Vaccinations, medications & health warnings for hikers.

Regulatory

• The Yellow Fever certificate — a legal entry requirement

  Yellow Fever is not just a recommendation — it is often a legal entry requirement. Travelers moving between an at-risk country (the Amazon basin in Brazil, Peru, Colombia, Ecuador; Sub-Saharan Africa) and certain third countries will be denied boarding without an official International Certificate of Vaccination (Yellow Card).

Viral outbreak

• Hantavirus (Patagonia, US Southwest & Rockies)

  Hantavirus is a severe, often fatal respiratory disease spread by breathing in aerosolized rodent urine or droppings. There is currently an elevated outbreak of the Andes strain in Argentina — the only strain known to occasionally spread person to person. Never sweep out enclosed, dusty trail cabins, avoid pitching tents in seeding bamboo, and strictly manage all food waste.

• Dengue surges across the Americas

  Central and South America have seen massive, recurring surges in Dengue Fever. There is no widely available preventative medication or vaccine for short-term tourists, so physical prevention is the only defense. Hikers in the lowlands should wear permethrin-treated clothing and use heavy DEET or Picaridin.

• Tick-Borne Encephalitis (TBE) is not Lyme disease

  North American hikers often confuse TBE with Lyme disease. TBE is a viral infection of the brain and spine spread by ticks in Europe (especially the Alps, Eastern Europe, the Baltics, and Scandinavia) and Central Asia. There is no cure once infected, but there is a highly effective vaccine — 3 doses over several weeks, start at least a month before departure. Lyme has no vaccine — nightly tick checks are your only defense.

• Japanese Encephalitis (JE) — rural Asia

  Like TBE, JE is a viral brain infection with no cure, spread by mosquitoes in rural Asia (especially near rice paddies and pig farms). It is highly seasonal, peaking in the rainy season. The two-dose vaccine series is highly recommended for multi-day trekkers in Southeast Asia, rural Japan, and Taiwan.

Zoonotic

• Monkey rabies (Southeast Asia & India)

  Most hikers associate rabies with stray dogs, but in Southeast Asia and India, macaques are heavily habituated to humans and will bite to steal food. If a hiker is bitten or scratched by a monkey, it is a Category 3 rabies emergency: abort the hike immediately and seek post-exposure prophylaxis within 24 hours, even if pre-exposure vaccine was given.

• Shepherd & feral dogs (Eastern Europe, Balkans, Central Asia)

  Feral and aggressive shepherd dogs pose a severe bite and rabies risk on remote trails in Romania, Bulgaria, Greece, and Central Asia. Carry trekking poles to keep dogs at bay and strongly consider the pre-exposure rabies vaccine series before your trip.

Environmental

• Altitude sickness — AMS, HACE, HAPE

  Altitude sickness is the primary cause of emergency rescue in the Himalayas, Andes, and high Central Asia. Never ascend faster than 300–500 m per day above 3,000 m; take a rest day every 1,000 m of elevation gain; descend immediately at the first sign of confusion, severe headache, or breathlessness at rest. Diamox (Acetazolamide) helps acclimatization but is not a substitute for a proper ascent profile.

• The Khumbu cough (Himalayas)

  The combination of extremely dry, cold air and fine trail dust in Nepal and Northern India causes a severe, hacking cough that can tear chest muscles. Bring a Buff or balaclava and wear it over your mouth and nose to pre-warm and humidify the air you breathe.

• Antibiotic resistance in Nepal

  The bacteria causing traveler's diarrhea in Nepal have developed extremely high resistance to standard fluoroquinolones (such as Ciprofloxacin). Ask your travel doctor specifically for Azithromycin as your emergency backup antibiotic for severe gastrointestinal infections.

• Leptospirosis in tropical freshwater

  Common in jungle mud and freshwater streams in places like Fiji, Vanuatu, and Hawaii. Never hike in sandals or cross streams if you have open cuts or blisters on your feet or legs.