Malaria, schistosomiasis and to a lesser extent liver fluke cause hundreds of thousands of deaths around the world each year. A Dublin researcher is working on a selection of vaccines which may help to reduce this toll on human life.
Dr John Dalton, of the School of Biotechnology at Dublin City University, began studying liver fluke as a UCD graduate student in 1980. He went on to work at the Johns Hopkins School of Medicine and then the US National Institutes of Health, before returning to Ireland in 1988 where he continues to examine ways to defeat those diseases.
The research involves using advanced microbiological techniques including genetic engineering to understand the life cycles of the parasites which cause these diseases. Although they are mainly associated with the Third World, Dr Dalton pointed out that about 60 new cases of malaria are discovered each year in Irish people returning from countries where the disease is endemic.
And while liver fluke is more a problem for cattle and sheep here, it is also a human disease in some countries, including Bolivia where he has carried out research.
His approach involves a detailed examination of the parasites, identifying essential proteins required to keep them alive and then attempting to target those proteins with vaccines.
The single-cell organism that causes malaria invades the bloodstream after a mosquito bite and reproduces by consuming red blood cells. Working with Dr Angus Bell at Trinity College and with Notre Dame University in the US and the Queensland Institute for Medical Research in Australia, Dr Dalton has identified and characterised key parasite proteins.
One is a receptor which enables the parasite to cling to the blood cell membrane, and another is an enzyme that helps it digest the haemoglobin contained within the cell.
"We have demonstrated in the laboratory that if you block the action of these receptors you can block the action of the parasite," Dr Dalton explained during a presentation to mark his DCU President's Award. The parasite only spends seconds outside the cell, however, and Dr Dalton has greater hope for a vaccine that interferes with the parasite's digestion once inside the cell and therefore its ability to reproduce.
He has found a vital parasite enzyme which breaks down haemoglobin. The parasite gene which produces it was transferred into another organism, so that larger quantities of the substance could be studied and a vaccine against it developed. If the vaccine proves successful it will stop the parasite from feeding itself and it will die off before causing disease.
Dr Dalton is using a related approach against liver fluke which must travel to the gut before beginning its life cycle inside its mammalian host, and for schistosomiasis, a disease caused by a parasite which penetrates the skin. This disease is endemic in 76 countries and has infected 250 million, Dr Dalton said. It kills about 80,000 people worldwide each year.
He has identified a schistosomiasis digestion enzyme which is being studied as a possible target for a vaccine. New drug therapies which disrupt the enzyme's action may also emerge.
The citation read by the president of DCU, Dr Danny O'Hare, noted Dr Dalton's achievement in becoming an internationally recognised expert in the development of vaccines against these parasites.