Scientists in the US have successfully created genetically engineered mice that produce a malaria vaccine in their milk, prompting hope that the animals can be used to cheaply immunize around 20 million people a year against the killer disease.

Anthony Stowers, lead malaria researcher at the National Institute of Allergy and Infectious Diseases (NIAID), reported in the Proceedings of the National Academy of Sciences that in his study, the mice were engineered to produce small amounts of Plasmodium falciparum, the parasite that causes malaria, in their milk. The study was successful and the mice produced enough of the protein, which works as an antigen and stimulates the immune system, to protect four out of five monkeys from the disease.

"A vaccine must not only be effective," said Stowers, however, "it must be cheap to manufacture if it is to be used in those countries hit hardest by malaria," he said. 

The disease, which kills 2.7 million people every year, is found predominantly in tropical areas. Around 90% of the registered cases are in Africa. Caused by a parasite carried by mosquitoes, the disease is treatable but there are no vaccines currently available. Malaria is difficult to vaccinate against, explained Stowers, because "people don't get natural immunity. They can be repeatedly infected throughout their lives and are."
 
"If it works," said Stowers, "a herd of several goats could conceivably produce enough vaccine for all of Africa."

Framingham, Massachusetts-based Genzyme Transgenics Corp, a company working with the researchers, has already bred two genetically engineered female goats that appear to be able to produce the necessary protein in their milk.

"The goats are too young to be naturally lactating but they can induce lactation for a very brief period of time and they have done that […] Up to 700 litres (185 gallons) of milk per year can be obtained from a single goat, with potential production levels of between one to 10 grams of protein per litre of milk."

This, explained Stowers, means that a single goat "could supply enough antigen to vaccinate 8.4 million people annually. ... Thus a herd of three goats could conceivably produce enough antigen to vaccinate 20 million African children a year."

Stowers added a note of caution however, warning that a malaria vaccine is unlikely to become available soon. "How it will go in people is very problematic," he said, explaining that the vaccine given to the monkeys included immune system stimulants called adjuvants, which are considered too dangerous for people.