Peru

Cusco at 11,200 feet, Lake Titicaca at 12,500 feet. 50-75% of travelers to Cusco develop some AMS symptoms. Acetazolamide (Diamox) recommended. Acclimatize 24-48 hours before trekking. Coca tea helps mild symptoms.

Common especially outside Lima. Carry azithromycin. Avoid tap water, raw vegetables, and unpeeled fruit.

Dengue is endemic on the coast and in the Amazon, with a national alert following more than 39,000 cases in December 2025; incidence is highest in adolescents aged 12-17 and adults aged 18-29, and 2023 and 2024 were exceptional years exceeding 250,000 cases each. Standard dengue precautions apply: DEET during daylight, and no ibuprofen or aspirin for fever until dengue is excluded. OROPOUCHE IS THE LESS FAMILIAR RISK AND DIFFERS IN WAYS THAT MATTER. First, the vector: Oropouche is spread mainly by biting midges rather than mosquitoes. Midges are small enough to pass through standard mosquito netting, so a traveler relying on ordinary bed nets and daytime repellent is less protected than they assume — fine-mesh netting and screened or air-conditioned accommodation matter more here. Second, the course: symptoms begin 3 to 10 days after a bite and last 3 to 6 days, but roughly 60% of patients experience recurrent symptoms days to weeks after the initial illness appears to resolve. A returning traveler who feels better and then relapses has not necessarily acquired something new. Third, the diagnosis: Oropouche is clinically difficult to separate from dengue, and Peruvian data show OROV and dengue co-infection profiles that are essentially indistinguishable, so testing rather than pattern recognition is what settles it. Illness is usually mild — a Loreto series of 100 confirmed cases recorded no deaths, no severe cases and no neurological presentations, with eight hospitalisations — but severe neuroinvasive disease is documented, and pregnant travelers should discuss the itinerary with their physician, as pregnancy complications were seen in that series and mother-to-child transmission remains under investigation. There is no vaccine and no specific treatment.