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New vaccine developed for parasitic worm

Scientists at the Queensland Institute of Medical Research (QIMR) have developed a vaccine against schistosomes (commonly known as blood flukes or Bilharzia) – parasitic worms that infect 200 million people worldwide and are responsible for hundreds of thousands of deaths annually.

By cloning two particular proteins from the African blood fluke, QIMR scientists are now able to alert the immune system to the parasite, which had previously evolved complex immuno-evasive strategies to avoid detection in the host’s blood.

One of the proteins, known as TSP-2, forms the basis of a very effective vaccine against the African schistosome, Schistosoma mansoni, and provides protection levels in excess of the 40 percent benchmark set by the World Health Organisation (WHO) for moving forward into clinical trials – an independent test of six other vaccine candidates funded by WHO showed that protection levels never exceeded 40 percent.

Head of QIMR’s Helminth Biology Laboratory, Dr Alex Loukas, says the vaccine resulted in reductions of up to 61% and 64% in worm burdens and liver egg counts respectively.

“Our studies have shown that this vaccine also reduces faecal egg outputs, which means that it not only reduces parasite load in the host, but in the environment as well, thereby reducing future transmission of the parasite,” Dr Loukas said. “This shows we can effectively reduce the number of new worms that can infect other people, to an amount that will make a tangible difference to the international community.”

“We also found that people who are naturally resistant to schistosomes, despite constant exposure, had antibodies that recognised the TSP-2 protein while people who were chronically infected with the parasite did not, further supporting the development of this vaccine.”

Blood flukes typically live in the host’s liver or in the veins that surround either the bladder or the small and large intestines, where a single female worm will release up to 300 eggs into the blood stream per day for the rest of its life (the lifespan of blood flukes can be as long as five years).

The eggs are passed out through the faeces and urine where the life cycle continues in bodies of freshwater, however, up to 50 percent of these can become trapped in the body, leading to the symptoms of schistosomiasis: fever, headache, lethargy, diarrhoea, abdominal pain, enlarged liver and spleen, and many more.

Schistosomiasis ranks second behind malaria in terms of public health importance and leads to damage to the intestines, bladder and other organs, which in turn can result in bladder cancer, renal failure, liver fibrosis and even death.

Over half a billion people around the world are at risk from the disease – which is prevalent in 74 developing countries – and hundreds of thousands of children under the age of 14 are infected each year.

The results of the study have been published in the highly prestigious journal, Nature Medicine.