A multi-drug resistant (MDR) strain of typhoid that is spreading through Africa and Asia is a threat to public health, according to a recent study. Researchers have identified the culprit as H58, which is driving antibiotic-resistant typhoid and displacing other typhoid strains.
Typhoid is a common disease caused by the bacterium Salmonella Typhi (S. Typhi), with 20-30 million cases occurring annually. The disease spreads through contaminated food or drink and symptoms include high fever and diarrhea.
Researchers analyzed the DNA of close to 2,000 S. Typhi samples, obtained from 21 countries across Africa and Asia, and found nearly half (47%) belonged to the resistant strain H58. The study, published in Nature Genetics, shows that the H58-resistant strain has spread dramatically since the early 1990s. As vaccines that can treat the disease are not widely available, antimicrobial treatments are more commonly used in these continents where the disease is endemic. The drugs have gradually become less effective due to the spread of a multi-drug resistant strain of typhoid over the last 30 years.
“It is important to know the true epidemiology of typhoid across the world because it facilitates the development of effective strategies to control typhoid. These include the introduction of vaccine programs, use of effective antimicrobial agents and development of water, sanitation and hygiene services,” says Dr. Vanessa Wong, first author from the Wellcome Trust Sanger Institute.
H58 has dethroned the other strains of typhoid fever that have endured for decades, “completely transforming the genetic architecture of the disease,” says Wong. The H58 lineage is already resistant to the first-line antimicrobials used to treat typhoid and it is also evolving to become resistant to the newer agents commonly used, such a ciprofloxacin and azithromycin, the study finds.
Typhoid is more of a problem for people who live in developing countries as it is associated with low socio-economic status, poor sanitation and inadequate safety standards for water and food supplies, Wong says. However, she points out that travelers from developed countries who visit typhoid endemic countries are also at risk of contracting the disease.
Wong and her research team were surprised by the extent of H58’s dissemination across the globe, as its lineage is “relatively young.” Researchers have found MDR-resistant outbreaks in areas in Africa where the disease was previously absent or unappreciated.
The disease particularly affects younger age groups, usually infants, children and young adolescents. Wong suggests this may be because they are more susceptible to infection with their undeveloped immune systems compared to adults who develop immunity through repeated exposure to the bacteria.
“The problem requires urgent international attention as over 200,000 people die each year from typhoid and the emergence and global spread of this MDR clade has made management of the disease even harder,” says Wong.
“It is highly probable that if it continues evolving we will run out of treatment options for drug resistant typhoid,” she adds.