Mosquitoes in Borneo: Knowlesi Malaria, Leeches & Jungle Lodges (2026)

The CDC lists malaria medicine for Malaysia's rural, forested areas, where a monkey malaria called knowlesi spreads, and most Borneo wildlife trips spend their nights there. Dengue is the town risk in Kota Kinabalu, Sandakan and Kuching, and on rainforest trails the biter guests talk about is the leech.

Yes, and they matter most in the rainforest. The CDC lists malaria medicine for Malaysia's rural, forested areas, where a monkey malaria called knowlesi spreads, and Kinabatangan, Danum Valley and Mulu trips spend their nights in that setting. On the trails, the biter guests talk about most is the leech.

Disease risk ElevatedCDC lists malaria medicine for rural, forested areas, where monkey (knowlesi) malaria spreads, and Malaysia's 2026 dengue count is running above 2025's.

Bite nuisance AnnoyingLeeches on rainforest trails, mosquitoes from dusk on river cruises and night walks, and day-biting dengue mosquitoes in the towns.

CirculatingKnowlesi malaria (forest)Dengue (above 2025)Japanese encephalitis (rural stays)No malaria in Kuala Lumpur or PenangNo yellow fever vaccine advised

CDC noticesLevel 1 · Global dengue (Malaysia listed) · CDC

Travel clinicCDC lists malaria medicine for Malaysia's rural, forested areas, the setting of most Borneo jungle lodges, river trips and treks, and reports no malaria in Kuala Lumpur or Penang. It says to consider Japanese encephalitis vaccine for shorter rural trips and recommends it for stays of a month or more.

When to goNo month is clearly safe. Sabah's east coast tends to get its heaviest rain from about November to March, with muddier trails and more leeches. Malaysia's 2026 dengue cases climbed from late March and stayed high through at least August. CDC's malaria advice applies in every month.

Data checkedOctober 2026 · sources

The CDC's forest rule

The CDC's Malaysia page says "Zoonotic transmission of P. knowlesi malaria occurs in rural, forested areas" and reports "No malaria transmission in other areas, including Kuala Lumpur (the capital), in Penang State, on Penang Island, or in George Town (capital of Penang State)." It names no Borneo place, but in our reading jungle lodges, river trips and forest treks fit, and a city hotel in Kota Kinabalu or Kuching doesn't.

What CDC says: "CDC recommends that travelers going to certain areas of Malaysia take prescription medicine to prevent malaria." It lists "In rural, forested areas: atovaquone-proguanil, doxycycline, mefloquine, tafenoquine." What we suggest you do with this: see a travel clinic 4–6 weeks before departure with your route night by night. Whether a night at Sepilok, Bako or Kinabalu Park counts as rural forest is the clinic's call. Ask about Japanese encephalitis vaccine too, which the CDC says to consider for rural stays.

Yellow fever vaccine isn't recommended, though Malaysia requires proof from travelers arriving from a country with yellow fever risk.

Knowlesi, the monkey malaria

A 2022 study in Sarawak traced human knowlesi infections to long-tailed and pig-tailed macaques, and forest Anopheles mosquitoes, which bite from dusk to dawn, carry it to people. A 2023 analysis found sustained person-to-person spread highly unlikely, so the exposure is in the forest.

The World Health Organization's World Malaria Report 2025 counted 2,164 knowlesi cases worldwide in 2024, 34% fewer than in 2023, and Malaysia accounted for 89.0% of them. State figures are older. In Sabah in 2015–2017, interior districts had a median of 2.1 knowlesi cases per 1,000 people, against 0.1 in most coastal districts, and Sarawak's 8,473 cases from 2011 to 2019 centered on the interior Kapit division. Visitors do catch it, and in one published case, from 2006, a Swedish traveler's rapid malaria test came back negative, one more reason to tell a doctor where you were.

Leeches, dusk cruises and town days

Leeches are the standard complaint at the rainforest lodges, and they tend to be busiest after rain. Pull leech socks over trousers tucked in at the ankle, and check your skin and socks after every walk.

From late afternoon, mosquitoes take over. Put repellent on before the river boat and the night walk, wear permethrin-treated long sleeves, and sleep under the lodge net, checked for holes, or in a screened, air-conditioned room.

In Kota Kinabalu, Sandakan and Kuching, the day-biting Aedes mosquito spreads dengue. Malaysia is on the CDC's Global Dengue list, and WHO counted 63,752 cases nationwide through late August 2026, above 2025 and the five-year median. Repellent goes on over sunscreen in the morning. The CDC also lists leptospirosis, so skip wading in rivers and floodwater.

When to go

No month is clearly safe. Sabah's east coast tends to get its heaviest rain from about November to March, with muddier trails and more leeches. Malaysia's 2026 dengue cases climbed from late March and stayed high through at least August, according to WHO.

