Image copyright SINCLAIR STAMMERS/SCIENCE PHOTO LIBRARY Image caption Ascaris lumbricoides, an intestinal roundworm, is one of the most common helminthic human infections worldwide

A large-scale de-worming treatment programme is needed to rid some 1.5 billion people of these harmful and unpleasant parasites, say researchers.

The Stanford University team says the World Health Organization needs to step up its response - but the WHO says this could breed drug-resistant infections.

Currently, eradication is focused largely on school-aged children living in high-prevalence areas.

The Stanford team's research recommends mass treatment of whole communities.

Worms affect a quarter of the world's population.

They are transmitted by eggs passed in the faeces of infected people that contaminate food or water supplies.

Image copyright DAVID SCHARF/SCIENCE PHOTO LIBRARY Image caption Hookworms cling to the bowel using their teeth

One type of worm, hookworm, can hatch in soil and burrow into a person's skin, for example, if they walk barefoot on contaminated soil.

People with mild worm infections have few or no symptoms - but as the worms multiply in the bowel, they feed on the host, causing malnutrition, weakness, diarrhoea and abdominal pain.

A flatworm found in fresh water, such as rivers and lakes, causes a disease called schistosomiasis or Bilharzia which can cause progressive damage to the bladder, kidneys, liver and spleen.

All of these parasites can be treated with drugs that are cheap and widely available.

The Stanford researchers calculated the costs versus the benefits of using these medicines in different communities in the Ivory Coast - a region where parasitic-worm infections are common.

The end goal they looked at was averting transmission, along with reducing ill health, in pre-school children and adults, as well as children of school age.

And they used a measurement known as the disability-adjusted life-year, a standard WHO measure to gauge the impact of disease.

By their calculations, outlined in The Lancet Global Health journal, it would cost about £109 per person per year, which they say is highly cost effective.

Lead researcher Dr Jason Andrews said: "We found that when you do so, the results strongly support a much broader treatment scope than has been historically recommended."

But the WHO says it has no plans of changing its current strategy. Targeting more people risks the development of drug resistant infections, it says.

"If drug pressure is too intense, it may promote selection of resistant worms, as has occurred in veterinary parasitology; repetition of the same error in tackling human health should be avoided," a spokesman said.

In 2013, more than 368 million children were treated with anthelminthic medicines in endemic countries, corresponding to 42% of all children at risk.

The global target is to regularly treat at least 75% of all children in endemic areas.