There have also been cases in Israel, Africa and Asia and parts of Eastern Europe.

There was a UK case of a bird with the antibodies of the West Nile virus, but there have been no human cases.

These can range from fever, headache and body aches to skin rashes on the trunk of the body and swollen lymph glands.

But more serious cases, less than 1% of those who become infected, can result in severe illness such as West Nile encephalitis or meningitis and sometimes lead to death.

Out of about 1,000 people who became infected in Europe recently there were about 40 deaths.

The mosquitoes which carry this disease bite at dawn, dusk and early evening, so if you are travelling to an area where the disease is prevalent you should either stay indoors, or wear long sleeved shirts and long-trousers and wear insect repellent.

People travelling with young children should ensure that they use a specially prepared insect repellent, rather than the adult version.

By the middle of April, it had killed more than 150 people worldwide and infected more than 3,000 more.

Most of those who have died have been older, or had pre-existing health problems which increased their vulnerability - but some younger, healthy people have died.

Patients suspected of having Sars are given a combination of antibiotics and antiviral drugs, which have produced an improvement in some patients, although their precise effectiveness is uncertain.

There is no vaccine for the virus that causes Sars, although a diagnostic test has been developed.

There has been concern about transmission within passenger aircraft. The latest advice suggests that those at risk of infection would need to be seated within a couple of rows of the infected person, with no evidence of risk to people sitting elsewhere on the plane.

People in the Far East have attempted to protect themselves by wearing face masks - it is uncertain how much genuine protection these offer against the virus.

Travellers should check the websites of the World Health Organization and, in the UK, either the Health Protection Agency or Foreign and Commonwealth Office for the latest advice.

All travellers to areas heavily affected by Sars should be aware of this and take account of the problem in their travel plans. Some countries have been screening passengers arriving from Sars-hit areas for early signs of the illness.

Patients usually self-treat, but experts say cases can be cleared up much quicker if sufferers take antibiotics.

About 10% of all cases are serious and people with long-term symptoms should seek specialist advice.

All patients with traveller’s diarrhoea are advised to ensure they replace lost fluids with fluids and rehydration tablets.

Infections may be asymptomatic, or may cause diarrhoea, nausea, abdominal cramps, fever, vomiting and headaches. Most people will recover within several weeks, but individuals with weakened immune systems, such as HIV/AIDS or cancer patients, may be unable to remove the parasites from their systems and can suffer debilitating illness and even death.

There are about 17 million cases of typhoid each year globally and about 600,000 deaths.

There is a vaccine that can protect against typhoid, but it will not protect against paratyphoid.

There is a vaccination against the disease, but once symptoms of rabies have developed the condition is almost always fatal - and the few people who have survived have suffered serious long-term disabilities.

The last case of rabies in the UK was in November 2002, when a conservation worker was bitten by a rabid bat.

But there have been no cases in the UK of rabies being transmitted by a dog over the last 100 years.

Travelling in developing countries is the most risky, particularly the more remote areas, as clinics do not always have supplies of the vaccine. The vaccine can be successful after a person has been bitten, if it is taken early enough.

The disease is present in 90 countries and infects one in 10 of the world’s population at some point in their lives.

Three-quarters of all malaria cases are in sub-Saharan Africa where it is a main cause of death and a major threat to child health.

But travellers should also ensure that they have the appropriate anti-malarial drugs for the specific region to which they are travelling.

The tablets, which are taken in either daily or weekly doses, need to be started before travel and continued for up to a month after return from the malarial zone.

The death rates are high in areas of sub-Saharan Africa, where medical expertise and malarial drugs are limited.

And recent climate changes have been blamed for an increase in the infection.

The mark can feel warm to the touch, but might not itch or cause pain.

After the rash appears sufferers may also start to suffer joint pains, fever, fatigue, stiff neck and facial paralysis or tingling as the bacteria starts to spread around the body.

More serious symptoms can include severe headaches, painful arthritis, joint swelling and heart problems.

Some patients even suffer mental disorders such as short term memory loss and difficulty concentrating.

But if the disease is caught early enough it can be treated with antibiotics, although later stage Lyme does not respond as well.

Walkers should wear light coloured clothing and gardeners’ light gloves, so they can see the ticks.

The ticks spread their disease slowly, so the quicker they are spotted the less chance there is of someone becoming infected.

The best way to remove a tick is by tweezers, although you should be careful to pull the tick out directly without jerking or twisting it. Antiseptic should then be put on the wound.

There are three sorts of leishmaniasis, which vary in severity.

The most dangerous is “visceral leishmaniasis”, which is also known as black fever. This is nearly always fatal if it is left untreated.

It spreads into the spleen, bone marrow and liver and attacks and destroys the immune system.

Another type, “mucocutaneous leishmaniasis”, produces disfiguring lesions which destroy the mucous membranes of the nose, mouth and throat.

“Cutaneous leishmaniasis” tends to cause sores on the skin. Some people have had up to 100 and these can vary in size from 2cm to 3cm in diameter.

Leishmaniasis is prevalent in about 90 tropical and subtropical countries around the world.

It is generally contracted by inhaling mists from water sources like showers, whirlpool baths and cooling towers which have become infected with the bacteria.

The most common cause of the disease is contaminated air conditioning systems; it cannot be passed from one person to another.

These progress to high fever, the chills, nausea, vomiting and diarrhoea.

On the second or third day the patient usually gets a dry cough and sometimes chest pains and they may have difficulty breathing.

Some patients also suffer from confusion; disorientation; hallucination and a loss of memory. Some also get pneumonia.

Firms and buildings should also ensure that they carry out good engineering practices and regularly check the operation and maintenance of air and water handling systems.

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.

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.

Children getting the disease will seldom become ill and once infected will carry a life-long immunity against the disease.

The older a person is, the more serious the disease can be. About one per cent of people with Hepatitis A will suffer from liver failure and some of these people will die.