Emerging Infectious Diseases Pose Current and Future Challenges

Newly recognized disease-causing viruses, bacteria and other infections are continually emerging around the world, posing difficult challenges for patient diagnosis and treatment and for public health responses. A special symposium section of the September issue of the American Journal of the Medical Sciences (AJMS), the journal of the Southern Society for Clinical Investigation, provides a research update on important new infectious pathogens.

Contributed by a distinguished panel of infectious disease experts, the papers in the symposium draw attention to emerging pathogens of various types and origins. The symposium emphasizes new infectious disease threats likely to be seen by doctors in the southern United States, while acknowledging the high impact of emerging pathogens in developing countries.

Of approximately 1,400 infectious pathogens recognized in 2005, about 180 met criteria for "emerging or re-emerging" pathogens, according to an introductory article by symposium editors Ronald A. Greenfield, MD, and Michael S. Bronze, MD. Many different factors contribute to their emergence, such as changes in land use, societal changes, population health, and hospital and medical procedures. The symposium includes a review of the essential role played by mathematical models in predicting the course of emerging diseases, and thus in anticipating the public health needs.

Most emerging infectious disease events are caused by "zoonotic" pathogens originating from animal sourcesmost commonly from wildlife. Many of these infections emerge in "hotspots" around the equator, such as tropical Africa, Latin America, and much of Asia. But new zoonotic pathogens are also emerging in the southern United States, where doctors are dealing with toxocariasis, a parasitic infection carried by pets; bovine tuberculosis, which can spread from cattle to humans; and some new tickborne diseases. The H1N1 "swine flu" is a zoonotic infection, while the threat of a H5N1 "bird flu" pandemic remains.

In the United States, the emergence of antibiotic-resistant bacteria is a major problem, including "superbugs" like multi drug-resistant strep. Two symposium articles discuss efforts to develop safe and effective vaccines against these difficult-to-treat bacteria. While some drug-resistant bacteria are declining, others are becoming increasingly important causes of clinical infection.

The emergence of a "hypervirulent" strain of Clostridium difficile is a particularly difficult problem. Once found only in patients previously treated with antibiotics, C. difficile is now appearing in other groups as well. Infections with fungal pathogens such as Candida and Aspergillusonce seen mainly in patients with suppressed immune functionhave now spread to other groups of patients.

Meanwhile, food- and water-borne infections continue to pose a major threat to human health. In developing countries, water sanitation techniques are cost-effective in controlling these pathogens. "In the United States, food safety could be dramatically improved by food irradiation," Greenfield and Bronze write.

Many other infectious pathogens could be added to the listincluding HIV, which is still considered an emerging pathogen, along with multidrug-resistant and "extensively drug resistant" tuberculosis. Hepatitis B and C virus and malaria also continue to threaten large segments of the world population.

Even as new pathogens are emerging, so are technologies that may lead to effective new prevention and treatment strategies. Molecular biology techniques are being used to study how infectious pathogens interact with human hosts, while advanced genetic techniques are being used to enhance diagnosis and treatment. Molecular approaches to the development of new vaccines are progressing as well. The editors hope the symposium will promote increased awareness of emerging pathogens, and encourage progress toward advances in monitoring, diagnosis, and treatment.