The human transport of microbes and microbial genetic material

Travelers carry microbes and microbial genetic material, a large portion of it the trillions of bacteria that form the commensal flora (Wilson, 2003a; Sears, 2005). They may carry and transmit pathogenic microbes and microbial genetic material, including resistance and virulence genes, sometimes in the absence of symptoms. Carriage may be transient or long term. Chronic infections, such as HIV, hepatitis C, and hepatitis B, can persist and be transmitted even if the individual is unaware that infection is present. Infections can be latent (e.g. tuberculosis) and can potentially reactivate at a time and place remote from acquisition. Potentially pathogenic microbes can be carried on the skin, in the respiratory tract, in the genital tract, in the gastrointestinal tract, or in blood and body fluids. There are thus multiple potential ways that pathogens can be transmitted.

Even when an infection is already found in a geographic region, travelers may introduce a new serotype or strain that is more virulent or resistant to antimicrobials. Wide use of antimicrobial agents puts pressure on microbial populations and contributes to the emergence of resistant microbes, but travelers may

*Routes (not all importation events) indicated by arrows.

+As of February 1, 2006, Niger and Egypt were considered no longer endemic for WPV because neither country had indigenous transmission during the preceding 12 months. ^Countries were considered to have reestablished transmission if WPV was detected for >1 year after importation. The majority of these countries have not experienced WPV type 1 transmission since July 2005.

Figure 1.4 Wild poliovirus (WPV) cases in 2005 and WPV importation routes during the period 2002-2005 worldwide. From CDC (2006b).

be significant in their dissemination. For example, only 10 clones of penicillin-resistant Streptococcus pneumoniae were responsible for 85 percent of invasive disease caused by this organism in the US in 1998 (Corso et al., 1998).

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