Herds of African cattle may hold the secret to new ways of fighting parasitic diseases like malaria, which kills some 600,000 people a year, scientists said on Friday. 

The researchers from the University of Edinburgh found that cows are protected from a parasite that causes a deadly disease called East Coast Fever if they have previously been infected with a closely-related but milder species of the parasite.

This discovery, they said, suggests that "fighting fire with fire" is a strategy that might work against a range of parasitic diseases, including severe malarial infection in people.

"Our results suggest seeking a simple vaccine that could protect cows from East Coast fever by inoculating them with a related but far less harmful parasite," said Mark Woolhouse, who led the study with a team from several other universities and the International Livestock Research Institute.

"A similar process might be at work in malaria, where infection with the less harmful Plasmodium vivax parasite may protect people from the Plasmodium falciparum parasite."

Like the cattle disease East Coast fever, malaria is caused by a single-celled parasite, Plasmodium, although more than one species of Plasmodium can cause the disease.

The deadliest species is Plasmodium falciparum, the most common in Africa and the cause of the vast majority of the world's 600,000 malaria deaths a year. Plasmodium vivax is more common in Asia and more widespread but causes a less serious illness.

For their study, Woolhouse's team tracked the health of 500 Kenyan calves from birth to one year old, building up data on the cattle's survival, growth, health and infections with viruses, bacteria, worms and tick-borne parasites.

They found that deaths caused by East Coast Fever, the biggest killer of East African cattle, dropped 89 per cent among calves which were also infected with other species of parasite that do not cause disease.

Something similar may occur when people are infected with the more deadly parasite P. falciparum at the same time as the less aggressive P. vivax, making them more likely to survive the disease.

"A better understanding of how this milder parasite may protect against the more lethal form of the disease could generate new approaches to reducing severe illness and deaths from malaria," Woolhouse said.