Mosquito-borne viruses (dengue, chikungunya, Zika, yellow fever, malaria) are increasing across the Americas due to climate change, deforestation and urbanisation. Peaks occur during local rainy seasons.
- Dengue: As of November, over 4.1 million suspected and over 1.6 million confirmed cases as well as 2,089 deaths were reported, with the majority in Brazil, where authorities issued a state of emergency (SoE) in São Paulo state. The 2025 figures represent a 10 percent decrease compared to the average of the last five years. Guyana, Brazil, Guadeloupe, Saint Martin, Belize, Panama and Paraguay reported the highest incident rates. Colombian authorities declared a six-month health emergency in the Huila department on 28 January, amid an outbreak of type II dengue fever.
- Chikungunya: Cases in the Americas rose sharply, reaching 107,860 confirmed and 267,265 suspected cases as of November, with 119 deaths reported. Cuba, Brazil and Bolivia had the highest infection rates and transmission spread beyond traditional areas.
- Zika: Zika virus cases in the Americas remained lower than 2022 – a peak year –, with around 1,620 confirmed and 25,473 suspected cases reported as of November, mostly in Brazil, Bolivia and Argentina, where the incident rates were also highest.
- Malaria: Outbreaks continue in Venezuela, Brazil, Colombia, Bolivia, Mexico, Costa Rica, Dominican Republic, Panama and Trinidad and Tobago; early detection is key for treatment.
Transmission and Precautions:
- Vectors: Aedes mosquitoes transmit chikungunya, dengue, yellow fever and Zika; Anopheles mosquitoes transmit malaria.
- Activity: Mosquitoes are most active in early morning and late afternoon; some are nocturnal.
- Prevention: Use insect repellent, long clothing, mosquito nets and ensure vaccination or prophylactic medication when available.
Symptoms and Treatment:
- Chikungunya: Fever, joint pain, headache; usually non-fatal.
- Dengue: Fever, joint pain, headache; severe cases may cause haemorrhaging; no treatment.
- Zika: Fever, rash, joint/muscle pain; may cause birth defects; no treatment.
- Yellow Fever: Fever, chills, nausea; may cause jaundice or organ failure; vaccination may be required.
- Malaria: Fever, chills, anaemia; treatable if detected early; prophylaxis recommended.
What to Expect:
The impact of the increased transmission will depend on several factors, including country capacities for a coordinated public health response, high mosquito densities due to interrupted vector control activities during the COVID-19 pandemic and the susceptibility to infections, particularly in areas where these viruses are newly circulating.