Human and insect diseases link found

They believe that there are similarities between the emergence of the infection and the appearance of bubonic plague.

In both cases, bacteria that caused disease in insects mutated into a new form that threatened humans.

About a dozen cases of infection by the new bug, Photorhabdus asymbiotica, have been seen in around a dozen people in the United States and Australia. The bug causes pustulant sores to appear on parts of the victim’s body.

Scientists believe it evolved recently from the bacterium Photorhabdus luminescens, which kills insects with the aid of nematode worms.

The family of bacteria is known as Photorhabdus - which means "glowing rods" - because they are bioluminescent.

Doctors think the sores caused by the new infection might also glow - but in the cases so far, sufferers have been cured before this could be properly investigated.

A spokesman for the University of Bath, where a team of researchers is studying the bacterium, said: "No-one’s actually been able to check this yet, because in the cases we know about the sores have been bandaged and then cleared up before anyone had a chance to look at them in the dark.

Scientists believe there could be many more examples of the unusual infection that have not been recognised.

But now as scientists are actively looking for P. asymbiotica infection, more cases are coming to light in Asia.

Professor Richard ffrench-Constant and Dr Nick Waterfield, at the University of Bath, and Professor Brendan Wren, of the London School of Hygiene and Tropical Medicine, are studying the bug as part of a wider research project investigating the emergence of diseases.

Their report on the role of insects and other invertebrates in the evolution of human disease appears in the latest edition of Nature Reviews: Microbiology.

Dr Waterfield said: "Most scientists are looking at diseases of farm animals as the biggest threat to humans.

"As well as passing microbes directly into our bloodstream when they bite us, insects can also act as a reservoir to ‘cook up’ future human diseases.

"Understanding the mechanism bacteria use to change their disease-causing ability is important if we are to treat emerging infectious diseases before they get out of control and become epidemics."