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Long-haul sick notes: what you can get and how not to get it

Malaria is caused by parasitic protozoans: single-cell bugs in the red blood cells, transmitted by the bite of infected mosquitoes, and is one of the major health threats to travellers. Travellers visiting malarial areas can take malaria chemoprophylaxis drugs but they do not give 100 per cent protection. (Many also have unpredictable and unpleasant side-effects, but malaria is worse than all of these.) The best thing to do is avoid being bitten. Wear insect repellent and sleep under nets where possible.

Typhoid is mostly transmitted through contaminated food or water: travellers to India and Pakistan in particular are advised to take precautions. A vaccine is available, but good hygiene habits - clean and boil or thoroughly cook everything you eat and drink - is important.

Hepatitis A is the commonest preventable disease caught by tourists. It is most commonly transmitted in water or uncooked food - boiling kills the bug. Recovery from the disease is long - up to 18 months. The death rate increases with age. Hepatitis A vaccine is recommended for people visiting Africa, much of Asia, South and Central America and the Middle East.

Encephalitis is carried by biting ticks which proliferate in heavily forested, humid regions. A vaccine is available which can give long-term protection, although insect repellents reduce the risk of being bitten.

Japanese B encephalitis is a strain of the disease carried by infected mosquitoes in parts of Asia. It is preventable with a vaccine.

Non-paralytic polio is rare among travellers - 0.7 cases for every 30,000 to 100,000 travellers - and is prevented by use of vaccine.

Cholera is becoming a big problem in parts of South America: it is an infectious disease caused by a bacteria and symptoms include abdominal pain, vomiting and severe diarrhoea. There is only a handful of cases each year among people in the UK, and current advice is to follow the traveller's hygiene code, paying special attention to procuring safe water supplies.

Dengue fever, a mosquito-borne infection, can be fatal, and has spread from Central and South America to parts of the US. There is no specific treatment or vaccine. Best to avoid being bitten; see Malaria.

Yellow fever is another mosquito-borne infection and is endemic in regions of Africa and South America. Symptoms include nausea, abdominal pain and jaundice. A vaccine is available which gives long-term protection.

Travellers' diarrhoea is one of the most common afflictions, affecting around 40 per cent of people. Good hygiene standards can help: use bottled water and, don't eat or drink anything you can't boil, roast or peel. In cases of severe diarrhoea it is important to rehydrate the body.

HIV and hepatitis B are two behavioural risks for travellers. Both are most commonly transmitted by sexual contact and by intravenous drug use. Safe sex is strongly recommended. A vaccine is available for Hepatitis B.