Hepatitis B is a virus that can cause a potentially dangerous infection of the liver.
The infection is spread through blood-to-blood infection and through unprotected sex.
It is the ninth most common cause of death worldwide, killing about two million people a year.
In Europe alone about one million people become infected each year.
The incubation period before the symptoms start to develop can be anything between six weeks and six months.
In about a third of cases people with the disease will show no symptoms; in the second third the illness will cause mild flu-like symptoms with headache, fever loss of appetite, nausea and vomiting.
But in the rest of cases the illness can be very severe with patients developing abdominal pain, diarrhoea and jaundice.
In the most severe cases patients will develop rapid liver failure, which may need a life-saving liver transplant.
The disease is most common in the Far East, the Middle East, Africa and Southern Europe.
But travellers can also protect themselves by avoiding unprotected sex, by not sharing contaminated needles and ensuring that any tattoos, body piercing or acupuncture are only carried out in reputable salons.
There is an effective vaccine, available from GPs and travel clinics, which can protect travellers from Hepatitis B infection.
Vaccination is usually advised if a member of your family or household becomes infected with the virus. Hepatitis B is considered an occupational hazard for healthcare workers, the emergency services and the police.