The overwhelming majority of illness on a long trip is one of four things: a stomach upset, something a mosquito gave you, sunburn or heat exhaustion, and an injury from a scooter. The first three are largely preventable. The fourth is entirely preventable, and it is the one that most often ends a trip.
None of this is medical advice — see a travel clinic six to eight weeks before you go, which is the single highest-value hour of preparation available.
Stomach illness
Almost universal on a first long trip to South or Southeast Asia, Africa or Latin America, and usually three unpleasant days rather than anything worse.
What actually reduces the risk:
Water. Do not drink tap water where it is not safe, and that includes ice, salad that has been washed in it, and brushing your teeth in some places. A filter bottle or purification tablets are cheaper and better than buying plastic bottles daily.
Hot, freshly cooked, and busy. A stall with a queue of locals turns its food over fast and cooks it in front of you. A hotel buffet that has been under a lamp for two hours is a worse bet than a street cart, which is the opposite of most people’s instinct.
Peel it, boil it, or leave it is the old rule and it still holds for fruit and raw vegetables.
Wash your hands. The most boring advice on this page and the most effective. Alcohol gel where there is no water.
When it happens: rehydration salts, and more of them than you think. Fluids are the treatment; the illness itself usually resolves. Anti-motility drugs like loperamide stop the symptom and are useful for a bus journey, not for getting better.
See a doctor if: there is blood, a high fever, it lasts more than a few days, or you cannot keep fluids down. Those are different problems from ordinary traveller’s diarrhoea.
Mosquito-borne disease
Malaria is the serious one, and prophylaxis is not optional in high-risk areas — sub-Saharan Africa, parts of South Asia and the Amazon among them. Which drug depends on the region’s resistance patterns, which is a conversation for a travel clinic. Take the full course, including after you leave.
Dengue, chikungunya and Zika have no prophylaxis. The only protection is not being bitten.
Not being bitten, practically: repellent with DEET or picaridin on exposed skin, reapplied; long sleeves and trousers at dawn and dusk for malarial mosquitoes and during the day for dengue’s, which bite in daylight; a treated mosquito net where rooms are not screened; and air conditioning or a fan, which mosquitoes struggle against.
Vaccinations
Book a travel clinic appointment six to eight weeks ahead, because several courses need multiple doses.
Commonly recommended by region: hepatitis A and B, typhoid, tetanus and diphtheria boosters, rabies for rural or long-term travel, Japanese encephalitis for rural Asia, meningitis for the African meningitis belt, and cholera in specific circumstances.
Yellow fever is the one that is sometimes legally required rather than merely advised: several countries demand a certificate for entry if you have come from an endemic country, and it is checked at the border. The certificate is valid for life now, but it takes ten days to become effective.
Rabies deserves a specific note. It is essentially 100 per cent fatal once symptomatic, it is present in dogs and monkeys across much of Asia and Africa, and pre-exposure vaccination does not remove the need for treatment after a bite — it buys you time and simplifies what treatment you need, which matters enormously if you are days from a city.
Any bite or scratch from a mammal in an endemic area is a medical emergency, not something to see about later.
Sun, heat and altitude
Heat exhaustion creeps up: headache, nausea, cramps, exhaustion. The response is shade, fluids with salt, and stopping. Heat stroke — confusion, no sweating, very high temperature — is a medical emergency.
Sun at altitude and on water is far stronger than it feels. High factor, reapplied, plus a hat.
Altitude is covered on the Andes and Everest pages. The one rule that matters: symptoms that get worse rather than better mean descend, immediately, regardless of what it costs.
The scooter
More travellers are seriously hurt on rented motorbikes in Southeast Asia than by every disease on this page combined.
If you ride: wear a helmet that fastens, have a licence valid for the machine, check your insurance covers it, and do not ride at night or after drinking. Most policies exclude all of the above, which means an accident is both an injury and a bankruptcy.
The kit
Rehydration salts, painkillers, antihistamines, blister plasters, antiseptic, plasters, a thermometer if travelling with children, prescription medication in labelled original packaging with a doctor’s letter, and hand gel.
Pharmacies across most of the world are well stocked, cheap and staffed by people who can advise. You do not need to carry a chemist’s shop.