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Tropical Diseases

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Tropical Diseases

Insect bites and dangerous snails

The combination of heat, humidity and water in much of the tropics creates a perfect environment for the transmission and survival of tropical diseases.

It also creates perfect living conditions for carriers of the diseases. We all get insect bites, no matter how well we try and protect ourselves, so what diseases should we be aware of and what symptoms should we look for? How on earth can snails be dangerous?


Malaria is a very common tropical illness, causing an estimated half a million deaths per year worldwide. The good news is that malaria has effective treatment options as long as it is suspected and treated early. The majority of bites we get will not transmit malaria, however we should always be suspicious of this disease if we have been to a malarial area and develop any new symptoms. These symptoms usually present within 10-15 days of being bitten, however can take up to 6 months to appear. The commonest symptoms of malaria are fever, headache, fatigue and vomiting, but in more severe cases can cause jaundice (yellowness of the skin and eyes), convulsions, coma and eventually lead to death.

The key thing with malaria is to suspect it. Research where you are travelling to and whether this is a malarial area. If it is, plan all your precautions to avoid being bitten in the first place. Stock up with good insect repellent and a good mosquito net. A trick I always use is to take a can of insecticide which I use to spray my room or tent before leaving it for the evening. This ensures there are no stowaways in our bug free zone. Have a conversation with your travel health advisor to decide if drug prophylaxis is appropriate and when you need to start and stop taking it. Prophylaxis does not guarantee malaria protection, therefore if you develop any of the above symptoms and have travelled to a malarial area, seek medical advice.


Dengue, or ‘breakbone fever’ is transmitted by the bite of the Aedes mosquito, which unlike the malaria Anophiles mosquito, flies in the daytime. There are 5 different types of Dengue fever, and when you have had one, you develop lifelong immunity to that strain. However this does not protect you from other strains. If you have had a simple dengue infection to one strain, contracting another can put you at higher risk of more severe disease and dengue haemorrhagic fever.

The incubation period for Dengue fever is 3-14 days, so if you return form a tropical area and develop a fever after more than 14 days, it is unlikely to be Dengue. The vast majority of dengue cases are self-limiting and require no medical support. However the symptoms are similar to malaria and other tropical diseases, so it is always wise to get checked out if you are in or have travelled to a tropical area and develop a fever.

Typical symptoms of Dengue are high fever, headache, significant joint and muscle pain and a widespread rash. As the fever resolves, the illness can progress to the “critical phase” when a haemorrhagic fever can develop, though this only happens in less than 5% of cases. If the disease progresses to this phase, supportive treatment will be needed in a hospital.

Once again, the key messages from this are bite avoidance and a high suspicion of tropical disease if you are travelling in or travelled from a tropical area. Don’t forget, that symptoms can appear after you get home, so it is vital to tell your health care provider your travel history if you are unwell. Healthcare providers in temperate countries without endemic tropical diseases may not consider tropical diagnoses, so help them out if they don’t ask.


This is a disease caused by parasites that are spread by the bites of infected female sand flies. Interestingly, conventional mosquito nets do not give full protection from these flies as the mesh is too course- full protection needs a mesh size of 0.6mm, which will give protection, but make things a lot hotter and airless inside. Leishmaniasis can affect the mucous surfaces such as mouth and nose, skin and in the worse cases, the bowel, liver and spleen. The usual presentation is with skin or mucous surface ulcers and it is diagnosed with blood tests. There are a variety of effective treatments if this is caught early. Bowel leishmaniasis can be a lot more serious and sometimes cause death- it tends to present later than skin and mucosal cases.

Once again, the key is bite prevention both day and night.

Schistosomiasis (Bilharzia)

Whilst not really a bite, this disease is common and easy to acquire from water, so worth knowing about. It is spread by parasitic worms that inhabit fresh water snails. Schisto can cause abdominal pain, blood in the stool, blood in the urine, and if infection continues, liver damage and kidney failure. After being exposed, symptoms can take about 4-6 weeks to develop and are initially non-specific with a feeling of feeling “a bit unwell”. This can be followed by an itchy rash at the site where the infection started. The infection can spread to the bowel, liver, spleen, brain and spinal cord and cause more serious illness. The vast majority of infected people do not experience any symptoms.

When we are travelling, it’s incredibly tempting to jump in that beautiful lake or river for a cooling swim- do your research and check to see if schistosomiasis is present in the area you are travelling to. Schisto is usually contracted when washing or enjoying recreational activities in fresh water. It is most prevalent in Africa, Asia and South America. It is best to avoid these activities in areas where Schisto is known to be present.

Diagnosis is by testing the urine or stool. Treatment is simple and effective, but avoidance is best.

African Sleeping Sickness (Trypanosomiasis)

As the title suggests, this disease is endemic in sub Saharan Africa and is spread by infected Tsetse flies. As you may have noticed, there is a developing theme here in terms of the symptoms of tropical diseases- they are common symptoms with a lot of overlap, including overlap with simple illnesses such as influenza and other infections. This is what makes it challenging to diagnose them unless we take a full travel history in any returning traveller. The presenting symptoms for Sleeping Sickness tend to be fever, headache, itching and joint pain between one and three weeks from infection! Sounds like a lot of the other tropical diseases doesn’t it? There can also be a classic red sore that develops at the initial bite site. If undiagnosed, Leishmaniasis can progress to a second stage of confusion, poor coordination and difficulty sleeping as well as other serious symptoms that can cause permanent damage and even death.

Leishmaniasis is diagnosed with blood/ body fluid tests and sometimes a lumbar puncture. The treatments use some powerful drugs, so the take home message as usual is PREVENTION, PREVENTION, PREVENTION.

As you can see, there is a myriad of tropical diseases and this is only a small selection. They can be challenging to suspect, diagnose and treat. If you develop any persistent symptoms, especially fever, headache or rash, that do not settle quickly, seek medical advice. Remember, the key approach is to prevent bites in the first place. It is worth putting a lot of time and effort into this to ensure safe and worry-free travel.

Useful resources:

Author: Dr Alexander Rowe

Medical Director, World Extreme Medicine

Clinical Lead and Honorary Clinical Lecturer, Postgraduate Masters Programme in Extreme Medicine, University of Exeter

World Extreme Medicine Conference Speaker

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