how diseases spread

infectious diseases

some resources



Among infectious diseases TB is the leading killer of adults in the world today.
It kills apporoximately 2 million people each year.
Someone in the world is newly infected by TB every second.
It is estimated that between 2002 and 2020 over 150 million people will be ill and 36 million will die if there is not more control.
The global epidemic is growing becasue of drug reistance, poor health care and the growth of HIV.

Tuberculosis is caused by a bacterium - Mycrobacterium tuberculosis. Overall one third of the world is infected although infected people don't necessarily get sick and it is only sick people who can infect others. If it's not properly treated each person with active TB will infect 10-15 people every year.

It is spread like a cold through the air and by relatively casual contact - when infectious people cough or sneeze they send the bacteria into the air where they can hover around before being breathed in by other people.

It leads to fever, tiredness, weight loss, coughing up blood, chest pain and if not treated properly death.

Unlike HIV, which is quite a new disease, TB has a very long history and at one point it was thought that science had beaten the disease but as those statistics show, it's on its way back. It seems that TB has always been with us - evidence of it was found in Egyptian mummies - throught time it's been bad, very bad or better but it's always been around. There were many attempts at cures but they were all pretty useless. In Roman times a recommended cure was bathing in human urine and drinking elephant blood. It didn't work. Depending on the time or country, people were either told to rest or exercise, to eat or starve, to get fresh air on mountain tops or hide away underground. It killed millions of people - in the 17th and 18th centuries it killed 1 in 5 adults. Some very famous people suffered from it including the composer Chopin, the novelist Emily Bronte, Henry VIII and George Orwell. In 1820 the poet John Keats coughed up a spot of bright red blood and told a friend -
"I cannot be deceived. That drop of blood is my death warrant. I must die"
A year later, aged 25, he died. TB is also called consumption and it actually became quite a romantic disease to have. It was written about in novels and plays where love struck heroes and heroines glamorously and movingly wasted away just as they had found happiness. It became so common that everyone would have known someone with it.

But the cause of it remained unknown. Generally it wasn't thought of as contagious, people thought it was hereditary, passed from one generation to another. There was an English doctor called Benjamin Marten who in 1720 wrote that he believed it could be spread by "wonderfully minute living creatures" which could be spread by contact between people. But it wasn't until 1882, 150 years later that an unkown German country doctor called Robert Koch discovered the organism that caused TB. He was able to show that it was spread from person to person which meant that it could possibly be controlled.

This led to a large scale public health movement in a number of countries to control the spread. Sick people were separated from well people. Sanatoria were developed which were special hospitals for TB sufferers often in mountain areas or by lakes where the air was fresh. They spent 3 months resting and had to eat enormous amounts of food.

In 1908 French scientists Calmette and Guerin developed a vaccine for TB. They isolated a bacteria which causes TB in cattle from a dead cow. They grew it so that each new batch of it became weaker - too weak to cause the disease but strong enough to make the human immune system protect a person from it. The vaccine was called Bacille Calmette-Guerin (BCG) and was first given in 1921. In Britain the vaccine was first used in 1953 - in the year before the vaccine was used there were 46,546 cases per year. This decreased to 5000 in the 1980s. Since the invention of the vacccine millions of people have been inoculate with BCG but scientists aren't completely sure how effective it is.

During the 1940s new antibiotics were developed to fight TB. As drugs became more effective the sanitoria closed. People believed that like other infectious diseases TB would be conquered. In fact the U.N. thought it would be completely eliminated by 2025. But this has proved not to be the case. A variety of medical and social factors have led to its resurgence.

The spread of HIV is helping it to grow again. People suffering from HIV have severely weakened immune sytems which make them more vulnerable to diseases such as TB.

In less developed countries the drugs necessary to control the diseases aren't always readily available.

There are now drug resistant strains of TB - this is because treatment oftn involves a number of different tablets which have to be taken for a long period of time, often six months. So people stop taking it and it's difficult to monitor to ensure that patients have finished the treatment. So if not properly treated they may remain infectious, the bacteria in their lungs may develop resistance and then they can pass this new drug resistant strain onto other people. By 1995 one in seven cases of TB was resistant to all known antibiotics.

As people travel more either on holiday or as migrants the disease is also spreading. It finds it particularly easy to spread in large, overcrowded cities or anywhere in fact where a lot of people are in close contact.

Today the disease is especially bad in the developing world where it accounts for more than a quarter of all preventable adult deaths. It 's incidence is growing in Asian countries with large cities and there have been new outbreaks in Eastern Europe. People in the UK have been warned about the possibility of catching it in nightclubs.
The World Health Organisation are trying to control its spread by introducing systems to monitor treatments to ensure that patients finish the course and by testing for infection before and after the treatment. It remains to be seen wether through global co-peration and new treatments TB will again be brought under control.