Target: ulcer
ever since Barry Marshall from Australia showed that stomach ulcer is caused by a germ and not by behavioural traits, there has been much progress on controlling this disease. Recent reports claim that the humble ulcer-causing bacterium may well be controlled by an oral vaccine. Furthermore, unlike all conventional vaccines which only help prevent future infections, the new vaccine could purge the ulcer-causing germ. Permanently. Helico-bacter pylori (H pylori) is a newcomer to medical science, discovered in 1983 by a group of Australian researchers.
Recently, Paolo Ghiara and his colleagues at Chiron Vaccines Immuno-logical Research Institute and the University of Siena, Italy, have deve-loped a special strain of H pylori that sustains a lasting infection and causes stomach ulcers in mice.Six weeks after the infection set in, the mice were given vaccines that included two proteins found on the surface of H . pylori cells. Of the 48 mice receiving the vacci-nations, 44 showed no trace of H . pylori a week later (Infection and Immunity , Vol 65, No 12).
The team had earlier shown that a similar vaccine could prevent uninfected mice from picking up H . Pylori and can effectively eliminate existing infections. Furthermore, the new vaccine does not require toxic compounds to boost its potency.
Ghiara claims that developing countries, where 80 per cent of the population get infected in early childhood, could benefit significantly as purely preventive vaccines often reach the infected population too late.
The team has tested the vaccine on laboratory animals as cure for several other diseases, including herpes. However, attempts to translate the techniques to humans have failed so far. According to Stanley Falkow, an expert on H . Pylori from Stanford University, California, usa, even if the vaccine is effective, it cannot possibly replace the conventional antibiotic treatment.
However, the triple-antibiotic treatment has several drawbacks. The most effective drugs are prohibitively expensive for use in the poorer nations where the number of H pylori -infected people is significantly large. Moreover, a number of germs are rapidly acquiring resistance to most known antibiotics. And this is where, Ghiara claims, the new vaccine scores over conventional treatment. Clinical trials for testing the vaccine on humans should start in the very soon, says Ghiara.
Meanwhile, scientists from the us and Sweden from the Institute of Genome Research, Rockville in Maryland, usa, have published the complete genome sequence of this gut pathogen (Nature , Vol 388, No 6642). The bacterium has a circular genome consisting of 1,667,877 base pairs. During its evolution as a pathogen, it acquired a range of bacterial and non-bacterial genes - some of which have learnt to mimic human genes.
John Atherton, a molecular geneticist and gastroenterologist based in University Hospital, Nottingham, uk, is hopeful that the sequence will change the way research is being conducted on H pylori , expediting the whole process of controlling the bacterium in humans.
H pylori has a significant number of genes similar to those found in other bacteria. This is of enormous help as a new range of enzymes and proteins can now be tested on a number of previously-unknown sites. H pylori manages to fool the human immune system, not just temporarily, but for an entire lifetime. Science will now seek newer chinks on the it's genetic "armour" to launch a stronger, and hopefully, more successful immunological assault.