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Typhoid

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Typhoid is an infectious disease that is spread through contaminated food and water. The burden of typhoid is likely underestimated due to difficulties in surveillance and diagnostic challenges, but recent estimates suggest that there are between 12 to 21 million cases and almost 150,000 deaths each year. The majority of deaths occur in Asia, and young children and adolescents aged 2 to 15 years are disproportionately impacted. Two vaccines are currently available for global use but both have limitations that prevent widespread use in routine immunization programs. Newer typhoid conjugate vaccines (TCVs) have the potential to address some of the shortcomings of the currently available vaccines. Although typhoid is treatable with antibiotics, resistance to commonly used antibiotics is on the rise.

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Typhoid disease

  • Typhoid, also known as typhoid fever, is a serious enteric fever caused by the bacterium Salmonella Typhi. It is spread by the fecal-oral route through contaminated food and water, usually due to unimproved sanitation and poor hygiene habits.
  • Symptoms of typhoid include fever, fatigue, headache, and abdominal pain. Other common symptoms include diarrhea or constipation. Symptoms are often mistaken for other diseases such as malaria, pneumonia, dengue fever, influenza, or other febrile illnesses, leading to frequent misdiagnosis.
  • If left untreated, typhoid can cause severe short- and long-term complications such as intestinal perforation, encephalitis, pneumonia, delirium, and severe dehydration, which can be life-threatening.
  • Typhoid has largely been eliminated in industrialized countries due to improved sanitation and antibiotics, but it continues to be a substantial public health issue in much of Asia, sub-Saharan Africa, and in parts of Latin America and the Middle East.
  • The burden of typhoid is likely underestimated due to surveillance difficulties and diagnostic challenges, but recent estimates suggest that the global incidence is between 12 to 21 million cases and almost 150,000 deaths per year. An estimated 90 percent of typhoid deaths occur in Asia, though recent data from Sub-Saharan Africa suggests that the typhoid burden may be greater than previously recognized. Young children and adolescents aged 2 to 15 years of age account for the heaviest burden of typhoid cases and deaths.
  • When diagnosed properly, typhoid can be treated with antibiotics, though the rate of cases resistant to available antibiotics is increasing globally. Antimicrobial resistant typhoid is a growing concern, particularly in developing countries. Besides vaccination, other preventative measures include an integrated approach to improve water, sanitation, and hygiene among at-risk communities.

Typhoid vaccines

  • There are currently two globally available typhoid vaccines: an oral live attenuated vaccine, Ty21a; and an injectable Vi capsular polysaccharide (ViCPS) vaccine. Ty21a is approved for use in children 2 years and older and requires three to four doses. The ViCPS vaccine is licensed for children 2 years and older with a booster dose required every two to three years. Studies have shown that these two vaccines protect 50 to 80 percent of recipients and are safe, yet exclude the vulnerable cohort of children between 0 and 2 years of age, limiting potential health benefits and inclusion in routine childhood vaccination programs.
  • These vaccines are often used during outbreaks; neither vaccine is currently used routinely in endemic areas, and uptake has been low. The Ty21a vaccine requires numerous doses, and the ViCPS vaccine has short-lived protection.
  • In 2008, the World Health Organization (WHO) recommended the use of the ViCPS and Ty21a vaccines for controlling endemic disease and for use during outbreaks, but highlighted the need for improved vaccines.
  • Two TCVs are licensed nationally—Typbar-TCV® in India and Nepal and PedaTyph™ in India—and several others are in development. TCVs have the potential to address the shortcomings of the currently available vaccines, including longer-lasting protection, fewer required doses, and suitability for children under two years of age in routine immunization programs.

References

Page last updated: June 2017.

Photo: PATH/Janet Shauri.