Boosting the fight against one of the world's oldest and most neglected diseases, Indian scientists have developed a new candidate vaccine against “kala azar”, also known as black fever or visceral leishmaniasis, which still kills thousands in India.

The vaccine, tested successfully on animals in the laboratory, is actually an enzyme that can protect people from the disease, which is transmitted through the bite of female sand-fly. Bihar is the global epicentre of the disease, even though it is reported commonly in Assam and West Bengal too.

There are drugs available to treat kala azar. But they are toxic, expensive and often lead to resistance. In the absence of better alternatives, doctors, however, continue with them.

The candidate vaccine, therefore, offers a hope, even though scientists have cautioned that it might take years to develop a commercial vaccine using the laboratory breakthrough.

The enzyme, HbR, could also be exploited both as a drug target and diagnostic, amplifying the significance of the discovery. However, it is the molecule's novel use as a candidate vaccine that the scientists found most exciting.

“We are looking at HbR both as a drug target and vaccine. We validated our results in preclinical studies in two animals. Now we would like to take up human trials. It requires long-term funding commitment and involvement of a pharmaceutical company,” Amitabha Mukhopadhyay, one of the lead authors of the study at National Institute of Immunology (NII), Delhi told Deccan Herald.

Besides NII, scientists from Indian Institute of Chemical Biology (IICB) in Kolkata and Rajendra Memorial Research Institute of Medical Sciences in Patna, too, were involved in developing the vaccine after 15 years of research. The findings have been reported in the September 11 issue of Science Translational Medicine.

When laboratory mice and hamsters inoculated with the vaccine were exposed to kala azar, caused by a parasite known as Leishmania donovani, the scientists found that they were more than 99 per cent protected. Because of its twin function, HbR could be exploited as a novel drug target besides a successful vaccine candidate, said Mukhopadhyay.

In its third avatar, the molecule can be used to develop a new diagnostic tool as it generates antibodies (a type of protein used in disease detection kits) in “kala azar” patients' serum. Currently there is no easy detection for “kala azar”. The gold standard is detection by bone marrow puncture, which requires hospital stay.

“Kala azar vaccines are not available because all clinical trials that tried different antigens failed. This is an important finding because the candidate antigen, haemoglobin receptor, is present in all Leishmania species. It is possible that the vaccine will succeed in clinical trials,” said Bhaskar Saha, who researches kala azar at the National Centre for Cell Sciences in Pune but is not associated with the NII-IICB study.

The disease affects 12 million worldwide, with 500,000 new infections and 50,000 deaths every year.