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To the Editor:

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Everyday travel by residents from industrialized countries to the Indian subcontinent and other typhoid endemic areas is coupled with a surge in Salmonella typhi and Salmonella paratyphi A infection.1,2 The ground record of the present vaccine lots, Vi polysaccharide or Ty21a has not been all that refreshing. Efficacy of full course of immunization with Vi polysaccharide vaccine in nonendemic areas upon arrival of the vaccinees in endemic areas might be far from ideal. Following their meticulous vaccination with Vi polysaccharide vaccine, during 2001 the French soldiers posted in Ivory Coast were afflicted with typhoid. Laboratory studies on 24 clinically labeled cases pointed toward 14 troops to be typhoid confirmed. The four Salmonella isolates during the outbreak had similar antibiotype.3 Moreover, among those on travel Ty21a vaccine may be less effective for S typhi though it may offer some protection against S paratyphi A.1

Pending marketing of vaccine lots operational against paratyphoid A, sequential vaccination with Vi and Ty21a vaccine might be an option. The oral typhoid vaccine M01ZH09 that is well tolerated and highly immunogenic in a single oral dose4 could interest those on unscheduled travel at a short notice. Nevertheless, institutions like the Tel Aviv Center for Geographic Medicine and Tropical Diseases would be indebted to characterize Salmonella isolates imported by local travelers from endemic areas. Search for any isolates without any phenotypic or genotypic expression of Vi antigen would be advantageous. Vi-negative strains would cause a disease resembling the one caused by Vi-positive isolates. Employing a multiplex polymerase chain reaction method for the genetic locus for the Vi expression, one truly Vi-negative strain has been reported from Pakistan.5 In the event of an infection by Vi-negative strains, upon their entry to intracellular niche, they would continue to be protected from Vi antibody. Acquisition of such isolates during travel following Vi vaccinations might well result in S typhi infection and vaccine failure.

International airlines handling traffic to typhoid endemic areas have had an indirect contribution toward spread of enteric fever in industrialized countries.1,2 They should better finance basic and applied research projects relating to enteric fever. Such fiscal support would emulate the Center for Industry Studies. The center has been multidisciplinary and spans a broad range of scholarship that is focused on manufacturing industries, service industries, and activities in nonprofit sectors.6

References

  1. Top of page
  2. To the Editor:
  3. References
  • 1
    Meltzer E, Sadik C, Schwartz E. Enteric fever in Israeli travelers: a nationwide study. J Travel Med 2005; 12:275281.
  • 2
    Threlfall EJ, Day M, De Pinna E, et al. Drug-resistant enteric fever in the UK. Lancet 2006; 367:1576.
  • 3
    Michel R, Garnotel E, Spiegel A, et al. Outbreak of typhoid fever in vaccinated members of the French Armed Forces in the Ivory Coast. Eur J Epidemiol 2005; 20:635642.
  • 4
    Kirkpatrick BD, Tenney KM, Larsson CJ, et al. The novel oral typhoid vaccine M01ZH09 is well tolerated and highly immunogenic in 2 vaccine presentations. J Infect Dis 2005; 192:360366.
  • 5
    Wain J, House D, Zafar A, et al. Vi antigen expression in Salmonella enterica serovar typhi clinical isolates in Pakistan. J Clin Microbiol 2005; 43:11581165.
  • 6
    Travel Grants. University of Pittsburgh: Center for Industry Studies. Available at: http://www.industrystudies.pitt.edu/researchtravelgrants.html. (Accessed 2006 May 20)