In the wake of a deadly outbreak of meningitis in India, research into the cause of this mysterious disease reveals an unexpected culprit. Scientists have long blamed a particular type of bacteria for the infection, but French researchers find that it is not completely the bacteria's fault.
Meningitis usually strikes without warning. Healthy children suffer from sudden high fevers, stiff necks, headaches, vomiting, and rashes.
The World Health Organization (WHO) estimates the disease kills nearly 200,000 people each year, many in the so-called "Meningitis Belt" of sub-Saharan Africa. A recent outbreak in India led to more than 400 cases, of which one in nine died, most within a day or two of their first symptoms.
Meningitis is an inflammation of the tissues, or meninges, that line the brain and spinal cord. Viruses and several types of bacteria can cause it, but one bacterium in particular is usually responsible for epidemic meningitis.
This microbe, called the meningococcus, is generally peaceable, like thousands of other bacteria living in our bodies. Only when it leaves its home in the nose and throat does it become dangerous.
"In some unknown circumstances, the bacteria is going to go into the bloodstream, and once in the bloodstream it is going to invade the meninges and be responsible for meningitis," said University of Paris professor Xavier Nassif. He has been trying to figure out why a normally harmless bacterium would suddenly attack its host and kill itself in the process.
"The problem is to know why the bacterium is doing such a thing to a human," Professor Nassif added. "Basically, you have to consider the disease as an accident for meningococcus because the bacteria does not benefit. Either the bacteria is going to kill the host or the bacteria is going to be killed by the host because he's going to receive antibiotics."
So why does the bacteria do this? Mr. Nassif and his colleagues analyzed the bacteria's genes to solve this dilemma. When they compared the DNA from a disease-causing strain with a harmless strain, they found a crucial difference.
"What we basically discovered in this work is that the strain that was responsible for meningitis was usually carrying what we call a phage," he explained. "A phage is a small piece of DNA that can be transmitted from one bacterium to the other. Those phages are considered like bacterial viruses. "
Mr. Nassif's team does not yet know how the phage makes the bacteria dangerous, but they think it might help the bacteria enter the bloodstream. If this is the case, then a vaccine targeted directly at the phage would keep the bacteria where it belongs and prevent meningitis in the process.
That kind of application is still a long way off. At the Meningitis Research Foundation in Britain, head researcher Linda Glennie is hopeful.
"It has been quite a long sort of struggle, really, to find the types of vaccine components that are most likely to be effective. This is one approach of many different approaches. Obviously we are hoping that it will bear fruit," she added.
Until then, Ms. Glennie and others are working to improve the existing meningitis vaccines.