Infections caused by microbes that have an animal reservoir (especially wild animal) or are found in the environment (soil, water, vegetation) are difficult to contain and to keep under containment with currently available tools. Even if an effective vaccine is available, as there are for the flaviviral infections, Japanese encephalitis and yellow fever, elimination of the agent is not feasible in most instances. Unless high levels of immunization are maintained or the vector (or contact with the vector) can be eliminated, risk of resurgence will remain. Even with vaccine-preventable diseases that do not have an animal or environmental reservoir, sustained, global control has been difficult to attain. Measles, for which a highly effective vaccine exists, still causes outbreaks, though endemic circulation has been eliminated in large areas of the world. As long as the infection persists anywhere and people travel, risk of reintroduction will persist.
The logical conclusion is that infections will continue to re-emerge in the foreseeable future because elimination almost never occurs and currently available tools (such as vaccines, vector control, education and change in behavior, screening blood and tissues, antimicrobial drugs, surveillance) are imperfect or incompletely or inconsistently applied. While efforts to control disease are taking place, microbes continue to evolve in ways to favor their continued existence in today’s world. The combination of population size, density, mobility, vulnerability (e.g., AIDS, aging, immunosuppressed populations), and location (increasingly in low latitude urban areas often without good infrastructure) provides the milieu in which continued episodes of re-emergence are likely.
Bibliography:
- Corso A, Severina EP, Petruk VF, Mauritz YR, and Tomaz A (1998) Molecular characterization of penicillin-resistant Streptococcus pneumoniae isolates causing respiratory disease in the United States. Microbiology and Drug Resistance 4: 325–337.