NEW YORK (Reuters Health) - Researchers have used tobacco plants to produce antibodies directed against the rabies virus and have successfully prevented rabies in hamsters and mice using the antibodies, according to a report released Monday.

The antibodies may one day offer a cheap and safe alternative therapy for rabies, which is sometimes treated with antibodies collected from horses -- which can cause severe allergic reactions -- or with antibodies from people, which can be expensive.

Rabies is a deadly viral infection of the central nervous system most commonly found in raccoons, skunks and bats. Dogs and cats can be infected as well, although vaccination has gone a long way to eliminating the disease in pets in the U.S.

Currently, people who are bitten by a rabid animal -- the usual means by which humans become infected -- are treated with a series of vaccine shots given over about one month.

The goal of the vaccine is to induce the body to produce antibodies against the virus that causes rabies, thereby preventing the infection from ever taking hold.

However, in an interview with Reuters Health, study author Dr. Hilary Koprowski of Thomas Jefferson University in Philadelphia said that the benefits of vaccines typically take a few days to kick in.

So a patient often needs a dose of rabies antibodies before being vaccinated, he said, "because you need to give immediate protection."

Until now, researchers have relied on products that contain antibodies collected from the serum of horses and from people previously exposed to the rabies virus. However, antibodies from horses have been linked to a host of side effects in the people who take them, such as fever, rash and allergic reactions, Koprowski noted.

Antibodies collected from horse serum are usually used in developing nations when human antibody products are not available.

And isolating antibodies from exposed humans has proven very costly, according to the report, published in the online early edition of the journal Proceedings of the National Academy of Sciences.

Now, Koprowski and his team have performed a series of genetic manipulations that has enabled them to extract antibodies from tobacco plants. Furthermore, the antibody appears to block the rabies virus just as effectively as antibodies taken from humans, and does so both in mice and hamsters.

Koprowski and his colleagues -- led by Dr. Kisung Ko, also of Thomas Jefferson University -- inserted the gene that encodes a rabies antibody into the tobacco plant. Once the plant began producing the antibody, the researchers collected the antibody and tested it in animals.

According to Koprowski, the antibody successfully prevented rabies in mice that received the antibody mixed with the rabies virus, and in hamsters that got the antibody after being injected with the virus.

Furthermore, the plant-derived antibody worked just as well in preventing rabies in infected hamsters as an antibody taken from humans, the report indicates.

"The plant antibody is as good as any antibody produced in animal tissue," Koprowski said.

It is safer to use plants to make antibodies than animals, he noted, for animals are more likely to carry something that can be dangerous to humans. He said he and his colleagues chose to work with tobacco plants because they can be grown in different regions around the world.

The researchers are now trying to get a drug company to take over and produce the product, Koprowski said. Once that happens, plant-derived rabies antibodies could be available for humans within a year, he estimated.