August 1998, Volume 48, Issue 8

Student's Corner

Helicobacter Pylori: A Review

Raheel Ahmed  ( Fourth Year Medical Student, The Aga Khan University Hospital, Karachi. )

Since its discovery in 19821, Helicobacter pylon has rapidly emerged as an important pathogen in gastric microbiology. It has led to a re-appraisal of our understanding regarding various gastroduodenal diseases and has therefore transformed their management.
Formerly known as Campylobacterpylori, H. pylon is a gram negative microaerophilic organism. Colonization is common throughout the world and approximately half the world’s population is infected2. Infection is usually acquired dung childhood3, probably through person-to-person transmission although no single vector has been identified4. Incidence rates in both children (36% per year) and adults (3-10% per year) in developing countries are significantly higher than in developed countries (0.4% and 2.7% per year respectively)5. These differences are attributed to the low socioeconomic status and low level of education indeveloping countries6.
H. pylori is one of the most common bacterial infections worldwide7, but in majority of the infected individuals it only causes a histological gastntis with no clinical manifestations8. It can lead to chronic active type B gastritis in virtually all infected subjects9 and is associated with an increased risk of chronic atrophic gastritis100. Infection has a four-fold likelihood of developing duodenal and gastric ulcerative complications11. In a small fraction of individuals H. pylon infection leads to proliferation of lymphoid tissue which progresses to a mucosal associated lymphoid tissue (MALT) lymphoma12. H. pylori infection also has a well-defined risk of causing the intestinal form of gastric adenocarcinoma13,14. In this respect, H. pylori has been categorized as a group 1 carcinogen2. Non-gastroduodenal disorders have also been preliminarily linked to its infection15.
However, host susceptibility, environmental and bacterial factors also modulate the clinical outcome. This explains the discordance between the proportion of people infected and the smaller proportion which develops symptomatic disease. Host factors include age at infection16 blood group O17 acid secretory capacity18 and specific genetic differences19. Environmental factors also play an important role20. The bacterial related factors are attributed to the varying pathogeneicity of the infecting strain21. Consequently, various colonization, persistence and putative disease inducing factors have been identified22. These include structural components (flagellae, adhesins), extra-cellular products (ureases, proteases), cytotoxin associated gene A (CagA) related factors, vacoulating cytotoxins (VacA and hemolysins. These aid in colonizaiton, evasion of host response, cause direct damage to the host and through the activation of the immune response and its mediators. (IL-1,IL-8, TNF-alpha)23. Therefore specific markers are associated with an increased risk of disease24. Strains expressing the CagA-protein are at an increased risk of developing2 duodenal ulcers and gastric MALT-type lymphoma25.
The two methods of diagnostic tests available for H.pylon detection are invasive and non-invasive tests. The biopsy based invasive tests include rapid urease testing, histology and culture. Non-invasive tests include various methods of antibody detection and the carbon labelled urea breath tests. The final choice of a test depends onthe economic cost, clinical circumstances like recent antibacterial therapy and the accuracy of the modality26.
Eradication of H. pylori has been recogrnzedas the most cost- effective treatment in the management of peptic ulcer disease, its recurrence and bleeding27. Modem therapy can achieve upto 80-95% eradication rates in compliant patients28. Dual therapy with a proton pump inhibitor and either amoxicillin or clarithromycin and bismuth based triple therapy were used earlier. The preferred newer triple combination therapy with a proton pump inhibitor and two antimicrobial agents has shownhigher eradication rates, faster ulcer healing, prompt symptomatic relief with fewer side effects29.
Research for the development of a vaccine for both therapeutic and prophylactic puiposes is underway.
In circumspect, the considerable public health impact due to H. pylori infection underlines the need for increasing our understanding regarding the virulence, transmission, pathogenesis, treatment and eradication of Helicobacterpylon.

References

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25. Eck M, Schmausser B, Haas R et al. MALT type lymphoma of the stomach is associated with Helicobacter pylon strains expressing the CagA protein. Gastroenterology, 1997; 112:1482-6.
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