Tropical diseases: symptoms and prevention

Recognising the early symptoms

Three days after returning from a trip to a faraway country, you develop a fever. You put it down to jet lag or the overnight flight. The next day, it’s still there. Then the question arises, a little too late: what if it came from your travel destination?

That’s the right question. Most so-called tropical diseases do not manifest during the trip, but afterwards. Some take a week, others a month or more. This delay makes it difficult to link them to the trip, which delays diagnosis.

This is by no means a trivial matter for a Belgian traveller. In 2016, Sciensano’s report listed between 250 and 300 cases of malaria imported into Belgium each year. The Institute of Tropical Medicine in Antwerp, the national reference laboratory for malaria, recorded 507 cases in 2023 and has observed a doubling of cases over the last decade.

This guide covers the two key stages when the issue arises: before departure and during your stay, to protect yourself, and on your return, to know what to look out for.

Which tropical diseases and in which regions?

The term ‘tropical disease’ encompasses a wide variety of illnesses, which have only one thing in common: the area in which they occur – the intertropical belt (between the Tropic of Cancer and the Tropic of Capricorn), in Africa, South and South-East Asia, Central and South America, as well as in several Pacific archipelagos.

They are classified by mode of transmission, as this determines the necessary protective measures.

To find out which diseases are prevalent at your destination, there are two authoritative sources for travellers departing from Belgium: the Institute of Tropical Medicine in Antwerp and the wanda.be website, which provides country-by-country advice. The Federal Public Service (FPS) Foreign Affairs, meanwhile, provides information on entry requirements and areas where travel is not recommended.

Mosquito-borne diseases

These are the most common among travellers, and the easiest to confuse.

Malaria is transmitted by a mosquito that bites between dusk and dawn. It is the most serious of all traveller’s diseases, and its progression can be very rapid. It is mainly found in sub-Saharan Africa, as well as in certain regions of Asia and South America. Malaria is prevented by medication, not by a vaccine.

Dengue is transmitted by a diurnal mosquito, which is most active at the start and end of the day. It is found in most tropical areas and experiences epidemic outbreaks, including in urban areas.

Chikungunya is transmitted by the same mosquito as dengue and is very similar to it, although it often causes more severe and longer-lasting joint pain.

The Zika virus circulates in the same regions, although it is more common in Latin America and the Caribbean. The main risk relates to pre : an infection contracted during this period can affect foetal development. Pregnant women, as well as those planning to become pregnant, should discuss this with their doctor before booking a trip to these destinations.

Water- and food-borne diseases

These are contracted by drinking, eating and sometimes simply by brushing your teeth.

Typhoid fever is transmitted via contaminated water or food. It presents as a gradually rising fever, accompanied by digestive problems and marked fatigue.

Hepatitis A is transmitted in the same way. It has a long incubation period: the illness often develops several weeks after returning home.

Traveller’s diarrhoea, or ‘turista’, is by far the most common. Although mild in the vast majority of cases, it becomes a cause for concern if it persists or is accompanied by a fever or blood in the stools.

Diseases transmitted by contact

Rabies is transmitted through a bite, scratch or an infected animal licking a wound. Stray dogs, monkeys, bats: after any contact, wash the wound thoroughly and seek medical attention immediately, regardless of your vaccination status.

Schistosomiasis is contracted by swimming in fresh water in certain regions, mainly in Africa. The parasite penetrates the skin. Hence the unequivocal advice: do not swim in fresh water in the affected areas, even in lakes and rivers reputed to be clean.

Transmission of tropical diseases

The vector (the disease carrier) indicates what you need to watch out for.

For malaria, dengue, chikungunya and Zika, the infectious agent is transmitted via a mosquito bite. The mosquito itself is not sick: it merely carries the pathogen. It becomes infected by biting a person who is a carrier, then transmits the infectious agent during a subsequent bite. This is why the risk increases where human populations are dense and mosquitoes are numerous.

There are, however, differences: the malaria mosquito bites at night, whilst the dengue mosquito bites during the day. Protecting oneself at night alone is therefore not enough.

The Zika virus is mainly transmitted by a mosquito but can also be transmitted sexually or from mother to foetus.

For typhoid, hepatitis A and traveller’s diarrhoea, transmission is via the digestive tract. Water and raw or undercooked food are the main vectors.

For rabies and schistosomiasis, contact is sufficient: a bite for the former, swimming in fresh water for the latter.

Diseases transmitted by mosquitoes do not spread from one person to another: you cannot ‘bring back’ malaria to those around you, nor can you catch it from a fellow traveller who is ill.

Digestive diseases, on the other hand, are indeed transmitted between people: typhoid and hepatitis A are spread via the faecal-oral route, and good hand hygiene protects both those around you and yourself.

What symptoms should raise alarm?

Common signs, and why they can be misleading

The difficulty lies in this: most of these illnesses start off like a ‘simple’ flu.

Fever, headaches, aching muscles, extreme tiredness, and sometimes nausea. Nothing that immediately distinguishes malaria from dengue fever, or from a simple virus caught on the plane.