Where you're going

jungle

Sepilok & the Kinabatangan

Disease risk ElevatedBite nuisance Annoying

River lodges in the rural, forested setting where CDC lists malaria medicine. Dusk and night boat trips and night walks are the mosquito hours, and the walks bring leeches.

jungle

Danum Valley

Disease risk ElevatedBite nuisance Annoying

Primary rainforest in the same CDC malaria setting, and the place leeches dominate the bite complaints. Leech socks over tucked-in trousers, and a check after every walk.

highland

Mount Kinabalu & Kinabalu Park

Disease risk ModerateBite nuisance Occasional

The forested lower slopes and farm villages sit in Sabah's interior, where knowlesi rates were highest in 2015–2017. Mosquitoes tend to thin out on the cold upper trail, so raise the park-headquarters night with the travel clinic.

city

Kota Kinabalu & the island park

Disease risk ModerateBite nuisance Occasional

Sabah's capital and the Tunku Abdul Rahman island beaches aren't rural forest, in our reading. Dengue is the risk here, so repellent goes on over sunscreen in the morning.

Sarawak's forest parks, such as Mulu and Bako, raise the same clinic question. Our Malaysia briefing covers Kuala Lumpur, Penang and Langkawi, and the Brunei briefing covers the country that shares the island.

The Borneo kit

Socks for the leeches, the rest for dusk.

Leech socks pulled over tucked-in trousers, a pair per person.
Permethrin 0.5% for trekking clothes: treat long sleeves, trousers and socks at home 48 hours before you fly. It goes on clothing, never on skin.
Picaridin 20% travel sprays: odorless in the humidity and layers over sunscreen for town days.

Permethrin → Carry-on trio → Full rankings

What travelers report

Paraphrased from rainforest lodge reviews and linked so you can read them in full. None is dated, and rain, the season and your lodge change the picture.

Borneo Rainforest Lodge, Danum Valley
A reviewer titled the review 'Great rainforest experience - get leech socks!', putting leech socks at the top of the advice for the lodge's forest walks. TripAdvisor ↗
Borneo Rainforest Lodge, Danum Valley
A reviewer titled the review 'great food, pity about the leeches', naming leeches as the downside of an otherwise good stay. TripAdvisor ↗
Sukau Rainforest Lodge, Kinabatangan River
A guest warned of hot, humid nights because the lodge has no air conditioning, recommended the optional night boat trip, and said the night walk was more about seeing leeches than anything else. TripAdvisor ↗

One rule outlasts the trip. Any fever during or after your trip means a doctor visit and a malaria test, and you tell the doctor you were in the Borneo forest. With knowlesi in the picture, the rule holds for a full year.

Traveler questions

Do I need malaria pills for Borneo?

The CDC lists malaria prevention medicine for Malaysia's rural, forested areas: atovaquone-proguanil, doxycycline, mefloquine or tafenoquine. It names no Borneo place. In our reading, Kinabatangan river lodges, Danum Valley, Tabin, Mulu and forest treks fit that description, and a hotel in Kota Kinabalu or Kuching does not. Which medicine fits you is a call for a travel clinic, made 4–6 weeks before departure with your route night by night. Our malaria-zone checklist covers the rest.

What is knowlesi malaria, and how common is it?

It's a malaria parasite of macaque monkeys that forest mosquitoes pass to people. The World Health Organization's World Malaria Report 2025 counted 2,164 knowlesi cases worldwide in 2024, and Malaysia accounted for 89.0% of them. A 2023 study of Malaysian case data found sustained person-to-person spread highly unlikely, so the exposure is in the forest, from dusk to dawn. Repellent, long sleeves and a net on lodge evenings cover those hours.

Do I really need leech socks in Borneo?

For rainforest walks, yes. Leeches are the standard complaint at the Danum Valley and Kinabatangan lodges, and they tend to be worse after rain. Pull leech socks over trousers tucked in at the ankle and check your skin and socks after every walk. Leeches have a reputation as a nuisance more than a health risk.

Is there malaria in Kota Kinabalu or Kuching?

The CDC names only Kuala Lumpur, Penang State, Penang Island and George Town as having no malaria transmission. A city hotel isn't the rural, forested setting where it lists medicine, in our reading, and in 2015–2017 Sabah's coastal districts had far lower knowlesi rates than its interior. Dengue is the city risk, so daytime repellent matters most there. A day trip into a forest park such as Bako is worth raising with the travel clinic.

Sources

Health authorities, surveillance reports and news coverage of official bulletins used for this briefing, last checked October 2026. Traveler reports are linked where they appear. This page summarizes public-health guidance and is not medical advice.

Borneo's jungle lodges sit in CDC's malaria setting. The leeches are the bite you'll notice.