SciDev.Net

 

[RIO DE JANEIRO] Researchers in Spain and Peru say they have taken an important step towards developing a vaccine against Chagas disease, which infects an estimated 12 million people in Latin America, killing tens of thousands each year.

 

 

If the vaccine is successful in the clinical trials, the scientists will have overcome a challenge that has mobilised research centres worldwide. To date, no vaccine exists against 'protozoans', a group of microscopic parasites that includes Trypanosoma cruzi — the causative agent of Chagas disease — and the species that cause malaria and leishmaniasis. Such parasites are renowned for their capacity to evade the human immune system.

 

 

Trypanosoma cruzi usually enters humans when they are bitten by insects called assassin bugs. It can also be transmitted through blood transfusions, and from mother to child during pregnancy.

 

 

The researchers used one of the parasite's genes as the basis for a 'DNA vaccine'. When injected into mammals, the vaccine, which contains fragments of DNA, causes the recipients' cells to produce a protein that would ordinarily be produced only by the parasite.

 

 

This in turn triggers an immune response to the protein, even though the parasite is not present. It means that if the individual is later infected by the parasite, the host's immune system will be able to recognise — and act against — it.

 

 

"In tests with laboratory animals [the vaccine] provided a high degree of protection — around 90 per cent — against Chagas disease," says lead researcher Antonio Osuna of Spain's University of Granada.

 

 

The protein being used in the potential vaccine controls the parasite's ability to take up of molecules of fat through its surface. It was identified by Ofélia Magdalena Córdoba, of the University of Trujillo in Peru, during a search for ways of blocking the parasite's normal metabolism.

 

 

Osuna says the researchers will continue working on the potential vaccine, hoping to take it up to the stage of clinical trials. Their next steps will include studies of 'adjuvants'; these are substances that make vaccines more effective at producing an immune response, and therefore result in smaller quantities of vaccine being needed.

 

The researchers say their work may also contribute to the development of new drugs to treat Chagas disease. Currently, drugs are only available for the acute phase but they can cause a number of side effects.

The chronic phase of the disease, which may exhibit no symptoms for a number of years, usually results in death due to heart disease, with heart transplants being among the few ways of saving patient's lives.

Chagas disease largely affects the poor. The assassin bug that carries the parasite is often found in houses with mud walls or thatched roofs, which are common in the rural areas of Latin America.

However, according to University of Granada researchers, it is also able to survive in foods such as sugarcane juice, which is widely consumed in Latin America, and cases of infection from this route of transmission have already been reported.