BBC News - Thursday, 10 January, 2002

BBC News Online examines why diseases that were once almost unheard of in the UK are now posing a growing threat.

More travel

Cheap air travel has allowed many people to travel to exotic holiday destinations where tropical diseases are a problem. A massive 56m foreign trips a year are made from the UK.

If travellers have not taken precautions before travelling, they may be vulnerable to infection - and to bringing that infection back into the UK.

Dr Vanya Gant, from the London School of Hygiene and Tropical Medicine, said: "I have come across patients who have nearly died who considered that going to Africa was the same as going to the south of France, only hotter.

"We need to educate the public."

An outbreak of tuberculosis at a school in Leicestershire last year is thought to have originated from a family that travelled to the Asian sub-continent for its holiday.

There is also a threat from immigrants arriving in the UK from countries where tropical diseases are found.

Changes to the environment

It is thought that some of the rare tropical diseases may have emerged from the forests of Africa where they have been harboured for thousands of years by species that would previously not have come into contact with humans.

However, these remote areas are increasingly being exploited by industry - thus increasing the risk that humans will come into contact with new types of disease.

Some experts believe HIV is a prime example of this.

The phenomenon of global warming is another factor that increases the threat of tropical disease in the UK.

A report published last year by the Expert Group on Climate Change predicted that by 2080, much of the south of the UK would be vulnerable to the milder form of malaria plasmodium vivax for up to four months of the year because of the change in weather conditions.

Mosquitoes will thrive in the higher temperatures, and predicted increases in winter rainfall would provide ideal breeding conditions. Areas with salt-marshes like south-east Kent would be the most vulnerable.

The impact of technology

New technologies can sometimes have an unforeseen impact on human health.

For instance, Legionnaires' disease thrives in air conditioning systems.

Human behaviour

Recent increases in the levels of sexually transmitted diseases including HIV have been directly attributed to changes in sexual behaviour.

Not enough people have heeded advice to use barrier contraception methods when having sex to prevent the transmission of disease.

Weakened immune systems

Advances in medical science have enabled many people with diseases such as cancer, or who have undergone transplant operations to live for longer.

However, the treatments that keep them alive often leave them with weakened immune systems which are ripe for attack by disease.

More virulent strains

Dr Nick Beeching, senior lecturer at Liverpool School of Tropical Medicine, said: "Compared to 10 years ago we have roughly the same number of cases of malaria, about 2,000 to 2,500 a year.

"But now the majority of them are the more lethal form of malaria."

Dr Beeching said sleeping sickness had almost been conquered in Africa during the last century, but there had now been a resurgence in many countries.

Since the early 1970s at least 30 previously unknown infectious diseases have been identified for which there is no fully effective treatment.

Growing resistance

Many bacterial organisms have a tremendous capacity for evolving into new forms which develop immunity to current treatments.

Dr Peter Chiodini, a consultant parasitologist at the Hospital for Tropical Diseases in London, said: "With the bacterial diseases, such as malaria, we are facing an increase in antibiotic resistance."

This problem has been exacerbated by the over-use of antibiotics, particularly in agriculture. The more a bacterium is exposed to an antibiotic, the faster it will develop resistance.

Dr Chiodini also warned that there were no effective treatments for some rare tropical diseases, including Dengue fever, Ebola or West Nile Virus.

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