Researchers developed transgenic mice which could secrete an experimental malaria vaccine into their milk. When a purified form of this vaccine was injected into monkeys, it protected four out of five animals from a normally lethal dose of malaria.

The researchers are trying to scale up their process from mice to larger animals such as goats and other livestock, in the hope they could become inexpensive, high-yield producers of malaria vaccine.

Malaria infects 300-500 million people every year and kills one million, according to World Health Organization (WHO) estimates.

Ninety per cent of cases are in sub-Saharan Africa where many nations are also struggling to cope with HIV.

'Exciting possibility'

The results of this development are published online in the Proceedings of the National Academy of Sciences.

"A vaccine must not only be effective, it must be cheap to manufacture if it is to be used in those countries hit hardest by malaria," said lead author Anthony Stowers, PhD, a malaria researcher at the National Institute of Allergy and Infectious Diseases (NIAID) in the USA.

He added: "Using transgenic animals to achieve both ends is an exciting possibility.

"If it works, a herd of several goats could conceivably produce proteins for all of Africa."

Practical potential

Previously, scientists have introduced genes encoding specific proteins into animals to produce large quantities of those proteins for medical use.

Dr Stowers and his colleagues investigated whether transgenic animals could produce proteins specifically for use in malaria vaccines.

They produced two transgenic mice strains, each carrying a form of the gene for a surface protein from the deadliest malaria parasite, Plasmodium falciparum.

They designed the transgenes to be switched on by the cells that line the mammary glands, so that the resulting proteins would be secreted into the animals' milk.

Both mouse strains produced large quantities of the desired vaccine protein, which was used on the monkeys.

Six out of seven unvaccinated animals had to be treated for virulent malaria.

Preliminary results of using the same technique in goats, which have not yet been published, suggest the procedure works well in larger animals.

This offers a far more practical option for large-scale vaccine production.

Professor David Warhurst, from the Public Health Laboratory Service in London, said: "It sounds very interesting. Four out of five isn't a brilliant result, but it's a nice approach and it might be a good way of producing large quantities of the material."