Infectious diseases,

Viral and bacterial dangers,

SOME POTENTIAL BIOHAZARDS

Tuberculosis

Nearly 2bn people, just under a third of the world's population, are infected with TB. Infection is estimated to occur at 20 times the rate of mortality but TB is still the leading cause of death from a single organism in the world today. It kills more adults each year than Aids and malaria combined.

The bacteria that causes the disease can survive for months if dry and is resistant to mild disinfectants. Historically, TB became an epidemic in the west during the industrial revolution when cramped living conditions in poorly sanitised cities aided its transmission. It was the leading cause of death in the industrialised nations until early last century.

TB's grip today is intensified by the emergence of strains that are increasingly drug resistant - and these can result in an incurable form of the disease that in most cases prove fatal. The World Health Organisation estimates that more than 50m people worldwide may be infected with such a strain.

The bacteria is spread when an infected person coughs or sneezes, or even talks, and the discharge is inhaled by a healthy person. TB begins with weight loss, lack of energy and coughing. As the disease progresses the cough gets worse and may start to bring up blood from a lesion in the lung, although any organ can be affected. When TB kills it is usually because damaged lung tissue prevents the sufferer from adequately breathing.

Since the 1980s, the spread of HIV has contributed to an increase in TB infections. It is a significant cause of death in developing countries.

Foot and mouth

Foot and mouth is probably more infectious than any other disease affecting animals - it spreads rapidly if uncontrolled. Sheep, pigs and cattle are susceptible and so are hedgehogs, elephants and rats. There are millions of ways in which the virus can be carried. A sandwich brought on an aeroplane from an infected country, for example, would be capable of carrying the disease.

The 1967 outbreak, which led to the slaughter of 400,000 animals, was traced back to an infected leg of lamb from Argentina. A farmer cooked the lamb and fed the bone to his dog, which left it near some pigs. However, it can also be spread by the wind.

Foot and mouth is an acute infectious viral disease causing fever, followed by the development of blisters chiefly in the mouth and on the feet. The UN warns that animals, animal products and humans crossing the world as either tourists or migrants could carry the virus.

Anthrax

A disease mainly affecting grass-eating hoofed animals, it can be contracted by humans who come into contact with infected beasts, eat infected products or breath in the tiny spores. As recent events in America have reminded us, it can also be spread by biological weapons.

In its most deadly form - inhalation - it is almost always fatal. Anthrax can be treated by antibiotics, but the use of antibiotics before infection can encourage the emergence of resistant bacteria.

Also known as splenic fever, malignant pustule, or woolsorters' disease, it is widespread among animals in Asia, Africa and South America. The anthrax organism - bacillus anthracis - can survive in contaminated soil or other material for years until conditions are right for the spores to germinate and become infectious.

Human symptoms include fever, coughing, delirium, chest pains, sweating, and breathing difficulties. They can develop at any time from two days to two months after exposure. However, the disease cannot be spread from person to person.