This is precisely why you mustn’t try to diagnose yourself. Any fever occurring during or after a stay in a tropical region warrants medical advice, and the crucial information to give the doctor is this: where you’ve been, and when.

Certain symptoms require urgent medical attention: a high fever, confusion or unusual drowsiness, repeated vomiting, bleeding, a widespread rash, difficulty breathing or bloody diarrhoea.

Incubation periods, by disease

The incubation periods for tropical diseases vary from one disease to another. For accurate information, please refer to the information provided by the Institute of Tropical Medicine in Antwerp.

These timeframes are intended to help you remain vigilant, not to make a diagnosis. Only a doctor can make a definitive diagnosis!

Symptoms on return, sometimes several months later

This is the point most often overlooked, and the one with the most serious consequences.

Many travellers consider the risk to be over once they have unpacked their suitcases. However, hepatitis A commonly develops a month after exposure, and certain forms of malaria can manifest much later still.

Good to know: for the three months following a stay in a tropical region, always mention this trip to any doctor you see, even for a reason that seems unrelated. This information can guide the diagnosis and save time that may prove crucial.

How can you protect yourself before and during your trip?

Protection against bites: the most effective measure

Protection against bites covers the widest range of diseases at once, and does not require a prescription.

• A skin repellent suitable for the area you are visiting, applied to exposed skin and reapplied as per the manufacturer’s instructions.
• Wear covering clothing, with long sleeves and trousers, particularly at dusk and dawn. Be careful with thin, lightweight clothing too: it does not protect against mosquito bites! Certain colours, certain smells and the CO₂ we breathe out can also attract mosquitoes.
• A treated mosquito net should be used whenever the room is neither air-conditioned nor properly sealed.
• Be vigilant during the day in dengue-affected areas, as the mosquito bites during daylight hours.

Preventive treatment against malaria

In affected areas, preventive medication against malaria is prescribed before departure. The choice depends on the region, the length of your stay, your medical history and any current treatments: there is no one-size-fits-all approach.

In Belgium, a prescription is issued by your GP or following a consultation at a travel medicine clinic. Specialised centres, including the Institute of Tropical Medicine in Antwerp, provide up-to-date recommendations for each specific area.

Three rules determine its effectiveness: start it before arriving in the area, do not stop taking it during your stay, and continue taking it after your return for the prescribed duration. It is this final phase that is most often neglected, even though it continues to provide protection.

No preventive treatment offers complete protection. You must remain vigilant for signs of fever, even when the treatment has been followed to the letter.

Water, food and hygiene

The following advice can help to avoid many risks:

• Drink bottled water with a sealed cap, or treated water, including when brushing your teeth.
• Do not use ice cubes if you do not know where they come from.
• Eat food that has been cooked and served hot, rather than raw or lukewarm.
• Fruit that you peel yourself.
• Wash your hands frequently, or use an alcohol-based hand sanitiser when water is not available.
• Do not swim in freshwater in areas where schistosomiasis is prevalent.

What about vaccinations?

Vaccines are available for several tropical diseases, including hepatitis A, typhoid fever, yellow fever and rabies. Whether they are appropriate depends on your destination, the length of your stay and your personal circumstances. You’ll need to start the vaccination programme several weeks in advance.

This topic is covered in detail in our dedicated guide: Vaccines and travel: which ones to have, what side effects to expect.

Malaria, however, cannot be prevented by vaccination: it is prevented through medication.

What should you do if symptoms appear when travelling?

Seeking medical advice whilst abroad: who to contact

In endemic areas, have any fever checked immediately. With malaria, a delay of just a few days can alter the prognosis.

However, finding a reliable doctor in an unfamiliar country can be difficult: you may not know which healthcare facility to visit, what standard of care to expect, and sometimes you may not speak the language. Your assistance platform or the Belgian embassy in the country can direct you to a suitable doctor or healthcare facility.

Always state the regions you have travelled through, the dates of your stay and any preventive treatment you may be taking. This information is useful for any diagnosis.

The role of medical assistance and medical repatriation

Medical assistance plays a vital role here: it takes charge of the search, puts you in touch with a suitable healthcare provider and monitors your case.

Thanks to your Redion assistance policy, our teams will identify the appropriate healthcare facility, cover medical costs in accordance with the terms of the policy, and decide, in consultation with doctors, whether medical repatriation is necessary.

On your return, when should you seek medical advice?

Don’t wait – see a doctor as soon as any symptoms appear!

Seek medical advice promptly if you have a fever, diarrhoea lasting more than forty-eight hours, unusual and persistent tiredness, yellowing of the skin or eyes, or a rash.

And make a habit of doing this for the following three months: mention your trip to any doctor you see, whatever the reason.

If diagnosis is delayed or if symptoms recur, a specialist consultation is required. Belgium has several travel clinics, and the Institute of Tropical Medicine in Antwerp is a leading centre for these conditions.

Are you planning a trip to a tropical destination? Check your cover before you set off.

Frequently asked questions about tropical diseases