “in Cambodia”.

Japanese encephalitis and vaccination

Japanese encephalitis is uncommon in travellers but can be severe. Risk depends on duration, season, rural exposure and the amount of time spent outdoors.

CDC recommends discussing vaccination for people moving to an endemic country, spending a month or more in areas with transmission, or travelling repeatedly in rural settings. Vaccination may also be considered for shorter trips that include villages, agricultural areas, hiking, camping or nights without screens and air conditioning.

It is not routinely recommended for every short urban visit. A person who lives in Phnom Penh for several years and regularly travels around the country, however, has a different exposure pattern from a visitor staying in the city for three days.

Plan the decision early because a vaccine series may be required before protection is established. Vaccination does not replace bite prevention.

Dengue vaccination is also not a universal substitute for mosquito precautions. Available vaccines have age, previous-infection and national-policy restrictions. A private clinic advertisement is not enough basis for a decision without individual medical review.

What to do if fever develops

Dengue, chikungunya, malaria and many other infections can begin with similar symptoms. A clinician needs to know where the person has travelled, whether there was forest exposure, whether antimalarial medicine was taken and which medicines have already been used.

When dengue is possible, do not take aspirin or non-steroidal anti-inflammatory medicines such as ibuprofen unless a clinician has advised that they are safe. They may increase bleeding risk. WHO and CDC guidance generally uses paracetamol, also known as acetaminophen, for fever and pain in suspected dengue, but the dose and contraindications still depend on the individual.

Dengue can worsen after the fever begins to fall. Seek urgent medical care for warning signs such as:

• severe abdominal pain;
• persistent vomiting;
• bleeding from the nose or gums;
• blood in vomit or stool;
• rapid breathing;
• marked weakness or restlessness;
• cold, pale or clammy skin;
• sudden deterioration after apparent improvement.

Do not wait to return to your home country if illness develops in Cambodia. Malaria needs rapid exclusion, and severe dengue can progress over a short period.

A person with dengue should also be protected from further mosquito bites. A mosquito can acquire the virus from an infected person during the period when virus is present in the blood and then transmit it to someone else.

A useful home kit may include a repellent with a clearly stated active ingredient, a thermometer, oral rehydration solution, an appropriate form of paracetamol, a pram net and the contact details of a clinic and insurer. This is not a self-treatment kit; it is a way to avoid losing time.

A practical plan after moving

During the first week, inspect screens, the balcony and air-conditioning drains. Remove standing water and ask management about roof drainage and mosquito control in shared areas. Buy a repellent based on its active ingredient, not simply a label saying “mosquito protection”.

Save the details of a nearby clinic and your insurer. Families with infants should have a suitable net for the pram. Anyone planning regular travel around Cambodia should discuss Japanese encephalitis and malaria-risk itineraries with a clinician in advance.

Check plant trays, drains and small containers weekly, and repeat the inspection after periods of heavy rain.

Reassess each trip outside the city. “Going to the provinces” is not a sufficient description: a city hotel and a week in a forest village require different precautions.

Common mistakes are predictable: using repellent only in the evening, relying on air conditioning, choosing a product only because it says natural, leaving water in plant trays, travelling into forested areas without advice, or taking ibuprofen for an unexplained fever before dengue has been considered.

Final takeaway

In Phnom Penh, mosquito protection is needed mainly because dengue is spread during the day and occurs throughout the year. Malaria is associated chiefly with particular forested and rural areas, so preventive medication is based on the route rather than on residence in Cambodia alone.

Effective prevention is layered: a proven repellent, suitable clothing, screens, closed windows, removal of standing water and competent management of shared building areas. A high floor, air conditioner, mosquito coil or occasional fogging does not replace that system.

The most important rule when illness develops is not to delay medical care. Fever after travel in Cambodia requires assessment, and deterioration as the fever falls can be a warning sign of severe dengue. Until dengue has been evaluated, avoid aspirin and ibuprofen unless a clinician specifically advises otherwise.

Sources

1. Centers for Disease Control and Prevention — *Cambodia: Traveler View*. Guidance on dengue, malaria and Japanese encephalitis. Updated 23 April 2025; reviewed 25 June 2026.
2. Centers for Disease Control and Prevention — *Cambodia, CDC Yellow Book 2026*. Sections on chikungunya, dengue, Zika, Japanese encephalitis and malaria.
3. World Health Organization — *Dengue and Severe Dengue*. Updated 21 August 2025. Symptoms, warning signs, treatment and prevention.
4. WHO Western Pacific — *Dengue Situation Update 741*, 5 March 2026. Cambodian surveillance data to 22 February 2026.
5. UK Health Security Agency — *Mosquito Bite Avoidance: Advice for Travellers*. Guidance on repellents, clothing and mosquito nets.
6. Centers for Disease Control and Prevention — guidance on preventing mosquito bites and managing dengue, including protection for children and medicines to avoid.
7. World Health Organization Cambodia — *Community Engagement Is Key to Malaria Elimination in Cambodia*, 24 April 2023. Remaining malaria geography and prevention measures.

Frequently asked

Which mosquito-borne risk matters most for a Phnom Penh resident?

Dengue is the main practical urban concern. It occurs throughout the year and is spread mainly by mosquitoes that bite during the day.

Is repellent needed only in the evening?

No. Protection against dengue is also needed during the day, particularly outdoors, in shaded areas, schools, gardens and open-air cafés.

Are antimalarial medicines needed simply for living in Phnom Penh?

They are not usually prescribed solely for a stay in Phnom Penh. The decision depends on travel to particular rural or forested areas and should be made with a clinician.