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The Rediff Special/M D Riti

A new rabies vaccine produced by Indian scientists, which is expected to revolutionise the fight against rabies, is ready for human trials. Rabies continues to be a serious public health problem in many countries, especially the poorer ones.

Scientists at the Indian Institute of Science's biochemistry department, who were led by Dr P N Rangarajan, collaborated with the Indian Immunologicals Ltd to design the world's first combination DNA vaccine against rabies. The process involves inoculating a DNA vaccine and a low dose of an inactivated virus vaccine. This, say the scientists, can be developed into a novel, cost-effective vaccination strategy for combating rabies in particular and infectious diseases in general. The vaccine works such that if a rabies-infected dog is vaccinated, his bite to a human being will not transmit the disease.

"Since bringing out a human vaccine is going to take time, we are thinking of bringing out a veterinary combination rabies vaccine first, since there are less regulatory protocols for bringing out a veterinary vaccine than a human vaccine," says Dr Rangarajan.

However, the latter plan was stalled when the team fell foul of animal rights activists who objected to testing the new vaccine on stray dogs.

"Earlier, scientists were allowed to test new vaccines on beagles," complains former IISc director G Padmanabhan, who is still closely associated with the project. "Animal activists have not only compelled companies that kept these animals for drug trials to release them, now they are protesting against trying the vaccine on street dogs for whom it is meant?"

Dr Rangarajan says since it is the world's first combination DNA vaccine, the scientists have to demonstrate that it is non-toxic. "The animal toxicity studies are being carried out at the National Institute of Nutrition in Hyderabad. Once the vaccine proves non-toxic to animals, we approach the drug controller to initiate human clinical trials. It may take two to three years to complete the human trials and if everything goes well, we may get the license for manufacture. Then with the Drug Control Board's permission, clinical trials need to be undertaken," he says.

Institute Director Dr Sandip Basu points out that the vaccine has already been tested successfully on mice and cats. "The vaccine is meant for street dogs only and it cannot be cleared for commercial production until it is tried out on dogs," he laments.

Since traditional rabies vaccines are expensive to produce and have to be kept under refrigeration, government hospitals in India treat rabies using nerve tissue vaccine, which is banned in most countries. India has three cell-culture rabies vaccines for humans that cost anywhere between Rs 200 to Rs 300 per shot and a patient who has contracted rabies needs four to five shots of the vaccine.

The new vaccine, by contrast, is expected to cost much less. "Since DNA vaccines can be produced at a low cost and stored at room temperature, they are ideal for prophylactic immunization against rabies in developing countries," says Dr Rangarajan.

The scientists have already filed for an international patent under the Patent Co-operative Treaty. "We now have to file for patents in all PCT countries and that could take another year,'' says Dr Rangarajan.

Indian Immunologicals Ltd, which was set up by the National Dairy Development Board, will produce the vaccine. It already markets two cell-culture rabies vaccines, including the popular Abhayrab.

Rabies is caused by a virus, which is a negative-stranded RNA virus of the family Rhabdoviridae. Human rabies has been controlled to a large extent in developed countries by the use of safe and highly effective cell culture-derived human rabies vaccines.

DNA vaccination, more precisely the DNA-mediated immunization, refers to the direct introduction -- by injection or particle bombardment into the host organism tissues -- of a plasmid DNA (or RNA) which is able to cause expression of an antigenic protein directly within the transfected cells. In this sense, DNA vaccination resembles a viral infection.

The IISc team first developed a DNA rabies vaccine by taking a gene from the rabies virus and introducing it into bacteria. But the vaccine produced was effective only 50 to 70 per cent of the time. However, the cost of production was less than that of a cell culture vaccine.

Then, the scientists found that adding a small quantity of the modern cell culture vaccine enhances the potency of the DNA vaccine, giving the vaccine 100 per cent result while keeping the price low. The principle works for both human and veterinary vaccines and has shown positive results in mice and cattle. It took the team five years to develop the vaccine thus far.

More reports from Karnataka

Image: Rahil Shaikh

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