How to avoid mosquito-borne illnesses
Costa Rica has experienced significant outbreaks of mosquito-transmitted diseases in recent years, particularly during the rainy season (May-November). These illnesses represent the most significant health risk for travelers.
No matter which illness you're trying to avoid, the general advice is pretty much the same:
- Use repellent with 20–30% DEET: Reapply it throughout the day, especially on exposed skin like your ankles and arms.
- Stick to light, loose clothing: Long sleeves and pants help cut down on bites, especially around sunrise and sunset when many mosquitoes are most active.
- Stay somewhere with air conditioning: Or at least make sure there are screens on the windows and doors that close properly.
- Do a quick room check once you arrive: Look under beds, behind curtains, and in the bathroom corners—mosquitoes tend to hang out in dark, still places.
- If you're heading into the jungle, consider permethrin-treated clothing and gear: It's a good extra layer of protection for hikers and adventure travelers.
- Be extra cautious during the rainy season: That's when mosquito numbers go up dramatically.
Dengue fever
Dengue is the most common mosquito-borne illness in Costa Rica, with over 31,200 cases reported in 2024 and more than 1,200 cases in early 2025. It's around all year, but it spikes during the rainy season (May-November). It's not limited to the countryside either—you'll find cases in cities, towns, and tourist areas.
The virus spreads through Aedes mosquitoes, which bite during the day, especially in the early morning and late afternoon. The symptoms can feel a lot like the flu—fever, severe headache, pain behind the eyes, joint and muscle pain (hence its nickname "breakbone fever"), and sometimes a rash. In more serious cases, it can lead to internal bleeding.
Cases are typically highest in the Central Pacific and central regions of the country. There's no specific cure, so treatment is mostly about staying hydrated and getting rest.
Malaria
Malaria risk is low in Costa Rica but still present in certain areas. In 2024, there were 232 locally acquired malaria cases reported, primarily in the provinces of Alajuela and Limón. The risk is highest in lowland areas and near the Nicaraguan border.
The parasite is spread by Anopheles mosquitoes, which typically bite between dusk and dawn. Symptoms include fever, chills, and flu-like illness that can become severe without treatment. If you're planning to spend time in high-risk areas, talk to your doctor about antimalarial medication.
For travelers visiting the provinces of Alajuela and Limón, antimalarials such as atovaquone-proguanil, doxycycline, mefloquine, or tafenoquine may be recommended. For all other areas, mosquito bite prevention measures are generally sufficient.
Chikungunya
Chikungunya has been reported in Costa Rica, with around 405 infections in 2024. This viral disease causes fever and severe joint pain that can last for months, along with headache, muscle pain, joint swelling, or rash.
The virus is spread by the same day-biting Aedes mosquitoes that transmit dengue. A vaccine for chikungunya is now available in some countries, including the U.S. Check with your healthcare provider about availability before your trip.