Patagonia's biters carry no disease. The summer pest is a horsefly.

A few, and none of them carries a disease of concern. Argentina's health ministry reported no locally acquired dengue or chikungunya in its southern provinces in 2025/26, and the CDC recommends neither malaria medicine nor yellow fever vaccine for Patagonia on either side of the border. The bug that bothers summer hikers is the tábano, a large horsefly that gathers near lakes from late December to mid-January.

Tábanos and the wind

Tábanos have a reputation on both sides of the border, mostly in humid areas near lakes on warm, still days. Forum regulars say repellent doesn't stop them, though they're slow and easy to swat once they settle. Experiences vary widely, from visitors who never see one over several summers to others who meet them thick on a single calm stretch of trail. Wind keeps them down, so breezy days are the easy ones.

Mosquitoes are a minor part of the picture. Posters report some around lakeshores and in humid forest near Bariloche and Torres del Paine. Farther south the list gets short. South of latitude 45°S, which takes in El Calafate, El Chaltén, Ushuaia and Torres del Paine, researchers have collected only one mosquito species, the floodwater mosquito Aedes albifasciatus, from temporary pools.

For lake hikes from late December to mid-January, wear light-colored long sleeves and trousers, and save lakeshore picnics for breezy days where you can. A picaridin spray handles the occasional mosquito.

Torres del Paine and the Chilean side

Across the border the pattern is the same. Tábanos gather near the lakes of Torres del Paine and in humid spots from about December into January, fewer on windy days, and the park is far calmer outside that window. Chile's Lake District gets them too, worst on still, hot days at the water's edge. The CDC's Chile page lists no mosquito-borne disease and no yellow fever recommendation. Our Chile briefing covers the rest of the country, and the Argentina briefing covers Buenos Aires and Iguazú.

Hantavirus in cabins and on cruises

One health item here has nothing to do with bites. Hantavirus spreads from wild rodents through their urine and droppings, and the Andes strain found in Patagonia can also pass from person to person. Argentina's health ministry reported Río Negro's highest incidence since 2018 in the 2025/26 season, including an outbreak in Bariloche with suspected person-to-person spread. In April 2026 an Andes virus outbreak hit people who had traveled on the cruise ship MV Hondius, which sailed from Ushuaia, with transmission on board. Most Argentine cases since 2018 were reported between October and May, which overlaps the high season.

In rural cabins, refugios and campsites, follow the CDC's advice to avoid rodents and the places they live, and keep away from anyone sick with a suspected case. See a doctor for fever with muscle aches or breathing trouble within six weeks of a rural stay or a cruise from Ushuaia, and mention the exposure.

Where you're going

Scores are for a December–April trip.

Adding Iguazú Falls? The CDC recommends yellow fever vaccine for Misiones province, and our Iguazú Falls briefing covers it.

What travelers report

Paraphrased from Fodor's and TripAdvisor threads and linked so you can read them in full. None gives a year, and visitors disagree on how often they met tábanos.

• Patagonia (Argentina and Chile) · late December to mid-January

  A poster said tábanos (horseflies) are found on both sides of the border from late December to mid-January. Fodor's ↗

• Bariloche and El Chaltén · November to February

  Replies conflicted: one poster who visited Bariloche and southern Patagonia about five times between November and February never saw a horsefly, while another described El Chaltén in mid-December as overrun with horse flies and fruit flies. TripAdvisor ↗

• Mountains outside Bariloche · summer

  In an older thread about mosquitoes and other insects, a poster called the mountains outside Bariloche the worst spot for horseflies, which ignore repellent but are easy to swat once they settle. TripAdvisor ↗

• Chilean Lake District · January

  Under the title 'Beware the flies in the Lake Country in January', a visitor described large, swarming flies that made being outdoors nearly impossible. TripAdvisor ↗

• Torres del Paine · January

  In a thread about mosquitoes in Torres del Paine in January, a poster said horseflies are possible in the first half of January, mainly in humid areas near the lakes, but rated the chance as low. TripAdvisor ↗

One rule outlasts the trip. Any fever during or after the trip means a doctor visit, and you tell the doctor where you stayed, including any rural cabin, refugio or cruise.

Traveler questions