Tweaking the rabies vaccine to spur the body into mounting a stronger immune response could lead to more effective and cheaper treatments. This could help save some of the 60,000 lives thought to be lost to the disease each year.
Around the world, more than two in three people live in regions where rabies is endemic. Something as simple as a dog bite or scratch from a bat can transmit the virus, but symptoms may not emerge for weeks or even months. If the infected person hasn’t received medical treatment by then, the death rate is virtually 100 per cent.
Unfortunately, the vaccines used both to protect people from a possible infection and to treat them afterwards are expensive and need multiple rounds to work. This prompted James McGettigan at Thomas Jefferson University in Pennsylvania and his colleagues to search for a way to make them quicker and more powerful.
The current vaccines use inactive virus to trigger special types of cells in the body, known as B cells. These cells remember the virus and produce antibodies against it if they see it again.
The team exploited this by attaching an additional protein to the surface of the inactive virus, called the B cell activating factor. This binds directly to B cells and alerts them to the existence of the pathogen more quickly than the traditional vaccine does.
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When the researchers tested this modified vaccine on mice, they found that the levels of antibodies in their blood jumped quicker and higher than in mice that had been given the traditional vaccine. Within five days, mice who were given the new vaccine had twice the level of virus-neutralising antibodies in their blood of the other mice, and by seven days this had risen to five times.
The team also found the mice needed less of the vaccine to get the same immune response, and that this immunity wasn’t any more likely to fade over time.
While McGettigan and his colleagues have yet to compare the survival rates of mice treated with the vaccine who have been exposed to the virus, Greg Moseley at Monash University, Australia, says the results are promising.
Since the new approach appears to require lower doses than normal vaccines, it may drive down the price, he says.
“When people are infected by rabies, it is a race against time to get them the vaccine,” says Moseley.
For people in wealthy countries, getting the four or five doses of vaccine required after a possible exposure to the virus is relatively easy. However, the majority of infections happen in poorer countries where people have limited access to medical treatment.
Because rabies is spread by animals, with dogs accounting for around 99 per cent of infections in the world, human vaccines won’t eliminate the disease. That is why vaccinating dogs and other animals is another key strategy in combating the global burden of the disease, says Moseley.
Journal reference: PLoS Neglected Tropical Diseases, DOI: 10.1371/journal.pntd.0007800
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