Dengue and chikungunya numbers with their dates, where malaria and yellow fever occur in Brazil, which mosquitoes bite by day and which by night, and when a bed net matters.
Why European winter is Brazil's high season
Travellers from Europe often leave a cold winter for a Brazilian summer, and that timing matters for mosquito-borne disease. The Pan American Health Organization frames its regional outlook around the approaching peak season for dengue and chikungunya transmission in South America, together with an anticipated intensification of the El Niño phenomenon over the coming months. So the season you travel into is the risky one, not a quiet gap between outbreaks. Three diseases deserve your attention before you book: dengue, chikungunya and yellow fever, all spread by Aedes mosquitoes, plus malaria in parts of the Amazon basin. Oropouche virus also circulates, spread mainly by a biting midge rather than a mosquito. This guide gives the newest figures with their dates, explains where each risk sits, and sets out which mosquitoes bite by day and which by night.
Dengue in the Americas: the newest figures and their dates
PAHO updated its dengue situation report on 23 October 2026, with data as of epidemiological week 39 of 2026. It records a regional total of 1,813,577 suspected dengue cases, which it says is 55% below the same period in 2025 and 62% below the five-year average. The report lists 565,945 laboratory-confirmed cases and 614 deaths, a case fatality rate of 0.034%. In week 39 alone there were 28,008 new suspected cases, including 76 classified as severe dengue and 10 deaths. Brazil carries the largest share: Table 1 gives 1,350,614 cumulative suspected cases through week 39 and 14,734 in week 39. PAHO says 21 countries and territories reported dengue in week 39, and 46 have reported cases in 2026. Lower regional numbers do not mean no risk where you are going.
Chikungunya and the four dengue serotypes in Brazil
PAHO's epidemiological update of 20 October 2026 covers dengue and chikungunya in the Americas with dengue data as of epidemiological week 37 and chikungunya data as of week 38, except where a country is given a later week. For chikungunya it records 213,919 suspected and 78,481 confirmed cases across the Americas, with 88 deaths in 20 countries and territories. Brazil reported 135,962 suspected chikungunya cases between weeks 1 and 40 of 2026, of which 56,759 were confirmed, including 58 deaths. For comparison, Brazil reported 253,753 suspected and 108,975 confirmed chikungunya cases in 2025, including 130 deaths. The same update names Brazil among countries reporting simultaneous circulation of all four dengue serotypes: DENV-1, DENV-2, DENV-3 and DENV-4. It gives no Brazilian dengue case total for 2026, so use the week 39 figure above. Co-circulation means repeat infection is possible over time, and second dengue infections carry higher risk of severe disease.
Malaria: confined to the Amazon basin
Malaria in Brazil is largely an Amazon problem. TravelHealthPro's Brazil page puts malaria at low risk in the Amazon basin, including the city of Manaus, and at very low risk in the rest of Brazil, with no risk at Iguaçu Falls. CDC is more precise about place. It records transmission in all areas of Acre, Amapá, Amazonas, Rondônia and Roraima, and lists the disease as present in Maranhão, Mato Grosso and Pará. It reports rare cases and sporadic foci in rural and forested parts of Espírito Santo, Goiás, Minas Gerais, Mato Grosso do Sul, Piauí, Rio de Janeiro, São Paulo and Tocantins. CDC states there is no malaria transmission in the cities of Brasília, Rio de Janeiro or São Paulo, or at Iguaçu Falls, and recommends prescription preventive medicine for travellers to certain areas. Discuss antimalarials with a travel health professional, because the two authorities define the risk area differently.
Yellow fever: vaccination and recent cases
Yellow fever vaccination is the main protection, and both authorities recommend it for travellers aged 9 months and older going to the listed states and designated areas. CDC also recommends it for travel to Iguaçu Falls. Neither authority recommends it for travel limited to unlisted areas, including Fortaleza and Recife. TravelHealthPro states that there are no certificate requirements under the International Health Regulations, and CDC records no entry requirement. Current risk is real but focused. PAHO's epidemiological alert on yellow fever in the Americas, dated 13 March 2026 with data to epidemiological week 7, reports 120 confirmed human cases and 48 deaths in Brazil in 2025, a case fatality rate of 40%. Cases were reported in Minas Gerais, Pará, São Paulo and Tocantins. PAHO states that no additional yellow fever cases had been confirmed in Brazil up to week 7 of 2026, after the last onset on 22 June 2025.
Which mosquitoes bite by day and which by night
Knowing when mosquitoes bite tells you when to cover up and when to use repellent. TravelHealthPro states that some mosquitoes bite during daylight hours, including Aedes species, while others are more active from dusk to dawn, including Anopheles species, which spread malaria. It adds that Aedes aegypti can bite at night in well-lit areas, and that Anopheles can be active during the day, at dawn and dusk, and throughout the night depending on species and place. WHO's chikungunya fact sheet states that the mosquitoes spreading that disease bite primarily during daylight hours, and that Aedes aegypti feeds both indoors and outdoors. In practice, Aedes risk follows you through the day, indoors and out, while Anopheles risk in the Amazon concentrates around night hours. Repellent containing DEET at 50% is recommended for all travellers over two months, with no further increase in protection beyond 50%.
When a bed net matters, and other barriers
A bed net matters most where malaria is present and the sleeping space is not sealed. TravelHealthPro advises that all travellers to malaria-endemic areas should sleep under a mosquito net unless the room is well screened or has working, switched-on air conditioning where mosquitoes cannot enter. Doors and windows to sleeping accommodation should be screened with fine mesh. WHO advises insecticide-treated nets for people who sleep during the daytime, giving young children, sick patients and older people as examples, because Aedes mosquitoes bite in daylight. Babies under two months should be protected with clothing and insecticide-treated nets draped over cots and prams, secured around the edges, since DEET is not recommended under that age. Apply repellent after sunscreen, and use a 30 to 50 SPF sunscreen. Oropouche, spread mainly by a biting midge, has no vaccine; PAHO's newest update, from 13 August 2025, reported 11,888 confirmed Brazilian cases in 2025.
Sources
- Report on the epidemiological situation of dengue in endemic countries of the Americas, as of epidemiological week 39, 2026: Pan American Health Organization / World Health Organization
- Epidemiological Update: Dengue and Chikungunya in the Americas Region, 20 October 2026: Pan American Health Organization / World Health Organization
- Brazil country information: TravelHealthPro (UK National Travel Health Network and Centre)
- Brazil, CDC Travelers' Health: US Centers for Disease Control and Prevention
- Insect and tick bite avoidance: TravelHealthPro (UK National Travel Health Network and Centre)
- Chikungunya (fact sheet): World Health Organization
- Epidemiological Alert: Yellow fever in the Americas Region, 13 March 2026: Pan American Health Organization / World Health Organization
- Epidemiological Update: Oropouche in the Region of the Americas, 13 August 2025: Pan American Health Organization / World Health Organization
This article is general information, not medical advice. Ask a doctor or pharmacist about your own health.