"Thy broken faith hath made the prey for worms," evil Richard III is told by an accuser in Shakespeare's drama.

The outburst turns out to be true in more ways than the playwright could ever have imagined.

Scientists have discovered that the hunchback king was infected with intestinal parasites, probably as a result of yucky mediaeval hygiene.

The remains of Richard III, who ruled from 1483-1485, were founded beneath a car park last year in the central English city of Leicester.

Since then, forensic scientists have been poring over the extraordinary find, seeking further details of the life and times of this controversial monarch.

Sifting through the sediment, University of Cambridge researchers say they have found "multiple" microscopic eggs of a parasite in the lower region of the spine, where the royal innards would have been in life.

"These results show that Richard was infected with roundworm in his intestines," they reported on Wednesday in The Lancet.

"Roundworm is spread by the faecal contamination of food by dirty hands, or use of faeces as a crop fertiliser."

The roundworm, Ascaris lumbricoides, is a particularly unpleasant parasite that is common in parts of Africa and Latin America today.

Eggs swallowed by humans hatch in the intestine, and burrow through the gut wall and migrate to the lungs through the blood system.

They are then coughed up and swallowed again, entering the stomach and intestine for a second time, where they mature into adult worms some as long as 35 centimetres (14 inches), "swimming" against the flow of liquids and particles in the gut.

An adult female can produce around 200,000 eggs a day, which are then passed on in faeces, according to the US Centers for Disease Control and Prevention (CDC) website.

In large infections, the worms can cause peritonitis, enlargement of the liver or spleen or intestinal blockage.

A lively panoply of intestinal parasites roamed England in the 15th century.

They included whipworm, liver fluke, beef tapeworm, pork tapeworm and fish tapeworm, which are transmitted through uncooked, or poorly cooked, infected meat.

None of these was found in Richard's grave, though.

"We would expect nobles of this period to have eaten meats such as beef, pork and fish regularly," says the probe, led by Piers Mitchell, a biological anthropologist

"This finding might suggest that his food was cooked thoroughly, which would have prevented the transmission of these parasites."

Vilified in Shakespeare's play -- unfairly say some -- as a murderous hunchback, Richard was killed at the Battle of Bosworth in 1485.

He was buried without recorded ceremony in nearby Leicester.

His death ended the "War of the Roses," the civil war between the families of Lancaster and York named after their respective heraldic symbols of the red and the white rose.