Centenary booster in hunt for malaria vaccine

August 1, 1997

AUGUST 20 this year marks the 100th anniversary of one of the most dramatic discoveries in medical science.

Ronald Ross solved the so-called "malaria problem" by showing that the disease was transmitted to humans by mosquitoes.

Ross's breakthrough, made while he was working as a medical officer for the British army in India, quashed the misconception that malaria was an airborne infection - the name "malaria" comes from the Latin meaning "bad air".

The seed of his idea was probably sown by his mentor, Patrick Manson, who had found that mosquitoes were the vectors of filariae, parasites that cause another tropical disease, elephantiasis.

Years spent dissecting mosquitoes fed on infected patients yielded no results until, in 1897, Ross found malarial cells embedded in the stomach walls of an Anopheles mosquito, a species he had not seen before.

To make absolutely sure that his hunch was correct, Ross went on to show that the parasites migrate to the mosquito's salivary glands, to be injected into a new human host when the insect bites, thus completing the circle.

Ross, who as well as being a scientist, was a mathematician and a published poet, was awarded the Nobel prize for medicine and a knighthood in recognition of his pioneering work.

Ironically, 100 years on from Ross's discovery, we are on the verge of what has been described as an "imminent catastrophe", with a sevenfold increase in malaria deaths during the past five years in parts of Africa. The epidemic, which accounts for the deaths of between 200 and 300 children every hour, has been, at least in part, attributed to resistance of the malarial parasite, plasmodium, to drugs such as chloroquine and mefloquine.

Ross's solution to the "malaria problem" paved the way for initially successful control of the disease by concentrating efforts on eradicating mosquitoes from areas where malaria was rife.

This strategy continued into the 1960s and was particularly effective in wiping out malaria from islands such as Sardinia.

But the success was not to last, as resistance to insecticides such as DDT spread throughout the mosquito population.

However, there is renewed interest in the control of mosquitoes, particularly through the use of mosquito nets, which are now often impregnated with per-methrin, an environmentally-friendly insecticide.

The race is now on to develop a vaccine. But David Walliker, of the University of Edinburgh, is "pessimistic" about the chances of success.

One of the problems is that plasmodium is genetically more complicated than the viruses and bacteria against which vaccines have been developed in the past, and research in this area has been somewhat hit and miss.

Potential vaccines that have so far been tested in the field have not worked.

"I don't see a vaccine being developed to eradicate malaria, but I can see that a vaccine may stop people dying from it, by boosting their immunity," Professor Walliker said.

The discovery of malaria is to be commemorated at the second global meeting on parasitic diseases in Hyderabad, India, from August 18 to 22.

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