The bacteria, called Neisseria meningitidis group B, is responsible for most cases in the U.S. of the life-threatening infectious diseases bacterial meningitis and septicemia, which occur most often in children and young adults.
"We have made such tremendous progress in the last year and a half that we should be able to start testing a vaccine in humans by 2001. The process has been moving so far, so fast and we want to keep the momentum," vaccine designer Rino Rappuoli, PhD, says in an interview with WebMD. He and colleagues from the Chiron Corp. in Siena, Italy, the Institute for Genomic Research in Rockville, Md., and Oxford University in England described the vaccine development process in two studies published in the March 10 issue of the journal Science.
Bacterial meningitis (not to be confused with the less serious viral meningitis) is an inflammation of the membranes that surround the brain and spinal cord. It starts as a flu-like infection or sore throat, but within 24-48 hours after the first symptoms appear, it develops into a full-blown disease with severe headache, a stiff neck, vomiting, fever, mental confusion, and, in some cases, coma or death.
Septicemia, also called blood poisoning or bacteremia, is the presence of bacterial infection in the bloodstream, marked by frequent and intermittent high fever, shaking, and chills. In severe cases, the bloodstream can carry bacteria to the brain, liver, or other organs. Both bacterial meningitis and septicemia can be fatal unless patients get immediate hospitalization and intensive treatment with antibiotics.
Many people (by some estimates, as many as 30%) are infected with the bacteria that cause meningitis, which live in the throat without harming their human host. But for unknown reasons, in a small percentage of people who harbor the bacteria, it enters the bloodstream, crosses the blood-brain barrier that normally protects the brain from infections, and sets up shop, rapidly multiplying and causing the body to respond with an immune defense that causes the severe inflammation and other symptoms associated with the disease.
Although vaccines are available to protect adults -- but not children -- from the devastating effects of meningitis caused by other forms of the bacteria, group B meningitis strains have proved elusive. Vaccines work by raising the body's natural antibodies to a protein or other feature that lies on the surface of the invader (in this case, a bacteria). The antibodies then move through the bloodstream looking for a specific intruder, using that identifying protein -- much in the way that a beat cop will memorize the photo of a wanted criminal. But group B meningitis strains are shape-shifters that keep changing their appearance to evade capture by the immune system.
"The historical problem with trying to find a vaccine for this particular strain [of bacteria] is the fact that almost everything on its surface varies ... and that has made it very difficult to identify good vaccine targets," researcher Derek W. Hood, PhD, says in an interview with WebMD. Hood is with the Institute of Molecular Medicine at Oxford University and the department of pediatrics at John Radcliffe Hospital in Oxford, England.
What the scientists did was to map out the entire genetic sequence, or genome, of one strain of the bacteria, identifying every bit of the more than 2 million pieces of paired DNA that make the bacteria what it is. They then went through the entire library of genetic information they had assembled and identified at least seven proteins that most versions of the bacteria wear like ID badges on their outer shells. These proteins could tip off circulating antibodies to the presence of the bacteria, allowing the antibodies to marshal their resources and close in on the perpetrators.
But, as a researcher who has worked with drug companies on developing other meningitis vaccines tells WebMD, the proof of the pudding will come in clinical trials of vaccines that incorporate one or more versions of the newly identified proteins.
"There's no evidence that these proteins are necessary for either survival or [for causing disease], and what you might do is just delete out these proteins and still have [disease-causing] strains," says Lee M. Wetzler, MD, associate professor of medicine and microbiology at the Boston University School of Medicine
The studies were supported by Chiron Corp, of Emeryville, Calif., which is developing the group B meningitis vaccine.
- Scientists have mapped the entire genetic sequence of a strain of bacteria responsible for most cases of bacterial meningitis and septicemia in the U.S.
- With this genetic map, researchers believe they will be able to develop an effective vaccine against these often fatal diseases.
- Vaccines are available to protect adults against meningitis caused by other strains of this bacteria, but this group B strain is particularly adept at changing its shape, thereby eluding the immune system and making vaccine targets difficult to identify.