Mixed infection with cagA positive and cagA negative strains of Helicobacter pylori lowers disease burden in The Gambia

PLoS One. 2011;6(11):e27954. doi: 10.1371/journal.pone.0027954. Epub 2011 Nov 29.


Background: The prevalence of Helicobacter pylori including strains with putatively virulent genotypes is high, whereas the H. pylori-associated disease burden is low, in Africa compared to developed countries. In this study, we investigated the prevalence of virulence-related H. pylori genotypes and their association with gastroduodenal diseases in The Gambia.

Methods and findings: DNA extracted from biopsies and H. pylori cultures from 169 subjects with abdominal pain, dyspepsia or other gastroduodenal diseases were tested by PCR for H. pylori. The H. pylori positive samples were further tested for the cagA oncogene and vacA toxin gene. One hundred and twenty one subjects (71.6%) were H. pylori positive. The cagA gene and more toxigenic s1 and m1 alleles of the vacA gene were found in 61.2%, 76.9% and 45.5% respectively of Gambian patients harbouring H. pylori. There was a high prevalence of cagA positive strains in patients with overt gastric diseases than those with non-ulcerative dyspepsia (NUD) (p = 0.05); however, mixed infection by cagA positive and cagA negative strains was more common in patients with NUD compared to patients with gastric disease (24.5% versus 0%; p = 0.002).

Conclusion: This study shows that the prevalence of H. pylori is high in dyspeptic patients in The Gambia and that many strains are of the putatively more virulent cagA+, vacAs1 and vacAm1 genotypes. This study has also shown significantly lower disease burden in Gambians infected with a mixture of cag-positive and cag-negative strains, relative to those containing only cag-positive or only cag-negative strains, which suggests that harbouring both cag-positive and cag-negative strains is protective.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Antigens, Bacterial / metabolism*
  • Bacterial Proteins / metabolism*
  • Child
  • Coinfection / epidemiology
  • Coinfection / microbiology*
  • Coinfection / therapy
  • Cost of Illness
  • Gambia / epidemiology
  • Genes, Bacterial / genetics
  • Genotype
  • Helicobacter Infections / epidemiology*
  • Helicobacter Infections / microbiology*
  • Helicobacter Infections / therapy
  • Helicobacter pylori / genetics
  • Helicobacter pylori / physiology*
  • Humans
  • Middle Aged
  • Stomach Diseases / genetics
  • Stomach Diseases / microbiology
  • Treatment Outcome
  • Virulence / genetics
  • Young Adult


  • Antigens, Bacterial
  • Bacterial Proteins
  • VacA protein, Helicobacter pylori
  • cagA protein, Helicobacter pylori