The candidate vaccine, developed by Brazilian and Spanish researchers, uses a modified version of the harmless adenovirus type 5 as an active mechanism, present in approximately 95 per cent of the global population. The researchers reprogrammed the adenovirus to carry genetic sequences of two different life stages of Trypanosoma (T.) cruzi.
According to the study published in PLOS Pathogens (24 January), the survival rate was 80 per cent among vaccinated mice. The immunising agents also reversed the levels of nitric oxide in the animals.
This substance, which is produced by the organism to combat the T. cruzi infection and which causes Chagas disease, can damage the heart when it is produced in a large enough quantity.
"We have shown that it is possible to redirect the immune response and reduce the parasite burden on the bodies of the mice,” Joseli Lannes-Vieir, lead author of the study and biologist at the Laboratory of Biological Interactions of the Oswaldo Cruz Foundation in Rio de Janeiro, tells SciDev.Net.
The genetic sequences activate the production of defence cells in the organism, which release toxic proteins that kill the infected cells.
For biochemist Renato Mortara, professor at the Federal University of São Paulo (Unifesp) who has studied the behaviour of T. cruzi since the 1980s, the study represents an important step forward in the development of therapeutic vaccines.
"The researchers have demonstrated a significant reduction of the parasite burden and of the damage to the heart of the animals who were previously infected with the parasite,” Mortara tells SciDev.Net.
Although the trials have been promising, there is a long way to go before the vaccine can be used on humans.
The development of an effective vaccine for Chagas disease is more than just a question of science,” explains Lannes-Vieir. “All of the economic barriers involved in the production of a medication for a neglected disease need to be considered.”
He adds that more trials will be needed to ensure that the vaccine does not cause damage to humans. “The next step is to test the vaccine on dogs that can act as a reservoir for the parasite,” Lannes-Vieir says.
According to the WHO, Chagas disease is one of the 17 neglected diseases. It musters little interest among pharmaceutical companies, as it mainly affects poor populations and countries.
The disease affects approximately 15 million people in Latin America. More than 40,000 new cases are reported each year, and the rate of congenital transmission from the mother to the foetus exceeds 14,000 cases per year.
However, increased global population mobility has increased the possibility of transmission to areas where Chagas disease was previously non-endemic, especially in Asia where the vector is naturally abundant and even infest houses in large numbers, says the WHO.
>Link to full paper in PLOS Pathogens
This article has been translated from SciDev.Net's Latin America desk.